ring main

[psdw]

How many straight connections are allowed in a ring main ?

 

[sxturbo]

Supposedly there isn't a limit to the number of sockets installed in a ring main, or ring final whichever electricians call them these days.

I think there is a limit on wire length and voltage drop, in 2.5mm a max length of 100m is considered maximum..

This is all according to what I've read on Google when working on mine and families houses

 

[Harry Bloomfield]

How many straight connections are allowed in a ring main ?

If you are asking how many sockets along the ring - there is no actual limit, only a practical one.

 

[psdw]

thanks. So its ok to join cable in a ring main.......

 

[EFLImpudence]

It probably depends what you mean by 'straight connections' and 'join cable'.

 

[ericmark]

I ring final (called that as outside the house we have a very different system called a ring main) can have to comply with volt drop with 2.5 mm² cable 106 meters of cable, histrionically we said should serve no more than 100 m² but rules on drilling beams has resulted in it being a lot less in some cases.

You are permitted three cables into the socket, over that one cable may not be clamped security in the terminal, and you can have as many sockets as you want in the ring final.

You can spur off the ring final with non fused only one BS 1363 device is permitted, but you can connect many items to the BS 1363 device as with a fused connection unit, so one (or two with double socket) BS 1362 fuse protects the spur, which would then make it a fused spur and you can have as many devices as you want after it.

You can only connect devices which have some form of overload direct to the ring final, as it's own overload is 30 or 32 amp, so most items are max 13 amp.

But your question has some ambiguity in it, not sure what you means by "straight connections"?

 

[delmel]

I think he means spurring of the ring main ?

 

[JohnW2]

I think he means spurring of the ring main ?

There's all sorts of things which he could have meant, and I think what we need is clarification, rather than speculation.

It was definitely unclear, but I suspected that the most likely meaning was simply a question as to whether or not it is permissible to have 'joints' in the cable of a ring final (e.g. at a JB) - and, if that is the question, the answer is obviously 'yes', provided that the joint in made in a satisfactory manner.

Kind Regards, John

 

[winston1]

You are permitted three cables into the socket,

Indeed, and I believe there is no reg saying you cannot have more. Four is quite common.

 

[JohnW2]

Indeed, and I believe there is no reg saying you cannot have more. Four is quite common.

Indeed, although four is probably the practical limit - and, even then, it is only some makes (like MK) that can fairly easily be persuaded to accommodate four 2.5mm² conductors.

 

[psdw]

Thanks for replies, I simply mean to join two cables together with a suitable joint box where the cable is too short for whatever reason.

 

[flameport]

If a cable is too short, replacing the cable back to the nearest socket is a much better option.
If a joint is absolutely necessary the junction box must remain accessible or be of a maintenance free type.

 

[JohnW2]

Thanks for replies, I simply mean to join two cables together with a suitable joint box where the cable is too short for whatever reason.

As I wrote, that's what I thought you meant. As I also said, to make such a join is acceptable (there must be many millions of such joins in UK electrical installations), provided it is done in a satisfactory manner.

Flameport is obviously right in saying that the ideal is to replace the cable with one long enough to require no joins (because the joins themselves are one more thing which 'can go wrong')- and if that can be done fairly easily, then that's what I would recommend. However, in the real world, that will not always be a realistic/practical option.

Kind Regards, John

 

[plugwash]

Indeed, and I believe there is no reg saying you cannot have more.

But nothing saying you can either. So like many things in UK wiring it's down to the professional judgement of the installer.

IIRC BS1363 requires sockets to take up to 3x2.5mm² or 2x4mm². Some manufacturers rate their sockets for more, for example MK rate their "logic plus" (and presumably other "plus" ranges) for 3x2.5mm² 3x4mm² or 2x6mm².

Which leads to the question of why they don't rate them for 4x2.5mm²? Did they simply neglect to consider it? Are they worried that with four conductors in the terminal the termination reliability could be affected?

 

[JohnW2]

IIRC BS7671 requires sockets to take up to 3x2.5mm² or 2x4mm².

I presume that you mean BS1363-2 - in which case, yes, it says :

11.5 Line and neutral terminals in fixed socket-outlets shall permit the connection, without special preparation, of one, two or three 2.5 mm2 solid or stranded or of one or two 4 mm2 stranded conductors.

Some manufacturers rate their sockets for more, for example MK rate their "logic plus" (and presumably other "plus" ranges) for 3x2.5mm² 3x4mm² or 2x6mm².

Indeed.

Which leads to the question of why they don't rate them for 4x2.5mm²? Did they simply neglect to consider it? Are they worried that with four conductors in the terminal the termination reliability could be affected?

We often debated that question here, and most people seem to suspect the former - i.e. they 'simply neglected to consider it', perhaps because 'they' were not practising electricians who would be aware that there might sometimes be situations in which one would want more than three conductors in a terminal.

Kind Regards, John