What RCD (GFCI) for SRT3000RMXLi and SUA3000RMI? (if any)

[Shalak]

I have a small server room at home, and the whole building is protected by a standard household 30 mA RCD breaker.

Everything worked fine when I was only using an SUA3000RMI, but after adding an SRT3000RMXLi, the RCD trips whenever the UPS switches to battery power.

What’s the best approach here? Should I bypass the RCD for the server room, or bypass the main RCD and install a dedicated one for it? If so, what type of RCD should be used, especially for the SRT3000RMXLi?

The only RCD-related information I’ve found is for a much larger 250–400 kVA UPS, which recommended using a Type B RCD — but those are quite expensive.

What would the community recommend?

[Teken]

I would ask you to validate this problem by doing the following:

SRT: Remove this unit from the mains outlet and power down.

SUA: Leave this unit in place and report back the behaviour. If nothing happens during the next power fluctuation disconnect this unit from the mains power and shut it down.

SRT: Connect and power up the system and report back what you observe. During this test only the UPS is connected with (No) loads to mains power.

If nothing happens during the next power fluctuation connect the same loads as before. Report back what you observe and if the GFCI breaker trips choose any random load and remove until the GFCI stops tripping.

If the GFCI breaker trips regardless of any connected load removed one at a time until none are present.

Provide the following logs when the system goes into battery only mode: Event, Data, UPS

Regardless of the above you have some options to consider and try in no specific order of relevance:

Power Quality: Decrease the sensitivity from normal to low and report back the results. This setting defines when the unit will go into battery only mode.

Transfer Voltage: Adjust both high and low transfer voltage to a wider range. This setting defines when the unit goes into AVR mode in Line Interactive systems.

On the SRT this defines when the bypass is available and used as a mains source.

Frequency / Slew: Adjust both to a wider range and report back the results and behaviour.

All of the above costs you nothing but time and effort. 

Should none of the above work than the following action items may be required or considered:

If the unit is still under APC Warranty submit a RMA and see if the problem is solved. If the new unit behaves the same than your options are these:

GFCI Breaker: Replace with a different make / model.

Bypass: Provide dedicated power from a standard breaker from the service panel and install a GFCI outlet (IF) available.

If a GFCI outlet is not available than use a GFCI power bar to mimic the same. Insure the power bar is short as possible and has the same or better wire diameter.

Given the SRT is a 30 amp unit it’s highly unlikely you’ll find a outlet. So the 220 - 240 VAC GFCI power bar is the only option. 

This last option circumvents the GFCI Breaker using a standard breaker. Using a GFCI power bar connected to the UPS outlets provides GFCI protection (IF) required and needed.

Questions Ask . . . 👍

[Shalak]

I got the reply from APC support - in general, they do not recommend putting RCD before their UPSes.

[Teken]

And this would help you how?!? The RCD / GFCI Breaker is in place as it’s a required safety device mandated by the building codes in your city / county.

The tests outlined by me and the other suggestions would either resolve the problem or lessen the likelihood of a tripped condition.

You didn’t even bother trying any of the above and simply stopped.

Based on a persons canned / formatted reply that hasn’t even tried to troubleshoot the problem?!? 🤦‍♂️

[Shalak]

First, I'd like to thank you for the time taken to write the initial reply, forgot to do it in my previous post, apologies.

> The tests outlined by me and the other suggestions would either resolve the problem or lessen the likelihood of a tripped condition.

I don't have the capacity to run all of those tests, as they would require shutting down server room, which I cannot afford. Especially since you mentioned waiting for power fluctuation. Detailed GFCI / RCD requirements should be defined by the APC, just like power rating etc. And they are defining them as: "do not use GFCI / RCD". My country code mandates GFCI only in places like kitchen and bathroom, so that's not an issue.

I also don't have budget to keep buying different RDCs to test which one will not trip during switch, especially since Type B (which is recommended by the doc mentioned in my original post) or Type A (usually mounted for inverters) cost an arm and a leg.

That being said, I went straight to your last recommendation, to circumvent the GFCI Breaker using a standard breaker 🙂

Thanks!