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Hi all,
Until I can catch up with my electrician Monday, I’ve got an issue driving me nuts.
A customer has picked out an electric cooktop to replace an existing one in a kitchen remodel.
At the panel the breakers consist of two 30A breakers tied together (for 240V – I get that part). However, the new stove is rated 40A @ 240V, which is too much amperage for gauge 10 wire (30A circuit wiring).
Conversely, the specs for the cooktop say the minimum amp load is 30A @ 208V. A quick call to my electrician yesterday, and he’s telling me that he thinks that can be made to work.
How? Does that make any sense to anybody else? Thank you in advance for any relevant information.
George Lentulo
Replies
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I'm not an electrician but in commercial applications, it's not unusual to run 240V equipment on 208V and vice versa. I can't tell you if it's actually a good idea but it's done alot and I've never encountered a problem before. There's only a 15% difference in voltage so it's probably not enough to worry about.
About the current, Using E=i/r, if this stove draws a max of 30 amps ar 208V, it will draw 38 amps at 240V (assuming that the biggest part of the load is just a simple heating element).
Seems like 10Ga wire isn't big enough to me.
I repeat, I'm not an electrician, I just play one on the internet.
*George: If a resistive element (stove, light bulb, electric heater) pulls 40 amps at 240 volts, then it will pull 34.7 amps at 208 volts. Conversely, if it pulls 30 amps at 208 volts, it will pull 34.6 amps at 240 volts (not 38 amps, Ryan is wrong). It could well be that a stove needs a 40 amp circuit when at 240 volts, but only a 30 amp breaker/wiring when at 208 volts (if it pulls more than 30 but less than 34.6 at 240 volts).If the nameplate says it pulls 40 amps at 240 volts, no, it does not make sense. But if it says that it needs a 40 amp service at 240, and a 30 amp service at 208 volts, that makes sense.Not to code, nor a good idea in a customer's house, but you could disconnect one burner.While the amps increase 15% from 208 to 240 volt service, the wattage (heat output) increases 33%. Something to think about when an electric hot water heater gives even worse performance than they usually do. You can get a "buck-n-boost" transformer to boost 208 volts 15% to 240 volts, if you need top performance out of your heating elements. Usually easier to just put in a larger element, but I've had to boost the voltage a few times on industrial equipment. -David
*because of code, you going to meed 3 cdr 6awg (6/3) and a 1 cdr 6 awg ground.
*Electricians.....good people to hire.near the stream,aj
*Light bulbs, and to a lesser extent most resistive heating elements, are not constant resistors like the ones used in electronic circuits. They vary in resistance depending on their temperature, with lower resistance at lower temps. For example, a 100 watt 120 volt light bulb should be pulling 0.8333 amp (= watts/volts), and its resistance should be R = E/I, 120/0.83333 = 144 Ohms. But take a 100 watt bulb and measure its resistance with an ohm meter. I generally find something in the 10 to 15 ohm range when the bulb is cold. With the old non-digital meters, the test current was higher, and you could actually see the resistance go up as the test current slightly heated the filament. Way back in the vacuum tube days, this property of light bulbs was actually used in a crude form of voltage regulator, documented in Tremaine's Audio Cyclopedia.-- J.S.
*Ryan C: You got the formula wrong. You wrote "Using E=i/r, if this stove draws a max of 30 amps ar 208V, it will draw 38 amps at 240V." The formula is actually E = IR which is slightly different. The resistance of the stove remains the same. If the volts go up, then the amps go down. As a practical matter, the 30 amp breakers will protect the 10 gauge wires. But how often does one have all four burners plus the oven running at full blast?- Peter
*Thanks for straightening this mess Ryan.fv
*George, I don't know about California but here, the power is nominally 110/220, take it or leave it. Even if was 120/240 I don't know how you would dial it down to 104/208. If your electrician has a trick, I'd like to know what it is. Someone said to use #6. I come up with #8 which is a heck of a lot easier to pull if it comes to that.Steve
*Peter, Thanksgiving & Christmas all 4 burners and an oven too. Meltdown? Joe H
*Joe,Cooktop = four burners and a clock. The oven is someplace else. Suspect they would be fine on 30 amps and #10 99.99% of the time. Of course, I would not want to be there when that .01 comes up. Think this is a moot thread. From what they are saying on TV no one in California will be able to afford to cook with electricity. Sushi anyone?Steve
*Steve,I think you are on to something. The brownouts should protect the wires!
