*
My house is wired with the old system,just a hot
and neutral but no ground. If I install a 3 prong
outlet and just jumper the ground to neutral, why
won’t this protect me from a possible short? If
you check this setup with circuit checker-it shows
OK. I know this is against code. But, can I
install a GFCI and will it work without having a
true grounding wire?
Appreciate any thoughts! Dave
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*
I'm not an electrician, but you can't do it that way cause somebody somewhere will have reversed hot and neutral in their amatuer wiring and then it will be all hosed up. Just use the GFCI without a ground. Its hard to find an old house where somebody hasn't crossed up black and white somewhere.
*Don't put in 3 prong outlets without a ground unless they have a GFCI protecting them. You can still get 2 prong outlets at the supply houses. I think that I read in the NEC code that the GFCI protected ungrounded 3 prong outlets meet code for retro-fit but I would still run new 2 wire plus ground to kitchens, workshops etc.
*NO! This is called a bootleg ground and misses the point of grounding -- a completely separate, INERT, path to ground. Current flowing through the device to the ground could kill you. Why do you think they created 3-prong outlets? Get an electrician to install GFCI's (which, yes, can be used to provide grounding at 3-prong receptacles in a 2-prong house) or real grounding. I SINCERELY don't mean this as a cheap shot, but ... that you ask this question suggests you shouldn't be doing this stuff. I've dug out so much bad wiring from well-meaning DIY's that I better understand where all these fires come from. It's just not worth it.To be fair, I've heard others, including a smart carpenter, speculate what all the grounding fuss was about. Here is a letter borrowed from JLC re bootleg grounds that explains the risk:>To the Editor: My experience with bootleg grounds is just as Rex Cauldwell speculates (“Plug-In Electrical Testers,” 12/95): Most of the bootleg grounds I’ve seen are in older houses where, when a room is changed into a home office, someone wants to give the illusion of a ground in a two-wire system. What I wonder is, since branch circuit neutrals and grounds are screwed to the same neutral/ground panel buss, can current backfeed from the neutral through the ground to the receptacle cover screw? >Rex Cauldwell responds: In such a situation, the current can most definitely backfeed from the neutral to the cover screw (and metal cover plate, if there is one). If someone touched the cover screw, there would be two current paths in parallel: a low-resistance path via the neutral wire and a high-resistance path via the person touching the screw (assuming he was somehow providing a path to ground). As long as the neutral circuit is intact and remains low-resistance, the path through the screw would normally not be lethal. But it could become so if the person also provided a low-resistance path by putting another hand on a grounded water pipe. The most dangerous situation would occur if the neutral circuit became open or developed high resistance (for instance, if a neutral wire came loose somewhere along the circuit). In that case, the cover screw would be the path of least resistance; if someone touched it, it could be lethal.
*After all that...what is the best solution? do you have to run a seperate ground to every outlet? I too just bought a new (to me) house and all the outlets are two prong, knob and tube. The house is built in 1950. I know the danger of bootleg grounding but I don't know what the best way to correct the problem of not having a ground. I will mosat likely have my electrician do it but would like to know anyhow. I just hate the idea of having to run another wire throughout the house...knocking holes in walls etc...Brushing up on my hole patching skills,Pete Draganic
*You can run grounds to every outlet or install GFI outlets. Since, GFI outlets can feed through you wouldn't need them everywhere, but only at the start of each run. At $7 or so per this would be a cheap fix.
*Does the GFI outlet work without a dedicated ground or are you suggesting only having to run a ground to the GFI and let the rest of the outlets past it in the series work off of it?Pete Draganic
*Come on guys! You bought an old house because you liked it and were willing to remodel to bring it up to today's, and your, levels. While you are in the remodeling process is a golden opportunity to update the wiring, probably update the service and in the process inspect for problems that have developed over the house's life and that may be just lurking for an opportune time to bite you. Don't pass up the opportunity to do the work on your schedule.
