Zero resistance for L-N doing IR test

[ewillday]

Hi all,

I'm testing a 35 year old system, with 11 circuits split across 2 RCDs. 3 of these are lighting circuits 2 come out fine with an IR test but one fails L-N with 0.0 ohms.

This lighting circuit is comprised of 3 ordinary lights, 3 chandaliers and 3 fluourescents. A number of switches including a 2-way that shares the box with an separate lighting circuit (that tested fine).

1. The result suggests a short but everything works as it should.

2. I've looked at everything that is easy to get to (30ft ceillings) and see nothing wrong. The circuit covers 3 floors and 8 rooms so I have no idea which way the circuit runs. Can anyone suggest where the problem may be and a good way of tracking it down?

Cheers!

Ps. I've tested with all lamps removed and all switches open.

 

[bugsy]

Er try disconnecting the fluoro's

 

[Hawk81]

looks like flouresants are causing your low reading.

 

[ewillday]

The other circuits had fluourescents in and tested ok but will do tomorrow.

Thanks both.

 

[Deleted member 9648]

Chances are youve missed a load on the circuit somewhere....shaver point,neon,pir...etc

 

[timo]

Have you tested both LN-E >? what did that give you.

 

[ewillday]

Disconnected all the fluoros and have "unlimited" resistance now . Made the stupid mistake of thinking that because the other circuits weren't effected by the fluoros on them that these wouldn't. DOH!

Many thanks to everyone who helped.

What is the crime of robbing a bank compared with the crime of founding one.

 

[sbarkeruk]

As already stated, the method using LN - E together as a limited test is also useful and a valid test (but comment as a limitation that this is what you are doing on the report), and is being used more and more in these situations.

Also agree that there may still be something 'unconventional' or just hard to spot (buried) causing this, such as a shaver, extractor, etc.

Regards,

 

[bugsy]

Disconnected all the fluoros and have "unlimited" resistance now . Made the stupid mistake of thinking that because the other circuits weren't effected by the fluoros on them that these wouldn't. DOH!

Many thanks to everyone who helped.

What is the crime of robbing a bank compared with the crime of founding one.

There reading you were getting was through the control gear

 

[chris gray]

its because of this senario that i initially test l-n at 250v - in case something has been missed

 

[Jason Smith]

sounds like you are describing something like a hotel or similar, you asked where to look, when I have exhausted all the brill advice suggested aboveI start with the jbs that would of been used back then, then obviously its the cables themselves, by then we are into re wire territory with lots of boards up etc. However, quick tip is find the mother jb, its usually in a hallway or similar out side of any rooms, start digging there first as it was the practice to put them there in the olden days. Piece of cake then to IR each leg. Hope this helps, sorry if you already know.

 

[ewillday]

Good idea Chris Gray.


Emile

 

[chris gray]

on another note, some of the type t florrys can give u a reading of around .14. just for future reference