Help with RCD - 100mA to 30mA

[rick.oshea]

Visited a job yesterday in an office to look at extending a ring to add some additional socket points - the existing RCD / isolator which covers the whole installation, is a Wylex 100mA 63A (fitted in the consumer unit). The installation has no 30mA RCD cover on the sockets.

There is a second consumer unit, fed from the output of the 100mA RCD in the first board - this is powering some oil heaters and the timer circuit (through a contactor).

Q. My simplist option was to replace the existing 100mA with a 30mA to bring the installation up to current regulations but wanted to check I'm not missing anything by removing the 100mA RCD and putting in a 30mA in its place - Can't fit an RCBO in the current board (not enough height room in the CU)....just checking I'm not going to introduce a problem, such as nusiance tripping because of the heating circuit / contactor on the second board.

Anyone see any problems?

Any advice would be much appreciated....

 

[topquark]

As you've already alluded to, why was the 100mA there in the first place. What type of earthing system is it? TN/TT?

It may be that someone (who didn't know better) just replaced a 30mA with the 100mA because of nuisance tripping.

 

[Des 56]

Offices and leakage tend to go one with the other nowadays

Perhaps divert the ring only to a seperate rcd enclosure to the side of the existing board

 

[rick.oshea]

Its TN-C-S

 

[topquark]

As Des said, I'd be tempted to have the RFC(s) fed from another source. Have you seen the effects on the system (leakage wise) when the timer kicks in and the heaters fire up, that may be the reason for the 100mA at the moment.

 

[rick.oshea]

Have you seen the effects on the system (leakage wise) when the timer kicks in and the heaters fire up, that may be the reason for the 100mA at the moment.

No I haven't (not got a EL Clamp meter :-( will see if I can get my paws on one and take a look next week and then discuss options with Customer ..... that's another one for the ever growing Christmas Tool list!

Thanks for the advice guys

 

[McN41R]

For extending a single or a few ring circuits you could take the existing circuit through a 30ma rcd in a surface grp enclosure (usually witin the db cupboard) ideally upgrade the main rcd with a type s rcd for time discrimination. However, whilst you should do this this is no a bs 7671 requirement.

 

[malcolmsanford]

As it is a commercial environment is there need to have additional protection via a 30mA

 

[telectrix]

if under the supervision of skilled personnel, perhaps not.

 

[Deleted member 26818]

Visited a job yesterday in an office to look at extending a ring to add some additional socket points - the existing RCD / isolator which covers the whole installation, is a Wylex 100mA 63A (fitted in the consumer unit). The installation has no 30mA RCD cover on the sockets.

There is a second consumer unit, fed from the output of the 100mA RCD in the first board - this is powering some oil heaters and the timer circuit (through a contactor).

Q. My simplist option was to replace the existing 100mA with a 30mA to bring the installation up to current regulations but wanted to check I'm not missing anything by removing the 100mA RCD and putting in a 30mA in its place - Can't fit an RCBO in the current board (not enough height room in the CU)....just checking I'm not going to introduce a problem, such as nusiance tripping because of the heating circuit / contactor on the second board.

Anyone see any problems?

Any advice would be much appreciated....

How would replacing a 100mA RCD with a 30mA RCD bring the installation up to current standards?
Is there a requirement in the current standards for 30mA RCD protection in this installation?
Is there a location containing a bath or shower, are the socket-outlets used to supply mobile equipment outdoors?

 

[topquark]

I'd assumed 30mA protection would be needed because of the cable runs (ie <50mm in the walls and not mechanically protected).

 

[malcolmsanford]

But even as with socket outlets TQ if the installation is deemed under the supervision of a skilled or instructed person, then even if the cable is <50mm and not mechanically protected you do not need the additional protection by RCD

 

[topquark]

Understand that Malc, I hadn't thought that the whole of the office staff could be deemed skilled in that respect though, if that's the case then fairy nuff

 

[Deleted member 26818]

The requirement for 30mA RCD protection allow excemptions where socket-outlets are to be used by skilled or instructed persons, or where the installation is under the supervision of skilled or instructed persons for both socket-outlets and cables concealled in walls.
It is just for socket-outlets used to supply mobile equipment outdoors, and for circuits of locations containing baths or showers where there are no exceptions.
In order to comply with EARW regulations, anyone using a socket-outlet as part of their work duties, must meet the requirements to be considered skilled or instructed.
It therefore follows that if everyone using the socket-outlets are skilled or instructed, then the installation must be under the control of a skilled or instructed person, perhaps even by many such persons.

 

[topquark]

Don't the sockets also have to be suitable labelled? What happens when the cleaning contractors come around at night etc.