Rcbo tests

[Chrisg88]

Hi i have just came across something on an eicr i havent seen before.

Set up is a db with mix of rcbos and mcbs
Tncs system
All tests on all circuits are great. Theres rcbos for the house ring kitchen ring cooker and shower.

When testing the trip times for the cooker circuit it was tripping but the readings were sky high, greater than the mft shows. But i only get they readings when the kitchen ring is energised. When the cooker is the only circuit on the trip times are perfect.
I have tested between the kitchen and cooker circuits and i have no readings.

Any feedback would be appreciated.

 

[JohnW2]

When testing the trip times for the cooker circuit it was tripping but the readings were sky high, greater than the mft shows. But i only get they readings when the kitchen ring is energised. When the cooker is the only circuit on the trip times are perfect.

Very strange. Did you also do ramp tests on the cooker circuit RCBO and, if so, were the figures again very different with and without the kitchen ring energised?

Kind Regards, John

 

[Chrisg88]

Yeah 24mA on both occasions

 

[EFLImpudence]

What about vice versa?

Ring test with cooker circuit on.

 

[Chrisg88]

What about vice versa?

Ring test with cooker circuit on.

That was ok, only when testing cooker with kitchen energised

 

[JohnW2]

Yeah 24mA on both occasions

In a sense, that's even stranger. If the cooker RCBO is behaving very differently with and without the kitchen ring energised, one might expect it to have at least some effect on trip thresholds as well as trip times.

Are the cooker and kitchen ring RCBOs next to one another in the CU? Were there significant loads on the kitchen ring when it was energised?

Kind Regards, John

 

[Chrisg88]

In a sense, that's even stranger. If the cooker RCBO is behaving very differently with and without the kitchen ring energised, one might expect it to have at least some effect on trip thresholds as well as trip times.

Are the cooker and kitchen ring RCBOs next to one another in the CU? Were there significant loads on the kitchen ring when it was energised?

Kind Regards, John

They are right next to each other in the board, no its an empty flat so nothing plugged in

 

[Chrisg88]

Its a brand new rcbo aswell

 

[JohnW2]

They are right next to each other in the board, no its an empty flat so nothing plugged in

That's really weird. Have I got this right - that the trip time of the cooker RCBO changes dramatically when you 'switch on' the adjacent kitchen ring RCBO even when that latter circuit is drawing no current?

Is this a new electrical installation - or, at least, have the RCBOs been recently installed?

Kind Regards, John

 

[EFLImpudence]

You say -

When testing the trip times for the cooker circuit it was tripping but the readings were sky high, greater than the mft shows. But i only get they readings when the kitchen ring is energised. When the cooker is the only circuit on the trip times are perfect.

General question:
If the time goes over the maximum allowed - 300ms or 40ms - does the test carry on until the device trips or does the test stop?

Does the fact that the device does trip indicate that it is alright but the meter has been confused by something?

 

[Chrisg88]

That's really weird. Have I got this right - that the trip time of the cooker RCBO changes dramatically when you 'switch on' the adjacent kitchen ring RCBO even when that latter circuit is drawing no current?

Is this a new electrical installation - or, at least, have the RCBOs been recently installed?

Kind Regards, John

Its an old install with new rcbos

 

[Chrisg88]

You say -



General question:
If the time goes over the maximum allowed - 300ms or 40ms - does the test carry on until the device trips or does the test stop?

Does the fact that the device does trip indicate that it is alright but the meter has been confused by something?

It carries on until trip. My readings are >300 for x1 and >40 x5

I did think that the meter could be playing up but just strange as its only that one circuit

 

[JohnW2]

It carries on until trip. My readings are >300 for x1 and >40 x5

Does it trip more-or-les 'immediately' (as you perceive it)?

You say that it is a brand new RCBO. Does that mean that it has never been tested before? Have you tried replacing the RCBO (maybe temporarily 'borrowing' one of the others, if you don't have a spare)?

Kind Regards, John

 

[EFLImpudence]

Just thinking out loud -

As the only difference with the Ring RCBO on is that the ring circuit line is connected to the cooker circuit line (N and E not changed), why should this make a difference when the ring results are normal?

 

[JohnW2]

Just thinking out loud - As the only difference with the Ring RCBO on is that the ring circuit line is connected to the cooker circuit line (N and E not changed), why should this make a difference when the ring results are normal?

Quite so - that's why it's weird, particularly given that we have been told that no current is (or should be) flowing in the kitchen ring circuit, even when it is 'on'.

Chris - do I take it that what you have observed had happened repeatedly (i.e. each time you switch on the kitchen ring RCBO, the cooker RCBO trip times go haywire, and each time you switch the kitchen ring RCBO off the cooker RCBO trip time becomes normal)?

Kind Regards, John