*Pete,The GFI will work without any ground at all. It looks for an imbalance of current between the hot and the neutral. If the differance is greater than 5 ma. it assumes that some of the current is going to ground externally and it trips off.Ron
*Rewiring an old house without demolishing everything was a fantastic experience for me, like climbing a mountain. It sucked sometimes, along the way, but man what a sense of accomplishment afterwards!I'm with FredB on this one. The best solution is to take it apart (if necessary) and redo it right. Now, my personal opinions aside about that matter, the GFI is certainly better than no ground at all, and ought to be done sooner rather than later (especially if re-wiring the whole place is something 'best put off til...').The best piece of advice that anyone gave me, when I began the process of rewiring the whole place was this: Inspect your whole system first.Take off the cover plate from each socket and switch and inspect the wiring (condition, correct polarity, screw tightness, device condition). This area is, I have been told, the most common source for electrical fires in houses (besides appliances like lights, heaters, etc that are plugged in to them!) and I found many, very scary things along the way.While doing this, you can also make a 'map' of your house's wiring to better understand where best to install GFI.Note that knob & tube wiring can be very unpredictable, with one common hot or neutral running willy-nilly, independantly from each other (I bet that when the house was built this method was logical and appropriate, but with modern Romex type wiring as your mind set it can really trip you up when you find hot wires after turning off the circuit breaker, no to mention whatever crazy thing someone did to modify the wiring over the years...).I sleep much better now, knowing that the live, bare wires tucked in to the insulation in the attic are now gone, as well as the live wires lying on the patio roof. Also, the cross-wired circuit in the bathroom (turn the circuit breaker off and it is all still hot, even though the lights are off due to a hot lead from another breaker was included behind the wall switch!), oh, I could go on.This was not a nightmare resto-project. The house was very well cared for, single family for 80 yrs place. The only obvious wiring concerns that were found by using a plug-in tester was several reverse-polarity circuits and some missing grounds, pretty common things to find.I got started by "just fixing what was unsafe", then progressed to "I'll just fix what is uncode", but after that there was so little left to do that I said "what the hell" and did the rest too.Read the books, hire a good electrician who will work with you, scour the web pages and learn. Rewiring a whole place without demolishing it first is fussy, time consuming and pretty frustrating. But why did we buy such old houses in the first place, if not to conquer these things and to glory in the results?
*Yes, of course real-world advice is what people want, not warnings.What I did in our house, which is a mix of 60-y.o. cloth wiring, incompetently wired 30-y.o. copper&aluminum, and tenant-damaged lighting wiring (overlamping cooked the insulation off): I check all the high-current circuits first and fixed them propmtly. Also fixed reversed polarity, exposed splices and other obvious faults. Abandoned some old runs by fishing Romex where needed -- it's not that hard once you get used to it, but bloody aggravating up until then unless you like punching holes in the wall.As remodeling progressed and wall spaces were opened, upgraded wiring as it was convenient. The oldest wiring, copper insulated with fire-retardent-treated cloth, was generally in the best condition except where excess heat from a ceiling fixture had cooked it off, so I only replaced it when it was easy to do so. I've heard knob-and-tube is often just fine provided it hasn't been abused.I've added two subpanels of nice neat wiring and pulled out the nightmarish stuff in the main box, which is particularly unpleasant to work on because it has no master breaker (it's always live). If I had it to do over again, I'd have had an electrician put in a larger service panel at the get-go -- at least ours is 150-amp and uses circuit breakers, but it has only enough room for about 20 breakers. The reason there are TWO subpanels is that after I did the first one the results were sooooo nice that I wanted another one. Again, hindsight is 20-20. Also, grudging and at the prompting of folks here, I've gone to all 12 gauge wire ... except where 14 gauge is much more convenient (e.g., difficult fishing situations or repetitive wiring of ceiling cans).Last point: Yes the GFCI can substitute for grounding, and do a very good job of it at that ... but they're still not reliable to put certain things like the refrigerator or sump pump on them. GFCI's are sensitive and will sometimes "nuisance trip"; this could cost you a lot of money. However, these are also devices where you really, really want grounding, so running a brand new cable to them is worthwhile.
