*Insulation Resistance Test Quiery*

[kathleenbilly]

Hello to those looking in,

My question is on Insulation Resistance testing.

The senario, PVC Conduit Singles 1.5mm two way light operating fluorescent tube lamps.

Now as i understand it the above fluorescent lamp have both a starter and a ballast. If a insulation resistance test was done ie: 500v sent down the live and neutral this would blow the ballast.

My quiery is if the light switch is in the off position would the insulation resistance test voltage/current only travel as far as the switch? Thus the fluorescent ballast which is sensitive be safe, if so how does this apply on the two way light switch how do you confirm they are both in the off position.

I also have heard that you can connect the live and neutral together and test between them and the CPC and this method protects sensitive equipment?

Can someone explain the benefit of this why it's used and where this pinciple is best used, i really need to understand this i don't want to ever damage equipment or any sensitive systems.

Thank you KB

 

[iceman]

to comfirm whether the 2way switches are in the off position just link out line neutral and earth at the ballest then wile performing I/R test operate the switches one at a time, you mite as well just test the whole thing wile the ballest is linked out, then reinstate the ballest once testing is finished hope this helps.

 

[lilygee]

When testing between live conductors, disconnect sensitive equipment, or if not possible, knock the switch off. As far as I'm aware, it's ok to test this sort of sensitive equipment to earth using the method you described-between earth and live conductors with live conductors connected together. Must admit, I have on occasion sent 500v through sensitive equipment and never blown them, although you can get some funny readings. I asked the nic man about this and he reckoned that even stuff described as sensitive should take it without damage to comply with british standards, don't know if that's true or not though

 

[kathleenbilly]

On my current install i won't connect the fluorescent tube lamps as it's a new install so i can test right up to them no probs then connect it all up afterwards.

But if a periodic and say you had 10 of these Fluorescents i'm sure you would not disconnect each one,

So in this case would the joining together of the live and neutral and test between them and CPC be good practice, and more importantly in doing so does this protect the ballast or any anther sensitive equipment that might be prone to damage from the insulation 500v test??

Or like you said then just test up to the switch then?


I just want to understand when to use this method or when not etc

 

[mechelec]

just join live and neutral together and test to earth, no damage to sensitive equipment and just note it on the PIR as LIM. It used to mention this method in the old blue OSG. Switching the switch off will result in not testing all of the circuit and should be avoided.

 

[kathleenbilly]

OK thanks so just to re-cap and so i fully understand,

So for example if you was doing a new install like myself would you connect up the Fluorescents and use this method, or do a normal standard insulation test and then connect up the Fluorescents afterwards?

Do you use this method only on Periodics or also on new installs?

If so how do you write it up as a limitation? what do you say, and at what point is it un-accepatable to use this method the cross over point, where it's deemed not practical to dis-connect sensitive equipment how many fluorescents is too many do you just use your own judgement.

Can you give any other examples where you use this, is it now almost common practice to do so on most testing out of 10 inspections/tests how many times would you use this method?

Thanks for the reply,

KB

 

[saveloy]

When testing between live conductors, disconnect sensitive equipment, or if not possible, knock the switch off. As far as I'm aware, it's ok to test this sort of sensitive equipment to earth using the method you described-between earth and live conductors with live conductors connected together. Must admit, I have on occasion sent 500v through sensitive equipment and never blown them, although you can get some funny readings. I asked the nic man about this and he reckoned that even stuff described as sensitive should take it without damage to comply with british standards, don't know if that's true or not though

Yep I've accidently sent 500v down various sensitive equipment and never blown anything. Not reccomending that you do it though!

 

[kung]

Yes you can connect line & neutral with link and test borad as a whole then on cert cross out L/N, L/CPC, N/CPC and write L/N + CPC and reading ie >299Mohm but although you can do it id only expect to do this on a periodic unless the tester you have doesnt have a 250v option and you cant isolate/discon a tranny/piece of sensitive equipment eg SELV or PELV etc.
As for sending 500v down an install with sensitive equipment on without linking line & neutral as said advoid ! ive seen a dishwasher tripping out RCD because this was done !
Regards
Kung.

 

[lilygee]

I would say on a new install you should really be testing 100% of new wiring on the full range of tests. Test method 2 would probably be more common in periodics where there are always impracticalities concerning disconnection

 

[kathleenbilly]

Thanks for the replies i am now able to understand when to use this method, cheers guys for the help, KB

 

[Graeme Harrold]

When testing between L+N and Earth, sending 500V down the L+N results in no PD at the equipment end, therefore saving precious delicate equipment. By using the earth as your test line, you are doing a more sensitive test due to the physical make up of T+E.

Was also taught this takes care of pesky neon lights located in switches and sockets that cause a miryad of problems when testing between L and N............

 

[Peter Woodford]

Can you link L-N and earth when carrying out the test when your replacing a fuse board and put lim on the cert as been to a house that has about 15no 12v 50w lamps in one room

thanks

can you do a L/N and earth test when doing a consumer unit change and put this on the cert as have been to a house and they have about 15No 12v 50w lights in one room