UPS's tripping RCD

[rwassell]

Dear Forum,

I am hoping you can help as not only have I already had a qualified electrician out who couldn't find the problem, I've put in hours of research myself so far and still not entirely sure what the solution should be.

I work from home and have a number of APC Back-UPS 850 UPS devices protecting key hardware, including router/switch, several computers, servers and printers. All in all there are 6 UPS plugged in supplied by the main domestic consumer unit.

After we installed the 4th UPS we started to notice that we had intermittent trips on the RCD. It would be reset, everything would be fine and at some point, possibly days or even a week or so, it may trip again. It could trip on its own. Sometimes it may trip when the computer is turned on that is connected to the UPS. It may trip when something else is plugged in in a nearby socket.

We've just added the 5th and 6th UPS and this seems to have made the electrical circuit even more sensitive where a trip may happen because a printer is printing and even after resetting it may trip again and then again. We've disconnected the 6th UPS temporarily and are back on just 5 UPS' at the moment. It will only be a matter of time before it trips again.

I've researched this in great length and it appears that electrical circuits can be very sensitive due to the way a UPS works and 'earth leakage' and it can convince the RCD to trip. I have read about time delayed RCD's and I've also read about separately earthing each UPS to prevent the RCD from tripping - however, I haven't found any specific, easy, simple solution that says, when running UPS on a domestic electrical circuit, do this and your problems will be resolved and that is what I am hoping someone on this forum may be able to help with.

I attach a picture of the consumer unit if it helps understand what we have already.

I appreciate any help you can give.

Any ideas what we can do to prevent further tripping?

Thanks.

Rob

 

[timhoward]

It sounds like cumulative earth leakage, you need a sparks with a sensitive clamp meter to diagnose further. The leakage can be measured with them all off, then one at a time, to build the picture.
It may be that something else on the board is already leaking to earth.

My hunch is that you may be better off with one bigger isolating UPS unit for several appliances on a dedicated non-RCD protected supply.

(It's been several years since I was an IT consultant but at the point I left the industry printers were generally not advised to be powered by UPS units, especially if they were laser printers.)

 

[Mikegh]

It's not a great setup ,5 or 6 ups on a single shared rcd

Are these UPS all in the same location ?

 

[Strima]

Too many UPS plugged into the circuits covered by one RCD. I'd look at replacing the MCBs with RCBOs and getting rid of the upfront RCD. You can get RCBOs for that board but they are expensive, I would look at replacing the board with a full RCBO unit.

As you have a lot of UPS on your installation you would also need A type RCD/RCBO protective devices due to the amount of DC interference you could have.

 

[pc1966]

As above: lots of IT stuff with mains filters, etc, adds up leakage current until it will trip.

If this is going to be your long-term configuration then your best option is a new board with several RCBO (combined RCD and MCB) so each couple of UPS has its own RCBO. Most new RCBO are 'Type A' and they are fairly tolerant of DC effects from faulting electronics.

A possible stop-gap is one big UPS that is less leaky, but that might still fail if there are lots of leaky loads on it.

Another option is to consider an isolating transformer feeding the UPS, but doing that properly for many loads and preserving good protection against shock, not tripping brekers on start-up surge, etc, is not as simple as it looks.

 

[WallaceP]

I would recommend looking st how many ups’s you need s others have said. I would also agree that an RCBO would be an improvement but dont think it will sort the problem. As all the ups’s are probably on the one circuit so you would still be tripping that one circuit but not the bulk of the installation
I would say you want a new circuit or number of circuits wired back to rcbos. Either as a separate board or upgrade the existing board and include the new circuit in the new board.
I would also recommend looking at your surge protection.

 

[timhoward]

As a side-note if the APC website is to be believed those units draw a maximum of 6 amps each, so if you have 5 fully discharged after a power failure on the same circuit things could get a little interesting.

 

[IAmSparkytus!]

Strange that your electrician couldn't give suggestions as to what the issue might be when it seems pretty obvious and the fact that you've said the more you've got plugged in, the more it trips spells it out for us you would have thought.

Did the electrician measure the earth leakage and find it to be not enough to trip the RCD by any chance and this is why wasn't sure?

 

[rwassell]

It's not a great setup ,5 or 6 ups on a single shared rcd

Are these UPS all in the same location ?

Yes, all in the same location.

 

[rwassell]

Strange that your electrician couldn't give suggestions as to what the issue might be when it seems pretty obvious and the fact that you've said the more you've got plugged in, the more it trips spells it out for us you would have thought.

Did the electrician measure the earth leakage and find it to be not enough to trip the RCD by any chance and this is why wasn't sure?

Well, it was an interesting experience as the electrician seemed to be more interested in getting the visit over as quickly as possible. He got us to unplug everything. He tested. The outside power was still on. We turned that off and he said 'leave that off and see how it goes'. We did and yet it still trips. He said he'd get back to us but hasn't, hence the question on here.

Thank you all so much for being so helpful in your replies. Especially knowing the potential load draw and the fact that they could be separated and the RCBO/MCD advice.

I will contact another electrician but at least knowing more about the potential issue and what needs to be done helps with a proposed solution and forearming me prior to a discussion with another electrician.

Many thanks,

Rob