To RCCB or not to RCCB?

[ipaq]

Trying to work out what circuits should be rccb protected in my house.
I have a small 2 bedroom house with a shed in the garden. A 10 way split consumer unit (busbar not cut yet). I was thinking of putting on the rccb side the shed,lights in the bathroom, front room ring,and boiller. I thought about the kitchen ring as well but someone told me thay had a problem with that ring triping out all the time.

 

[Adam_151]

What earthing system do you have? TT, TNC-S, or TNS?

And are you sure that you are safe changing a consumer unit, its a job which takes quite a bit of knowledge, and test equipment

Anyway, assuming TNx what needs to be on RCD are outlets of 32A or less that can be reasonably expected to be used for portable equipment outside, and 240v Equipment in zone 1 of a bathroom excluding water heaters and showers (though putting showers on RCD is a very good idea IMHO)

I'd install local RCD protection at the shed and put that on non RCD in the house, assuming that bathroom lights arn't in zone 1 (or only selv lights are in zone 1) then I'd put bathroom lights on none RCD, Front room ring would go on RCD (possiblity of using outside, plus I think its a good idea to have general purpose outlets on RCD), kitchen would go on rcd (same reason as lounge, + possibily of portable appliances mixing with water....), boiler should go on non RCD side, and consider an non RCD side radial for the freezer

 

[Big G]

Interesting recommendation about the shed.

Firstly, I am not an electrician – far from it. When you say:

I'd install local RCD protection at the shed and put that on non RCD in the house

presumably there needs to be a cable run from the house to the shed. More than likely routed where there is a danger that it could receive some sort of mechanical damage. Would you not want to protect the person who has just put their spade through the cable buried 18 inches below the garden.

As mentioned though, I’m not an electrician – it’s just I want to do a similar thing in replacing a supply to my detached garage. I know that putting a new supply to a detached garage is covered under Part P, not sure about replacing an existing damaged supply though.


G

 

[Qedelec]

Regulation 522-06-03, which applies to the installation of cables underground, states that:
‘Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground shall incorporate an earthed armour or metal sheath or both, suitable for use as a protective conductor, or be of insulated concentric construction. Buried cables shall be marked by cable covers or a suitable marking tape. Buried conduits and ducts shall be suitably identified. Buried cables, conduits and ducts shall be at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground.’

 

[Qedelec]

Cables to be at Sufficient depth

Underground low voltage cables must be laid deep enough (normally taken as a minimum of 600 mm in the absence of more precise requirements) so that they are unlikely to sustain damage from the use of hand tools such as spades, forks and picks (unless being used for excavation work).
The present and potential use of the ground should be taken into consideration. It is essential to ascertain whether the ground level is to be altered, such as for the formation of a roadway or for landscaping. Where this is the case, the proposed ground levels should be determined and the cable laying depth should be calculated from these. If proposed ground levels cannot be determined, it may be prudent to lay the cable at a greater depth. If the ground level is to be substantially raised, it may be prudent to delay cable laying until the landscaping is complete. In every case it is wise to record the levels which have been ascertained.

 

[sparkybird]

If the kitchen circuit was tripping, this was for a reason. It could have been a faulty appliance, but equally a problem with the cables or accessories. Be worth a bit more investigation I reckon

SB

 

[Adam_151]

Interesting recommendation about the shed.

Firstly, I am not an electrician – far from it. When you say:

I'd install local RCD protection at the shed and put that on non RCD in the house

presumably there needs to be a cable run from the house to the shed. More than likely routed where there is a danger that it could receive some sort of mechanical damage. Would you not want to protect the person who has just put their spade through the cable buried 18 inches below the garden.

G

Its a good point, but aside from the fact that its going to be very hard to put a spade through SWA, if you do somehow manage it, the spade will be in contact with the earthed armor when it cuts the phase conductor, and will trip the overcurrent device. Its not as if you could 'nick' the phase conductor and pick up an energised conductor thinking 'what the **** have I done', as you could when you are using your hedge trimmer in the garden (which I presume is the reason for requireing RCD on outlets likely to be used for supplying stuff outdoors)