*Yes, of course real-world advice is what people want, not warnings.What I did in our house, which is a mix of 60-y.o. cloth wiring, incompetently wired 30-y.o. copper&aluminum, and tenant-damaged lighting wiring (overlamping cooked the insulation off): I check all the high-current circuits first and fixed them promptly. Also fixed obvious faults like reversed polarity, Romex with staples driven through it, exposed splices, splices with tape but no nut, and "fake grounds" installed by the electrician we hired before move-in -- he pigtailed to the outlet boxes, never checking whether they were themselves grounded. Some rocket scientist had wrapped tape around the BX to "protect" it from the box, so the ground wasn't intact.Abandoned some old runs by fishing Romex where needed -- it's not that hard once you get used to it, but bloody aggravating up until then unless you like punching holes in the wall.As remodeling progressed and wall spaces were opened, upgraded wiring as it was convenient. The oldest wiring, copper insulated with fire-retardent-treated cloth, was generally in the best condition except where excess heat from a ceiling fixture had cooked it off, so I only replaced it when it was easy to do so. I've heard knob-and-tube is often just fine provided it hasn't been abused.I've added two subpanels of nice neat wiring and pulled out the nightmarish stuff in the main box, which is particularly unpleasant to work on because it has no master breaker (it's always live). If I had it to do over again, I'd have had an (honest) electrician put in a larger service panel at the get-go -- at least ours is 150-amp and uses circuit breakers, but it has only enough room for about 20 breakers, not enough for even a 2000 sf Cape with the usual gadgets. The reason there are TWO subpanels is that after I did the first one the results were sooooo nice that I wanted another one. Again, hindsight is 20-20. Also, grudging and at the prompting of folks here, I've gone to all 12 gauge wire ... except where 14 gauge is much more convenient (e.g., difficult fishing situations or repetitive wiring of ceiling cans).Last point: Yes the GFCI can substitute for grounding, and do a very good job of it at that ... but they're still not reliable enough to put certain things like the refrigerator or sump pump or grandma's life support on them. GFCI's are sensitive and will sometimes "nuisance trip"; this could cost you a lot of money. However, these are also devices where you really, really want grounding, so running a brand new cable to them is worthwhile. (I think there are hospital-grade GFCI's out there?) Also, a GFCI at every outlet could prove quite expensive, and would not protect light fixtures and such which are now supposed to be grounded (besides, who would ever test them all?). You can protect downstream devices with GFCI's, but then you must make sure everything is daisy-chained, and the more devices there are the greater the chance of nuisance tripping. Finally, you could install all GFCI circuit breakers, but they only seem to come in full-size and cost a fortune.Whew!
*FYI, At the electrical supply house I saw that Murray now makes a 30 position 100 Amp panel. Alot less money than a 200 Amp panel and you don't have to double up circuits on breakers. With a breaker interlock and hold-down you could even use it as a generator transfer without an additional box.
*More thoughts about re-wiring:Can't emphasise enough how valuable the right tools are. Fish wires, super-super long drill bits, a 90deg drive drill (or a 90deg attachment for your drill) to get in to those terribly small spaces with, drill bit extensions that you can build up one piece at a time because the work space is too small to feed in one really long bit, 'live wire' tester for quick confirmation that the circuit is dead before working with it and for tracing a wire quickly through the attic or basement spaces (it senses the alternating current even if none of the current is being used - but these are easily fooled by neighboring, hot wires (there is another post today about this induced current caused by AC) at least these simple testers mis-read 'safe'), a voltmeter for more accurate testing, a helper to pull some wire from up in the attic while you feed it from down in the basement (or strong legs to run up and down the stairs for every 2 inches of that 50ft run you're trying to get up there!).Man, the first wire fishing job was insane and I wasted days screwing around trying to do it - and I started with an easy one! But by the end (flash forward about 4 months) I could feed wires through just about anything, with the right tools, and experience, and luck. And all without making any new holes in the walls.Knob and Tube wiring is safe when it is not over loaded and kept in the open air. But when you want to insulate that air space you really ought to change to modern wire to avoid any risk of over heating (I really don't know why K&T requires open air, but suspect it has to do with the copper purity back then and the quality of the insulation materials).There was a lot of K&T wiring in my house that looked fine until I went to remove it and all the insulation crumbled when I rolled it up for disposal. It might have been fine for many more years, left undisturbed, but I feel better now with it gone.Also, when running new wires, be GENTLE with the stuff. It is pretty strong and forgiving but there are limits. If you feed 100ft of it through a 1/2" hole in a joist, look at how much the jacket heats up and is damaged unless you take some care with it. And don't pull everything too tight when you're done, make all corners gentle and leave a little loose at each end to allow for the building to grow and shrink with the seasons and avoid chafing.When I was done with all this activity I was paranoid that I had done some things wrong (after all, this is ELECTRICITY, and all that). But my electrician and the city inspector gave me thumbs up. Man, what a great feeling!And, yeah, andrew d, having a pro start you off by installing a new service and box is a GREAT way to get started. More room in the box, clean & neat looking.And a pro to get you off to the right start!
*... unless it's the same *&^%*^! pro who installed our grounds!Wire pulling lubricant, too -- great stuff. For fishing, i like to drop a small weight on a string until it just touches the bottom, then slip a coat hanger with a curve and a hook at the end into the bottom hole. Spin the wire around and it will snare the string.
