Two Rings Across One Breaker

[TheScullster]

Hi all

Please can someone advise best practice for the following:

1970s extended property with subject extension to rear Extension adjoins both the house and garage with fuse box located in garage Currently the sockets in the extension are a radial spur from the breaker covering the upstairs main house ring main Similarly the extension lighting is a radial spur from the upstairs lighting feed

My questions:

In an ideal world I suppose I would have a separate breaker covering the extension supplies, or have them form part of the existing downstairs ring/lighting. Is it a big no-no to power more than one circuit from a single breaker? There are currently 3 single sockets in the extension, so I presume that the power to this room should be converted into a ring whether it returns to a shared fuse or not? There are currently no spare fuse ways in the CU so it would be an expensive upgrade for one room to provide individual protection for these two supplies.

Any comments on IEE Regs compliance welcome

TIA

Phil

[Andy Wade]

A spur from the origin is perfectly valid, but to count as a 'conventional circuit' it should obey the usual spur rules, i.e. feed no more than one single or double socket or else be fused down to 13 A. Also the whole area served should remain within 100 m^2. You mention three single sockets on this spur - are they wired in 2.5 mm^2 cable or

4 mm^2? The circuit would not comply with BS 7671 (== IEE regs. 16th ed. as amended) if the former (unless it is a fused spur) but may comply in the latter case as a special design. On the whole though it sounds like a cowboy job as the rules hare haven't really changed since the '60s (if not before).

No problem there, necessarily, provided that the total load (assume 100 W per lampholder) stays within the cable and breaker ratings. Nevertheless it is considered desirable to spread lighting over a reasonable no. of separate circuits to avoid the problems of sudden total darkness in the event of a fault or nuisance trip.

Whatever you feed from one breaker is /ipso facto/ a single final circuit. What you have is composite circuits with multiple parts or sections.

What floor area? A (separate) 20 A radial circuit would be OK for general use if it's under 50 m^2. (Assuming no major kitchen/laundry appliances or water heaters are involved.)

From the date I'm imagining a Wylex-type brown consumer unit with rewireable fuses, or perhaps BS 1361 cartridge fuses. Nothing wrong with those /per se/ until you start to run out of fuseways.

Perhaps it's time to bite the bullet and invest in an upgrade to a modern split-load MCB consumer unit. Sort out the extension power circuit and provide a few spare ways, and RCD protection for the socket circuits too.

HTH

[TheScullster]

Andy

Apologies for delay!

Thanks for comprehensive response! The room area is a maximum of 20 sq metres, intended as a teen chill out zone for kids.

Your comments re: new CU are noted:

[bigcat]

Do you want 16th edn compliance, or making it work ok safely? Why?

if its from teh CU it could be put on its own breaker, although the trip would have to be low current if its just 2.5mm. 2.5 radials are not reg compliant afaik, but if MCBed at suitably low rating, and youve not got all your lighting running off it, theyre safe and workable.

no problem with that.

breaker?

More to the point I wouldnt put a 2.5 radial on a 30/32A mcb/fuse. Is the 2.5 clipped direct, buried in thermal insulation, what? With that info one can current rate it, thus know what fuse/mcb to put it on. However its not gonna be reg compliant whatever you do with it, unless you rewire it as a 2.5 ring or a 4mm radial.

In some cases you do need reg compliance, in some you dont. The regs are mainly about safety, but not entirely. Theres nothing unsafe about a 2.5mm radial circuit on a 16A breaker and RCD, but it might trip on some heavy-startup loads, hence the need to not have all your lighting on it.

A split CU kit is only =A370, plus wiring it up, plus fixing the inevitable problem circuits. Another 4 way Wylex fusebox is of course much cheaper, if its that tight.

Do you need compliance in your case? Given what youve found though, I would want to check the whole system over and see if any nastier bodges have been done.

NT

[TheScullster]

Thanks, BigCat

Yes I want to be regs compliant and will look at running a return 2.5 for the socket circuit. I have found one or two nasties, mainly associated with extensions, the original wiring seems sound. Although the original 70s wiring can take some sorting on occasions, with lives looped around switches and neutrals around ceiling roses - very strange, but standard for the area and era apparently!

Currently the 2.5 is clipped along the inside wall of garage, through the end wall between ceiling of extension and upper floor then down "top hat" type conduit behind plaster to sockets.

What would you recommend to protect the 2.5 in the garage? I am considering running the feed, return and lighting cable in some kind of trunking.

TIA

Phil

[Andy Wade]

[snip]

With the cowboy's spur not sorted out - oh dear. I take it there are no spare ways in the new CU.

So four sockets (single or double) on a single unfused spur.

Well, yes and no. Yes, you can have as many sockets as you like on a fused spur, but no in the sense that you must also consider whether such a 13A rated sub-circuit is appropriate for the loads likely to be connected. In your circumstances it would seem entirely possible that two 2 or 3 kW electric heaters could be plugged in (e.g. central heating breakdown) thus overloading the spur. Thus it's not an ideal arrangement, but would still be better than what you have now.

Fair enough, but can you rule out the use of multiple heating appliances on occasion?