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Double pole breakers on 208y 3 phase panel

hannahbsturm

Plastic
Joined
May 1, 2016
I have a 150 amp service panel that is 208y/110 3 phase. At least I am assuming it is 208y because this is what I have been told and because when I test any two leads, I get 208.

But I am having some issues involving the placement of double pole breakers in the panel that are used to power 240 single phase equipment. It doesn't seem that I can just put them in anywhere...result of this is a pop at the outlet when I flip the breaker on. I have to skip a leg on the panel, but this is most confusing to me because I thought that skipping a leg was only necessary on 3 phase Delta configurations that have a high leg.

Any advice?
 
What kind of outlet is giving this problem?

The problem with the high leg is usually due to wanting to run 120V equipment, which can only be done off the A and C legs, because the B leg is the high leg and is not the same voltage to neutral. But 208/240 equipment that does not use the neutral should not have an issue with standard or high leg service. Neither should any 240V outlet.

There are 240V household outlets that include the neutral, but they should not have any difficulty with any form of 208/240. In fact, I use them for 3 phase in my personal shop, due to their being easily available, rated for the voltage and current, and not used anywhere else in the facility.

I don't know why there should be a pop from any outlet, unless maybe it is a GFCI. Does it open the breaker?
 
If you cannot physically install 2 pole breakers in some of the slots, it sounds as if someone used a 120/240 3 phase "high leg" designed panel on a 208y120 system. Some panel mfrs physically alter the bus stab arrangements so that you cannot plug 2P breakers into some slots.

That doesn't necessarily explain the "pop" however. Even if you tapped off of the wrong two legs of your 208V, nothing should be popping. You have something else going on here, likely some other mistake in the wiring by whomever installed that panel in the first place.
 
!danger!

What kind of outlet is giving this problem?

The problem with the high leg is usually due to wanting to run 120V equipment, which can only be done off the A and C legs, because the B leg is the high leg and is not the same voltage to neutral. But 208/240 equipment that does not use the neutral should not have an issue with standard or high leg service. Neither should any 240V outlet.

There are 240V household outlets that include the neutral, but they should not have any difficulty with any form of 208/240. In fact, I use them for 3 phase in my personal shop, due to their being easily available, rated for the voltage and current, and not used anywhere else in the facility.

I don't know why there should be a pop from any outlet, unless maybe it is a GFCI. Does it open the breaker?

It is at the very least bad practice, but in reality, actually quite dangerous to put a hot leg on a recepticle slot intended for a neutral. I know its done all the time, partly because certain big box stores don't carry 3 phase stuff,
and because its usually cheaper, but how cheap would it be if someone else plugs something in and it starts a fire, or worse gets hurt? its very simple really, just don't do it. use 3 phase stuff, such as L15-20 (for 208-230 20A)
saying to your self "I'm the only one who uses it" just isn't good enough, there is no way to insure that will always be the case. you wouldn't wire a 120v outlet with 240 would you? so how is it ok to put 240V where there should be 0v?
don't use 14 series receptacles for 3 phase!
 
I have a 150 amp service panel that is 208y/110 3 phase. At least I am assuming it is 208y because this is what I have been told and because when I test any two leads, I get 208.

Any advice?

You should verify what you really have my measuring each phase to the neutral or ground. If 1 phase is closer to 200 Volts, you do not have a 120/208 service.

Bill


Edit to deal with the off topic: The current L14 20 connector pin shape was rebadged several times over the years. Things get dicey in larger operations where the L1420's are used on literally everything from 120 to 480. Smoke gets let out quickly when one plugs in a 120 or 240 Volt load into a receptacle wired for 480 "because the plug fits". The Silver pin should NEVER have a phase attached to it.

Bottom line: For new installs use the correct plugs and receptacles or just use the old non NEMA devices.
 
There is a new thread in which to debate the off-topic matter. Please take it over there.

http://www.practicalmachinist.com/v...ing-connectors-creatively-321746/#post2785007


Getting back on-topic.............

It would be strange to find 208V high leg power. I don't think I have ever heard of it, and certainly have never seen any.

The whole point of 208 is to have all 3 phases at 120V from neutral. it makes no sense to do unless you preserve that. I suppose that really poor power with substantial drops in the wiring etc might have 208 when it is supposed to have 230V, but I'd be surprised to find it well balanced in that case. However, I have been surprised by things before.

We need to find out more about the problem described, and what sorts of receptacles are being discussed.
 
It would be strange to find 208V high leg power. I don't think I have ever heard of it, and certainly have never seen any.

