GFCI with UPS

[SceneryDriver]

I have an install where there is a 19" rack with a TrippLite UPS feeding various IT components (switch, server, router, etc...). The fiber modem is on the other side of the basement, and needs UPS backup as well. Simple solution: install a male cord cap and tail in the IT rack, and run UPS power to a receptacle at the fiber modem. This works just fine; fiber modem receptacle is color-coded and placarded so someone doesn't try to plug in a shop vac and trip the UPS.

The issue is that this is an unfinished basement. A dead-front GFCI was installed to protect the fiber modem receptacle, but it trips every time the UPS transfers to/from battery power. This obviously defeats the purpose of placing the modem on UPS power. The UPS in the rack is fed from a GFCI receptacle, and that receptacle holds just fine.

We've tried ferrites to help control any switching spikes, to no avail. Whatever the UPS is doing to the AC waveform, the dead-front GFCI doesn't like it. I suppose we could try something like a line reactor with more inductance than a ferrite choke to help control switching transients, but I'm hesitant to just shotgun parts at this.

A coworker argued that the dead-front GFCI isn't necessary, as the circuit is already GFCI protected by the receptacle feeding the UPS. For now, we removed the dead-front GFCI, and everything is working just fine. Thoughts?



SceneryDriver

 

[ptonsparky]

like the idea that the first GFCI is sufficient.
I've had such good luck with RK electronics and GFCI inductive feedback, I would try one of theirs or similar.
RCS1A6. RKERCS1A6
Most likely somewhat less expensive than a constant conversion type UPS.

 

[synchro]

Perhaps an isolation transformer could help because it would significantly attenuate common mode transients. There's no guarantee that it will keep the GFCI from tripping, however.

https://www.testequipmentdepot.com/bk-precision/isolation-transformers/1604a.htm

 

[winnie]

What sort of power does the fiber modem use? I understand that you have a 120V AC receptacle at the fiber modem, but does the unit take 120V, or does it have an external power supply plugged into the receptacle, and then low voltage going to the modem?

Could you put the power supply in the 19" rack, and then run low voltage across the basement?

-Jon

 

[winnie]

The UPS is providing continuous power. If the GFCI upstream of the UPS trips, then you still have a shock hazard present.

-Jon

 

[SceneryDriver]

What sort of power does the fiber modem use? I understand that you have a 120V AC receptacle at the fiber modem, but does the unit take 120V, or does it have an external power supply plugged into the receptacle, and then low voltage going to the modem?

Could you put the power supply in the 19" rack, and then run low voltage across the basement?

-Jon

We looked at that. It's a Verizon power supply, with some kind of proprietary DC barrel-like connector, so probably not an option. Good idea though.


SceneryDriver

 

[SceneryDriver]

like the idea that the first GFCI is sufficient.
I've had such good luck with RK electronics and GFCI inductive feedback, I would try one of theirs or similar.
RCS1A6. RKERCS1A6
Most likely somewhat less expensive than a constant conversion type UPS.

I think we have a few of those kicking around from a previous project. I'll give it a try. Good idea!


SceneryDriver

 

[SceneryDriver]

like the idea that the first GFCI is sufficient.
I've had such good luck with RK electronics and GFCI inductive feedback, I would try one of theirs or similar.
RCS1A6. RKERCS1A6
Most likely somewhat less expensive than a constant conversion type UPS.

We tried the surge RC suppressor. Didn't do a thing, unfortunately; GFCI still trips when on UPS power and/or switching to/from UPS. I even tried lifting the ground on the deadfront GFCI with no effect. The GFCI must not like the waveform of the UPS for some reason. I haven't had a chance to put my scope meter on it to see just how bad the UPS waveform is, but it's likely not pretty.


SceneryDriver

 

[ptonsparky]

We tried the surge RC suppressor. Didn't do a thing, unfortunately; GFCI still trips when on UPS power and/or switching to/from UPS. I even tried lifting the ground on the deadfront GFCI with no effect. The GFCI must not like the waveform of the UPS for some reason. I haven't had a chance to put my scope meter on it to see just how bad the UPS waveform is, but it's likely not pretty.


SceneryDriver

Well, I guess my UPS does not have a GFCI on the load side of it.

 

[hbiss]

Well, I guess my UPS does not have a GFCI on the load side of it.

And unless somebody says something, I wouldn't even worry about it. Same with the OP.

-Hal

 

[synchro]

... GFCI still trips when on UPS power and/or switching to/from UPS.

Does the GFCI still trip if the power supply for the modem is unplugged? Or if just the barrel connector feeding DC to the modem is unplugged?

 

[SceneryDriver]

Does the GFCI still trip if the power supply for the modem is unplugged? Or if just the barrel connector feeding DC to the modem is unplugged?

It does still trip even if nothing else is connected. It's definitely not happy with the UPS waveform for some reason.


SceneryDriver

 

[SceneryDriver]

And unless somebody says something, I wouldn't even worry about it. Same with the OP.

-Hal

Exactly my plan.


SceneryDriver