Zs tripping rcd

[jord35davies]

hi guys,
Hoping for a little advice.
Been working on a property this week and have been having trouble getting zs readings as it trips the rcd on a 17th edition cu.
Property is pme. I've tried testing idividual circuits one by one and completely disconnecting all the others but it still trips. It doesn't seem to matter what circuit is tested it trips on every one.
I've checked absolutely everything and all tests leading up are fine. Zs tests however trip rcd.
I've done a ramp test on rcd to check that and it's fine.
I've got a feeling it's a Dno issue but they have now confirmed there are no faults on the line. Anyone had similar issues.
Thanks in advance

 

[telectrix]

what tester are you using, and are you sure you have it set to no trip. here's an alternative method whereby you can test Zs without worrying about the RCD.:

View attachment 34970

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[telectrix]

oops uploaded 3 times...... daaaaaan?

 

[Octopus]

Have you tried your tester at home?

 

[GMES]

You know what they say Tel, 3rd time lucky

 

[hightower]

I'm with tel, if it's happening on every circuit it sounds like you're running a standard Zs test rather than a no-trip.

Also, make/model dependent, make sure you are using 3-leads if your tester requires it. When I first got my tester, I was running a no-trip Zs, but only with 2 leads having been used to a Megger. Turns out my Metrel needs 3 leads to do the no-trip.

 

[telectrix]

the 1552/3 meggers use 3 leads. it's only the 1700 series that can do no trip with 2 leads.

 

[jord35davies]

Definately no trip guys.
Megger 1730. Two settings hi and low and I'm on low
Yes tried it on next doors circuits. Worked fine. It's the first time it's tripped rcd on a zs test with me.

 

[jord35davies]

Thanks tel,
I'll def try that method

 

[polo1]

Are you using the two or three lead test?; using probes/crocs or the plug with the leads?

 

[jord35davies]

Are you using the two or three lead test?; using probs/crocs or the plug with the leads?

Plug with three leads and two leads on lighting circuit. Doesn't matter what combination still trips

 

[polo1]

I've experienced this before with the 1730, but at the mo can't recall the cause! Let me have a think

 

[buzzlightyear]

on testing zs on the megger 1730, it is possible you have a problem tester I self.
when testing 3 low using plug or leads their should not have a problem
I had same problem many years back with 1502 sent it back megger sent me a new one .
did you turn the dial to off position and start again.

 

[davesparks]

Were there any suspicious IR readings? Particularly in the N-E department?

Plug with three leads and two leads on lighting circuit. Doesn't matter what combination still trips

The question was no how many leads did you connect, but whether it is a two or three lead test? These are different things!

 

[tony mc]

Try clamping the tails to see what leakage is there before you test as even on No Trip your still injecting 15mA into the cct so you may have a leakage which puts the RCD above its Ramp value just a thought!

 

[Midwest]

Were there any suspicious IR readings? Particularly in the N-E department?



The question was no how many leads did you connect, but whether it is a two or three lead test? These are different things!

Ditto IR fault (neutral-earth), can cause RCD to trip on Zs 3 lead test.

 

[davesparks]

Ditto IR fault (neutral-earth), can cause RCD to trip on Zs 3 lead test.

Exactly, and you'd hope that anyone who is carrying out these tests would actually understand what they are testing and the basic principle of how the tester performs the test.

I don't understand the mindset of just pushing the test button and writing the number down, what does it really achieve?

 

[davesparks]

Try clamping the tails to see what leakage is there before you test as even on No Trip your still injecting 15mA into the cct so you may have a leakage which puts the RCD above its Ramp value just a thought!

Odd, I thought the megger used 200mA with DC blocking on the low current test?

 

[Midwest]

Definately no trip guys.
Megger 1730. Two settings hi and low and I'm on low
Yes tried it on next doors circuits. Worked fine. It's the first time it's tripped rcd on a zs test with me.

My 1730 has three loop impedance functions on the L-PE setting:

3Lo (3 wire non tripping loop for RCD protective circuits (Zs))
2Hi (2 wire high current loop measurements (Ze/PFC))
2Lo (2 wire non tripping loop for RCD protective circuits (Zs)

 

[Midwest]

Odd, I thought the megger used 200mA with DC blocking on the low current test?

You'll know better than me, my manual for Loop Tests says, test current 4.0 A (at 230v) on Hi, and Pulsed on Lo (Megger 1730).