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.

 

[Deleted member 26818]

The excemption for labled socket-outlets only applies where socket-outlets are used by ordinary persons, and are intended for general use.
Which to be honest is a bit pointless, as the exemption is for socket-outlets that are provided for a particular item of equipment, which would not require RCD protection in any event.

 

[rick.oshea]

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

No skilled or instructed person in the office I'm afraid and TQ was correct , the cables are run in the plaster (less than 50mm and not mech protected)

 

[Deleted member 26818]

No skilled or instructed person in the office I'm afraid and TQ was correct , the cables are run in the plaster (less than 50mm and not mech protected)

No skilled or instructed persons.
I suggest that you point out to the duty holder, that they are in breach of the statutory requirements and are breaking the law.

 

[rick.oshea]

Hi SpinLondon,

Sorry, I missed your post above re:EAWR which has cleared up quite a few things....

I went to the length of checking the 'definition' of a skilled person with the NAPIT tech line as well, as I wasn't 100%, hence my post and mis-understanding.

Just for the record, they said that a skilled or instructed person was relative to the electrical installation, e.g. a permanent onsite technician...... so they got that wrong.

What you have said makes sense.......

So (if we take it to the letter), legally an employer has a duty to ensure its has at least one member of staff has the relevant skills training to a operate socket / is aware of the concequences of drilling into walls etc and is therefore classed as skilled...... This individual can then instruct others who haven't had any training yet.... and they are classed as 'under supervision' or 'instructed'- Have I got that right?

And with the EAWR covering every working environment, then the above will remove the need for a 30mA RCD to be present (as far as the regs is concerned).

.........so the only time you are going to see a situation where an 'ordinary person' comes into play is in a domestic environment, as the EAWR is going to enforce all other situations to ensure they have a skilled person?

How am I doing...???

 

[Deleted member 26818]

Sounds good so far.
There are circumstance where RCD protection will allways be required, even if the installation is under the supervision of a skilled/instructed person.
For instance where there is a socket-outlet used to supply mobile equipment outdoors, and for circuits of special locations.
Then there are installations such as in hotels, residential care homes, perhaps internet cafes. Anywhere where a member of the public as an ordinary person would have unsupervised use of a socket-outlet.

 

[rick.oshea]

Much, much clearer....thanks Spin

 

[nick611]

i try to avoid rcd,s in commercial properties, rcd the staff room power fit rcd sockets in the corridoors and one by the exit doors. lable them general use rcd protected. this should cover all angles