Mixing UPS and normal power neutral or EGC branch ckt wires

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housemoney

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Wiremold multioutlet assembly with 3 separate channels for 2 -120V/20A normal power circuit outlets (each from separate ckt) and 1 -120V/20A UPS power outlet per workstation. Engineer is trying to get us to apply wire markers and cable ties on the UPS circuit citing 200.4(B). That's fine, but I'm trying to understand the hazard with somehow mixing a branch circuit neutral or EGC between the UPS and non-ups systems would necessitate such stringent labeling during construction. The UPS circuits are fed from a single phase 120/240 panel board that's stepped down from a 208V 3 phase output of a static UPS, so it derives it's a SDS that derives it's own neutral point.

If the neutral was accidently swapped between a UPS and normal power outlet, this would simply result in an open circuit, would be noticed and corrected?

If the EGC was accidently swapped between a UPS and normal power outlet, the fault current would take the neutral and the breaker would still trip, just no safety ground on that outlet?

Sorry just thinking out loud as to what the Engineer is thinking here, not trying to challenge him, just understand the deeper technical issue.
 
That was suggested by another, response was that "UPS and Non-UPS power could still be accidently mixed". Just trying to understand the technical issue or hazard (without asking the engineer and put them in defense mode) of the ground and EGC of the two systems somehow being crossed accidently in the future.
 
An effective fault clearing path, you stated the UPS derives it's own neutral the engineer seems to be taken caution that the neutral path stays effective in fault clearing
 
david said:
An effective fault clearing path, you stated the UPS derives it's own neutral the engineer seems to be taken caution that the neutral path stays effective in fault clearing
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I don't see how that changes anything. Both neutrals are connected to ground so they are connected to each other anyway.
 
In my way of thinking the SDS system bond is done close to the source and the equipment grounds bond to the Ups neutral close to the source with a path direct back to the source. I would think that would make a difference in fault clearing, in the event that the service branch circuit neutrals and the UPS branch circuit neutral's got tied together or mixed up somehow
 
housemoney said:
... I'm trying to understand the hazard with somehow mixing a branch circuit neutral or EGC between the UPS and non-ups systems would necessitate such stringent labeling during construction. The UPS circuits are fed from a single phase 120/240 panel board that's stepped down from a 208V 3 phase output of a static UPS, so it derives it's a SDS that derives it's own neutral point.

If the neutral was accidently swapped between a UPS and normal power outlet, this would simply result in an open circuit, would be noticed and corrected?
Click to expand...
As pertersonra said, both neutrals are connected together through the EGCs.
And so if you swapped the neutrals, current drawn from the non-UPS system would return back thru the neutral of the UPS system over to its N/EGC bond, then across the EGCs to the N/EGC bond of the non-UPS system, and back to the source which is the non-UPS transformer. And vice-versa for currents drawn from the UPS system if its neutral was swapped.
 
synchro said:
As pertersonra said, both neutrals are connected together through the EGCs.
And so if you swapped the neutrals, current drawn from the non-UPS system would return back thru the neutral of the UPS system over to its N/EGC bond, then across the EGCs to the N/EGC bond of the non-UPS system, and back to the source which is the non-UPS transformer. And vice-versa for currents drawn from the UPS system if its neutral was swapped.
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So would this impact breaker fault clearing times? Any other negative impacts to note?
 
At some point it would violate the code requiring all conductors of a circuit to be in the same raceway.

When conductors of a circuit are in different raceways it adds 'loop area' which means increased circuit inductance and increased EMF production by the circuit

-Jon
 
In normal circuit design current travels the neutral of the circuit not the equipment grounds or building steel you want to keep objectionable currents to a min.
 
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