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Discussion Starter · #1 ·
Hi Everyone,

First off, thanks for this great site; the Internet has, and is doing wonders to bring information to the forefront.

I've been retired for a few years from commercial, and light industrial work as a Journeyman. Presently, I'm making a little extra ends meat by still 'turning screws' as a part time electrical service contractor; doing residential.

My present question is regarding a 3 phase high leg delta system, and hooking up A, and B phase(wild leg) to a 2 pole 50 amp GFCI(at location being used as equipment disconnect) for a spa. The spa isn't hooked up yet, but the GFCI is tripping once I energize it via the 50 amp 2 pole breaker in the service panel..

Considering there's zero load, as the spa isn't hooked up(whip simply terminated inside of equipment with wire nuts), why is the GFCI tripping? It's hooked up properly.

Would the high leg in some way be the cause of the GFCI tripping, or is there something I'm missing?

In all honesty, doing the electrical work I've known for so long, that being commercial, and light industrial, I've not had too much experience with spas, or even high leg systems.

Any suggestions would be appreciated.

Thanks,

Joe
 

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Discussion Starter · #2 ·
I forgot to mention a couple pertinent events when first energizing the 50 amp 2 pole GFCI's.

Once I energized it the first time, the GFCI was on, I hit the test button, and it performed perfectly.

I reset the breaker, and re energized; this time there was a slight 'hum' sound, but hardly audible; it didn't trip the 50 amp breaker at the service panel.

The GFCI then tripped after a few seconds, and then again. It will only trip now. My thoughts are, that possible the high leg is causing the problem.

Do I try to figure out how to avoid the high leg altogether, or is the GFCI potentially just flawed from the manufacturer? I've dealt with a lot of nuisance problems over the years, where the problem was due to the 'new' switchgear.

Thanks again,

Joe
 

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Yeah, you may have smoked the breaker too.

Any 2-pole breaker connected to the high leg must be rated 240 volts, NOT 120/240. You cannot use a "slash rated" 2-pole breaker on the high leg, GFCI or otherwise.

There are no straight 240 rated 2-pole GFCI breakers, so you'll have to go another route. Find a spot to plug that breaker to C-A. You absolutely need to terminate the pigtail to the neutral bar to make the internal electronics work.
 

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Probably not much help here because I have no idea what a high leg delta system is:blink:... but it's not something silly like the test button stuck in is it?
 

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High legs kill GFCI breakers as far as what I know.

I'm pretty sure the directions for every GFCI breaker explicitly say something like only for use on 120/240 1 phase 3 wire or 120/208 3 phase 4 wire, or the 120/240 portion of a 120/240 3 phase 4 wire not the high leg.

Sometimes it pays to RTFM :laughing:
 

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Any 2-pole breaker connected to the high leg must be rated 240 volts, NOT 120/240. You cannot use a "slash rated" 2-pole breaker on the high leg, GFCI or otherwise.
The NEC as referenced by Marc.


240.85 Applications.

A circuit breaker with a straight voltage rating, such as 240V or 480V, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the circuit breaker’s voltage rating. A two-pole circuit breaker shall not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1–3 to indicate such suitability.

A circuit breaker with a slash rating, such as 120/240V or 480Y/277V, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the circuit breaker’s voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the circuit breaker’s voltage rating.

FPN: Proper application of molded case circuit breakers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the circuit breakers’ individual pole-interrupting capability.
 

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I'm pretty sure the directions for every GFCI breaker explicitly say something like only for use on 120/240 1 phase 3 wire or 120/208 3 phase 4 wire, or the 120/240 portion of a 120/240 3 phase 4 wire not the high leg.

Sometimes it pays to RTFM :laughing:
What a bunch of crap. When was the last time you read directions for anything?:jester:
 

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High leg will also smoke spa controls if they are 120 volts and tied to the wild phase.
 

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I have a theory.

Since the GFCI reads and compares amperage of the two legs, wouldn't the amperage be lower on the higher voltage leg?

