8 hots, no neutral, 1 ground?!?

[makeb4break]

I just checked out a friend's new place, an old cigar factory (now residential). He wants power outlets on his walls, so I opened up the j-box that used to be feeding some roof-mounted air conditioning units. What I found were 7 120v lines, one line at 208v to ground, and one ground. All were 12 ga. multi-strand. There are a few things I don't get: a) how can one line be 208 w/respect to ground, rather than w/respect to another as in 3 phase wye. B) why no neutral, and what can I do about it to get the guy some power in his place? The subpanel had 4 wires coming in: 3 2 ga. wires at 120, 120, and 208, and one flimsy ground wire (10 ga). No neutral bus, no ground bus. Plus, the 208 feed was at 240v w/respect to the other two 120 feeds. Anybody have any insight? Thanks!

 

[davidbeach]

You are dealing with a 240V delta system with the midpoint of one winding grounded. 240V phase-to-phase, all combinations. By usual naming convention, phases A and C will be 120V to ground/neutral and phase B will be 208V. If the subpanel was intended to feed only 3-phase loads, there would be no need for a neutral. The ground is certainly undersized per current code requirements.

You have two options to use this and meet NEC requirements.

1) Bring properly sized ground and neutral conductors to the subpanel.

2) Remove the subpanel and use that circuit to feed a 240V delta - 208Y/120V transformer. The transformer can then feed a new panel with a main breaker, or you could use an enclosed breaker as the main and potentially reuse the subpanel on the 208V system.

 

[ccjersey]

The service is 120/240 3phase 4 wire, (center-tapped delta connection). Lines are 120, 208 usually,120 - to neutral. Line to line is 240 each way as you found out. This used to be common when there is a mix of 3 phase and single phase needed, with either not a lot of single phase or not a lot of 3 phase needed. Works pretty well either way if the power co sets the right mix of transformers for whichever load mix there is on the service. It is an easy upgrade for the power co if they have two phase conductors on the line, because they can give someone 3phase by adding only one more transformer to the single phase service making it an "open" delta. Or it may have 3 transformers for a stiffer service less prone to voltage dips from large loads.

The "B" phase is about 208 VAC to the neutral point. The ground wire in the box feeding the rooftop units would be connected to neutral back at the service, so it works to test the voltage of the 3 hot legs, but not to run loads. Maybe you can reposition the "B" phase hot to the subpanel and J box and label it to get the neutral you need.

Just stay off that 208 with your plugs!

 

[makeb4break]

Thanks guys for your help. You've just saved me a lot of head scratching. The building is a nightmare from a wiring standpoint, so I'm going to look into running a proper neutral and ground to the panel from another location. In any event, I need to make at least one of those hot legs a neutral. Thanks again!

 

[cuky2000]

I just checked out a friend's new place, an old cigar factory (now residential).

Should a delta system installed in residential environment be a concern from the safety point of view?

 

[abcd3286]

240V delta system with the midpoint of one winding grounded. 240V phase-to-phase, all combinations. By usual naming convention, phases A and C will be 120V to ground/neutral and phase B will be 208V.

Phase B is commonly called the wild leg.
I thought the voltage was higher than 208 (wild leg to center tap / neutral / ground)

 

[davidbeach]

sqrt(240^2-120^2)=208. Simple geometry.

 

[ccjersey]

not sure how or why, but I have measured some here at 190 on the low end to as high as about 216 on other. Different services over a number of years.

 

[geso52]

The name for the leg with the higher voltage is "high-leg" and it should be marked with an orange color tape at the points of connection and at junction boxes.
I would not want to have this setting in a dweling unit. (I don't like this setting even in a commercial or industrial facility)If possible, cap the high-leg at the source (Main disconnect at the electrical service) and keep the other 2 phases and provide an approved neutral and ground conductor as per David advice. With this new set of conductors, feed a 120/240V, single phase, 3 wire panelboard or load center and rewire the branch circuits that need to remain operational.

 

[itsmoked]

The "wild leg" or "stinger" as it's called around here is often in the range of 190-216V nothing to worry about. When hooked to a 3 phase load it will be about where you want and expect it.

Invest in good smoke detectors.