IR Test

[Baker1988]

hi was just wondering if some one could clear this up for my i keep seeing on the open forum that people do a ir test between l+n to cpc i get shown at college to do the ir between l to e and n to e and l to n so why is it that i keep seeing people say about doing a ir by connecting live and neutral then testing from the connected live and neutral to earth wont this defeat the object of doing the ir test as it wont test between l and n as there connected together,

here is a link to the last one i saw
http://www.electriciansforums.net/i...allations/73680-ir-method-2-a.html#post732492

 

[Floody]

In college they show me...
L + E
N + E
L + N

 

[Baker1988]

Yeah thats what they show me but people I see on the open forum keep saying about connecting the l + n and then testing between earth

 

[Happy Jack]

Funny that, we are going through T & I at college at the moment and this method hasn't been discussed.

To short L and N only seems practical if you've already proved that the IR values between all conductors are acceptable, and no dead-short exists between L and N.

I assume this method is used when attempting to determine if there is a path to earth via one of the live conductors, in the event of nuisance tripping of an RCD, for example. It makes sense to short L and N in this case.

 

[Mark1985]

I thought testing between L+N to CPC was so that any sensitive equipment that hasn't been or can't be removed from the circuit does not get damaged. ie if you put 500v between L and N it would fry any sensitive equipment. I could be wrong as i'm a trainee too..

 

[trev]

Mark gets one point.

 

[Baker1988]

So how will that stop sensitive equipment from being damaged it will still send 500 volts down it and also if it does stop equipment getting damaged then why dont we always do the test this way

 

[Happy Jack]

ie if you put 500v between L and N it would fry any sensitive equipment.

Directed at Trev, then, why could one just not reduce the test voltage to 250Vdc?

 

[trev]

Even at 250, testing between L and N you'll not get an answer in Mohms. You won't even get an ohm most times, an example is those plug in air fresheners. They usually give you 0.57ish