*
Yep, the GFCI's like to nuisance trip, especially when they
are used upstream of other outlets and as a means of
protecting them. This is how I set up a few areas, but now
I only use them individually, works much better.
MD
*
couldn't you use a GFCI circuit breaker?
*Yes. But, you can buy 5 GFCI outlets for the cost of 1 circuit breaker.
*Dave, the dangerous side of wiring the ground terminal to the neutral terminal is that the electricity returning via the neutral conductor to the neutral buse in the panel is now also traveling back to the appliance via the ground wire and can energize the appliance or tool or whatever and you are now the path to ground should you touch it.regardsJim
*It's also a hassle to have eight outlets trip an have to run to the basement for every nuisance trip.
*Hi Mike,Question, you said you can buy 5 GFCI for cost of 1 breaker? For the few wiring jobs I've done, I've used Cutler-Hammer or SquareD. Breakers are 3-15$ depending on amperage. Are these 2 brands crap?. GFCI's are about 7$. I'm going to be wiring my first complete house in the near future. I was going to use one of those "starter packs", 200-amp, 40 spaces with main breaker and 5 other breakers for my main panel (79$). Bad choice?thanks, jim
*I think he meant a GFCI breaker, which is much more expensive than a standard breaker. Your brands are fine.
*Home Depot: GFCI $6; GFCI breaker $30 (a regular breaker is always needed after all, and yeas costs $5 or so)
*Yeah, thanks guys, upon re-reading the thread it seems obvious now - GFCI vs GFCI breaker.But hey, its Friday, late, I'm brain-dead and headed to the Tavern....
*If anyone here is still awake, there is a letter to the editor regarding the "scare tactic" of those suggesting that neutral and ground are actually different. Rex Caudwell writes an unusually emotional (for a building mag!) rebuttal, saying "Please listen, your life depends on this." (ie, they are critically different ... it's too bad people who see them bonded at the main panel conclude otherwise) FH128
*I just bought three 20 amp Square D GFCI breakers, and they were $48 not $30 (15 amp might have been $30).Personally, my advice regarding those $79 packages is don't. Stick to the QO breakers and not the homeline ones in those packages. I can't really give you a reason, but I feel like everytime I tried to save $100 on a $750 project, it was a mistake. I don't know what the difference between the two lines is, but unless you really have to pinch pennies I find it hard to imagine that saving $75 or so is worth it. QO has been around a long time, homeline not as long I don't think. So if a line gets dropped by the manufacturer, which one do you think it will be?
*
Check the backs of the boxes closely David, sometimes they grounded the box and cut the ground wires off short, if this is the case you are in luck and can join on to them and get a proper ground. If not you will have to
a) rewire (a costly option)
b) get a ground wire the same size as the feed conductor and take it to a know good ground eg; copper water pipe. I don't enver your position, GFIC outlets are cheaper than GFIC breakers here in the Great White North.
*
Water pipe is no longer up to snuff for ground. True, armored cable may ground the box so that all you need is a pigtail in each to provide that 3d wire.
*
For a GFCI to operate correctly its suppose to be connected to a conductor that is grounded.
*Not so. The GFCI monitors the current flow of the hot and neutral wires. When there is an imbalance, the GFCI trips. The ground wire is not required for the GFCI to work . That's why the NEC allows you to replace a two prong outlet with a GFCI. If you try to test a GFCI with one of the plug in testers, those with the three lights, it will not work if there is not a ground attached. That has nothing to do with the operation of the GFCI, only with the operation of the tester.
*
I don't like the Homeline either. You must use Homeline breakers in them. Other similar breakers ALMOST fit but not quite. GE has the same problem. Murray is a much better choice if you don't want to use the QO series.
*ditto ... I think the built-in tester will still work? Or not?
*I couldn't figure out the Homeline thing at all. The breaker box is just one area I'm not willing to be cheap -- maybe they came up with it to make the regular line look less expensive?I used Square D, but they are generally thought to be overpriced. For the small subpanels I needed, it didn't matter.
*
Yes, the built in tester will work. The test button shunts current flow around the internal circuitry so the GFCI thinks it is seeing an imbalance between the hot and neutral and trips off (simplified but I believe accurate). The ground is not part of this test.
