3-way light switch with 240

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BenS

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I have a building project that is just about to the wiring phase. The owner wants the lights to be on a typical 3-way switch with one switch at each entrance. No problem, but the lighting is all 240. Is there anything wrong with wiring up the lights like you would for 120?
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Normally, manual control does not require breaking all lines, but I'm not sure about lighting control. What kind of fixtures?
 
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BenS

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The fixtures are just four the run of the mill 32 Watt electronic ballast fluorescent fixtures. Voltage rating on the fixture is 120-277. Power is coming from a 240Y139 transformer, so I suppose I could run them from the neutral too?
 
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hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
BenS said:
The fixtures are just four the run of the mill 32 Watt electronic ballast fluorescent fixtures. Voltage rating on the fixture is 120-277. Power is coming from a 240Y139 transformer, so I suppose I could run them from the neutral too?
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What country are you from, I know of no 240/139 Y type transformer here in the US?

And if you do have a neutral, it is not allowed to be switched.

you need to clarify this post.
 
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winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
240/139 is an oddball system that you get if you need 240V 'line-line', but want to supply it with a wye transformer (say for impedance grounding). The 139V line-neutral generally doesn't get used.

Before using the 139V for anything, I'd carefully check to confirm that you can use it. Is the transformer rated for continuous load on the neutral? Is it an impedance grounded system where all loads _must_ be line-line? Etc.

-Jon
 
Jim W in Tampa

Jim W in Tampa

Senior Member
Location
Tampa Florida
Not sure what 139 would do with a 120/277 balast. Will it even work ? My understanding is it goes to first system it sees either 120 or 277 and cant be changed. How do we get 139 out of a Y ? Delta maybe and sounds like a unbalanced high leg.
 
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BenS

Member
hardworkingstiff said:
The relationship being 1.732 from the phase to phase voltage to the phase to neutral voltage we get:

240/1.732 = 138.56 AKA 139

It's all about the windings. I have no idea of why they would do this.
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I don't either.. really. I am working at a small remote site that has a hydro generator producing 3 phase 480. Almost everything except the housing units is on 208Y/120 transformers which seem to work very well. I think the idea behind the 480-240Y/139 transformer was to balance the legs on the hydro a little better while providing 240, but the thing is only 1/10th the KVa's of the hydro so not much help in my opinion. The transformer is a really nice looking stainless steel 30KVa unit. Really pretty to look at but probably would have been better using 3 smaller individual 480-240/120 transformers to balance the hydro. The owner was a little confused when I told him we had to install yet another transformer to get 120 in the building. I figure the best way to go about this is to run the heat and lights off 240 so I can install a smallish 2-3KVa transformer for a couple of outlets. This is just for a storage building with no occupancy, appliances etc. Just heat, lights, and a 240 volt air compressor.
All that said, I don't think I technically have to follow any code since the building is floating and not connected to a utility, however I believe following the NEC is the best way to ensure I don't run into any issues or create a potential safety/liability issue for someone in the future. Can of worms?
 
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