Testing CBR units

[frank goddard]

CBR units appear difficult to trip time test on some occasions. Not only myself but other colleagues too when testing 300ma/500ma CBR units find even using a variety of manufacturers instruments that multiple trys are required before a succesful trip test. Often no trip occurs at all. Is this impedence related. ie TT systems.

 

[davesparks]

I'm not good with acronyms so you'll have to remind me what a CBR actually is.
I know it's one of the permutations of an RCD, my guess would be its an earth leakage relay operating a circuit breaker via a shunt or release

 

[frank goddard]

I'm not good with acronyms so you'll have to remind me what a CBR actually is.
I know it's one of the permutations of an RCD, my guess would be its an earth leakage relay operating a circuit breaker via a shunt or release

Hi Dave.

It is a moulded case circuit breaker mccb with either remote setting device or add on Vigi Unit.
Frank

 

[static zap]

a) Do any specific MFTs take offense.
b)( is first trip event a common fail - next one better )
..never fully trusting RCD technology has a reason for existence ...

 

[frank goddard]

a) Do any specific MFTs take offense.
b)( is first trip event a common fail - next one better )
..never fully trusting RCD technology has a reason for existence ...

:Any number of manufacturers mft units are used. Seems to be a common thing amongst electricians I have come across. Perhaps 60% or so such units act this way.

 

[davesparks]

Is it vigi type units which fail or seperate earth leakage relays with core balance transformers?

Core balance transformers need to be correctly installed to work properly, including getting the conductors centred in the coil, not off to one side etc.

 

[frank goddard]

Is it vigi type units which fail or seperate earth leakage relays with core balance transformers?

Core balance transformers need to be correctly installed to work properly, including getting the conductors centred in the coil, not off to one side etc.

Seperate controls. You know the type. 3 "inch square panel small rotary knobs for time delay and Current setting. Core installation complete in all cases. This issue is just occasional but given we install dozens annually the test failure rate though small is significant. It's a mystery though an Engineer from Kewtech did suggest that rcd testers specific to CBR units were available.

 

[davesparks]

Seperate controls. You know the type. 3 "inch square panel small rotary knobs for time delay and Current setting. Core installation complete in all cases. This issue is just occasional but given we install dozens annually the test failure rate though small is significant. It's a mystery though an Engineer from Kewtech did suggest that rcd testers specific to CBR units were available.

I know the type very well, I've installed a fair few in various bits of equipment.
I've never yet had an issue testing them, I usually test them at 30mA and a randomly selected higher setting.

At the moment I can't think why they would not pass testing with a normal tester.

 

[frank goddard]

I know the type very well, I've installed a fair few in various bits of equipment.
I've never yet had an issue testing them, I usually test them at 30mA and a randomly selected higher setting.

At the moment I can't think why they would not pass testing with a normal tester.

Thanks Dave.
If we ever discover the answer I will be sure to let you know.