*Thanks all.My electrician called me this afternoon - apparently I misunderstood him the other day. He DOES NOT have a special trick to step it down to 208V and mimic 3-phase. What he meant was to check if it was a 3-wire or 4-wire 240V set up.Then, his thinking goes, if it's a 4-wire then half the amperage load goes off one, half off the other, and we're still okay on a set of 30A breakers and gauge 10 wire.Now I do know that the only dif between the 3 and the 4 wire set-ups is the presence of the neutral - and I still don't see how one neutral can serve a split set-up. Admittedly, I'm somewhat baffled by this, but he's done a lot of work for me over the years and so I trust his judgement, he's a damn fine electrician. If I find 4 wires and tell the customer we can satisfy their desire of putting this particular cooktop in their new kitchen, then he damn well better make it work!Thanks again everyone for your thoughts. Steve, pass the sushi - the wholesale price of a megawatt hour of electricity in these parts shot up 1,600% two days ago.Geo.
*George,If you have the two appliances on one circuit, in one room, you're looking at a 53A maximum demand. See 220-19. This is consistent with Johnnie's suggestion of #6 copper. I can e-mail you the calcs if you want to see them.If the appliances are on separate circuits, then the stove, at 40A, needs #8, and the cooktop will do fine on the #10. In fact, I believe that the right formula to use to calculate the cooktop demand is: P = I x ESo P = 30A x 208v = 6.24kWAt 240v, I = 6,240W / 240v = 26A.I can't see how Ryan got 38A or David got 34.6A. The power (wattage) of a resistance heater is fixed; if the voltage goes up, the current goes down, in direct proportion. Ryan or David, care to explain?
*C. Popejoy,No, actually I would consider it one appliance (a four burner cooktop) on a dedicated circuit.As stated previously, it is a 240V service connected at the panel w/ 2 30A breakers which are "tied" together.Are you able to tell me if the amperage load could be equally split in such a service provided that it was a 4-wire and not a 3-wire 240 set up?Geo.
*Sure, I can explain. I messed up the math. Should have said the following:b e/i=ri=current, e=voltage, r=resistance of the heating element(s)because the resistance of the heating element remains the same, you can setb e(1)/i(1)=e(2)/i(2) where e(1) is the 208V e(2) is 240 volts i(1) is the known 30A at 208V i(2) is the unknown current at 240Vsolving for the unknown, you get a current of 34.6, which makes david right.The wattage of a heating element is not fixed, they're nothing more than high resistane wire and as voltage increases, current also increases, making the wattage also increase. If your claim that as voltage went up, current went down keeping the product of voltage and current the same was true, then at 1.5V from a AAA battery, the element would be able to draw over 5,500 amps.
*Was that sarcasm? Are you in my face over this?
*OK amateur electricians....b 1 YOU CAN NOT HOOK TWO APPLIANCES TO ONE CIRCUIT. NO....NO.b 2 YOU NEED A 40 AMP 4 WIRE CURCUIT IN RESIDENTIAL RANGE WORK MINIMUM.b 3 MANY RANGE OVENS REQUIRE 50 OR 60 AMP BREAKERS WITH THE PROPER WIRE.Ryan and Johnnie are doing well so far and are the top two amateurs in this contest of armchair wit and house burning down thread.near the electrical fires in the amateur stream,aj
*You may run a separate cooktop and oven on the same circuit, provided they are in the same room. Branch circuit conductor size and OCPD are calculated as if they were one unit, and tap conductors to each must be rated at 20A or greater.The circuit conductors and OCPD are determined by the nameplate rating on the appliance. Usually #8/40A minimum for ranges/cooktops/ovens.While the 10ga/30A existing may work, the danger is that because of frequent tripping, the homeowner will replace the 30A breaker with a 40 or 50 and then the 10ga wire is allowed to carry more than its rating.The only difference between a 3 wire and 4 wire 240V circuit is the presence of separate neutral and ground wires. The neutral is the return path for the 120V circuitry; the ground carries no current except during a ground fault (ie: it is a safety valve to interrupt the circuit in case of a short).
*Jack, You forgot to throw in George's electrician. He sounds like the worst one of all !! P.S. Did you get the Isuzu powered Chevy yet?? Any road reports.....
