rcbo zs test

[ample current]

I was in a house the other day having a look at the electrical installation for a potential buyer of the house. The house was rented out previously, and labels on the consumer unit say the installation was last checked in 2011. However there appears to be no paperwork available to support this. Upon opening accessories and the consumer unit I find the system mostly wired in the harmonised colours indicating the house has (mostly) been rewired since 2006, Anyway I carry out continuity tests and insulation resistance tests, all look perfect. I reconnect the supply and try to get the Zs readings, trip goes the RCBO. there was nothing plugged in.
split load board 1 rcd
On the non rcd side the circuit was protected by a 32amp RCBO as were the upstairs sockets, the same problem occurred. The Rcd protected side of the board recorded satisfactory readings without any tripping issues.
I'm not sure why I couldn't get a Zs reading any one have any ideas?
r1+r2 through the socket outlets using the plug in lead read 0.78
Insulaton resistance was +999
TNS supply
Ze 0.18
PSCC 1.44kA
Thanks in advance for your comments
Mark

 

[Leesparkykent]

Did you ramp test the RCBO?

 

[ample current]

Did you ramp test the RCBO?

Yes I did, 23 mA f I remember correctly.

 

[Leesparkykent]

Yes I did, 23 mA f I remember correctly.

what MFT do you have? Was it definitely set to no trip?

 

[SirKit Breaker]

Set to "no trip" or "ATT ON" or similar depending on what tester you are using. You may need to look at the instructions for the tester, i don't all the phrases used, but that is your problem i would think.

Cheers...............Howard

 

[Richard Burns]

I would tend to go for the wrong setting on the meter as above (or even wrong mA setting), but it is odd that the main RCD was OK and the ramp test was OK for both of the RCBOs.
Were you testing at the board or at a socket?
You did put the neutrals back in the RCBO(s) and not back to the neutral bar didn't you?

 

[ample current]

I would tend to go for the wrong setting on the meter as above (or even wrong mA setting), but it is odd that the main RCD was OK and the ramp test was OK for both of the RCBOs.
Were you testing at the board or at a socket?
You did put the neutrals back in the RCBO(s) and not back to the neutral bar didn't you?

Yes I'm a little bemused. My tester is a Megger 1730 which has a no trip loop test. Yes I put the neutrals back into the RCBO.

 

[Richard Burns]

Yes I'm a little bemused. My tester is a Megger 1730 which has a no trip loop test. Yes I put the neutrals back into the RCBO.

Back into the right RCBO?
However you would not be able to ramp test (unless the ramp test was at the board and the Zs test at a socket.)
An instant trip certainly sounds like a wrong setting or an interconnected neutral.

 

[ample current]

Back into the right RCBO?
However you would not be able to ramp test (unless the ramp test was at the board and the Zs test at a socket.)
An instant trip certainly sounds like a wrong setting or an interconnected neutral.

Yes I removed each circuit, tested it and replaced it, one at a time.

 

[ample current]

Ive just had a thought, I didn't actually check which neutral bar the rcbo's were connected to (it was a bit of a birds nest especially with the rcbos, very little room or anything else), would this affect it?

 

[Richard Burns]

That could cause the main RCD to trip not the RCBOs

 

[tomspark93]

I've had this before using a megger 1730 and I remember being told it was a common problem due to the two wire loop test. It didn't happen often but occasionally an rcd or rcbo would trip whilst carrying out a zs. Try another tester if you get chance.

 

[stevethesparks]

Just wondering as with my tester (Metrel) I have to do a 3 lead test when using the no trip setting?

 

[PEG]

1700 series has 2 and 3 wire "no-trip" test,i wonder if both were tried?

 

[shanky887614]

1700 series has 2 and 3 wire "no-trip" test,i wonder if both were tried?

Just wondering as with my tester (Metrel) I have to do a 3 lead test when using the no trip setting?

peg is right there is two lead hi/low setting for zs