ECN Forum Forums General Topics of the Trade General Discussion Area 3-phase no nuetral problem

I have a customer who wants to add a bunch of kitchen equipment into his resteraunt. The problem is that the 120/208 service with a neutral is maxed out. There is another service, 3-phase (120/208) with out a nuetral that is basically un-tapped. The building used to be a machine shop. Is there a solution to this problem that can be fixed with a transformer?

208 implies wye so there should be a neutral at the service disconnect panel although it may have never gone beyond there. This is common in computer rooms too. You should be able to exted that neutral to the load if there is room in the pipe.

I checked, but not very hard. The switch gear looks like it is from the '50s. I mean it is really old. It's a metal cabinet and when you open it you see 3 metal bus bars with cartridge fuse holders and lugs for the load side. I'm going to get some pics and post on here.

Start with the actual service entrance conductors and see if there are 4. It may never get out of the CT can but it really should make it to the MBJ.

otherwise, yes, you can create a neutral with a transformer.

I can't imagine how you can have a wye without a neutral and 208 always means wye doesn't it? That is how it gets grounded. Is there 208 floating delta somewhere?

No, not really, but wye only means the transformer has a grounded star point, there is no need to provide a neutral conductor anywhere in the system! For example if you only have symmetrical 3ph loads or all loads are connected in delta (don't forget, a wye system allows you to connect loads both in wye or delta) you won't need a neutral conductor. That's why European motors only have a 3w+ground cord supplying the three phases. Old 3ph plugs didn't even have a neutral terminal. So maybe you need to go all the way up to the transformer.

250.24 (B) requires the grounded conductor, if there is one, to be brought to the service .
Some installations using 3 phase only try, and sometimes do, omit it but it is needed as a fault path to the transformer.
Check the weather head and see if the drop from the utility co is 4 wire or 3 with a messenger. The messsenger will be bonded at the point of origin.
Alan--

*smack* I forgot the NEC doesn't allow systems that are grounded via local ground rod only. That rules out a wye system w/o neutral.

As I said upthread, computer rooms did not bring the neutral beyond the service disconnect since the standard was only line to line loads. It should still be in the service disconnect enclosure where it gets attached to the main bonding jumper and the grounding electrode. I suppose if you held your nose real tight that connection could be in the metering equipment but I can't see it being very much farther toward the line side.