Insulation Resistance Testing

[dizz]

I have neon indicators in four circuits, 13A FCU, 3A FCU, Cooker, Shower circuits.

1. Should the tests be done with these switches closed, or is there a chance of damaging the neon lights?

2. If they should be excluded because they are "sensitive" equipment, are the tests done ...

2a ... with the switches open (which means you are excluding part of the circuit?

2b ... with the DP switches taken out so you can test from the CU to that switch and then test at the switch for the remainder of the circuit?

2c ... with a connector block to connect the ongoing leg so a full test can be done from the CU?

 

[17thman]

2b good

2c good

or connect Line and Neutral together and test LN to Earth. keeping all neons connected.

why are you asking?

 

[EFLImpudence]

I have neon indicators in four circuits, 13A FCU, 3A FCU, Cooker, Shower circuits.

1. Should the tests be done with these switches closed, or is there a chance of damaging the neon lights?

I don't think you will damage the neon but they are connected between L & N so you will not get a reading. L & N connected together tested to earth may be sufficient.

2. If they should be excluded because they are "sensitive" equipment, are the tests done ...

If you wish but not good.

2a ... with the switches open (which means you are excluding part of the circuit?

That will verify the circuit from CU to the switch.

2b ... with the DP switches taken out so you can test from the CU to that switch and then test at the switch for the remainder of the circuit?

That would be good.

2c ... with a connector block to connect the ongoing leg so a full test can be done from the CU?

If you wish - 2b is good.

You particularly need to test all the shower circuit

 

[PrenticeBoyofDerry]

The neon will give you poor readings rather than damage being caused.
You can test whole circuit by linking the neon switch out.

 

[ban-all-sheds]

I don't think you will damage the neon

OOI I once did a 1000V IR "test" of an FCU with a neon. It worked fine afterwards.

 

[chivers67]

Always was told to disconnect as inaccurate readings could be obtained...

 

[dizz]

Thanks.

I have >299Mohms for each "leg" without the neon FCU's, but when I include them (had to give it a go), I get 29Mohms for the for each of the circuits concerned, and for the installation as a whole, just under 9Mohms.

I guess that >299Mohms should be recorded even though the other readings aere acceptable?

 

[thomo27]

Thanks.

I have >299Mohms for each "leg" without the neon FCU's, but when I include them (had to give it a go), I get 29Mohms for the for each of the circuits concerned, and for the installation as a whole, just under 9Mohms.

I guess that >299Mohms should be recorded even though the other readings aere acceptable?

yes as you have proved that the insulation is >299 when you link out the neon

 

[securespark]

I find the LN-E trick does not always work, even when rducing test voltage to 250V.

 

[PrenticeBoyofDerry]

I guess that >299Mohms should be recorded even though the other readings aere acceptable?

As you are not testing the IR of the circuit with neon, the reading that should be recorded would be the the one without neon.

 

[JohnW2]

I find the LN-E trick does not always work, even when rducing test voltage to 250V.

It obviously won't 'work' if anything connected to the circuit (e.g.a computer PSU) introduces an L-E leak (or an N-E leak, although that would be rare). However, if one is confident that there is no such L-E leak (e.g. if one knows for certain that the only things connected to the circuit are neons connected between between L & N) then the 'LN-E trick' has got to work.

Kind Regards, John.

 

[EFLImpudence]

I find the LN-E trick does not always work, even when rducing test voltage to 250V.

It obviously won't 'work' if anything connected to the circuit (e.g.a computer PSU) introduces an L-E leak (or an N-E leak, although that would be rare). However, if one is confident that there is no such L-E leak (e.g. if one knows for certain that the only things connected to the circuit are neons connected between between L & N) then the 'LN-E trick' has got to work.

Conversely, if it doesn't work - there is something wrong.

 

[JohnW2]

Conversely, if it doesn't work - there is something wrong.

Exactly - that is obviously the implication of what I said. When I said that, in the absence of any leakage paths to earth, the 'trick has got to work' I assumed it would be clear that I meant in the sense of eliminating the effects of any L-N loads and protecting any loads connected between L and N from damage (which is what 'the trick' is all about). In the absence of any known sources of leaks to earth, a low IR reading obtained using this method then obviously indicates the presence of an unknown cause of an L-E or N-E path - as you say 'something wrong'.

Kind Regards, John.