*Norm....Your post is ludicrous....You are posting to DIYers...I would never ever say a 30amp circuit is anything but wrong for kitchen ovens and ranges...Go to Lowes and find one oven or range that is rated for a thirty amp circuit....This thread as usual is full of bad info....b all beware!near the stream,aj
*Article 422-17 of the NEC allows for wall mounted ovens and counter mounted cook units to be cord- and plug-connected. It does not say anything about treating them as one unit. Accessibility of the plug as a disconecting means is addressed in article 422-22.That said, wire it for the name plate amperage with the appropriate size wire, as reguired by article 422-4(a).The name plate should have both 208v and 240v amperage ratings. If it dosen't; call the mfg. and get it. Your electrician knows this. He dosen't want to burn anyones' house down either.Dave
*Thanks, everyone, for all your thoughts on this. Based on some comments by my electrician, it resulted in a real head-scratcher for me this week end.In one post AJ stated: YOU NEED A 40 AMP 4 WIRE CURCUIT IN RESIDENTIAL RANGE WORK MINIMUM.Well Hey! - that’s simple enough even for me .However, I may yet get a reprieve from having to rewire the entire circuit. Not in the budget, know what I mean?We found a white-on-white 30” electric radiant cooktop by Jenn-Air that the owner’s will accept as their “second choice”. The manufacturers data sheet tells me (quote) …“Electrical requirements: three-wire, single phase AC 120/240 or 120/208 volt, 60Hz (Load 28.0 amps @ 120/240VAC). Properly grounded. Protected by 30 amp circuit. 45” flexible cable with 6” wire leads is furnished. Locate electrical box a min. of 7” below the cooktop.” Lucky, lucky me!Geo.
*pmusing your formula ( which is correct) plug in numbers and you will see when volts go up, current also goes up if resistance stays the same.Why would the current go down if the volts went up?Frank DuVal
*Good going Ryan!Why do these people not understand that for a fixed resistance, the current and voltage will be proportional, NOT inverse proportional?Your figures are correct.Frank DuVal
*George> Now I do know that the only dif between the 3 and the 4 wire set-ups is the presence of the neutral - and I still don't see how one neutral can serve a split set-up. I i thinkthe 4 wire adds a ground, not a neutral.Also, I i think the reason you can use 1 neutral for 220 circuits is that each 110 leg of the 220 circuit is 180 degrees out of phase, so any 220 current draw is effectively neutralized. (Although it's also my understanding that this is somewhat simplified.)> We found a white-on-white 30” electric radiant cooktop ....> The manufacturers data sheet tells me (quote) … “Electrical requirements: three-wire, single phase AC 120/240 or 120/208 volt, 60Hz (Load 28.0 amps @ 120/240VAC). Properly grounded....I believe that "properly grounded" might be the fly in oitment; suspecting "properly grounded" means a 4 wire circuit.
*Isn't this the part where someone talks about legs being 120 deg. out of phase and the quadrilineal acreage between the poles equalling 208 zapparoonies?Sorry, it's way past my bedtime...i tried to find where i read the explanation, but apparently the search function doesn't search for numbers, at least not "208" or "120".
*Th 208 3 phase discussion is under "wiring 240 V outlets"
*I can't believe how confusing people can make an issue. George, your electrician is grasping at straws probably trying to avoid the pain of routing heavy cable in tight areas. Get someone else to do what must be done. After all, the home owner is paying for this and has a right to have it to code. There is no out that code is a bit of overkill -- alot of factors at work especially length of the wiring run. Those of us who have wired in industry know many tricks and workarounds to save on wire and take advantage of 3 phase wiring. You only have 2 legs of 240, 220, 208 or whatever leg to leg voltage you have . These legs, if connected to 2 sides of a 40amp 240V heating element will both be pulling the 40amps that the element asks for -- NOT 20 maps each. Now ranges and cook tops with fans, lights, timers, and lower voltage (lower temperature setting) elements also use 120 volts. That current (WHEN REQUIRED) comes from one of those 2 legs also. This would add current only to the ONE leg and return through the neutral wire (4 wires) or the ground wire (in a 3 wire hookup), instead of returning through the other leg.Also 8 years from now, someone is going to want to put a 50 amp range cook top microwave convection infrablast ultra zap combo in and they're going to need that expensive heavy clumsy 6 a cable, and it's less costly now and they will think positive thoughts about you and you'll feel a warm and fuzzy buzz as you lounge in a hammock on your own warm island acquired from 7 years of working with impeccable integrity.Happy building,Jim alone
*George....More breaktime breakdown....Your specs call for 3 wires...and a ground...That is four wires to DIYers....b READ MY LIPS....4 WIRES.....DID I SAY FOUR?...YES...SURE DID....4 ...FOUR...1 +3= 4....FOUR.And well howdy doody...ya found a rare top that takes 30 amps....Well it doesn't make your circuit a smart choice!near the savings of less than two twenties for common sense,aj
*I would use my framing square to do this. If I line up the short side and the long side correctly, I get the phone number of my electrician.
