UPS output

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rich000

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When installing a single phase UPS 208V.

The output of the UPS does not have OCP, but will feed a distribution panel in another room that has OCP.

At what distance should the OCP on out of the UPS be from the UPS? I think it is 10ft. (feeder tap), but I am not sure.

Thank you
 
Re: UPS output

APC Symmetra LX recommends a 90A output breaker on the output. It does not say how far away though.
 
Re: UPS output

To clarify, the system lineup is:

100A input to the UPS
100A main input breaker in the UPS
Rectifier
Battery Bus
Inverter
Bypass Contactor
Hardwire output

The manufacturers drawing then has a dotted line to a UPS System Output panel provided by others. A 90A 2-pole external breaker is recommended.

I would think if this panel is in a different room, then you would need to protect the wiring.
 
Re: UPS output

Since it is single phase, I would think the 100A breaker on the input would protect the wiring (assuming you use 100A wire for the output.) There is an exception in the NEC that lets the wiring on the output of a transformer to be protected by the input OCP if it is a single phase 2 wire transformer.

And I'm not really even sure you even have a transformer in the UPS, so the secondary wiring would be protected by the primary.

I would just put a 90 A main circuit breaker in the panel no matter how far away it is.

Steve
 
Re: UPS output

Thanks Steve.

There is no transformer in the UPS. So if there is no requirement, and the input to the UPS is protecting the output wiring, this seems like a bad idea. I would think you would want to protect the UPS internals from anything happening.

So a local breaker on the output of the UPS close to the UPS would provide protection for the line and prevent damage to the UPS.
 
Re: UPS output

How can the input to the UPS protect the output?? There is no input power when the UPS is needed.
In my opinion the output of the UPS is a SDS and the output conductors must be protected per 240.21. The problem with this is that none of the tap rules exactly fit a UPS so the UPS secondary conductors must be protected at their source of supply.
Don
 
Re: UPS output

I was thinking of the UPS as a black box with a 2 wire input and a 2 wire output. I forgot about the batteries being a second source. But if the batteries are considered a second source, the OCP for them would have to be at the battery terminals, not on the output of the UPS after the electronics.

Steve
 
Re: UPS output

1, the input and output of this UPS is completely isolated from each other via rectifiers, inverters, and output transformer. Don is correct, it is SDS.

2. Never seen a UPS of this size that did not have some kind of OCPD. However, I believe it is a dual conversion type of UPS, which means the output is continuously powered by the inverters. An inverter would not be capable of damaging the output conductors via power limitations.

Not familiar with this line of UPS, but I bet the inverters have some sort of shut-down circuitry that is UL listed for the purpose, check with the manufacture.
 
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