Delta High-Leg Mystery

[jmbelectrical]

I'm working on a tenant improvement project that was initially visited, documented, and photographed by another engineer. His notes indicate that the building and the tenant space are supplied by a 240/120-volt, three-phase, delta high-leg system. A photo of the tenant's exterior disconnect switch revealed that the three phase conductors serving tenant's panelboard were tagged as black, blue, and red. The absence of an orange tag on the "B" phase conductor had me suspicious, but it wasn't the first time I had encountered an installation that didn't comply with the NEC's high-leg marking requirements. I contacted the utility and they confirmed that the facility is indeed being provided by a 240/120-volt, three-phase, delta high-leg system.

Here's the part that is completely throwing me off: a photo of the tenant's panelboard shows a huge lineup of single-pole circuit breakers connected to all three phases. No doubt they're connected to lighting and receptacle loads. I could see fluorescent lighting with universal voltage, electronic ballasts operating on a 208-volt circuit, but surely any 120V cord-and-plug equipment connected to the "B" phase would have been damaged. I suppose that autotransformers could have been used to step-down the voltage from 208V to 120V where needed, but it seems highly unlikely. It's also, as far as I know, prohibited by the NEC to use the high-leg for phase-to-ground loads in the first place.

Any ideas?

 

[SceneryDriver]

Since the incoming feeders aren't marked properly, and thus violate the NEC, it stands to reason that some unscrupulous (or unknowing) person may have used a bunch of single pole breakers instead of the correct either 2-pole or 3-pole breakers. Only way to know would be to go and have a look and do some testing with a meter.


SceneryDriver

 

[PHovnanian]

I concur with SceneryDriver. This isn't right.

Its possible that the universal voltage ballasts are connected between 240V legs, along with a lot of other equipment. By itself, that would be OK, but would require a 2 pole breaker.

It wouldn't be the first time I've seen non-ganged single pole breakers installed to feed line to line loads. Its possible that whoever did the wiring just left handle ties off. Not unlikely given the other workmanship issues in evidence here.

 

[davidbeach]

Or, is it possible that the panel with all the single pole breakers is actually only a single phase panel?

 

[SceneryDriver]

Good point David. Come to think of it, I have seen a single phase panel in an installation at a theater out in the middle of nowhere; very old electrical service from the utility. They had a high-leg delta service with a much smaller third transformer. The three phase service served only a few loads, namely the compressors and air handling motors for the air conditioning, and everything else, including the huge load represented by theatrical lighting instruments, was served as 120/240v split-phase loads. Very strange, as almost all theaters are wired as wye-connected 120/208v services these days, but it WAS an old service.

I jumped to the conclusion regarding improper use of single pole breakers since the OP mentioned the improper labeling of the high leg. Maybe I'm just becoming too cynical about the state of workmanship these days... Handle ties would be an easy fix if they really need to be multi-pole breakers. If the breakers were improperly used though, I'd probably start going through everything with a fine tooth comb. No telling what else one might find.


SceneryDriver

 

[waross]

I agree with David and SceneryDriver. Check to see if the panel is single or three phase.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jmbelectrical]

The panelboard is three-phase. In fact, there are two three-pole circuit breakers serving some rooftop HVAC units.

 

[waross]

Are there wires connected to the wild leg breakers or are they being used as lace holders.
Or
You may have 208 Volt supplied loads on the wild leg.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[SceneryDriver]

waross,
My high-leg delta rules are a little rusty. Is it legal (or even a good idea)to serve 208v single phase loads from the wild leg to neutral? jmbelectrical mentioned that it's (now?) illegal to do that, but was it OK at some earlier time?


-SceneryDriver

 

[davidbeach]

Doubt that it's been legal any time in recent memory. Was never a good idea, it's a bad use of transformer capacity.

 

[waross]

Despite legalities, it is what it is. Not all wiring is done to code by trained electricians.
Another possibility is that 240 Volt loads may have been fed from two breakers but the handle ties were not installed.
We have given you a number of possibilities to check but the bottom line is you or someone must do some on-site investigating before any of us know for sure what is in use.
Let us know what you find when you are able to do a site inspection.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

I once looked over a job where a three phase wye source was connected to a panel that was labeled for use on a 120/240 delta. Two pole and single pole breakers were installed. Upon further inspection, I determined the not so high leg simply terminated at the panel and did not feed any of the loads; even though there were no blank slots. I asked the electrician to replace it with a proper wye panel to balance the loading across the three legs. I presume the delta panel was reconfigurable for the number of three phase circuits, and in this case it was configured for zero.