*Steve --Here in Los Angeles, the DWP is required to provide you the nominal voltage plus or minus 5% as measured at the service entrance, and nominal for residential is 120/240. I found this out from them when I was spending a lot of money replacing light bulbs and measuring 125.5 volts. I got some 130 volt rated bulbs, problem solved.-- J.S.
*Frank --See my previous message in this thread (2.2 or 5 depending on the mode). Heating elements are not fixed resistances. Derating from 240 volts to 208 volts based on the assumption of constant resistance will give you a lower current value than the unit will really draw.-- J.S.
*I am big fan in doing your own thing, but get an electrician. I am told, by electrical inspectors that the most common cause of house fires is electrical problems. AJ is right, this is nuts and much of the advice is terrible. On current versus voltage, if you don't know Ohm's law, look at the power lines. They use higher voltage to reduce amerage and hence line size. If you really want to run 10 Ga wire, have 440 piped into the house and the wire size will be plenty. No, I am not being sarcastic just a little humor. It is good judgment to know when you are in too deep, and in this case, you guys (most) are in too deep.DennisIncidentally, 208 voltage is found in light commercial 4 wire three phase, and is the result of summing the sine waves out of sync - the humps are not exactly opposite eachother - seems to me they are 30 degrees off.
*Dennis...you were doing well till ya mentioned the 30 degree part.near all the electrical know nots,aj
*Bob Walker,In a 3-wire 240V system, there is (from the supply) two hots and a green or bare wire (the Ground).In one of the few exceptions to the code, this ground may be used as a neutral at the stove for running the clock and/or the thermostat at 120.The heating element is always 240 (or 220, whatever you got).Geo.
*Jim Malone,You said it pal ... people can sure make something confusing - and my sparky is grasping on this one, I'm sure. Someone was kind enough to E-Mail me and show quite simply that the two 30A breakers "tied" at the panel is still ... a 30A circuit.While I agree with your concept of principle ... Whatever someone wants to do 8 years from now ...? Maybe *they* can pay for the heavier wire then ... this is an elderly couple who just want to pretty up the house, get a small addition, a couple new bathrooms and a kitchen out of the deal.Geo.
*I give up.....Just beware....No one do as is suggested in this thread.What a bunch of whacky electric gab,aj
*AJ,Actually, what I think I've found is an appliance that's purposefully designed to retro-fit the old 3-wire, 30A circuits common to the older cooktops.Whether it's a smart choice, or involves common sense? ... would depend on priorities based on the scope of the job and the budget. Certainly I'll look into this top further, and you can rest assured I won't endanger the occupants w/ any hazards related to over-currents in their 30A run.What the customer is *not* gonna do is find the money to knock out a bunch of walls (it's all open beam, no crawl space) and pull new wire all the way back to the panel. It's my job to find a solution where at all possible. If you like, I would be happy to keep you posted on how we resolve this thing.yours,George Lentulo
*Bob Walker,Sorry, I forgot to mention but you may be right about the "Properly Grounded" part - on another job today and no time to look into this cooktop. The way I read the Jenn-Air info was that, if wired to an old 3-wire 30A circuit, the grounding of the appliance housing will be "Proper" - however they mean to do that remains to be seen.Geo.
*George....I coulda run that wire coast to coast by now....And budget?....If this is a budget issue for a c note or two...Get out!....Don't you make dozens of c notes a week just to cover your pay let alone your company?follow the yellow brick road...And the baseball stars are signing for damn near billions this year!aj
*Hey, jack, what if it were YOUR mom and dad? (And you couldn't be bothered because you were watching baseball...) I think George is to be commended (Congrats, George!)for a creative, conscientious approach given the old folks' circumstances.Now back up and i'll hit you a few... ;-)
*One more thought. If you use aluminum wire, you got to go one size bigger. I got the 6ga from the electrical inspected at the local power company. He told me this was minumim code for this area on new construction. rate for 50 amp at 60 degress
*Right....George is doing fine...But it shouldn't be posted on the net cause it is damn confusingly wrong advice to follow for the present codes and overloaded overly applianced Gringo kitchens of today and the near future....Someday when power starts to cost as much as it does now in San Diego...we will learn how to live with no utilty grid... I just checked out a sterling motor power source that heats as well as produces electricity...the only first drawback is that it puts out DC.near a stream that needs a power wheel,aj
*Jack, when i was a kid we had a water wheel (maybe 12'D) for generating electricity--only drawback was the 16 months of winter! The folks would thaw it out the first few cold snaps and keep it running, but then it was back to Coleman lanterns and kerosene lamps until March.