*
... shouldn't the shunt be of null effect? I.e, the parallel GFCI circuitry still sees the same in/outflow? (Just being a pain ... I've got to pry one of these things open one of these days.)
*Both the neutral and hot wires run through the center of the same magnetic coil. It's actually a toroid wrapped with wire and looks like an RF choke. As long as the current flowing one way on the hot is the same as the current flowing the other way on the neutral, the coil senses no magnetic field. As soon as there is an imbalance...trip.I don't know exactly how the "self test" on the GFCI works but if it shunts one wire around the coil, it would work without needing a ground.
*I bet you're right. But the short (or the coil) must be tuned somehow for the 30-50 mA threshold at which the GFCI is supposed to blow the whistle.
*Our 100yr+ house was wired knob&tube probably in the 30's. When we bought it there was a fuxe box with 4 fuses/circuits. A little note inside the fusebox read: "if fuse blows and you don't have one, put a penny in socket". Apparently they must've always had enough fuses. There were overhead wires going to the barn to a white porcelain throw switch with room for 2 fuses. The first fuse was a 20 amp and the second was a 15. One wire came into the barn and hooked up to the 20, ran thru the building outlets and exited thru the 15!! Neither hot or neutral was indicated so that some poor person could've had a fuse blow on the neutral side and still have all the wires hot.
*Saw a diagram on this. They use a resistor (think it was 6000 ohms) to shunt current between hot and neutral on "opposite" sides of the coil. This causes a current imbalance determined by the resistor value.
*
There have been a couple of points brought up in this discussion that need to be addressed.
b This gets long, so unless you are really interested in the difference between a neutral and a ground, I'd suggest you skip to the next response.
i Having warned the reader, the narrator puts on his lecturer's cap and begins:
Synopsis for those who usually read the last page first: We want current to flow in a neutral, but we don't want current to flow in a ground.
There is a definite difference between a ground and a neutral. Look down (distance depends on which level of the building you are on). THAT is ground. It is where we put current that we want to go "some place safe" rather than into YOU when there is a PROBLEM with the circuit. It is NOT where we WANT the current to go.
Now, the neutral is different, and requires a tiny bit of background. Electricity runs in "circuits." A little thought concerning the origin of the word will let one see that it is very similar to the word "circle." That's the point of electricity. You have to have a "complete path" for current to flow INTO and OUT OF a device for it to work. A classic case of "what goes around comes around."
Note birds on wires: There's an INTO connection, but no OUT OF connection, so there is no current, and the birds survive. Note bear climbing the utility pole: Everything is fine until the bear touches the power wire. His feet are hanging onto the OUT OF connection, when his paw touches the INTO connection. Result: Current flows in the circuit, and the bear (aka Circuit) no longer climbs the utility pole.
Now, the power company sends out ONLY hot connections. These are both the INTO and OUT OF connections. There are three total connections, and we refer to them individually as a PHASE. There are three phases. We call them A, B, and C phase, to distinguish between them. These three phases are actually the opposite ends of coils back at the power company's generators. A-phase goes through a generator coil to B-phase, which goes through a different coil to C-phase, which goes through still a third coil back to A-phase. This arrangement makes a triangle, which engineers call a "Delta" configuration, to confuse non-engineers.
The generator electricity comes out of A phase, and back into either B or C phase, depending upon the circuit configurations. Additionally, electricity from B can return to either A or C. And for those of you who didn't read ahead, C can return to either A or B. Current alternates going in and out of each phase, giving us the term Alternating Current or AC.
At this point, many of you are probably thinking "what does this have to do with neutral?" I'm getting there.
Now, Power companies generally generate around 200,000 volts. They step it down for use by us customers. To do this, they use transformers. Sometimes, they connect their coils in a "Y" configuration so-named because the shape of the coils in-circuit looks like the letter "Y" (which engineers spell "Wye," again to confuse non-engineers). Note that in a Wye, the coils all come to a natural, fixed centerpoint. Still current will flow back to the main generator as if from the end points only, but now we have a fourth point (the center) where we can hook up a wire.
We now have a problem. Most houses only have two hot wires from the power company. These are 220V connections if you use both wires for a single purpose. These connections are either A/B, B/C, or C/A, to the power company. Which two they are cannot be found by the customer, using just these two wires. When you connect something, like an electric range, to both of these wires, the path is something like (ignoring transformers): Generator A-phase through range to Generator B-phase through Coil back to Generator A-phase. This makes a complete circuit.