Wait. The spa isn't hooked up yet. never mind.
 

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I have a theory.

Since the GFCI reads and compares amperage of the two legs, wouldn't the amperage be lower on the higher voltage leg?

Wait. The spa isn't hooked up yet. never mind.
A 2 pole GFCI measures the current differential between all three conductors ( phases and neutral). If everything is in order, current out = current in. I agree that the breaker is smoked since it was connected to the high leg.
 

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The only loads on a wild leg should be 3 phase! The smoke tends to leak out otherwise!

The only time I had issues was when someone connected the 120 starter coil from phase to ground, the machine was moved and the coil ended up on the wild leg. Fix, new 240 coil. Another time the landlords electrician changed out a service and put a 2 pole circuit across the wild leg, was a multiwire 120 circuit feeding a surge outlet, smoke leaked out again.

If your running out of space, find room for a 2 pole breaker and feed a small subpanel.
 

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The only loads on a wild leg should be 3 phase! The smoke tends to leak out otherwise!
I disagree.

There is absolutely nothing wrong with using the high leg and one of the other phases to supply a 240 two-wire load provided the breaker is rated 240 and not 120/240 and the neutral is not involved.

Most 4 wire ∆ systems are unbalanced because the two 120 volt legs are loaded to the gills while the high leg has little load on it.

3ø motors don't like that.

If you can load the high leg, the system will be balanced better and 3ø motors will last longer.
 

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The transformer bank may be supplying multiple buildings. Several of these loads may be 120/240 single phase. The wild leg transformers are smaller becouse the 3 phase loading is smaller. There is no f***ing way your going to even out the loads across the 3 phases.
120/240 Delta is the way the poco can supply 3 phase and single phase in one bank.
What if the poco cheaps out and gives you open delta and your 240 volt single phase load is across that!
 

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Discussion Starter · #15 ·
I appreciate the responses. In thinking about this last night, my mind did wonder across the prospect of installing a small sub panel to handle the single phase loads. It might be the route I go.

As to this system being used in a residence, I understand a lot of the reasoning was due to chilled water cooler systems, but not too many of those being installed anymore.

I know the high leg can be used for 240v applications, but as was pointed out above, many of those loads have 120v loads internally.

Thanks,

Joe
 

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I appreciate the responses. In thinking about this last night, my mind did wonder across the prospect of installing a small sub panel to handle the single phase loads. It might be the route I go.

As to this system being used in a residence, I understand a lot of the reasoning was due to chilled water cooler systems, but not too many of those being installed anymore.

I know the high leg can be used for 240v applications, but as was pointed out above, many of those loads have 120v loads internally.

Thanks,

Joe
It's time for a service upgrade. If the newer AC is single phase, get rid of that dinosaur 3 phase..


Back in the day, the only AC systems made were 3 phase (commercial/industrial) so they started installing 3 phase delta in the neighborhoods to power these new fangled things.

Now days, the SEER rating is higher on single phase units (supply and demand at work) so there is no reason to have it. We use the opportunity of adding a new big load to get rid of that nasy old FPE or Zinsco and sell a new service. Somebody has to do it someday so it might as well be you, today :)

And, I almost never use that high leg for anything other than a 3 phase load. Too many potential issues in the future.

It would work perfectly on a straight 240 appliance but when a service guy came out, he'd likely be confused and tell the HO to call an electrician cause sompthin aint right.:laughing:
 

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It would work perfectly on a straight 240 appliance but when a service guy came out, he'd likely be confused and tell the HO to call an electrician cause sompthin aint right.:laughing:
ive had this happen before .. the CM called and said something must be wrong with your outlet the coffee machine guy said he got 300v out of it ...
 

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Did a call some years back at a pawn shop where someone wired a few range and dryer receptacles so they could demonstrate how the ranges and dryers worked to the customer. Most of them were across the high leg. Bunch of failed appliances in the aftermath.
 
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