*Everytime I've tried to "help" by finding cheap ways to do something in violation of good practice, I've ended up losing my shirt and leaving the client with a sub standard product.If they want a half assed job on the cheap, I'm not their man anymore. My advice: If you can't afford to do it right, don't remodel your kitchen right now.
*Ryan,>If they want a half assed job on the cheap ...While I might agree with you that there are people who haven't got a clue as to what it takes to do a job right, either w/ regard to time or money ...finding an appliance that will satisfy your customer's budget concerns while matching up to the existing rating of your electrical system can hardly be viewed as substandard or a violation of good practice. While we in this business are hardly a charity, nor can we solve all issues for all clients ... it's certainly a worth-while endeavor to explore all sides of an issue in an attempt to uncover a way to make it happen for them. I regret that you lost your shirt and left your customer w/ a substandard product - in my business I push on almost daily to make sure that neither of those things ever happen.Have a good day, young man.Geo.
*So I'll bite, how many degrees out of phase is each leg of a 3 phase circuit?Dennis
*Can't "resist", so I'll confuse the terminology even more. There are no legs "out of phase" on a 3 phase circuit unless there is some negative sequence power (what's that, you say?). (Hint: for a pure resistive load on a 3 phase generator one measures 3 phases with 120 degree phase separation; out of phase is a different terminology)
*My comment was in reply to somebody else. Not a suggestion that you would ever personally do imperfect work.I'm sure your work is impecable, that you'll be following the electrical code and planning ahead to protect the next owner of this house who might go out to home depo and buy a new stove to replace the one you're putting in.Don't get yourself all worked up. Watch that heart old fella.
*I'm using a stationary phase converter to get 3 phase for a lathe. Uses capacitors to create a third leg. What's the phase separation for this set up?
*pm is right about the law, which is E=IR, which is more than slightly different. However, his math is faulty. If resistance is to remain the same, then in order to balance the equation, when E goes up, I has to go up.As far as the voltage goes, different appliances are built to have different voltage tolerances, to wit, an incandescent bulb, or a resistive heater will work at almost any voltage lower than design--just not as well, while a TV or microwave will likely crap out below about 70% of design voltage. Hence, it would not be unlikely the stovetop would run at 208 or 240 volts. Getting 208 volts is another matter. 208 is normally only available in commercial areas, as it is generated from 3-phase electricity transformed by what is called a delta configuration, while 240 volts is obtained from a transformer in a 'wye' configuration. Household electricity is transformed from what amounts to two phases, in a way that more resembles the 'wye' configuration, so you'll need 8-gauge wire on a 40 amp breaker minimum.
*Well, there I go, again. I've got to start looking at the number of replies before I jump in. I agree with with Jack: forget it. Put in a gas range.
*George, there is another solution to the 208v problem. Have your electrician look at the cost of adding "buck and boost" transforner to the circuit. It will step the 240v down to 208v. Good luck.dave
*Do I get it right, here? Apart from the knobbly sine wave?I don't want my college ejumacation to be all for nothin'...did
*Ryan, considering the advice and info you gave in your first post, perhaps you are not the best qualified person to judge another's work.
*Doc,delta or wye are transformer winding configuration correctly enough, but secondary voltage has do due with were the winding is tapped. It is the number of turns in the winding that determine the secondary voltage,either in a step up or step down type use. By moving the tap up or down on the winding you get more or less voltage.I've got 120v/208v panels where I work, and they are fed from wye configured dry type transformers.This thread has stayed off of the original post as usual, but what the heck, I'm learning to review what I thought I knew. I'll post the transformer winding relationship if anyone is interested.By the way power companies are generaly required to keep the voltages within 10% of what they are supose to be on low voltage systems. For 120v that means + or - 6volts. Low voltage is considered any at 600v or less.Dave
*Posted by FryedThe original circut should be upgraded to 40 amps. All stoves run on 40 now. All you have to do is fish an 8 guge line.
