Doesn't this seem like a bad idea?

[doubleE]

I'm doing work for a client designing a facility with UPS backup.
This is what the client wants to do:

They are basically suggesting having one panelboard fed directly from the utility, and one fed from the UPS, then run wire from both and connect them to the same outlet, for "redundancy" as they put it. Does this seem like a bad idea to anyone else but me?

As I understand it, they'd have to make damn sure they connected the same phases (since they're 3-phase panelboards). But even then, if the power from the UPS inverter leads or lags the power coming from the other panelboard, even a little bit, wouldn't that be disasterous?

 

[charlie b]

I share your concern, and agree with you that this is a bad idea, one that quite possibly could result in a vast great deal of sparks. But I do not know anything about the electronics internal to a UPS system, and cannot say whether there is a chance the two sources will be in sync. I have a feeling there might even be a code violation in this, but I have to look around.

Welcome to the forum.

 

[nakulak]

am I reading this correctly - you want to supply a receptacle from two sources ? if so this is a violation. I know it violates 210.4 A and B (2005)but I believe there are other violations.

 

[charlie b]

I know it violates 210.4 A and B (2005) . . . .

I'm not so sure. I sense a violation, and I can't pin it down, but I don't think it comes from 210.4. We are not talking about a MWBC here. We are talking about supplying a single outlet from two separate branch circuits. We are talking about parallel power sources to the same load.

 

[drbond24]

Yep, bad idea. Just put in another receptacle. One for 'regular' and one for 'back-up.'

 

[nakulak]

also violates 240.8

- how can it not be a violation of 210 - it originates from more than one panel board ?

 

[charlie b]

It doesn't violate 210.8. The two breakers are not in parallel. The load sides of the two breakers are indeed connected to the same point. But you don't have the same connection point on the line sides of the two breakers. That is not a parallel connection.

As to conductors originating in separate panels, that again is a requirement for MWBCs. This is not a MWBC. What you have is two separate branch circuits that supply the same load.

Bad idea? Yes I think so. Code violation? Probably, but I still can't name the article being violated.

 

[charlie b]

OK, here?s the best I can offer at the present. Generally speaking, the code is treated as allowing anything that is not explicitly forbidden. But in some cases, the code language includes phrases that essentially mean that ?this is OK, and nothing else is OK.? I think there is just such a phrase in the beginning of 210.2. It says that branch circuits shall comply with this article. From that, I infer that anything that is not described in ?this article? is not allowed. The circuit connections shown in the sketch above are not included as being allowed in any sub-article of 210. Therefore, they are a violation of 210.2.

Does that work for anybody?

 

[doubleE]

That will definitely help to argue my case. I've tried to explain that the UPS is inherently redundant and the parallel circuit is not needed. I don't think they're quite understanding how the UPS operates.

I'll just have to try harder to change their mind, and if I can't, flying sparks will.

 

[don_resqcapt19]

I see this as a violation of 702.6.

 

[nakulak]

what concerns me is the available current at the receptacle

 

[charlie b]

I see this as a violation of 702.6.

I'm not so sure about that one either, Don. I would not call a UPS a standby system, optional or otherwise. It can only power the equipment for the length of time that the battery holds out, and the battery cannot be "replenished" in the same sense as a generator's fuel tank.

 

[charlie b]

what concerns me is the available current at the receptacle

That's a good point. You could draw over 40 amps through that receptacle for an extended period of time, without tripping either breaker.

 

[doubleE]

Oh, I probably should have mentioned that the "service entrance" noted on my sketch actually comes from an automatic transfer switch and generator.

 

[quogueelectric]

How about 230.74?? It is not just a bad idea it is a very bad idea.

 

[iwire]

I would not call a UPS a standby system, optional or otherwise. It can only power the equipment for the length of time that the battery holds out,

An emergency battery unit for egress lighting only has to last 90 minutes and yet Article 700 applies.

 

[charlie b]

An emergency battery unit for egress lighting only has to last 90 minutes and yet Article 700 applies.

Even so, would you treat a UPS as an Article 702 system? I would not. It might be an SDS, but that doesn't bring 702 into play.

 

[Pierre C Belarge]

I see this as a violation of 702.6.

UPS systems that have battery backup are standby systems


I would also cite 210.7(B)Multiple circuits.

 

[iwire]

Even so, would you treat a UPS as an Article 702 system? I would not. It might be an SDS, but that doesn't bring 702 into play.

I do not think we have a choice. I see nothing in 702 about time.

 

[charlie b]

I would also cite 210.7(B)Multiple circuits.

That works for me.