If you connect one of these wires to a device, and the other wire to the center of the Wye, you get about 120V, instead of 220V. But, you don't have the transformer there at your house. It is outside on a pole somewhere. Usually, the electric company is good enough to give you this center tap connection, which is your NEUTRAL point. I prefer to use the term "return" to distinguish it from "source," but "hot" and "neutral" will also suffice, until one encounters a "hot neutral" in a three way circuit.... But I digress.
Now, in our transformer, that center of the Wye is "neutral." If EVERY PHASE draws the same amount of current, exactly, then this point will have the same potential as ground, which is zero volts, by definition. However, if one of the phases draws a different amount of current, the coil associated with that phase will develop a different voltage than the other two (which may or may not have the same potential/voltage as one-another for the same reason).
We have a dilemma. A plus B plus C MUST equal zero. That is, all of our "goes out" must add up to all of our "comes in" in alternating current. To do this, Line-to-neutral voltages will be different. The electrical center of our circuit has moved, but our physical center (the middle of the Wye) has not. Now, the potential on the center is NOT ground; that is, NOT ZERO.
This center-tap is usually connected to ground for safety. The potential on the center is now FORCED to zero. All of our phase voltages balance to neutral, and are all 120 volts with respect to ground again. But to accomplish this, some of our current is forced into the ground (to equalize the voltage between the ground and the wanna-be-different neutral).
Now, in your house, some of your 120V circuits are connected A-Phase to neutral, and some of them are connected B-phase to neutral. Are they all drawing EXACTLY the same current levels? Probably not. Your neutral therefore is NOT zero. For safety, though, and to keep both lines at the same level, your neutral may be connected to ground at your electrical service box. If not there, it is definitely connected at the transformer or at a neighbor's service box.
Therefore, we WANT current to flow in the neutral, to return to the center of the wye through the normal path. We DON'T WANT current to flow in the ground, except when there is something wrong. Note that in either case, current returns to the Wye point either through the neutral or the ground.
Now we come to a Ground Fault Current Interrupter, or GFCI. It trips when current flows into GROUND, not in the neutral. Thus, it interrupts when there is ground current. Isn't it amazing how engineers come up with names for things? "What do we call this thing that Interrupts the circuit when there is a Fault resulting in Ground Current?"
What if we didn't have this ground? Then, my friend, when YOU touch something metal with a slight current unbalance and you are standing on something that touches ground (look down again), guess who becomes the circuit.
As we near the end, we come to the question of "why did they have 2 wire circuits before, if three wire (grounded) circuits are safer?" Actually, if there are NO GROUNDS, then it is safer to touch something that is hot than if there IS a ground. However, things break. Let's say that you are touching something in our un-grounded world that is energized, but since there is no ground anywhere, except through you, there is no "OUT OF" path, ie, no circuit. Now, while you are still touching this energized object, a toaster is dropped on the floor, where it breaks, and its broken coil wire falls against the case of the toaster, which is metal, and now touching ground. We will call our toaster the OUT OF path, for clarity, while we call you the INTO path. Guess what? You're toast.
Sorry for the length of this. Note to those who already knew the difference, I left out terms such as "sine wave" and "virtual ground" on purpose since many folks don't like math. They understand things fine, as long as you don't tell them it is really arithmetic. :)
Also, I didn't go into the fact that even without the connection in the wye (or in fact, even in the delta) there is always a neutral point. By definition, this point is where the potential in the three phase circuit equals zero volts, even if there is no wire hooked up to it.
*
Quibble: having chatted with an electrician and our friendly VA Power fella, as I understand it we have single-phase service from a center-tapped 19.1k-to-240 VAC transformer. So the tri-phase info has no effect on ordinary domestic load power: the 2 hots at the panel are 240 volts relative to each other, and each in identical phase 120 volts relative to the neutral.
Now explain how a phaser works.
*What is a delta y (wye) system? Some years back we had a portable building that we hauled out to offshore oil rigs. Depending on the rig we went to,sometimes we had to swap the hot and the neutral .... what worked on land was reversed offshore. A rig electrician said to install an isolated ground in the box which I did .......it cured the problem. Could you explain why the isolated ground worked. Thanks.
*My house is only 100 years old. When I moved in, I decided to convert an old 2 car (two buggy?) garage into my shop. I was going to install a new breaker box in the shop and rewire everything.I had only 110V comming across the triplex into the shop's fuse box. I went back out and checked it again a few minutes later...220V. The next day...110V. I finally figured out that there was a switch in the kitchen of the house that turned on an outside light that also turned on one hot leg to the garage's fuse box. Turn on the yard light, any you get 220V.I rewired more than the garage.
