Insulation resistance test on a ring final circuit

[mak]

Might be trivial question. My understanding is that we test on either leg of the ring since both legs make up a radial, but some say they test both legs at once, i.e. LL to NN, it would make sense if the other leg is not insulated since this is a live test, but I don't see why not if the other leg is "wago-ed".

 

[DPG]

Yesterday.....is that what you've christened your IR tester?

Blinking flip! And it's too late to edit it now.

 

[ipf]

Blinking flip! And it's too late to edit it now.

Don't worry, it seems IR dead testing is all in the past anyway.....

 

[Pete999]

Maybe I did or maybe the training these days is rubbish. I guess my question is how big is the current while performing the test, if it's not considered to be a live test then the current must be very little...

Yes that's plain to see.

 

[Mark Wright]

500v/1MΩ minimum how many amps is that?

 

[mak]

Blinking flip! And it's too late to edit it now.

It has a "tester" sound to it.

 

[DPG]

It has a "tester" sound to it.

Yeah close enough eh

 

[mak]

500v/1MΩ minimum how many amps is that?

0.5mA not much to munch on.

 

[DPG]

0.5mA not much to munch on.

Enough to make you jump and maybe fall off a set of steps though.

 

[davesparks]

I know it's a test done on an deenergized board/circuit but you still send 500V through the circuit so it's kind of live.

Sorry mate, I'm not a linguistics engineer, what's the principal difference between "sending" and "applying" in this context.

So you virtually can't get a shock from it?

You apply a test voltage of 500VDC to the circuit, you don't send the voltage. It might seem like a daft point but it is important, voltage doesn't flow or move in any way, it is the pressure that causes current to flow. This is a very important concept to understand before you can properly understand a lot of electrical theory.

Ir testers are current limited so that they only allow a tiny current to flow even if the leads are shorted. When you short the leads of an IR tester you get a tiny spark which shows there is very little energy there. If it was a 500V supply without the current limited you would get a much bigger spark and a loud bang.

You can get a shock from an IR tester but it is at a tiny current so it is more of a surprise than anything else.
You can also get the same little shock from a cable which has been IR tested (if the IR is very high) as the cable acts as a capacitor and stores the charge. IR testers automatically discharge this stored charge from the cable if you let go of the test button before disconnecting the leads, it only leaves the cable charged if you disconnect the leads with the tester latched on.

 

[radiohead]

You can also get the same little shock from a cable which has been IR tested (if the IR is very high) as the cable acts as a capacitor and stores the charge. IR testers automatically discharge this stored charge from the cable if you let go of the test button before disconnecting the leads, it only leaves the cable charged if you disconnect the leads with the tester latched on.

Back in the day when pretty much everything I did was pyro or steel there were hours of entertainment to be had charging up pyro's prior to your mate second fixing.

 

[davesparks]

Back in the day when pretty much everything I did was pyro or steel there were hours of entertainment to be had charging up pyro's prior to your mate second fixing.

Pyro always gets associated with this, but it is equally possible to do with any other multicore cable.

It's very entertaining until you forget and touch one of the charged cables yourself.

 

[ipf]

Pyro always gets associated with this, but it is equally possible to do with any other multicore cable.

It's very entertaining until you forget and touch one of the charged cables yourself.

Who provided that jug of cold water, Dave?
Chill out and smile a bit...or give others a chance to.
Pyro, RIGHTLY, get's the association because each individual length of cable had to be fully tested for continuity and IR, due to termination....and massive installations were done with it. In every other multicore the cores had individual insulation. OK, we found the odd ones with all the same colour, unmarked .....but rarely.

 

[jay sean]

can you remember the sequence the tests have to be carried out continuity is 1st so you can prove your ring main

 

[ipf]

Can anyone say if the term 'ring main' was EVER actually, officially, used as a term for a ring final circuit, according to regulations.
The term was used in general (and still is to some extent). I served my time with it, but, even in the 14th edition regulations, the circuits are referred to as ring final sub circuits. I'm sure they were known as RM's when I was at Tech and it was certainly never insisted upon that we refer to them otherwise.

 

[davesparks]

Can anyone say if the term 'ring main' was EVER actually, officially, used as a term for a ring final circuit, according to regulations.
The term was used in general (and still is to some extent). I served my time with it, but, even in the 14th edition regulations, the circuits are referred to as ring final sub circuits. I'm sure they were known as RM's when I was at Tech and it was certainly never insisted upon that we refer to them otherwise.

I don't believe it has ever been the correct terminology for the ring final circuit.
Ring mains exist in gas, water, HV distribution and LV distribution but I don't think it has ever been used for LV final circuits.