Insulation resistance

[Regs]

O.k. forgot in 1 bed room there was surge protector under the bed, removed this and instantly gained from 0.36 to 1.6 M.O. Also found that unplugging my monitor for my mac gained another 1 meg to total 2.6 M.O. I'm happy for now with that, guess the rest could be the dishwasher or washing machine.
Again would this imply monitor or lead on way out?

 

[telectrix]

a lot of electronic gear has earth leakage. always disconnect before testing. as cpl. jones famously said " they don't like it up'em".

 

[Regs]

a lot of electronic gear has earth leakage. always disconnect before testing. as cpl. jones famously said " they don't like it up'em".

So as long as the cause of low insulation r. is not the cable insulation, then it doesn't matter if the insulation reading drops right down to 0.1M.O. The reason has been investigated and would still be acceptable of course then?

I take it some items of equipment are more prone to leakage than others then

 

[Marvo]

What you've discovered is that the earth is functional as well as protective. Depending what test voltage you use to mega test all surge arrestors will show as low insulation.

 

[Regs]

What you've discovered is that the earth is functional as well as protective. Depending what test voltage you use to mega test all surge arrestors will show as low insulation.

Now you mention it at 250v reading was 0.9 Mohm and 500v it read 0.36 if i remember correctly.

 

[Marvo]

A surge arrestor would see 500volts as a surge which it would allow at least a portion of the waveform to pass safely to earth. It's possibly a good job there were surge arrestors left plugged in because you're likely to damage electronics if you run around IR testing at 500 volts on circuits with appliances still connected. I'd count myself lucky and do some more reading on correct testing procedures if I were you.

 

[Regs]

A surge arrestor would see 500volts as a surge which it would allow at least a portion of the waveform to pass safely to earth. It's possibly a good job there were surge arrestors left plugged in because you're likely to damage electronics if you run around IR testing at 500 volts on circuits with appliances still connected. I'd count myself lucky and do some more reading on correct testing procedures if I were you.

Ive been taught and told as long as you don't fire down line to neutral at 500v it would be fine.

 

[Octopus]

This is basic stuff really.

Test IR at 250v first, 90%+ of low readings are due to appliances plugged in and always go round and unplug EVERYTHING, some sockets are SP isolators, as are some FCU's.

Never fire 500V at a circuit with really low IR unless you are 100% certain everything is unplugged.

And yes I mean test the circuit in question only, all 3 to each other.

 

[Regs]

This is basic stuff really.

Test IR at 250v first, 90%+ of low readings are due to appliances plugged in and always go round and unplug EVERYTHING, some sockets are SP isolators, as are some FCU's.

Never fire 500V at a circuit with really low IR unless you are 100% certain everything is unplugged.

And yes I mean test the circuit in question only, all 3 to each other.

If you still had a low reading after unplugging everything then last resort you would disconnect FCU's and once all avenues had been exhausted then you would have to put it down as cable insulation then?

 

[Marvo]

You assume that once you've unplugged everything and switched off any isolators you're seeing the IR reading for the circuit cabling and the actual sockets only but the problem you have is the hidden appliances you don't find such as TV antenna amplifiers in lofts etc will give false readings.

 

[Regs]

Going back to what i asked originally, i thought the insulation resistance test before fitting an rcd was for nuisance tripping not to see if you had over 1 M.O.