Have I done anything wrong?? Boss not happy!

[flyingsparks]

Sorry this is a bit long but really would like some answers before I go back to work tommorow!!

I was asked to check out a tripping RCD fault. On arrival she told me that it will trip anytime, no specific appliances are ever on at the time etc. It even trips in the middle of the night.

Got the megger out, all circuits were ok-ish, about +4meg ohms neutraul and live to earth, apart from one labeled sockets office and utility - these at the time read 0.8M - (the RCd was staying in whilst I was there.)

In the office there was loads of computer equipment, home cinema equipment etc etc... all pluged into one extension lead and in one socket. Pulled this out and got the poor reading on this equipment. The circuit then went up to abouit 4M as well. Tested each individual applicance nothing was particularly bad but I think a few faults combined were bringing it down to 0.8M.. old the customer that its prob ebst to have a dedicated office ring with T-bar sockets installed not on the RCD.

Am I correct in thinking that computer equipment will leak to earth ({had the figure of about 3mA per computer)? The RCD was also tripping at 18mA according to the ramp test.

I put the fault down to too much computer equipment being on the 30mA RCD.

Boss doesnt think this can be right and that I have missed something...

What do you think? Thanks!

 

[ban-all-sheds]

That type of equipment can leak to earth, and if hers trips at 18mA then that could be easy to reach.

(BTW - 607-02-04.... )

But she says that the tripping is not associated with any particular loads being connected...

Would it be easy to add a non-RCD socket to plug all that stuff into, to see if it cures the tripping?

It worried me when you wrote this:

In the office there was loads of computer equipment, home cinema equipment etc etc... all pluged into one extension lead and in one socket. Pulled this out and got the poor reading on this equipment. The circuit then went up to abouit 4M as well.

You meggered the circuit with equipment plugged in????

 

[flyingsparks]

I did megger it but only on 250V.

Dont have a regs book handy right now - could you enlighten me what that reg says!?

Could only add the non rcd socket as a temporary measure by means of an extension lead I would think.

 

[ban-all-sheds]

I did megger it but only on 250V.

So not a proper test, alhough it's hard to see how something could be OK at 250V but break down at 325....

Dont have a regs book handy right now - could you enlighten me what that reg says!?

If the cpc current exceeds 10mA you need the circuit to have a high-integrity cpc. Not that that would do anything for the tripping problem.

Could only add the non rcd socket as a temporary measure by means of an extension lead I would think.

Might be worth a try? How often does she get trips? e.g. if she went a few days, or a week without one how conclusive would that be?

 

[RF Lighting]

You meggered the circuit with equipment plugged in????

I was just going to say the same thing.

You are supposed to remove everything connected to the circuit prior to carrying out any IR testing.

You are supposed to test L>E N>E L>N. You must only test L&N>E as a last resort if it is completely impractical to test properly.

Testing L&N>E can give misleading results.

Firing 500v DC up a very delicate (and expensive) piece of electronics can (and does) cause allsorts of damage.

You could put a mA meter on the CPC for the circuit concerened if you suspect high protective conductor currents (or wire the CPC in series with an ammeter) to prove or disprove this theory.

Did you test and ramp the RCD in isolation, and then again connected to the installation?

Have you ever been on any formal testing courses?

 

[DIYANIMAL]

were they plugged into a filtered socket or extension lead?

We always do an initial all neutral to earth reading on issues like this, gives a good idea of the state of the installation with the appliances connected.

 

[flyingsparks]

were they plugged into a filtered socket or extension lead?

We always do an initial all neutral to earth reading on issues like this, gives a good idea of the state of the installation with the appliances connected.

They were plugged into a filtered extension yes.

Did the ramp test with the RCD isolated, didnt actually try it again with the loads on. Not exactly sure how often it was tripping, but I think once every day or 2.

I know I was only meggering at 250V but the results are not going to be a million miles different from doing it at 500V, and I would be able to locate where the problem was. Can meggering L&N to E at 250V damage electronics? This is what a PAT tested would do. How can this give missleading results?
Thanks all....

 

[DIYANIMAL]

filtered sockets give readings of around .3 meg when connected

 

[holmslaw]

..

 

[flyingsparks]

flyingsparks - good name, seems to fit the situation.

Whats that meant to mean??

 

[flyingsparks]

filtered sockets give readings of around .3 meg when connected

Mmm.... ok. Thanks.

 

[DIYANIMAL]

unique fit sockets marked computer use only would be a good solution, if it's the computers bringing the IR down

 

[flyingsparks]

unique fit sockets marked computer use only would be a good solution, if it's the computers bringing the IR down

Thank you - thats exactly what I suggested to the boss.

 

[Spark123]

Can meggering L&N to E at 250V damage electronics? This is what a PAT tested would do. How can this give missleading results?

Depends who is operating the PAT tester
The Megger ones we use have a code to test PCs/IT equipment which does not involve an IR test, it does however perform an earth leakage test as part of the operation test.

 

[securespark]

So tell me, I'm intrigued, why is your boss unhappy??