Insulation Resistance....

[Mikey_A]

Hi

'Remove all lamps during an insulation resistance test'.

My undersatanding is because it will affect the results of the test, not because they are vulnerable to the test voltage unlike electronic devices such as dimmer switches, touch switches etc...

Am i right or wrong?

 

[Lectrician]

Do you know what you are testing for when performing an insualtion test?

Do you know what reatings are acceptable and those that are not? And which reading maybe somewhere in between?

If you do, they you will realise that even a single tungsten lamp is going to have a resistance in the region of hundreds of ohms, the more you have, the lower the resistance will be still......

Umm.....hundreds of ohms vers Mohms?

 

[jeepmadmike]

the reason is otherwise you will measure the lamp resistance and neutral conductor impedance to the earth reference point of the supply if the neutral is not isolated also you will measure the IR of the other circuits. I disconect the neutral and then you measure the IR of live, neutral and the light fittings. i've never caused a problem with a lamp or fitting

 

[Lectrician]

the reason is otherwise you will measure the lamp resistance and neutral conductor impedance to the earth reference point of the supply if the neutral is not isolated also you will measure the IR of the other circuits. I disconect the neutral and then you measure the IR of live, neutral and the light fittings. i've never caused a problem with a lamp or fitting

BUT - you would always drop the neutral to perform test wouldnt you DP CU switch off for a start

Where in devon you to jeepmadmike?

 

[jeepmadmike]

im just outside newton abbot

Lots of 3phase boards have main switches which do not disconnect the neutral also the number of final circuits is several times more than a domestic CU

 

[Lectrician]

A TP board usually have means of disconnecting the neutral and earth for testing reasons. Usually loosening a screw and moving a link.

You do have to test the IR between N and E aswell, so this link does need removing, or the cct neutral removing from the neutral bar.

Newton Abott - Was there this morning going down to Dawlish to the Linhay Pet Rehab Centre......actually live in Croyde.

 

[jeepmadmike]

your right there but the biggest danger is forgetting to refitting the link after, now that can result in some damage! it does amaze me that all DB isolators do not disconnect phase or phases and neutral.

 

[Lectrician]

Some DB's do have four poles as standard, and all can have them if you specc it - MEM, Merlin, Square D, Crabtree for sure. The on the shelf isolators generally dished out are TP as the wholesaler prefers to be competitive....but they are out there

In commercials, especially on construction sites and caravan parks etc, I actually use DP breakers on a SP install.

 

[plugwash]

In commercials, especially on construction sites and caravan parks etc, I actually use DP breakers on a SP install.

How exactly do you do that? Aren't the busbars in single phase units designed to feed live to every breaker pole?

 

[Lectrician]

Merlin and type A and type B boards have a neutral bar running down the busbar under a cover. There DP MCB's have an 'empty' terminal to take one busbar stab, and then a neutral link to the top bar - I will see if I can find a photo.

MEM do boards that look like TP boards which are specifically done to provide LN LN LN LN up the busbars.