I/R testing a single circuit when unable to turn off main switch

[waynehayes]

At college it was drummed into us that dead tests should be done with the main switch open. This is great at college, but not practical in the real world. When testing insulation resistance on a single circuit in a live board (when the main switch can't be turned off for whatever reason) we remove the line conductor from the breaker, the neutral from it's bar and the same for the cpc. Right?

Cheers.

 

[Andy™]

as long as LN & E is isolated from board, then you can do IR

 

[ADS]

At college it was drummed into us that dead tests should be done with the main switch open. This is great at college, but not practical in the real world. When testing insulation resistance on a single circuit in a live board (when the main switch can't be turned off for whatever reason) we remove the line conductor from the breaker, the neutral from it's bar and the same for the cpc. Right?Cheers.

I don't like this, as I've said before!!

If you're leaving the rest of the installation 'live', whilst disconnecting a circuit to perform a 'dead' test, you better make sure that:

1/ You disconnect the RIGHT neutral - How do you know someone hasn't mixed them up?? Disconnect the wrong one and it rises to 230V

2/ If you do get the right Neutral, no one has borrowed it somewhere in the installation for another circuit - otherwise, same result!!

But otherwise, good luck.

 

[sellers]

switch relevant mcb off and remove the relevant neutral with long nose pliers, give it a flash on the neutral bar to double check. Still treat as live. clamp one probe on earth bar, other on the neutral, depending on your mft it may flash up if its got voltage. (mine does) If all ok, press the big button and record your result.

 

[Andy™]

switch relevant mcb off and remove the relevant neutral with long nose pliers, give it a flash on the neutral bar to double check. Still treat as live. clamp one probe on earth bar, other on the neutral, depending on your mft it may flash up if its got voltage. (mine does) If all ok, press the big button and record your result.

or you could use a proper voltage tester....

 

[waynehayes]

Thanks for the replies. Shouldn't the cpc be removed from the earth bar to totally isolate the circuit?

 

[ianmacd]

Thanks for the replies. Shouldn't the cpc be removed from the earth bar to totally isolate the circuit?

No because there may be multiple cpc paths so it should be either tested in the block or tested independently and then the same test against the block too.

 

[sellers]

[quote name='Andy

 

[S60TEM]

flashing down the neutrals with long nose pliers is sometimes the only way to check if its 3 phase, wired in singles that havn't been numbered and you can't get a clamp meter in to measure the current because there's no room!

Am sure EaWR wouldn't be too understanding though!

 

[Adrian]

We all at some time or other work live but at the end of the day, who are you saving, not you, the customer, and if it goes wrong who is at fault, you.

turn the main switch off, think safe and be safe

 

[steptoe]

Never work live,

dont even take the cover off the consumer unit until you switch it off,

in fact, for some members, you probably shouldnt even get out of bed if your consumer unit is turned on.

 

[sparkymalarky]

Best way i've found for finding neutrals, as I can't afford huge money for circuit tracers, is to send an apprentice around with a kettle randomly boiling it off the socket, meanwhile I check through live/neutrals for confirmation of the right circuit, boring and unprofessional, I know, but would rather do that than turn off 15 PCs or a Server

 

[Revved Up Sparky]

Perhaps it would be safer to leave the neutrals alone, do a L-N, L-E and put the N-E down as a limitation on the certificate. This might be fine if you are doing a routine test, however, if you are tracing a fault then you will obviously need to disconnect that neutral.