Zs tripping RCD on no-trip setting

[Grant Naylor]

Practicing with my tester so I wanted to measure Zs on my cooker (At least I now have clean floor behind the cooker ).

The cooker is on its own M6 Type 1 - 32 A MCB. It is protected by an 80 A / 30 mA RCD. I have tested the RCD and it is functioning correctly (x0.5=NO TRIP / x1=27ms / x5=11.1ms). The RCD does not trip when either the cooker or socket are in normal use.

My cooker is wired to an isolator with a socket outlet, then down to the cooker connection accessory.

If I take Zs at the socket outlet using the no-trip setting it reads 0.22Ω

However, if I try and take Zs from the cooker connection accessory the RCD trips out?

I haven't done any other tests. I know sometimes RCDs can trip even on no-trip setting but this puzzled me as the socket is OK.

What am I doing wrong?

 

[kamkam]

what tester are you using? are you using three leads to get your zs? L N E?

 

[truckster]

What am I doing wrong?

Probably nothing, it's one of those quirks of d-lock. I've heard a couple of reasons which may or not be correct
1) Low battery
2) Performing the tests too quickly
3) Just chance in where the tester hits the sine wave

Theres probably an electronics expert here who will say that they are all tosh

 

[Electricalserv]

If you have the Dilog 9083p some of these are faulty and sometimes trip RCBO's and RCD's when doing ZS

You will have to get intouch with the manufacturer.

 

[Guest 004]

Megger MFT 1552 is what I use, and does not trip RCD's 95% of the time, but I must admit has on occasions

 

[Mr Mark Sparks]

my 1552 is the same mate just one of those things (i hope)

 

[Guest 004]

Practicing with my tester so I wanted to measure Zs on my cooker (At least I now have clean floor behind the cooker ).

The cooker is on its own M6 Type 1 - 32 A MCB. It is protected by an 80 A / 30 mA RCD. I have tested the RCD and it is functioning correctly (x0.5=NO TRIP / x1=27ms / x5=11.1ms). The RCD does not trip when either the cooker or socket are in normal use.

My cooker is wired to an isolator with a socket outlet, then down to the cooker connection accessory.

If I take Zs at the socket outlet using the no-trip setting it reads 0.22Ω

However, if I try and take Zs from the cooker connection accessory the RCD trips out?

I haven't done any other tests. I know sometimes RCDs can trip even on no-trip setting but this puzzled me as the socket is OK.

What am I doing wrong?

Having read this post again, I would advise to do an insulation test at the cooker connection, as you could have low readings, which is causing the meter to trip the RCBO

 

[Mr Mark Sparks]

you could run a ramp test from both points to see if ther is any differences

 

[Grant Naylor]

It's a Metrel 3125B and the battery was getting low, but I had no warnings.

I'll do a IR test and see what that gives.

 

[Grant Naylor]

what tester are you using? are you using three leads to get your zs? L N E?

Metrel 3125B so N and PE are joined for the test.

 

[Grant Naylor]

IR gives >999 MΩ from both the plug socket on the isolator and the connection accessory.

I guess I need to try a Zs on full charge and see if this makes a difference.

 

[Guest 004]

>999, wow

 

[SPARTYKUS]

My Megger only goes up to >299M Ohms

 

[Electricalserv]

My Megger only goes up to >299M Ohms

Mine >200

 

[AlanWirral]

I'll bet on the sine wave....

 

[Grant Naylor]

Doh!

Turns out simple user error to be the issue.

I didn't check lead configuration and got it in my head you connected N and PE together for the test. It's a three lead instrument and requires all three leads for Zs.

I've only been practicing on sockets as it was safer for me to do so since this is a live test while I got used to the instrument and it came with a 3-pin test lead.

Thanks for the replies...

Oh and it is >999 for IR on the Metrel I checked :-D

 

[kamkam]

wow that's quite dangerous!