Question about Insulation Resistance values

[flyingsparc]

Job is to extend a kitchen ring circuit, and have a question about Insulation Resistance values.

Tests on existing ring (2.5/1.5 t&e) carried out and results as follows -

Ring continuity (end to end)
R1-R1 = .38W
RN-RN = .42W
R2-R2 = .64W
Continuity W
R1-R2 = .34W

Insulation Resistance MW
R1-R2 = 30.4 MW
R1-RN = >299 MW
RN-R2 = >299 MW

I have inspected and checked for tightness all (except one difficult to get to socket) terminations at each accessory.

I know that above 2MW is considered acceptable, but what could be the cause of this R1-R2 value of 30.4MW? when each conductor tested in a different configuration (R1-RN & RN-R2) reaches >299MW ?

Any clues/ideas would be greatly appreciated, many thanks.

 

[telectrix]

30Meg. could just be a bit of damp. record the readings as they come. don't worry about it.

 

[Paul.M]

Agree with Tel.

You say its in a kitchen??? Check sockets for grease build up on the earth strap on the socket also condensation from kettle or boiling pans could give you a residue??? 30M Ohms is acceptable and should'nt give you any problems.

PS. Has a plasterer been spreading his muck about near your sockets?

 

[flyingsparc]

Telectrix - Thanks for your reply, I am not so much worried about the value, more just want to know how that combination can give that result compared to the other two results.

Paul.m Thanks also for your input, will do as you say and look much more closely at earth straps on sockets etc. No skimmers been in yet as have only been in to confirm suitability for extending etc circuit.

 

[Paul.M]

Combine R1 and Rn and test to R2. This will eliminate cable damage on the circuit. If your still getting 30.4 Ohms, you have a problem.

 

[telectrix]

what problem? when i started doing IR testing 10Meg was infinity.

 

[Rockingit]

I've said this before somewhere else, I think it's the problem with modern MFT's measuring up to silly values (half of which I wouldn't trust at that range anyway) and people getting used to seeing them makes us unneccessarily cautious.

Even at the 1MOhm minimum limit your leakage current is 'only' 23mA. 30M and it's 700 MICRO amps. Go figure!

 

[telectrix]

slipped decimal point there i think ... 230/1000000 = 0.00023A or 0.23mA


10k ohms would give 23mA.

 

[wildgoose]

Any number of things can cause these sorts of readings - especially if something is still connected into that hidden socket or FCU that you don't know about, or even because of a damp atmosphere!!

If you start trying to analyse everything, it will just cost you and your customer time and you will end up frustrated. In a ideal world I would be able to find an explanation for everything.

Your readings are good, so suggest you walk away with confidence and accept that these things will happen from time to time!!

 

[Octopus]

Job is to extend a kitchen ring circuit, and have a question about Insulation Resistance values.

Tests on existing ring (2.5/1.5 t&e) carried out and results as follows -

Ring continuity (end to end)
R1-R1 = .38W
RN-RN = .42W
R2-R2 = .64W
Continuity W
R1-R2 = .34W

Insulation Resistance MW
R1-R2 = 30.4 MW
R1-RN = >299 MW
RN-R2 = >299 MW

I have inspected and checked for tightness all (except one difficult to get to socket) terminations at each accessory.

I know that above 2MW is considered acceptable, but what could be the cause of this R1-R2 value of 30.4MW? when each conductor tested in a different configuration (R1-RN & RN-R2) reaches >299MW ?

Any clues/ideas would be greatly appreciated, many thanks.

Good detail and information posted. I wouldn't be worried about the results in any shape or form.

 

[richy3333]

what problem? when i started doing IR testing 10Meg was infinity.

And I thought you started working as a spark before the invention of electricity

 

[telectrix]

uncle tesla would confirm that if he were still alive.

 

[Rockingit]

slipped decimal point there i think ... 230/1000000 = 0.00023A or 0.23mA


10k ohms would give 23mA.

Cheers Tel - I thought it seemed a bit high when I typed it in!! :dunce2:

 

[DieselShunter]

Flyingspark,

That 30M ohm leak will result in a shameful waste of energy!

By my calculation it will waste one kWh over the next 67 years.

Make sure the punter pays your bill before he finds that out.....

 

[GLENNSPARK]

Any number of things can cause these sorts of readings - especially if something is still connected into that hidden socket or FCU that you don't know about, or even because of a damp atmosphere!!

If you start trying to analyse everything, it will just cost you and your customer time and you will end up frustrated. In a ideal world I would be able to find an explanation for everything.

Your readings are good, so suggest you walk away with confidence and accept that these things will happen from time to time!!

its R1-R2 thats `low`....well it isn`t low but anyway......
so whats between R1 & R2 got to do with stuff connected at sockets?...

 

[wildgoose]

its R1-R2 thats `low`....well it isn`t low but anyway......
so whats between R1 & R2 got to do with stuff connected at sockets?...

I was thinking about electronic circuits eg: R/C Networks, surge protectors.....

These are likely candidates! I've recently had a multiblock surge protector for IT equipment, that was 10Mohm at 250v and 500Rohm at 500 volts. Then you have those cheap nasty PIR flood lamps that can also leak - often connected to the ring via a FCU.

Have you never experienced these things too???????????????????