*Don,The neutral in a single phase transformer is a center tap. This creates a 2/1 ratio. 240/120, 230/115 or 220/110. You don't anywhere get 220/120. In 3 phase Y applications the neutral is the center of the three windings and is a (squrar root of 3)/1 ratio. You get, most commonly 480/277 or 208/120. You still don't get 220/120.
*There are two types of three phase systems. One is called delta (because the transformers form a triangle which looks like the greek letter delta) and the other is wye which looks like the letter...well you get the point.There are a bunch of ways that these two types of three phase systems can be set up depending on what voltage you need.The picture below will help to make this more clear. (hopefully)The common ways to deliver three phase power are:* Wye: voltage between A,B, and C is 208V, voltage between center tapped ground and any leg is 120V.* Wye: voltage between A,B, and C is 480V and voltage between ground and any leg is 277 Volts which is used almost exclusivly for fluorescent lighting. A step down transformer is often used with this system to deliver 120/240V* Delta: voltage between A,B, and C is 240V, voltage between C&t os 120V, voltage between B and t is also 120V. Voltage between A and t is 208 volts (called the wild leg)With three phase systems, sometimes on of the transformers is left out of the delta configuration and this is called an "open delta". Any transformer can be center tapped and secondary transformers can be added to provide any voltage needed.As to why the isolated ground worked...I can't think of any reason.
*Andrew,The 2 hots cannot be "240 volts relative to each other, and each in identical phase". If they are in phase there is zero volts between them and must be 180 degrees out of phase to see 240 volts between them and 120 volts to neutral. In fact, both ends of a center tapped transformer will be out of phase with respect to each other. In any case, as the consumer, it wouldn't matter to you what type of tranformer configuration you were connected to.Jerry
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I've decided to respond to each of the responses in this one reply. All of you have valid points, and I didn't mean to offend or misinform anyone in my original post. What it was meant to do was inform without completely boring the reader.
I agree that I could come up with no reason for the isolated ground to work, and for the system to have to be reverse-phased on land as opposed to what it was on rig power. Having worked on drilling rigs and power generators, though, I wouldn't doubt that there were separate feed-plugs for each, with one of them phased incorrectly on the rig.
The delta-wye drawing submitted by Ryan Cruzan is essentially correct. I have not done the math to see if the voltages he gives are correct, but they should be close enough. One other quibble, though, is that there are even more configurations for power than the two you've submitted. However, your two do supply the major two needed for ordinary applications.
I am well-aware of the root-3 rule, but I was trying to simplify. Sorry if I oversimplified this point and used 208/220/240 interchangeably. I apologize for any confusion/misinformation this conveyed. It is just that I've gotten into many drawn out discussions when I mention that twice 120 is actually 208, or that three phases minus one phase is actually one phase. The point of center tapped single phase transformers did not occur to me. To further complicate matters, 120 VAC on USNavy vessels is actually a 120 VAC winding center-tapped to ground, giving one 60 VAC to ground on each leg in a standard 120 Vac outlet.
To quibble back-atcha.... If you were to draw three transformer secondaries, each center-tapped, you'd end up with six independent windings to three different neutrals, as below:
A-N1
B-N1
B-N2
C-N2
C-N3
A-N3
Each of the phases is now Wye connected to neutral, but the phase voltages themselves would always balance to the center tap, giving one 120/240, as you stated.
Now, if all phases are balanced on each transformer secondary, once again, you have balanced voltages to ground. Assuming you connect each neutral to ground (go look in any household service box), then each neutral is grounded, and the coils are now in parallel, giving one a Wye connection once again, but now with two sets of windings in each leg of the wye(s). But your point is well-taken. I'll refrain from such simplifications again.
To further cloud the issue...
Ground remains ground, no matter how you wire a circuit. Neutrals are the "balance point" on every secondary of every transformer. Wherever the natural zero-volt potential is, THAT is your neutral. However, where one hooks up his return (aka neutral), is not always this point. All this having been said, I'll go back to my original synopsis. You desire current flow in a neutral, but want none in the ground.
I would like to apologize if my original post caused anyone to develop heartburn. Also, I'd like more information on the delta-wye question. I have extensive experience on power generation and controls, and with a little more information, I think we could clear up this issue. In addition, I have quite a bit of both power generation (aka power company) and oil rig experience, and am interested in the particulars of this. It sounds, on the surface, that this was a "quick fix" that made the problem go away, but didn't address the root issue.
