UPS fed RCD sockets tripping

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EXC

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Hello

I hope someone may shed some light on this problem that I looked at today. 

 A number of 30mA RCD twin sockets (Timeguard passive) on a reception desk, fed buy a local DB which is UPS fed, keep tripping every now and again , with only one item plugged in to most of them , one had only  a double insulated power supply for a phone.

 I ruled out earth leakage of the plugged in devices but wondered about the if the UPS supply was to blame? I have not tested the loops at the sockets at this stage but I am sure that they will be ok as the DB is new as is the sub main from the UPS MCCB panel and final circuit.

I was thinking of replacing the socket with another make like MK to rule out a problem with the sockets themselves.

Any one else had this problem ? 

 
Strikes me as a strange set up. Why have separate RCD sockets on a desk, rather than protection at the DB?

However, it should work, so the following thoughts would be going through my head.

1. I assume you have checked for loose or insecure connections.

2. Are there any other similar sockets on other circuits from the DB?   If so, have they been used/checked, (as you say its a new installation), and are they OK?

This could eliminate or re-inforce the case against the UPS.

3. Are there any other RCD circuits of any type off the DB;    -same logic.

4. Is the UPS correctly installed IAW manufacturer's instructions, with particular attention to earthing?

5. If the UPS is suspect, I can only think of transients, or an impure waveform upsetting the RCD electronics.  Could be hard to prove unless you have some sophisticated test gear, such as a 'scope. 

6. A different brand socket, (or a device at the panel), could well behave differently in the presence of transients, etc,  but this is totally unpredictable in my view.

7. Perhaps you can run without the UPS for a while, to see if the problem disappears.

I hope that something there may help. 

Regards

 
Hi Geoff 

 Thanks for your reply

 We normally put RCD sockets on a surface install for important equipment to prevent total circuit loss incase of a faulty item.

The whole DB is fed from a UPS backed up MCCB panel . I have yet to test or inspect the circuit as I can not turn anything off till next weekend,  but know the engineer who installed so it should be ok , but you never know.

 I don't think there are any other RCD sockets from that DB.

I will be checking the earthing when I have a shut down. I know the earthing of the UPS and MCCB are ok, or was when it was installed a couple of years ago.

 Cheers

 If I find something next week end I'll report back. 

 
Go back to basics, before you do anything else, I'd isolate from UPS and do the standard dead tests before going on to anything else. You state you know the guy who installed it ,however that's no guarantee it's all in order, we've all made a daft mistake at some point, trapped a cable or something. It's better to start from scratch, rather than dive in looking for a major problem, only to find out it's something silly, I have seen something like this a long time ago, but can't remember what it was at the moment.

 
As  Phil said, the golden rules of fault finding are Assume nothing, Only make evaluations on investigations, inspections and test readings you have done yourself. Write down all test results as you go along including the state of the item under test when you got those results. So far it appears you haven't actually investigated or tested anything. How sensitive are these RCD sockets? i.e. what is their trip current when ramp testing?

Doc H.

 
Last edited by a moderator:
Hi

 Thank you for all your replies.

I haven't presumed anything, I will be carrying out my own testes next weekend as I am unable to turn off any equipment until then.

I posted the question just incase someone has had the same problem with Timeguard RCD sockets or something.

Cheers

 
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