*Sorry, diddidit, but your two sine waves should be out of phase with each other, when one goes up, the other should go down, if 120/240 single phase is what you mean to illustrate. -- J.S.
*i But it shouldn't be posted on the net cause it is damn confusingly wrong advice to follow for the present codes and overloaded overly applianced Gringo kitchens of today and the near future.... But apparently it's ok to post about plugging an electric range into a 110 outlet and using it...
*Confused Luka?just helping things go round,aj
*If they are out of phase with each other, won't the resultant be zero volts? Feel free to correct me, I'm a mechanical engineer and don't speak wire all that well. Fortunately my father-in-law (soon to have his first grandkid courtesy of my wife and I) is an electrician.did
*This whole thread must be a joke. Nice going guys - I knew it when I saw a comment by a mechanical engineer who had to have physics and calculus to graduate. The phases are basically in the moon and the 60 cycles are all in a bicycle rack along with AJ who is streaming along. Merry Christmas to all and I hope to see you next year.DennisP. S. I don't know "wye" I posted this as I am sure that one of the old posters from down on the "delta" could have done better than I did.All tanagled up in my wires and uncertain on how I sould guage my response, I remain neutrally yours.Dennis
*Congratulations Derek, looks like the father-in-law had the wife wired up right and that the 2 of you are in phase. As my grandson says if the tree is off, p'ug it in!
*diddidit - if you touch the two out of phase hots together you have essentially zero volts between them - and one hell of a lot of current flowing... It has been a while since I dozed through an electricity and magnetism class, but let's see if we can puzzle our way through this. The old formula E=IR that they must have hammered into the heads of even mechanical engineers supposes that the "E" is the voltage across the load. If you hook two hots together that are in phase, they are both at the same point in the voltage sine wave at the same time and you have no voltage between them or across the load - i.e. both ends of the load are at, say, +240v at the same instant. If you place a resistance between two hots that are out of phase, you have a voltage difference with one being at, say, the peak voltage of 266v neg. and the other at 266v positive. This allows you to create the little sparks and such as the electrons rush from surplus to scarcity through the widget placed between them resulting in maximum smoke and such.Now, you do get the out-of-phase voltages cancelling out if you have equal loads from each of the hots to a shared common. Thus if you have 15amp draws between each hot and a common neutral (with the attachment to the neutral being at the same point), the common wire should be at, or close to, zero volts with respect to ground. The electrons getting spewed out of the 120v negative leg are getting sucked up by the 120v positive leg rather than zipping back to the grounding point via the neutral - or in theory at least. Confirming this by touching the common wire with your tongue to determine if there is any 240v current is not recommended, however. Let me conclude with the usual disclaimer: All I know is what I read in my physics book - I am not an electrician although it might appear that I occasionally play one on this board.
*i Confirming this by touching the common wire with your tongue to determine if there is any 240v current is not recommended, however. Why ? Does your tongue get stuck like on the flagpole in january ? If so, all you have to do is douse it with water to get it unstuck...
*I really hate to see people talking about using Ohm's law in AC circuits. It is only valid for perfectly resistive loads and determining if your load is 100% resistive is not always easy.The best bet is to use the nameplate amperage times 1.25 to see what size circuits you need, unless the nameplate recommends a circuit size.Allan
*Now to really get all your shorts in a knot....It is actually not the electrons flowing in a wire. It is actually the holes that flow. The hole where the electron was snatched from.The negative terminal was mislabeled from the beginning and has never been changed.near the electron hole in the stream,aj
*No, No, No.The elecrons realy do flow, just not from positive to negative, they flow the wrong way.I think Ben Franklin got the positive and negative thing backwards and his convention stuck.They just tell you in electricity texts that the holes are moving because that lets you picture things going from positive to negative and seems easier to understand.
*Talking about electron flow, do you know it takes a typical electron 1 minute, 10 seconds to go just 1 inch in a 10AWG copper wire carrying 10Amps (I bet you can win a few bar bets with this one, correct terminology is electron drift). We can start talking holes if anyone from Intel wants to relate details about chip (no jokes on wood chips or cow chips please-sure to keep thread going) fabrication.
*You made my brain hurt! OW OW OW OW OW !!!! Pneumatic power is just so much easier for me to design, although it's hard to make a light bulb light with shop air...Just to power up some good jealousy, I got to go to breastfeeding class last night! What fun!did
*What sort of grades you pulling down, did?
