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Zs tripping rcd

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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
 
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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.
 
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the 1552/3 meggers use 3 leads. it's only the 1700 series that can do no trip with 2 leads.
 
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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.
 
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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.
 
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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!
 
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Midwest said:
Ditto IR fault (neutral-earth), can cause RCD to trip on Zs 3 lead test.
Click to expand...

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?
 
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tony mc said:
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!
Click to expand...

Odd, I thought the megger used 200mA with DC blocking on the low current test?
 
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jord35davies said:
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.
Click to expand...

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)
 
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davesparks said:
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?
Click to expand...

Well I have to plead guilty there, but when something doesn't function as it should, there's always a reason. And in this case, I suspect the neutral-earth fault, somewhere.
 
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Midwest said:
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).
Click to expand...

Not necessarily, I've only had the megger a few months and don't get much use out of it so am not so familiar with it as I should be.

The pulsed current I guess would be the 2 wire no trip?
 
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Midwest said:
Pulsed current for 3 wire low & 2 wire low.
Click to expand...

Yeah I just read the manual, interesting.

I also noted how the manual talks about the possibility of RCD tripping even on low current tests, the possible cause and that an alternative method may need to be used.
I guess the OP didn't bother to read the manual for his tester!
 
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Your a bit harsh davesparks, most blokes get their new playstation out and connected it up. When it doesn't work, only then will they read the instructions. Still learning now with my MFT.

Never had a prob tripping RCD's on the low test currents, other than when I installed a luminaire for a customer and did a Zs test, for old times' sakes, and tripped the RCD. It was only going back to basics, did I find a neutral-earth fault on the circuit, re hum dinger!
 
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Guys, I'm not new to the trade, I know what my meter is testing and I'm not just pushing the button and hoping for the best.
My meter does not give me the option of 3 lead test or 2 lead lest although it will carry out the test with two leads.
P-le on low or hi
And p-n on hi only.

I have been testing correctly. I came on here to see if anyone has came across anything similar
 
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jord35davies said:
Not yet Dave I'm there tomorrow and will keep you posted
Click to expand...

I've tested every circuit individually from start to finish. Every circuit trips the rcd with no others connected. The cooker circuit even trips it with nothing connected. Ir shows up clear on every one. Get to zs and it trips
 
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davesparks said:
Yeah I just read the manual, interesting.

I also noted how the manual talks about the possibility of RCD tripping even on low current tests, the possible cause and that an alternative method may need to be used.
I guess the OP didn't bother to read the manual for his tester!
Click to expand...

Thing is Dave it's never happened before and I've tested many circuits/properties. Why now???? Why the 2 rcds????
 
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