Generate a Neutral?

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sparkslord

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Is there any way to generate a neutral for a UPS system? We have a customer that purchased a 12KVA 208v UPS, that does not have a neutral output. We want to install a subpanel on the output side of the UPS, but we need 120 volts for some of the loads to be served. We do not feel that the utility supplied neutral can be used for the output side of the UPS.
 
Re: Generate a Neutral?

Originally posted by sparkslord: We do not feel that the utility supplied neutral can be used for the output side of the UPS.
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You are right about that. You need to talk with the manufacturer or vendor of the UPS equipment. If you don?t know how they wired the internal inverter circuits, you will not be able to ?generate? a neutral. In fact, it might not be possible at all.
 
Re: Generate a Neutral?

The manufacturer sells step-down transformers to create a 120v circuit with neutral. The problem is we want to feed a subpanel. We feel that we would not be able to use a 240v panel, altering the UL listing. We are unable to locate a 120v, wall mounted, distribution panel.
 
Re: Generate a Neutral?

Originally posted by sparkslord: We feel that we would not be able to use a 240v panel, altering the UL listing.
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Are the step-down transformers single phase 120 volts or three phase 120/208 volts? If you have a neutral on a 120/208 volt system, you can feed a 120/240 volt single phase panel. But you need to make sure any 240 volt loads that might be connected (I think you have none of these) can tolerate a 208 volt supply. Better still, can you get a single phase 120/240 volt transformer?
 
Re: Generate a Neutral?

The problem is that the output of the step-down transformer is single pole 50Amp 120v. There are no 240v loads to be served.
 
Re: Generate a Neutral?

Sparks with a little searching on the internet I (edit bad link) found a 15 KVA 208 primary - 240/120 secondary transformer. You would have to bond and ground this new neutral.

If you talk to a supply house I am sure they could round one up.

Size the transformer as small as possible as it will be shortening the UPS run time with this set up.

[ September 22, 2004, 08:08 PM: Message edited by: iwire ]
 
Re: Generate a Neutral?

I personally don't see any problem with just running the 50A, 120V output to a one phase of a 240V single phase panel. The other phase would just be dead, and unused.

Steve
 
Re: Generate a Neutral?

It depends on the UL listing. If a manufacturer builds a 50 amp 120/240V panel, and tests it to its rated limits, then 25 amps will flow along one side and 25 amps along the other. If you put all 50 amps through one side, it might be more of a stress than the panel endured during the UL test period. We are supposed to make an effort to balance the load between (or among) all phases on a panel. 0 on one side and 50 on the other side is not balanced. I can?t say that it is a violation of the UL listing. It would be up to the manufacturer to say whether this is acceptable.
 
Re: Generate a Neutral?

Guys,
Would I be way off base to say: Install a one-to-one transformer 208v 3 phase delta primary 120/208volt wye secondary. Bond your xo terminal and presto now you have a neutral?
May be a little costly depending on the Kva
 
Re: Generate a Neutral?

I agree with what Charlie said about balancing load on the panel busses, so why not just tie both line lugs together and put half the single pole circuits on one side and half on the other? JMO
 
Re: Generate a Neutral?

The panel was not listed for use in that manner and the potential for overheating the neutral bar would be present.
 
Re: Generate a Neutral?

the potential for overheating the neutral bar would be present.
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You are right Bob. Normally neutral bar current would be only the unbalanced load, here it would be 100% :eek:
 
Re: Generate a Neutral?

Both Bob (iwire) and Dirk have good solutions. They do cost money. But it is not ?the solution? that creates a need to spend money. Rather, it is ?the problem? that creates a need to spend money. There is a problem here, and it is going to cost money to find a solution.
 
Re: Generate a Neutral?

The technical documentation of the UPS must be checked, some manufactured UPS 208 V units need a step down transformer to be used in 120 V, I almost sure the unit you are talking about it's a 1-ph 208 V to be used on servers.
 
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