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Don,
some questions:
On this rig, what was the 3phase voltage? were you just using two legs of their 3 phase to get your single phase or did they operate at higher voltage and provide 120/240 via secondary transformers?
I've never heard of the Navy system before. Is the outlet configured differently? It seems that if there was a switch turned off, there would still be 60V on the circuit...or are all switches double pole?
It's impossible to read a persons tone in a typed message but I hope you were not offended that I didn't realize you understood three phase systems.
BTW, I still don't know what a "delta-why" system is but most three phase transformers use delta connected primary windings and wye connected secondary windings. I may have this reversed and I don't know why they prefer this. I was told once that this allowed the primary winding to pass current in a circle (through the delta) instead of sending it back to the utility in the event of a short or other problem in the secondary windings. I was told this by another student in college, so I have no reason to believe it is true. This type of transformer is called a "delta-why transformer"
*I'm not sure how a phaser works, the ones I've seen were solid state and obviously worked using alchemy and black magic just like my computer.I do know what a phaser is. A phaser lets you figure out the the "firing order" of your three hot wires in a three phase system. Because each leg is 120 degrees out of phase, they come to their peak voltages in a specific order. Three phase motors will rotate one direction if wired one way and will rotate the other direction if wired the other way. I've always uncoupled the motor from whatever it was driving and just hooked it up. If it was running the wrong way, reverse two of the wires and it will run the right way. I guess on some motors, it's not practicle to uncouple the motor so you want to know before you connect the wires.I was also going to mention the other type of phaser but there is no lack of star trek stuff on the internet already.
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This was not originally my question, concerning the rig. I've been on probably 50 or more drilling rigs, so I was using generalities in my statements. I don't get offended easily, so I hope my tone doesn't and didn't convey that I was.
Most rigs operate at 600 Vac directly from their generators. Some are at 480, while others have 4160V. There are transformers installed for whatever application is necessary. 600:120/208 transformers are common, as are 600:277/480. The first is generally for hotel loads such as outlets and appliances. The second are generally "lighting transformers," used to provide illumination and often used for auxiliary motors such as cooling blowers and lubrication pumps. The 600 is generally used to do the real work of poking a pipe into the ground.
Delta and Wye are just conventions for winding arrangements, as you showed. One of the main differences between them is the fact that there is a tie point for your neutral on the Wye. Sometimes they call these 3 wire and 4 wire systems. As I stated earlier, every transformer secondary has its own neutral, because of the isolation provided by the transformer itself. Making the secondary a wye, then makes sense to allow direct, immediate access to this point. I've been on Delta systems where I had to use three resistors in a Wye to simulate the neutral point so I would have a tie-point for my meter (black wire) while troubleshooting.
Other reasons for the Delta or Wye configurations have to do with the voltage across the winding itself. In a Wye, Line-to-line voltage is 1.732 (root 3) times the winding voltage; in a Delta, Line to line voltage is equal to winding voltage. These trivia are only necessary if one is trying to do something unusual like designing a transformer, or one has a dual-voltage application (4160/2400 being the most common use for this type of change). Anyway, in the long run Delta-Wye means exactly what the speaker/writer wants it to mean.
Another interesting thing about Delta and Wye windings are the phase-shifts that occur when you pass current through this configuration. There is a 30 degree shift between the Delta and the Wye. In addition, it is possible to stack two secondaries (one Delta, the other Wye) on a single primary, and thus get two sets of three phase voltages, 30 degrees out of phase between the sets. This is used to do some fun stuff like calculating KVAR loading (120 - 30 is 90 degrees, which is a fun angle in trigonometry).
Anyway, we've gotten far away from the topic of two versus three wire household wiring systems. Feel free to email me if you have any other comments, questions, or quibbles.
*
Many thanks Ryan and Don!
*Oh, I meant the Star Trek kind. I was hoping for the real explanation.Jerry, I misstated -- all i meant to point out was the the hots and neutral are tied to a center-tapped transformer.
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My house is wired with the old system,just a hot
and neutral but no ground. If I install a 3 prong
outlet and just jumper the ground to neutral, why
won't this protect me from a possible short? If
you check this setup with circuit checker-it shows
OK. I know this is against code. But, can I
install a GFCI and will it work without having a
true grounding wire?
Appreciate any thoughts! Dave