Customer thinks he has 3 phase power. At the top of the panel is a 200 A three pole breaker. There’s only two feeders going into the main. This is single phase power in a three phase box, true?
Three wires come into the panel. One goes to the neutral bar.
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Well there are 3 phase system where one leg is grounded. Called a grounded Delta.
But I really don't know much more than that.
Measure the votlages N to L1, N to L2, and L1-L2. If it is 3 phase they will all be the same.
I suppose there is some chance that the previous owners may have moved, taking their phase converter with them. If they had one they could have driven the three buses with it. When they left it just became a huge kludge.Big Macs - 99 cents
Somehow, this doesn't sound right. If this is a commercial panel, wouldn't the third phase be connected to the third lug on the three pole breaker?
Anyway, if L1 to L2 = 240 volts, then you are probably dealing with a Delra system.If L1 to L2 = 208 volts, then you probably have a Y system.
~Peter
1. What color is a green ground screw?2. To trip a circuit breaker, you must stick out your foot as you walk by it. T or F3. A keyless fixture cannot be unlocked? T or F4. A circuit breaker reads "20" on the handle. This means it can trip only 20 times before it wears out. T or F5. A flush mount device may only be hooked up to a toilet. T or F6. An Ohm is a Hindu measurement of voltage. T or F7. Electrical inspectors are known as ________.8. If you have a molded-case circuit breaker, the mold can be washed off with warm soapy water. T or F.
9. What type of bender is required for flexible conduit? _______
"Somehow, this doesn't sound right. If this is a commercial panel, wouldn't the third phase be connected to the third lug on the three pole breaker?"I did a little googling and aparently grounded delta (aka corner delta) or not very common.From what I have seen it appears that in general a 3 pole disconnect is used, but only 2 poles are FUSED. However, I guess a 3 pole breakeer could be used as all poles would open together.But look here http://www.iaei.org/magazine/02_a/johnston.htmAt figure 3 and 4. In 4 they show no disconnect on the grounded leg and 2 pole breakers.But in 3 they show show 3 pole disconnect and motor starter, but only fuses on the ungrounded conductors.Here are some other discussion on it.http://www.electrical-contractor.net/ubb/Forum7/HTML/000347.htmlhttp://www.electrical-contractor.net/ubb/Forum7/HTML/000225.htmlhttp://electrical-contractor.net/ubb/Forum15/HTML/000078.htmlAnd as rare as it appears (I think that one guy said that he has seen one in 20 years) it would not be surprised to see one miss wired (if it is miss wired).And compounded by the fact that Farmer is in an area without an inspections."Anyway, if L1 to L2 = 240 volts, then you are probably dealing with a Delra system." Or single phase.Realy don't know enough about this make any guess.PS, I like your quizz. Got any more.
It sounds like your customer is using a piece of 3 phase equipment for single phase purposes.Is every third breaker dead? Tell us what your voltage readings are.
The cornerstone ground service that others have mentioned is indeed very rare.I know of one municipality with their own generating plant that uses it in some industrial settings.It's why we're always taught when reading voltage in a panel to measure between phases at the main lugs.Not just main lug to ground or neutral.If you're undisciplined and in a hurry and quickly read from main lug to ground,read zero and assume the panel is dead...and then find out you unluckily picked the grounded phase to check...you're going to get hurt.
The first picture below is the disconnect that was installed for my house. It's a commercial 3P box for 1P power.
The second has nothing to do with anything discussed here."Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
JJSHAW,
Photo#1:
I'm curious what the 3 ph. disconnect is for.There is only a handful of reasons that the Code will allow more than one service to a building(different voltages,rate schedules,etc.).Or do you have one service on the other side of the wall with more than one disconnecting means?And then what are the different purposes for the single phase panel and the 3 phase disconnect? I've said here before that I do more 1000 amp services in a year than 100 amp,so I'm always interested in how others do residential services around the country.
Photo #2:
Absolutely perfect.Thanks.
Barry
I wanted a single service that would provide power to both my house and my workshop. Since the workshop was built first, I located the meter there. That photo is on the workshop wall. The panel on the left is the 150amp panel for the shop. The disconnect was put in to allow for a 300amp feed to the house. I have no idea why they had to use a 3P disconnect for 1P service."Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
Hi Jon,
I couldn't tell if your shop panel had a main breaker or not from the photo.The fusible disconnect on the house feeder made me think they tapped two feeds after the meter and brought them in unfused.Or do you have two disconnects outside?I'm not keyed into price always, but I'd think the 3 phase disconnect would be more money,unless you had it left over from another job of course.Just curious.
Barry
The only thing on the other side of that wall is a meter socket. As I understand it, they split the power at the socket, sending two 120V legs to both the main shop panel and the house disconnect switch.
Yes, there is a main breaker in the shop panel. There is no other disconnect, beyond what you see in the picture. (The FIRST picture.)
The 3p disconnect was ordered new for this job. I have no idea why they ordered a 3P box. Could be because of the size - it's a 300amp disconnect. If they make 300amp 1p disconnect boxes, then I may have to have a talk with my electrician.
On a side note, the first disconnect box they brought out to my sight was nearly TWICE as big as the one you see. There was some mixup at the supply house. I was going to keep it, just for the novelty of it. But it was going to cost me well over $1000 just for that disconnect, so I sent it back. I think this disconnect cost me close to $800."Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
Once you get above 200 amps, many manufacturers only offer a three pole fused disconnect switch. I just took a quick look at a couple of my catalogs to confirm this - for 300 amps or above, some of them come right out and say, "Use three pole switch for this application." The supply house your electrician got the switch from may have been able to find a 300 amp switch with only two poles, but chances are it was simpler and cheaper to just go with a product they normally carry. As far as I know there aren't any Code issues when this is done.
