Ring Circuit

recs · 25 May 2004

Regardings your advice on ring circuits, the maximum floor area allowable underBS7671 is 100 sq. metres not 120. What must be taken into account is the fact that the maximum lentgh of the ring (to the last outlet and back to the board) using 2.5mm cable must not exceed 66 metres. Remembering that all sockets on an earth rod system and sockets on ground level on a PME system must be protected by a RCD.

breezer · 25 May 2004

thank you i / we really wanted to know that

plugwash · 25 May 2004

recs said:
Regardings your advice on ring circuits, the maximum floor area allowable underBS7671 is 100 sq. metres not 120. What must be taken into account is the fact that the maximum lentgh of the ring (to the last outlet and back to the board) using 2.5mm cable must not exceed 66 metres. Remembering that all sockets on an earth rod system and sockets on ground level on a PME system must be protected by a RCD.

agree with you on the floor area point

i presume you calculated the cable length

on a TT (earth rod) system EVERYTHING must be on some form of rcd (generally a 100ma type S) and all sockets must be on a 30ma non time delay rcd

never seen any sepecif reference to pme regarding rcds on sockets BUT on any install all sockets that can feasiblly supply outdoor equipement must be on a 30ma rcd

ban-all-sheds · 26 May 2004

recs said:
Regardings your advice on ring circuits, the maximum floor area allowable underBS7671 is 100 sq. metres not 120.

The advice in the section you referenced says 120sq yards, not 120sq m.

120sq yds = 100sq m. But true they made a mistake there and wrote 110.

Are you MB's brother? How's his pocket consulting business going?

recs · 26 May 2004

Ref
on a TT (earth rod) system EVERYTHING must be on some form of rcd (generally a 100ma type S) and all sockets must be on a 30ma non time delay rcd

There is no requirement under BS7671 for all equipment on a TT system to be protected by a RCD, only sockets and any outdoor fixed equipment. However, it is good practice to supply an electric shower through a RCD.
The reason being all other equipment in a building has a maximum disconnection time of 5 secs, whereas sockets are 0.4 (0.2 in agriculture or construction sites)

masona · 26 May 2004

recs said:
the maximum floor area allowable underBS7671 is 100 sq.

2.5mm cable must not exceed 66 metres

Okay, so why is the floor area taking into account ?

Why not say maximum cable 66 metres instead ?

So if you have 66 metres cable in a 200 sq metres, what the difference ?

plugwash · 26 May 2004

recs said:
Ref
on a TT (earth rod) system EVERYTHING must be on some form of rcd (generally a 100ma type S) and all sockets must be on a 30ma non time delay rcd

There is no requirement under BS7671 for all equipment on a TT system to be protected by a RCD, only sockets and any outdoor fixed equipment. However, it is good practice to supply an electric shower through a RCD.
The reason being all other equipment in a building has a maximum disconnection time of 5 secs, whereas sockets are 0.4 (0.2 in agriculture or construction sites)

sure the 5 secs makes a time delay rcd acceptable
but a rcd is still needed (usually a 100ma type S is used as incomer or before the CU) as the TT earth simply cannot carry enough current to trip the larger values of mcb

ban-all-sheds · 27 May 2004

recs said:
What must be taken into account is the fact that the maximum lentgh of the ring (to the last outlet and back to the board) using 2.5mm cable must not exceed 66 metres.

I think you'll find that the maximum length depends on the type of protective device, the type of supply, and the value of Ze.

What do you hope to achieve here by telling people that the limit is 66m, when it might be lower, or higher than that?

recs said:
on a TT (earth rod) system EVERYTHING must be on some form of rcd

and then he said:
There is no requirement under BS7671 for all equipment on a TT system to be protected by a RCD

Which is it?

securespark · 27 May 2004

Quack Quack Ooops!!

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Ring Circuit

breezer

Similar threads