Interesting IR Readings - Any ideas?

[SparkyChick]

Hi all,

Well, this one is interesting and I have absolutely no idea what could be causing this.

Just added a PIR to a lighting circuit, very simple, disconnect the lamp and move the feed cables to feed a PIR and then onto the lamp itself. Nice straightforward.

Doing my testing for the minor works cert and the IR readings go something like this:-

2, 10, 100, 200, 450, 4.5, 350, 5.5, 400, 5, and so on.

The ramp up at the beginning I expect to see, but then flipping back and forth between lower values and higher values. All above the minimum 2Mohm, but a cyclic flip back and forth with steady timing.

I didn't test L-N, but the same thing happens on L+N-E, L-E and N-E and it happens at 250v and 500v.

Anyone got any suggestions as to what could cause this because as I say, I've got nothing?

 

[telectrix]

i wouldn't worry about it.could be a parallel path. i had a call-out this morning. MCB tripped on a lighting circuit. (fluorescents). IR L-E was 0.00Meg. on continuity was 34 ohms L-E. even after fault was cleared (a cooked ballast), same readings. testing properly was impossible due to being unable to ID which N and E's belonged to the circuit in an originally wired in singles installation with loads of additions bodged on with T/E.

 

[Specialist]

What type of lights ?. PIR out of circuit ?

 

[telectrix]

one of those occasions where the bang test rules.

 

[Specialist]

Bang & the problem is gone

 

[telectrix]

Bang & the problem is gone

you know it makes sense, who dares wins.

 

[Specialist]

Not seen a wall blown out on a 6" nail for donkeys years

 

[SparkyChick]

It was mixed lighting, the PIR was in circuit because I needed it to be to test as much of the cabling as possible.

If it had been flipping between high and very low (less than 2Mohm) I might have been really worried, but all readings were well above that.

Oh well, one of those things I guess, just never seen anything like it before so figured I'd seek some sage advice

 

[Specialist]

Why have the PIR in circuit to test ?, just bypass it to do the testing.

 

[Octopus]

If its a simple change of accessory just do a Zs..... before you fit the lamp.

 

[SparkyChick]

Why was the PIR in circuit... no reason really, other than just wanting to be thorough and include as much of the final circuit as possible. There's got to be a notification as it's a modified outside circuit, so just wanted to be doubly sure there were no issues.

Change of accessory... one was a change, and that was fine, the other was on the circuit that gave the flip flop readings and that was a change to the circuit.

 

[Wilko]

Question is - what value will you put on the MWC?
I'd probably have a little investigate as I'm just not happy at achieving 2meg without knowing why. But that's why they give me meds

 

[SparkyChick]

Once the initial ramp up was out of the way, it didn't drop below 4.52Mohm when it flipped, so that's what's going on the cert.

 

[westward10]

Did you test the circuit prior to the alterations.

 

[SparkyChick]

No I did not test it before hand, which I'm thinking is something I'm going to do in future to rule out the possibility that I may have introduced an issue.

 

[westward10]

My golden rule test before you touch.

 

[HandySparks]

No I did not test it before hand, which I'm thinking is something I'm going to do in future to rule out the possibility that I may have introduced an issue.

If the PIR doesn't need an earth connection, which most don't, then it's unlikely to the the cause of the odd IR measurements.

 

[SparkyChick]

It has an earth terminal, but it's not connected, just there to allow termination of the CPC.

 

[SparkyChick]

My golden rule test before you touch.

For bigger jobs I totally agree already.... going to adjust my approach for the smaller job

 

[Marvo]

Even if it's Class II are you sure the earth terminal isn't functional, use for internal MOV's surge arrestors maybe?