RCD not Resetting

[Spikenaylor]

Hi there
Local church
TT system,
CU with RCD as protection as main switch.

Had a problem with the dishwasher tripping the RCD when running a intensive program, but that is a other issue.

the main issue is when the RCD has tripped, you cannot reset it.

There usually is no power on the circuits, as the church has been empty when the RCD tripped, maybe fridge, dishwasher, boiler etc, no lights or PA system etc.

I have traced the fault back to the two computer suites they have, one in an office, one in the main hall, both on seperate circuits.
I understand that this may be a high integrity problem and earth leakage in both these systems.
What I dont understand is why just turning off the MCB's those two circuits does not allow me to reset the RCD, but turning off all the MCB's does let me reset the RCD.

I have disconected the computer equipment from the circuits and am able to reset the RCD with all MCB's on so it's nothing else causing it.

any ideas or answers as to why this happens.

 

[telectrix]

have you done a ramp test? have you tried measuring leakage?

 

[Spikenaylor]

No I havent mainly because the computer suites do not trip the RCD, We suspect the dishwasher is tripping the RCD.

As a test.

I disconnect the Dishwasher and manually trip the RCD, at this point I cannot reset it until all the MCB's are turned off.

the question is why do I have to turn ALL the MCB's off before I can reset the RCD.

 

[bigbaddave]

Have you tried a global IR test on the cable? What is the rated current of the Main RCD (Amps) & (Ma)

 

[telectrix]

i've had this with some RCDs. had to turn off all breakers, reset RCD , then turn breakers back on.

 

[Plonker 3]

Have you disconnected the RCD from the outgoing cables ( both the live and neutral)and tried turning it on?

 

[Spikenaylor]

I have tried another make of RCD
80A 30ma

As per Telectrix's post
just wondering why this is the case.

physically disconnecting the computer items from the circuits ie unplugging them causes the RCD to reset normally with all MCB's on.
Plugging in the Computer stuff, but not turning on the computer stuff DOES NOT trip the RCD, but when the RCD is tripped and the computer stuff is plugged in but turned off, the RCD will not reset unless all MCB's are turned off.

I cannot see how an IR test will do anything, nor ramp testing etc the RCD, because as far as I can see there is no fault with any of the circuits, just a problem caused by the earth leakage of the computer stuff, but why does it seem to affect all the MCB's

 

[decolad69]

Have you checked polarity on all the computer sockets ?

 

[Spikenaylor]

tried moving the computer stuff onto different ciruit and the same thing happens.

I have checked the socket that the computer stuff is plugged into and that is fine.

 

[Steve_P]

How many RCD's are there?

 

[Spikenaylor]

just the one which is the main switch also

 

[Steve_P]

but why does it seem to affect all the MCB's

It probably doesn't, it just affects the RCD which has something in common to all the MCB's.

 

[The_Body]

I don't do domestic stuff I work in industrial settings but to me its pointing to the cpu's and I think (pretty sure) that in a CPU line and neutral both connect to earth through filters (capacitors) perhaps the fault lies there?

How old are the computers?

 

[Knobhead]

I thing we’re looking at a cumulative leakage problem. If the circuits are turned on individually the build up is gradual and not pushing the RCD over it’s trip limit. As with all protective devices an inrush will cause tripping. Being in the industrial sector you should know this.
As to curing the problem. The loads need splitting across a couple of RCD’s. And sort the dishwasher out.

 

[The_Body]

This is still when they are switched off? So where's the leakage?

 

[shanky887614]

I have tried another make of RCD
80A 30ma

As per Telectrix's post
just wondering why this is the case.

physically disconnecting the computer items from the circuits ie unplugging them causes the RCD to reset normally with all MCB's on.
Plugging in the Computer stuff, but not turning on the computer stuff DOES NOT trip the RCD, but when the RCD is tripped and the computer stuff is plugged in but turned off, the RCD will not reset unless all MCB's are turned off.

I cannot see how an IR test will do anything, nor ramp testing etc the RCD, because as far as I can see there is no fault with any of the circuits, just a problem caused by the earth leakage of the computer stuff, but why does it seem to affect all the MCB's

computers are always drawing power. the 5v rail inside is always on. this could be why its tripping it.


this is because most pc psu are cheap crap

 

[Spikenaylor]

Yes i understand all that, but still I don't understand why I have to turn off all the MCB's in order to Reset the RCD!!!

 

[shanky887614]

This is still when they are switched off? So where's the leakage?

pc's are ALWAYS drawing power


the cable goes from psu to motherboard to case.

press butten on case then motherboard draws more power from psu which creates more heat so fans kickin

 

[daiplayer]

i heard that in college.

cant put more than 5 pc's on one radial circuit due to a lot of earth leakage as a result. ( just what ive heard, not that ive ever installed in a computer room)

???

 

[JD6400]

Yes i understand all that, but still I don't understand why I have to turn off all the MCB's in order to Reset the RCD!!!

You say they are turned off , but is it a 2 pole switch in the socket outlet ?
Why don't you just ramp it and find where the underlying fault / faults is , because it sounds like Tony is spot with his thoughts on .