Advice on meter readings

[J_T]

Hi
I wired the first fix upstairs in a new house 2 years ago and am now returning to carry out the second fix.
On the lighting radial I have been using a fluke multi meter to check the resistance from ceiling rose to celing rose as I go along to check that all is good with the connecting 1.5mm T&E.

All seemed fine fine until the 3rd rose along, 1 live was 0.7 ohm (obs from the previous rose) but the next line (which shouldn't be connected to anything) gave 4Mohm with ref to the previous rose.

I tried a seperate test from the next un connected rose to the next rose after that (just the cable, not terminated) and the resistance showed 40Mohm spuriously.
It would be 40 M one sec the OL then I would touch the probe with my hand and it would jump back to 40M or 50M.

Has anyone come across this? The house is dry and I'm pretty sure no cables were squashed etc since the 1st fix but I ready don't want to start cutting plaster to try and find a fault if there isn't one there.

Thanks

JT

 

[davesparks]

What exactly are testing between and on what settings on the multimeter?

 

[markc123]

What he said ^^ + am i reading correctly that you're touching the probes whilst conducting a IR test?

Do you have an afro ?

 

[J_T]

I connected my meter at the unterminated live wire at the fuse board and using a long piece of wire and multimeter I checked the cable at the 1st rose to make sure that that was the 1st rose (resistance = 0.4ohm). I then connected the meter to the next cable at the 1st rose and checked the resistance to the 2nd rose to make sure that was the same cable. Again under 1ohm. The meter is on auto range resistance mode.
On the third rose the cable coming from rose 2 again was less that 1 ohm but the other cable that travels to rose 4 and is unconnected read 4Mohm while the other end of the Meter was still connected to rose 2.

 

[J_T]

Ps. It's just a multi meter not a megger

 

[davesparks]

How long did you carry out the test for?

 

[J_T]

How long did you carry out the test for?

Few minutes maybe. I'm still here and seeing the same thing.

 

[marconi]

I wonder if your test leads are faulty. Connect them together and observe the Ohmmeter as you you wriggle the test leads along their length. This is what I once found with my test leads.

I assume you are testing cable links between CR positions, but no actual CRs wired in yet. Or, are you working away along the radial from the DB and wiring in a CR and then taking measurements?

 

[davesparks]

I wonder if your test leads are faulty. Connect them together and observe the Ohmmeter as you you wriggle the test leads along their length. This is what I once found with my test leads.

You would expect faulty test leads to give a higher value than expected, not lower

 

[snowhead]

Plasterer or joiner has cut them and taped them together.
Or you've missed a rose out.

 

[Toonlad]

2 years is a long time between 1st and 2nd fix, a lot can happen to those cables in that time. someone else could have re routed them for you.

 

[davesparks]

Terminate it all and then test it.

 

[Hellmooth]

Try mft see what results you get

 

[PEG]

Hi dude,you obviously have a poor connection between your test points,but whether this is due to damage,poor jointing or alteration...who would know...

I would suggest a further poke about,before livening up,and re-testing with the appropriate test equipment. Good hunting:artist:

 

[davesparks]

Hi dude,you obviously have a poor connection between your test points,but whether this is due to damage,poor jointing or alteration...who would know...

I would suggest a further poke about,before livening up,and re-testing with the appropriate test equipment. Good hunting:artist:

Poor connection? He's getting a reading between two points which are not supposed to be connected at all.