I'm mostly a residential guy but took a look at an old industrial facility in chicago and I came up with this question. At the main service they had a cabinet with 6 main disconects from there branched off a 30 space panel 3phase 3 wire with the 3 phases marked with the colors black, red, and blue. I had 240 between a-b c-b a-c and 120 between A and ground and 120 between C and ground and the high leg B was about 208 to ground. My question is there anyway to get 120v receptacles off of this setup without the use of a transformer? They had some receptacles running off of this my guess is that they must be using the grounding system for the neutral which is bad in my book unless I'm missing something. And is it likely to have just the 3 ungrounded phase conductors with a ground and no neutral at the main service with this type of setup or might I find a neutral bus inside that main cabinet.And would this be considered a center tapped delta as opposed to a corner tapped delta? The panel off of the main in question is serving mainly 3 phase loads such as conveyors and compressors. Any help on this would be much appreciated.
120/240 delta question
- Thread starter dave81
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Re: 120/240 delta question
If you have a 3 wire service from the utility you can not get 120 volts. If you have a 4 wire service the center transformer may have its coil grounded and you can get 120 volts from phase to neutral. Using the grounding conductor is not allowed.
If you have a 3 wire service from the utility you can not get 120 volts. If you have a 4 wire service the center transformer may have its coil grounded and you can get 120 volts from phase to neutral. Using the grounding conductor is not allowed.
hurk27
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- Portage, Indiana NEC: 2008
Re: 120/240 delta question
Dave what you have there is a 4-wire delta (that has a center tap between "A" and "B" phases), that has a three phase only panel which should not have been used for and 120 volt loads without a isolated neutral bar and neutral bonded at the main service disconect. yes thes is not code compliant. What should be there is a single phase panel with a neutral bar and a seperate grounding bar. with only "A" and "C" phases and a neutral ran to it. while it is allowed to use a three-phase panel for this as long as there is the proper neutral bar installed it's not a good idea as someone unknowing connects to the "B" phase can cause a fire and or do alot of dammage to equipment.
The NEC also requires that the "B" phase be marked with orange tape.
[ July 28, 2004, 06:57 PM: Message edited by: hurk27 ]
Dave what you have there is a 4-wire delta (that has a center tap between "A" and "B" phases), that has a three phase only panel which should not have been used for and 120 volt loads without a isolated neutral bar and neutral bonded at the main service disconect. yes thes is not code compliant. What should be there is a single phase panel with a neutral bar and a seperate grounding bar. with only "A" and "C" phases and a neutral ran to it. while it is allowed to use a three-phase panel for this as long as there is the proper neutral bar installed it's not a good idea as someone unknowing connects to the "B" phase can cause a fire and or do alot of dammage to equipment.
The NEC also requires that the "B" phase be marked with orange tape.
[ July 28, 2004, 06:57 PM: Message edited by: hurk27 ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: 120/240 delta question
Also look at the service drop wires coming from the transformer. If there is a bare message wire then that is the neutral and should be in the main disconnect for the building. This needs to be ran to the panel with 120 volt loads and landed on a isolated neutral bar, unless this panel has a main breaker that is the first disconnect then the grounding and neutral can use the same bar. But either way once the neutral has passed the main disconnect it can no longer be bonded together with the grounding. It must be kept separate.
Also look at the service drop wires coming from the transformer. If there is a bare message wire then that is the neutral and should be in the main disconnect for the building. This needs to be ran to the panel with 120 volt loads and landed on a isolated neutral bar, unless this panel has a main breaker that is the first disconnect then the grounding and neutral can use the same bar. But either way once the neutral has passed the main disconnect it can no longer be bonded together with the grounding. It must be kept separate.
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