That's pretty much what I assumed. I have faith in my electrician (a good thing) and believe that he put that disconnect in for a good reason.
It was a big chunk of change though for something that seems pretty simple!
"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
I see no harm at all in having that unused switch and fuse holder in the box. It's probably a case of having the 3P box left over from another job, or mis-ordered.
I did see a big delta three phase setup about 30 - 40 years ago, in a hotel that was probably built in the teens or 1920's. It had big boards of slate, big bars of copper, ornate knife switches.... So, I've been under the impression that delta 3P was an older thing, and that wye is more recent. IIRC, N-L1 = 120, N-L2 = 120, L1-L2 = 240, all just like conventional single phase. L1-L3 = 240, L2-L3 = 240, but N-L3 = something else, maybe 208?
-- J.S.
John,
The nominal voltages you state are correct for a 240 volt 3 phase 4 wire distribution system.The bastard or "high" leg is 208 to ground and has to be marked with orange tape and identified at every accessible point.The phase conductors are all ungrounded.
If a factory has a high current need but limited voltage needs it's supposedly superior.Where I've seen it is in a plant that has many 3 phase motors and overhead high bay lighting.Everything is 240V (or 480v for that matter) and for the limited amount of 110v needed,they center tap one of the phases(on 240v).The problem is then that you create one high leg that f's people up that aren't careful and paying attention.It seems to me this kind of delta transformer can deliver something like 58% more current than a wye configured transformer.That's from memory and not a Google report.A wye configuration gives you more flexibility with usable voltages but can deliver less current.For example a mall store would give you three pairs of conductors with 208 between them but all three conductors would have 120v to ground to meet the increased needs for 120v power.
You're right the unused third phase terminal in JJShaw's service isn't a problem at all.
Barry
Looks like he got a deal on a three-phase disconnect. That slpit-phase system looks workable.
No way do I believe this is 3 phase.
The 3 phase I've dealt with had 3 hot lines coming into the panel. Two of the are 110V to ground. The 3rd phase is the "wild" phase, and is 220V to ground.
I also think he would be paying an upcharge for 3 phase service, and it would show up on his bill.
One other clue would be 3 power lines outside instead of 2.
I wonder if maybe someone just used a 3 phase box in a 2 phase house?
Got a picture of the thing? I'm sure that would go a long way in sorting this out.
This panel is in the city where they got inspectors. It looks old. The maker was Federal Pacific Electric.
Three wires in the service to this panel. One goes to the neutral bar. The other two to the 200A main breaker. It's 240V all the way around, N to L1, N to L2, and L1 to L2.
All the breakers are two pole.
I'm going to hook it to a new IR air compressor. Some say a good sparky has a devices to hook the lines up so the motor spins the right direction the first time. What's this device called. Would I have to worry about it on a modern piece of eq? Of course, switch two lines will reverse the direction of rotation.
IR AC is to arrive about Monday. No pdf installation istructions are available at http://www.irco.com/air.
Big Macs - 99 cents
Yes, that is a grounded delta 3 phase system.The device that you are talking about is a phase sequence test, phase sequence indicator, 3 pahse motor rotation indicator.http://www.professionalequipment.com/xq/ASP/ProductID.2373/id.15/subID.284/qx/default.htmhttp://www.goodmart.com/products/83418.htmhttp://www.twacomm.com/Catalog/Model_61-521.htm?ovchn=FRO&ovcpn=Froogle&ovcrn=Froogle&ovtac=PI
Dave,
In your first post I thought you said there was a three pole breaker,which lead me to assume three vertical supply bus plus a neutral bar.If you're correct about the voltage readings I don't think that's kosher.Bill H. has a link that I think shows the third (grounded) phase to the neutral bar but I've never seen it done like that.If it is a three pole main(three feed bus) and they have two phases on the mains and one phase to the neutral that doesn't sound right to me.And if it's only a two pole main(two vertical feed bus) with a third grounded hot phase going to the neutral bar then someone is using single phase equipment for a three phase service,and that really sets off my BS alarm.
It sounds like you're asking about a phase rotation meter.It's just a three phase load that turns either clockwise or counterclockwise.When you're changing a service you first hook up the meter and see if it's going CW or CCW.You change the service equipment and then hook up the meter again to see if it's going the same direction(there's no guarantee that the utility hooked their phases to yours in the same pattern).If you don't do this step you risk having all the pumps, fans,motors running backwards.A phase rotation meter can't tell you up front which way a 3 phase load will run though.Just because it might run CW doesn't mean your motor ,looking at the end shaft,will also run CW.It's always a 50-50 shot.Scroll compressors don't like to run backwards for very long,but we always check rotation on three phase loads at start-up anyway.Once I saw a brand of three phase pump that had to be taken apart and re-assembled if you started it up in the wrong direction,but that was a German POS.
From your post you do know that changing any two leads on a three phase motor will reverse rotation.But you state that all the breakers in the panel are two poles,so doesn't that mean they are only supplying single phase power,and they're only going to rotate one way?Reversing connections on a single phase motor doesn't change direction.Or are you going to tell me that they are using two wires from the two pole breaker plus the neutral to get their three phases?If someone asked me to hook something like that up I'd either pass,or make them assume the risk to their equipment.
Barry
"If you don't do this step you risk having all the pumps, fans,motors running backwards."Hear a story, probably when I was in school about 40 years ago, about this kniting mill down south.The power co did some work on the lines and when after they reconnected the phases where reversed.None of the 3 phase kniting maching liked to run backwards.Understand the poco paid about about a weeks worth of labor to cut all of the yard out of the machines.