Since we don't know much about what he really has, it makes a lot of sense to ask him to VERIFY his assumption of having 120/208 power.
I have been in many arguments over the years concerning low or high voltages with people who should know better. Usually turns out to be not knowing how to check the measuring equipment and it is not reading correctly. So I suspect he really has 120/208, or a meter reading low and he has 120/240 Delta system.

We can offer lots of advice based on assumptions that may, or may not be valid.

I prefer to verify assumptions at the start.
 
Since we don't know much about what he really has, it makes a lot of sense to ask him to VERIFY his assumption of having 120/208 power.
I have been in many arguments over the years concerning low or high voltages with people who should know better. Usually turns out to be not knowing how to check the measuring equipment and it is not reading correctly. So I suspect he really has 120/208, or a meter reading low and he has 120/240 Delta system.

We can offer lots of advice based on assumptions that may, or may not be valid.

I prefer to verify assumptions at the start.



She did verify 208V between all lines. So far, she seems to be competent and capable of doing the measurements, etc. Naturally, we can't see the install, so we will have no way to be sure.

And we have asked for pics of the install. As you say, it could be something quite different from what seems to be described. Hopefully, with pics of the various parts, some clarity can be had

That said, if it really IS 208, it pretty much has to be regular wye unless a real moron wired the place. No powerco would supply 208 high leg service. The only reason for 208 is to be able to load it with 120V loads and maintain balanced loading, which cannot be done if there is a high leg.
 
This is a NEMA 6-20 receptacle. It has a 20 AMP double pole Siemens push-in breaker and the line was run on 12 gauge, 2 conductor, 1 ground (not sure whether to call this 12-2 or 12-3).

I discovered the problem, which was completely unrelated to breaker location in the panel. In fact, I feel sheepish admitting it, but the circuit was shorting out at the outlet because the screw holding the receptacle to the box had damaged the outer jacket of one of the wires and was touching it. I had moved the location of the breaker but had also moved the location of the receptacle and re-wired it, so the issue was me having re-wired it, not moving the breaker.

On a side note, I am not a complete idiot. I take performing electrical work very seriously, am extremely cautious, but my limited experience does cause me to run into issues and occasionally feel, well, like a complete idiot.

This is probably fodder for a new topic, but am I to understand that I should not use 2-conductor wire on a 3-phase panel?
 
And I do have 208y, not delta. 208 between any two hots, A-B, B-C, A-C. Just made a mistake by not clipping off the screw to a shorter length. It was quite long and the wires just ended up directly behind it with no place to go.
 
On a side note, I am not a complete idiot. I take performing electrical work very seriously, am extremely cautious, but my limited experience does cause me to run into issues and occasionally feel, well, like a complete idiot.

Get to learn new things all the time, Hannah. I bet everyone here has allowed a conductor to get pinched or pierced at one time or another. Congratulations on being able to trouble shoot and find it on your own. For the future, even though I happen to like the "T stripper" type wire strippers, I keep one of the stripper / crimper combo tools with the holes for cutting machine screws handy for those times when it looks like the supplied screws are going to cause trouble.

This is probably fodder for a new topic, but am I to understand that I should not use 2-conductor wire on a 3-phase panel?

I am having a little trouble envisioning the reasoning behind taking a single phase circuit off a 208V panel; I thought we were discussing a three phase load in your last thread... or is this for different equipment? My concern is while many 3 phase motors are rated 208-230, or 208-230 / 460, most single phase dual voltage motors are 120/240, with no rating for 208. Running on low voltage is a recipe for having the motor run hot. Of course a buck-boost transformer can be used to boost the voltage to 240. Care to discuss the project a bit further?

Dennis
 
If you do have a 208 single phase load, you DO wire it up with 2 conductor (W/gnd) cable. No need for any other wires, just the 2 hots and equipment ground.
 
" most single phase dual voltage motors are 120/240, with no rating for 208. Running on low voltage is a recipe for having the motor run hot."

There was no mention that the load was a motor. In any event many modern motors are dual rated 240/208 and even those
not so rated handle the 208 just fine. Work around for that if not, is a boost transformer.

I've been guilty of punching through insulation with the odd fastener now and again....
 
The outlet is for a motor, and it is single phase 240v. I have not run it much on the wrong voltage, and if I do use it more frequently I will think about a buck booster. But actually the reason for moving the outlet/rearranging the breakers in the panel was because my focus is on a different machine which I am trying to step up to 575v. One thing at a time...
 








 
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