RCBO taking too long to trip on X 5

[Benjo]

I have just tested an RCBO on a new consumer unit and its taking approx 100mS to trip on X1 and >50mS on X5, so its a fail. I have only tested it from the sockets so I suppose I should test it from the Consumers Unit.

Does anyone have any ideas as to what may cause this if its not a faulty RCBO?

 

[batty]

I have just tested an RCBO on a new consumer unit and its taking approx 100mS to trip on X1 and >50mS on X5, so its a fail. I have only tested it from the sockets so I suppose I should test it from the Consumers Unit.Does anyone have any ideas as to what may cause this if its not a faulty RCBO?

I generally find that they sometimes won't trip correctly if you test them at the consumer unit mem ones don't seem too and a couple off others. Is it just the one thats playing up. Welcome to the forun see this is your first post maybe introduce yourself.

 

[Benjo]

Thanks for your reply.....

There is only 1 RCBO in the C/U serving the Ring Final Circuit. The other 3 are MCB's serving 2 x Lighting and a Cooker Circuit.

r1 = 0.40

rn = 0.64

r2 = 1.09

R1+R2 = 0.37

 

[initforthemoney]

Looks like a faulty unit.

Swap it out for a new one.

 

[m4tty]

Is it a tt with a high Ra by any chance as I had the same happen and the meter wouldn't allow the 5x test as the touch voltage was over 50v and the meter wouldn't allow the test. I may be barking up the wrong tree tho.

 

[ianmacd]

Why are your r1 and rn so different? Was anything connected when testing? What's your IR?

 

[Benjo]

Cheers Guys....

Its on a TNCS system.

Originally I had an open loop on the Neutral and after taking all the socket fronts off and sods law it had to be one of the last ones I opened, where I found the Neutrals loose in the back-box. I remade the connection and the rn was then 0.64. I am going back for further investigation because I'm gunna suggest to the customer that I replace all the socket fronts as they are very old, that way I can ensure all connections are made and tight. Hopefully bringing r1 and rn closer in result.

Regarding the RCCB, I think the suppliers have sent me a time delayed version because it has the printed on it and it works perfect on the time delayed setting on my tester. So im gunna ask them to send me what I actually ordered!! :slap

Regards

Benjo

 

[batty]

Don't think you can get time delayed RCBO's.

 

[ianmacd]

Nore did I.

 

[Benjo]

I've just spoken to the supplier and you cant get a time delayed RCBO. So they are sending me a new one to try.

Hopefully this will sort the problem!!

 

[ianmacd]

What was your IR like? Did you try testing in isolation?

 

[SPECIAL LOCATION]

Thanks for your reply.....There is only 1 RCBO in the C/U serving the Ring Final Circuit. The other 3 are MCB's serving 2 x Lighting and a Cooker Circuit.

r1 = 0.40

rn = 0.64

r2 = 1.09

R1+R2 = 0.37

r1 0.40ohms of 2.5mm conductor = 53.98m length

rn 0.64ohms of 2.5mm conductor = 86.36m length

Thats nearly a third of a drum of cables difference! 32.4m

between the Live & Neutral conductors

or some really bad joints!!!

your r2 of 1.09ohms is that 1.5mm or 1.0mm?

If 1.5mm conductor = 90.08m length

or

If 1.0mm conductor = 60.22m length

I guess the real ring cable is somewhere between 55m & 60m...

I don't know if your high N could be affecting your RCD test...

But either way I would always test RCDs at the CU with loads disconnected..

as per page 91 On site guide

Chapter 11 operation of RCDS

Paragraph 11.1 general test procedure!

 

[batty]

r1 0.40ohms of 2.5mm conductor = 53.98m lengthrn 0.64ohms of 2.5mm conductor = 86.36m length

Thats nearly a third of a drum of cables difference! 32.4m

between the Live & Neutral conductors

or some really bad joints!!!

your r2 of 1.09ohms is that 1.5mm or 1.0mm?

If 1.5mm conductor = 90.08m length

or

If 1.0mm conductor = 60.22m length

I guess the real ring cable is somewhere between 55m & 60m...

I don't know if your high N could be affecting your RCD test...

But either way I would always test RCDs at the CU with loads disconnected..

as per page 91 On site guide

Chapter 11 operation of RCDS

Paragraph 11.1 general test procedure!

No good if its a mem one though.

 

[Benjo]

The r2 of 1.09 is 1mm CPC.

The IR was >500Mohm across all circuits.

I'm pretty sure there are some bad joints so i'm going back to replace the RCBo today and whilst im there i will open all the sockets and check the connections!!

I will let you know the outcome!!

 

[Benjo]

I replaced the RCBO yesterday and it still failed the x5 test. I moved it to the Cooker circuit and it tripped within the times needed.

I think it can only be because my r1 and rn are very different causing and inbalence.

Going back on Friday to check all the terminals in the sockets to try to fing the loose neutral connection!