RCD fused spur unit fault

[lim88]

A customer has a RCD spur unit spurred off a ring supplying their garage. It is all wired in 2.5mm twin, and in the garage there is only two sockets with nothing plugged in.

The RCD spur unit would not reset so have replaced with an identical one. When the power was turned back on the the spur unit was already on and everything was working fine, but when i tested it via the test button there was a lovely flash and the RCD in the ccu tripped too. And that broke the spur unit.

I have dead tested all the cables and all the readings are perfect.

Is it a problem with the RCD spur units or is there anything else I can check that I have missed?

Thanks

 

[telectrix]

if all connections are correct, it's got to be a faulty RCD FCU. does it say made in china?

 

[tony mc]

You have a problem which seems to be the RCD socket.(Made in China ????) I would carry out a full range of dead tests to make sure there is no faults on the cct and if thats the case its the RCD socket.

What is the RCD in the CCU 100mA ????

 

[truckster]

Assuming you had the polarity correct I would think it's a faulty RCD spur

 

[nickblake]

disconnect the out going of the FCU ,RCD see if it still trips , if not do a few RCD tests on the FCU if all ok test the circuits in the garage

 

[londonlec]

Why the need for two RCDs?

 

[72-van]

Forgive my interupting coz i aint no spark but i was under the impression that you needed to have these at a three to one ratio ?

ie 100 mA rcbo with 30 mA rcd for additional protection .

72-van

 

[londonlec]

Forgive my interupting coz i aint no spark but i was under the impression that you needed to have these at a three to one ratio ?

ie 100 mA rcbo with 30 mA rcd for additional protection .

72-van

No, the 100mA RCD would have to be Type S/time delayed, or else its pot luck as to what would trip first.

 

[nickblake]

Forgive my interupting coz i aint no spark but i was under the impression that you needed to have these at a three to one ratio ?

ie 100 mA rcbo with 30 mA rcd for additional protection .

72-van

With a TT system you needed RCD protection and it used to be a main switch RCD at 100ma for protection, due to the improvements to installation and the change of regs to 17th edition where all circuits require RCD protecting the standard 30ma trip is required therefore there is no need for the additional 100ma RCD unless you require additional protection for cabling supplying sub boards or discrimination of circuits

 

[72-van]

Ok i do apologise BUT it says that the circuit is spurred of a ring main and if its wired to the 17th then it should surely be with 30 ma additional protection for the sockets ?

original poster makes no mention of the rcd size ?


Remember i only do pat

72-van

 

[nickblake]

No, the 100mA RCD would have to be Type S/time delayed, or else its pot luck as to what would trip first.

not quite i think you'll find the 30 ma would trip before the 100ma so no need for time delayed if you have a fault drawing more than 100ma then both will trip , but think youll find that a 30 ma RCD will trip at around 24ma so way before the 100ma

 

[nickblake]

Ok i do apologise BUT it says that the circuit is spurred of a ring main and if its wired to the 17th then it should surely be with 30 ma additional protection for the sockets ?

original poster makes no mention of the rcd size ?

Remember i only do pat

72-van

you dont actually have to change an old installation , but any works carried out on that installation must comply to 17th edition the RCD FCU may well have been installed to protect the additional works in the garage ,which may have all that was required and may have been to 16th edition regs without seeing the install its difficult to say we as electricians do advise cutsomers that RCD s should be installed but we can force people to have them dont get me wrong i will do a CDU channge at a drop of at hat , and belive it or not old rewireable Fuses still comply with the regs

 

[telectrix]

you dont actually have to change an old installation , but any works carried out on that installation must comply to 17th edition the RCD FCU may well have been installed to protect the additional works in the garage ,which may have all that was required and may have been to 16th edition regs without seeing the install its difficult to say we as electricians do advise cutsomers that RCD s should be installed but we can force people to have them dont get me wrong i will do a CDU channge at a drop of at hat , and belive it or not old rewireable Fuses still comply with the regs

assuming they've got the correct size nails fitted!

 

[72-van]

Nae the nails only come in when i am pat testing a site and i have to provide upteen brand new lovely shiny fuses costing me 12p each for free in exchange for rusty nails n smoke papers ..lol

72-van

 

[nickblake]

Nae the nails only come in when i am pat testing a site and i have to provide upteen brand new lovely shiny fuses costing me 12p each for free in exchange for rusty nails n smoke papers ..lol

72-van

masonary bits was a fave when i was doing pat testing

 

[truckster]

not quite i think you'll find the 30 ma would trip before the 100ma so no need for time delayed if you have a fault drawing more than 100ma then both will trip , but think youll find that a 30 ma RCD will trip at around 24ma so way before the 100ma

Disagree, unless you have a fault of less than 50mA it is likely that both will operate, agree with Londonlec the upstream RCD would need to be time delayed.