Insulation Resistance query

[Amp David]

Just at a job this morning where customer has an RCD that trips whenever it likes with no pattern in when it trips.

Testing lives to CPC found that RFC was showing 10.5 Meg ohms which as opposed to >299 for all other circuits. The only item of equipment that wasn't unplugged due to location of the socket was the Sky box in the bedroom.

I then managed to get the drawer unit pulled forward to unplug the said Sky box then re tested and got >299Meg Ohms. What puzzled me was how can an item of equipment which is double insulated affect Ins Res readings between Live conductors and CPC?

 

[Silly Sausage]

Faulty plug/lead?
Have you IR tested the plug/lead?



+tion:

I was thinking if its got a 2 core power lead.

 

[malcolmsanford]

Switch mode switching ..............................

 

[oldtimer]

Is the SKY box still working after you put 500vdc across it ? if then you were lucky also you say the RCD trips anytime I had a job like this and I mentioned to the customer I cannot find the problem so you need to take note of what you were doing when it tripped and a week later I was told it was the dishwasher.

 

[Amp David]

Course its still working, why wouldn't it be.

Told them the same, that all fixed wiring was ok so will have to keep an eye on what is being used etc.

 

[Amp David]

Faulty plug/lead?
Have you IR tested the plug/lead?



+tion:

I was thinking if its got a 2 core power lead.

That was what I was thinking, the plug or lead, but then saw the plastic earth pin and thought what the hell

 

[Amp David]

Switch mode switching ..............................

How would this show as a lower Ins Res reading when the item of equipment has no connection to the CPC at the socket Malc?

 

[telectrix]

must be the leakage fairies.

 

[ackbarthestar]

The aerial coax lead is likely to be grounded to provide a screen for the signal line. A signal ground rather than an electrical ground. This maybe where you are getting lower than expected readings.

 

[telectrix]

must be the leakage fairies. don't forget that the neutral is connected to E at source ( TNC-S ) so that could affect your reading .

 

[Amp David]

must be the leakage fairies. don't forget that the neutral is connected to E at source ( TNC-S ) so that could affect your reading .

Main Switch on CU isolated though and bonding disconnected

 

[telectrix]

so, it's back to the fairies then. unless it's the coax, as said previously.

 

[Amp David]

The aerial coax lead is likely to be grounded to provide a screen for the signal line. A signal ground rather than an electrical ground. This maybe where you are getting lower than expected readings.

See what you mean, but no coax there, just scart from sky to TV.

 

[Amp David]

so, it's back to the fairies then.

Must be then. End of the day the installation passes so thats all I need to be worried about I suppose

 

[telectrix]

what about the coax from dish to sky receiver?