*Hey !! Can I go next time ? Tell the teach that I'm an old pro, and I will volunteer to teach all the kiddies by example...
*I alsways wondered.... If'n all them holes and electron thingys and molecools, etc, is all a moving along that piece of wire... why don't the piece of wire get moved into the light blub er somethin ? When one molecool moves out, does another one move in ? Ok, then, with the 'electricity' starting at the hydro plant, why doesn't the copper wire at the generator end of things eventualy dissappear ? All it's holes and electrons and stuff have only one direction to go. Once they're gone, where do the new ones come from ? The water ? (If so, how come our light blubs can't be used as aquariums ?) Do new copper electrons and holes and stuff just materialize outta thin air ?
*Got other things to do Art, haven't had the time to sit around timing electrons lurching along, but I appreciate your doing it. Besides, my eyesight isn't quite what it used to be so those pesky little electrons are a bit harder to see these days. If I remember correctly, it takes something more than 10 to the 19th power of the little buggers zipping past each second for each ampere of current. In normal metal wiring, electrons are what flow. In semiconductors, electrical flow in certain situations is described as holes. Ryan, it's been a long time since high school physics, but I thought the labeling of positive and negative predated Bennie - I think his primary accomplishment was avoiding getting fried with his famous kite and key experiment. However, he did prove that lightning was electricity and invented the lightening rod. The positive and negative terms may have been around in the days that electricity was produced by rubbing things like amber with fur and zapping the cat, although maybe it came about during the days or Leyden jars. (However, I did run across something that indicated that he is given credit for deciding that things can have a plus or minus quantity of "electric fire".) Anyway, you are correct in that they labeled things before they knew about electrons and such and with a 50/50 chance to get it right, they didn't (unless you count holes or plasmas and such...)Luka, I just threw that bit in about the tongue because I had read on another site someone saying that an old electrician he worked claimed that he could tell whether a wire carried 220v or 110v by putting his tongue on the wire (WARNING - don't try this at home, kids!) Doing an Internet search on "tongue" certainly turns up lots of electrifying sites, although none concerned with electricity (i.e. most of the hits on the web search for "tongue" turned out to be porno sites)...The electrons sort of meander from atom to atom. The magnetic field of the generator sort of kicks the electron out, leaving a temporary hole, and the electron sort gumpily slouches along and then finds an electron on another atom and kicks it out and takes it place - something like with sea gulls that one-up each other. The bumping continues along the wire until an electron ends up filling the first hole and continues as long as the generator keeps twisting out its magnetic field. This is why you have to have a complete circuit, so the incoming electrons can get whipped around and pushed out again. Except, of course, if you are filling up capaciters or inductors which can only continue for a brief period of time and then it all starts to get complicated...
*In breastfeeding class, I succesfully deciphered the difference between me and my wife. I also managed to refrain from demanding the right to convert my PC pancake compressor into a breast pump. Also I was only one of 2 guys there, so I got extra points for that. Grading period begins roughly February 16!did
*Luka, your brain must hurt too!! Alas, there was nary a nipple in sight, not even a video. And the lactation consultant says it's important to build up callouses on the nipples to allow more vigorous suckling.did
*Knew of a physicist who judged laser power by staring into the beam...did
*Breastfeeding class? Who needs a class? If we can figure this electricity stuff out so well, I'm sure we can figure out breastfeeding. Haven't seen any electricians going hungry lately, have you?
*Where there refreshments?
*OK, I goofed. I blew it - hard to believe, I know, but I did. I am surprised that all of you history of science buffs didn't jump all over me. Anyway, old Benj is indeed credited with the concepts of positive and negative and thus gets the credit for being misleading in terms of current in a wire even if it can be said to be right for semi-conductors. The earlier experimenters understood that there were two kinds of electricity that cancelled each other out, but they thought of them as separate "fluids" and labeled them as such things as "male and female electrical fire", etc. So my fullest apologies to Ryan C for having the slightest doubt as to his knowledge in this area...By the way, can any of you historians out there answer whether the rather randy Benj Franklin, when asked about his dalliances with the Parisian ladies, actually said that he prefered older women because "they don't tell, they don't yell, and they don't swell?
