RCBO trips when power is turned OFF

[Gees]

My Kitchen RFC RCBO trips if i turn OFF the power at the main switch.
It also tripped last time i did a Ze test at the board.
My supply is overhead concentic ( TT ) with a Ze of 14 ohms
IR tests show 99.9 megs and continuity are also OK.
Gas and water bonds are in place and everything works fine.
The problem is if the power goes off while i am not at home ( holiday times)
then the lack of power will ruin all the food in the freezer.
No trip Zs at the furthest piont on the RFC is 17 ohms. ???
I think a seperate freezer radial may be a smart move !!??
Oh and the rcd trip times are well within the regs

 

[EFLImpudence]

My Kitchen RFC RCBO trips if i turn OFF the power at the main switch.

Sometimes they just do.
Have you done a ramp test - the current at which it trips?

It also tripped last time i did a Ze test at the board.

Was it a 'no trip' test?

My supply is overhead concentic ( TT ) with a Ze of 14 ohms

That's very good.

IR tests show 99.9 megs and continuity are also OK.
Gas and water bonds are in place and everything works fine.

All good then.

The problem is if the power goes off while i am not at home ( holiday times)
then the lack of power will ruin all the food in the freezer.

Do you mean by someone turning off the main switch while you are away or has it tripped at other times?
Has it ever done that?

No trip Zs at the furthest piont on the RFC is 17 ohms. ???

3Ω for the circuit is a lot. Have you investigated?
(By the way - R stands for Radial as well)

I think a seperate freezer radial may be a smart move !!??

It's up to you.

Oh and the rcd trip times are well within the regs

Ok.

Apart from the 3Ω, do you have a problem?

 

[Gees]

The ZE was a 25 amp test
The no trip loop at the board is 16.5 ohms
If we have a power cut the RCBO trips!!
I will do a ramp test when i get the oppertunity.
Its not an issue as long as we are at home but its still a bid "odd"
My MFT1502 is a bit long in thr tooth now but hey ho its all I have.

 

[John D v2.0]

The ZE was a 25 amp test

my comment would be how do you get 25 amp through a 14 ohm impedence, with only 240 volts to do it with? Or is it max-25A test?

any more detail about the rcbo, is it an active one or something? some require power to hold in.

 

[JohnW2]

The no trip loop at the board is 16.5 ohms

That being the case, if the Ze is, as you said, 14Ω, where on earth is most of the extra 2.5Ω 'at the board' coming from - the supply L cannot account for much of that difference.

Kind Regards, John

 

[Gees]

Sorry i think we are at cross purposes
The "no trip" shows 17 ohms at the furthest socket on the RFC
The test at the board ( no trip) is 17.1 BUT the "normal" test shows 14
thats when the RCBO trpped.

 

[John D v2.0]

any more detail about the rcbo

are you looking into this still?

 

[JohnW2]

The test at the board ( no trip) is 17.1 BUT the "normal" test shows 14 ... thats when the RCBO trpped.

Fair enough - are you saying that a "normal" (not "no trip") loop measurement upstream of the RCBO at the board causes it to trip?

Kind Regards, John