RCD before or after a UPS?

[Susan_electrical]

Hello all
In a UPS Planning Guide by ABB, it is advised not to place a residual current breaker before the UPS, but after it. I'm confused.

An RCB protects against earth leakage faults (downstream), am I correct? Then what difference does it make placing it before or after the UPS? Am I missing something here?

 

[tortuga]

Hello all
In a UPS Planning Guide by ABB, it is advised not to place a residual current breaker before the UPS, but after it. I'm confused.

An RCB protects against earth leakage faults (downstream), am I correct? Then what difference does it make placing it before or after the UPS? Am I missing something here?

It says your in the Emirates, they use a TT or a TN-S system, which is different than what most on here are used to (TN-C-S).
Presuming your working under the 'The Electricity Wiring Regulations of 2020', (those are almost an exact copy of the International Standard IEC 60364 or BS 7671).
You need to provide protection to people against electric shock (due to Direct or Indirect Contact with electricity) for the final portion of the circuit regardless if the UPS is on or off.

5.1.3 Protection of persons against electric shock due to Direct Contact or Indirect Contact
must be provided by one of the methods detailed in Regulation 5.3.

A 30ma RCD provides electric shock protection for the end users so that needs to be after the UPS.
You also probably need to provide Earth Leakage Protection (ELP) on the feeder that supplies a UPS, what we call GFPE protection, and that is sizing that is more complicated depending on if your on a TT or TN-S.
Hope that helps

 

[Susan_electrical]

It says your in the Emirates, they use a TT or a TN-S system, which is different than what most on here are used to (TN-C-S).
Presuming your working under the 'The Electricity Wiring Regulations of 2020', (those are almost an exact copy of the International Standard IEC 60364 or BS 7671).
You need to provide protection to people against electric shock (due to Direct or Indirect Contact with electricity) for the final portion of the circuit regardless if the UPS is on or off.


A 30ma RCD provides electric shock protection for the end users so that needs to be after the UPS.
You also probably need to provide Earth Leakage Protection (ELP) on the feeder that supplies a UPS, what we call GFPE protection, and that is sizing that is more complicated depending on if your on a TT or TN-S.
Hope that helps

Thank you @tortuga . I was wondering why ABB worded it like this
We advise against the use of a residual current circuit breaker BEFORE the UPS, especially so as not to compromise the envisaged protection concept.

My apologies if I sound silly, but, won't placing the RCCB before the UPS protect whatever is downstream (ie the UPS and the load circuits)?