*Casey: I wouldn't have jumped on you (about BF's contributions - his treatise on electricity was probably the last time the US had an ambassador who was also the most knowledgable scientist in his field). But I would have corrected you, if I hadn't been in Mexico last week (Copper Canyon). But I will jump on Art about the "typical electron takes 1 minute, 10 seconds to go just 1 inch in a 10AWG copper wire carrying 10 Amp". At least in my house, it's AC in the wires. So the average electron goes nowhere, it just moves a fraction of a 0.001" back and forth 60 times a second. The power company is not selling you new electrons. They just push the same old electrons back and forth. One could set up a business running DC through a house's wiring for a day or so to flush out the old tired electrons. Allen: If a range isn't a resistive load, what is? It might have a tiny load on a fan if it is a convection oven, but would still be pretty dang close to 100% resistive, denying us science dweebs the opportunity to use complex number vectors to do the math. -David
*No, in phase means no difference, zero volts between them. Out of phase means that when one is up, the other's down, and the resulting voltage difference can drive current thru a load and do some work.-- J.S.
*>Allen: If a range isn't a resistive load, what is? It might have a tiny load on a fan if it is a convection oven, but would still be pretty dang close to 100% resistive, denying us science dweebs the opportunity to use complex number vectors to do the math. -David It is resistive in the sense that it doesn't mess with the phase between voltage and current the way inductive or capacitive loads do.But the resistance isn't constant. It varies with temperature. It's that assumption of a constant number of ohms that'll get you in trouble.-- J.S.
*OK, electrons and holes and stuff.... Atoms consist of a nucleus which is where all the weight is, and the positive charge, in the form of protons. That positive charge has to be balanced by the negative charge on the electrons that orbit around the nucleus. In some materials, the ones we call conductors, the electrons can to a limited extent move from one atom to another. In other materials, the ones we call insulators, they can't. It's only the electrons that move, and not most of them. The nucleus and most of the electrons stay put. It works kind of like traffic on the freeway. The concrete road is the atoms, it stays where it is. The electrons are the cars, and the holes are the spaces between the cars. On the freeway, most of the time all the cars are at a dead stop. Then way up ahead, one of them moves forward maybe 10 - 15 feet, and stops again in its new position, creating a space (hole) behind it. Then the next car moves forward into the space in front of it, creating a space behind it. Viewed from above, the cars seem to move one way, but the spaces move the other way. Of course, electrons and holes move a lot faster than freeway traffic. An inch in ten minutes would be six inches per hour.-- J.S.
*John - true enough when you are talking about the common solid stuff. However when you are talking about current flow in electrolytes and plasmas, then you have the "holes" moving about. The galvanic action that has been discussed in Breaktime threads regarding the joining of water pipes of different metals comes about because the ions (atoms short an electron or two from a full complement) gravitate away from one of the metals. (And, of course, electroplating in which this is done on purpose). Then we also have plasmas, such as in my plasma cutting torch that also has the "holes" blasting out to do potential damage to all sorts of things...Since it has been many years since my last class on semiconductors, I have forgotten why it is that holes rather than electrons were found to provide a better description of the current flow in certain situations.
*Casey --You're absolutely right about electrolytes and plasmas, where charged atoms (aka ions) can move around. One of the great things about these internet discussions is that you get reminders of what you didn't think of the first time around. As for electrons vs holes in semiconductor thinking, it's a question of which is the majority carrier, and which is the minority. It's easier to visualize the majority as a background against which you see the minority moving, like the example of watching the spaces between cars moving the other way on a jammed freeway.-- J.S.
*
Hi all,
Until I can catch up with my electrician Monday, I've got an issue driving me nuts.
A customer has picked out an electric cooktop to replace an existing one in a kitchen remodel.
At the panel the breakers consist of two 30A breakers tied together (for 240V - I get that part). However, the new stove is rated 40A @ 240V, which is too much amperage for gauge 10 wire (30A circuit wiring).
Conversely, the specs for the cooktop say the minimum amp load is 30A @ 208V. A quick call to my electrician yesterday, and he's telling me that he thinks that can be made to work.
How? Does that make any sense to anybody else? Thank you in advance for any relevant information.
George Lentulo
If anybody is wondering how David came up with the 34.6 amps for the 208 voltage. He used the 20 amps for the 120 volt leg from the manufacturer and he used 14.6 volts for the 88 volt leg. 120 volts + 88 volts=208.
Here's how he got the 14.6 amps. He set up a relationship or as i do and find it handy is to cross multiply.
88 x 20/120 = 14.6.
14.6 + 20 = 34.6 amps
I'm not sure if the 14.6 volts is right, but that's how he came up with the voltage or used a similar method.