Fault or faulty testers

Marvo said:

Maybe your Steinal thingy and your digital tester were picking up some kind of induced or coupled voltage from another circuit in close proximity. If your mates insulation tester showed no fault and it was definately working then I'd take that result over the Steinal gizmo any day.


What was the original problem exactly. How frequently was the RCD tripping and was it only in wet weather for example. Do you have an earth leakage clamp meter in you tool kit?

Click to expand...

steinel is just an AVI marvo...like this:





- - - Updated - - -

Lambretta phil said:

Hi glenspark what's Sils

Click to expand...

scooters India LTD

- - - Updated - - -

indian Lammy....

Oh ya think there about as crap as my testers.

Thanks Glenn, we're not big on those types of tester (or Indian Lambrettas for that matter) where I am.

If the SWA was a problem you'd almost certainly see a low insulation reading with a mega tester if you disconnected the armour at both ends and tested between the internal wires and the armour and between a known earth and the armour. This would indicate if the cable sheath had been damaged along the run somewhere. Replacing it without conclusive test results is a bit hit and miss.

The RCD is seeing the cumulative leakage of all the circuits it's supplying so an earth leakage clamp meter around the L+N of each circuit whilst they're live would be the best way of finding the leakage problem(s).

Lambretta phil said:

Oh ya think there about as crap as my testers.

Click to expand...

the engines are a bit beefyer on the sils....

hence the reason most tuning & performance lads use them over the stock italian unit...

- - - Updated - - -

Lambretta phil said:

Oh ya think there about as crap as my testers.

Click to expand...

nowt wrong with the steinel....
you have chosen an AVI of quality....they self prove as well....

Back to the OP. Sounds like you need a real MFT to do the tests properly!

How the hell do you test your completed installations for god's sake? Never heard of an electrician without an IR test kit, and relying on voltage tester with a naff continuity facility!!

Engineer54 said:

How the hell do you test your completed installations for god's sake? Never heard of an electrician without an IR test kit, and relying on voltage tester with a naff continuity facility!!

Click to expand...

the pocket friendly fluke t-130 can do ir.

No excuse really not to own a ir tester

Lambretta phil said:

Ya TA going with insulation tester triped every few days .course wouldn't trip when I was there put new swa in so see if that sorts it thanks.

Click to expand...

If your mates Insulation tester showed no faults why replace the cable ?.

I used to use a steinel test lamp all the time,only trouble is they read a fairly high resistance on continuity,so holding wires onto the probes with fingers can give a reading,especially if fingers are moist.

my fluke T3 is the same. 100ohms or thereabouts, it sees as continuity.

Thanks specialist replaced cable as it was PVC t+e ,found joint under floor connectors in a box went in a tube under a path under stone steps etc so may not have been in tube entire route . Think been in about 20years so best to replace.

Thanks engineer54 I never said I didn't own a I R test kit my mate had his with him so we used his .we seem to have strayed from my main point of why 2 buzz testers show short and 1 buzz and 1 I R tester show clear.

Lambretta phil said:

.....why 2 buzz testers show short and 1 buzz and 1 I R tester show clear.

Click to expand...

The reason you get different results from different testers is firstly because they're actually performing completely different tests. The IR tester is using a very high test voltage on a dead circuit whereas the volt testers are not using any test voltage on a live circuit.

Secondly the characteristics of the different voltage or continuity testers aren't the same. There will be a difference in their sensitivity and a difference in their input impedance so depending exactly what you're testing they'll often show different results.

Finally you need to use the right tester in the right way and test for the right thing.

Here's an example;
If an RCD is tripping occasionally and I suspect it's being cause by a cooker. Here's some tests I could do.

1. I could connect an earth leakage clamp meter around the cpc in the isolator and take a reading with the cooker on.
2. I could disconnect the cooker and use a continuity tester on the Mohm scale to test the resistance between the L+E and the N+E.
3. I could disconnect the cpc whilst the cooker is on and use a voltmeter with one probe on a known good earth to see if leakage is causing a voltage on the CPC.
4. I could use an earth leakage clamp meter around the L+N simultaneously at the isolator whilst the cooker is on.
5. I could disconnect the cooker and use a mega tester to test L to E and N to E.

All these tests will show some of the effects or the possible potential of the cooker to produce a leakage current to earth but only one of them will definitely give you an accurate indication of the actual earth leakage being detected by the RCD.

Like I said it's about using the right equipment in the right way and understanding exactly what the reading it's giving you means.

Thanks for that marvo think we will invest in a e l clamp meter.just to make it clear was using fluke /buzz testers on dead circuit as well . To see if conductors /earth etc were touching each other 2 said yes 1 said no with cable disconected at both ends.

I would say an earth leakage clamp meter is an absolute necessity for any electrician. There's a Dilog E/L clamp tester that has been given good reviews by a lot of guys on this forum and it's inexpensive by most accounts.

You can also get a discount from testmeter who are forum sponsors which might help.