13A Twin sockets.

[Boulevardier]

@ Skywave

"Experience is a bad teacher. Gives you the exam first; the lessons come afterwards."

What a brilliant way of putting it! Go to the top of the class! I'm going to write that down for posterity!

Mike

[Boulevardier]

@ Hannahs Radios - "I wonder why manufacturers don't simply uprate the internal busbars so that you can,"

And if MK design for 20A-ish, then why not for 26A? Perhaps the cable receptacles/screws would have to be uprated too, and the contact area/riveting between them and the busbars. Perhaps the design was so tight to get the outlets (and two switches) into a space that's less than 2x single sockets that these improvements would have pushed it over the edge on size. Perhaps we'll never know!

[OscarFoxtrot]

Originally Posted by Dai Corner

That extra bit of brass, copper or whatever would cost a few pence.

And part of the ethos of the ring final circuit was the saving of materials, so they possibly took that into consideration too.

[barrymagrec]

I don`t remember double sockets even existing in the early days of 13A ring mains - one single socket in each room whether you needed it or not - and in the most inconvenient place as well.

[usradcoll1]

Originally Posted by Boater Sam

When I look at the American 117v bipin plug I shudder. And when they are used on 240v in the far east they are terrifying.

The NEMA devices used in some of those far-east countries were used in areas were there was a large American presence and it was originally supplied with 115 volts.
One prime example is the Philippine Islands, where it seems that no electrical code is adhered to. The mains voltage was increased to 240 volts to increase capacity. Their wiring practices are very crude, at best.

[hannahs radios]

In Metro-manilla area of Phillipines they have a bi phase supply with 115 volts either side of earth to give 230 volts supply. I agree wiring standards are a bit suspect in that part of the world. Because RCDs are almost unknown there it known for people with US appliances to connect a wire to the metal water pipe and the other to one leg of the supply thereby avoiding the need for a transformer. Check out gadget addict channel on YouTube some of his earlier videos show some of the wiring used there

[dave walsh]

SNAP Barry p212*. [My post 9*-Ring Main but not many sockets 1958]. In fact we were on Kerosene lamps in this brand new house on the first night-no power

Someone had nailed through the ring cable When the electrician came the next day he replace the distribution box as one fuse holder was burnt out. He gave it to me as I was so interested in his Megger Testing for the short. A couple of years later, I wired the Box Room [no sockets] to replace power tapped of the light circuit 30's style that I worked from. I wired it to feed my bench through 5 amp fuses [from a socket] as the RSGB Handbook recommended an emergency switch that the family should know about, in case I fried myself. The one socket in the lounge was a bit dodgy so the electrician came back and fitted a marvellous new double socket. We were in awe off as we didn't know they existed. Having moved from a terraced house we only knew single bakelite sockets and adaptors!

Dave W

[usradcoll1]

Originally Posted by OscarFoxtrot

And part of the ethos of the ring final circuit was the saving of materials, so they possibly took that into consideration too.

Is there an instrument that can check the integrity of the ring circuit. I understand the concept of the ring circuit. One of the conductors at a power point, either the live or the neutral could come loose or burn off. The circuit would appear to work properly, but the circuit wouldn't be able to carry the current as intended.
Ring circuits are not allowed in the US and other countries.

[Brigham]

If ring circuits had been fused at 15 Amps at each end, rather than 30 Amps before the ring, then they would still be safe even if the ring parted.
I suppose the cost of the extra fuseways was taken into account, the whole thing being a safety/economy compromise.

[OscarFoxtrot]

Originally Posted by usradcoll1

Is there an instrument that can check the integrity of the ring circuit. I understand the concept of the ring circuit.

Resistance tester and follow the appropriate test procedure

http://www.sparkyfacts.co.uk/Inspect...it-Testing.php

[Nickthedentist]

Very useful link, thank you!

[Skywave]

Originally Posted by Boulevardier

"Experience is a bad teacher. Gives you the exam first; the lessons come afterwards."

What a brilliant way of putting it! Go to the top of the class! I'm going to write that down for posterity!

Thank you, Mike, but in all fairness I must state that moral is not of my creation. I believe it was first voiced by the American folk-singer Woody Guthrie or possibly Pete Seeger.

Al.

[Boater Sam]

Originally Posted by Brigham

If ring circuits had been fused at 15 Amps at each end, rather than 30 Amps before the ring, then they would still be safe even if the ring parted.
I suppose the cost of the extra fuseways was taken into account, the whole thing being a safety/economy compromise.

NO! A terrible idea, not allowed. It is dangerous to feed any circuit from 2 sources as there is no way to guarantee disconnection.

[Boulevardier]

Also, at the danger of expanding slightly beyond the core thread topic (I won't do it again, mods!), the following (from the IEE;s "A Practical Guide to the Wiring Regulations") is worrying -

"..for example, for a 30 A circuit protected by a 30 A rewirable fuse and drawing an overload current of 60 A, disconnection on overload may take up to 4 h. Clearly, this phenomenon needs to be taken into account and this is done by the application of the 0.725 factor as a multiplier to the current-carrying capacity of the circuit cable. One effect of using a rewirable fuse to BS 3036, therefore, is to increase the required cable cross-sectional area for a given load, other parameters being equal."

Perhaps there's something in that I'm not fully understanding...?

Mike

[barrymagrec]

Originally Posted by Boater Sam

NO! A terrible idea, not allowed. It is dangerous to feed any circuit from 2 sources as there is no way to guarantee disconnection.

As somebody where I was working found out after someone else wired a 20 amp
air conditioner to two 13A plugs...

[dave walsh]

Oh dear but surely that's total incompetence not just breaching the regs?

I was interested in Brigham's post and didn't spot the obvious flaw, although I'm sure I do have a book somewhere that illustrates a separate 15amp fuse each way. I might even have seen a box wired in that manner. Going back to the [I think less concerning safety wise ] double socket and whether there is enough amperage available, I mentioned my assumption that there was 20amps each way [see post 81* and before].

In the recent thread about classic speaker cables, someone mentioned using 7/029 t+e cable [the sort of thing I used to wire with but I have never been a professional "spark"]. The comment was that ring main cable was often utilised for this but the modern stuff was less flexible [and maybe lower rated?] Perhaps this is why my mentor said 7/029 could carry 20 amps back then? I still don't think it's a problem though, either way.

Dave

[Boulevardier]

@ Dave Walsh

"In the recent thread about classic speaker cables, someone mentions the previous use of 7/029 t+e cables"

I seem to remember that Douglas Self somewhere mentions the use of 2.5mm T&E as a cheap and entirely adequate speaker cable. Hope I'm not "mis-remembering" him! Admittedly, you'd be wasting an earth core..

Mike

Admittedly, you'd be wasting an earth core.

1.5mm 3&E in parallel? Back on topic, apart from the safety of shuttered sockets, fused plugs (assuming one fits the right fuse) and a reasonable current capacity. The good old 13A socket holds wall warts quite securely.

[G6Tanuki]

Originally Posted by dave walsh

I was interested in Brigham's post and didn't spot the obvious flaw, although I'm sure I do have a book somewhere that illustrates a separate 15amp fuse each way. I might even have seen a box wired in that manner.
Dave

The obvious problem with fusing both sides of the feedpoint of a ring is that if one fuse fails..... I can forsee a situation where a high-current appliance plugged into an outlet at one end of the ring, or a fault at that outlet would preferentially blow the fuse between that outlet and the nearby feed-point (because the resistance on that path is lower), the current on 'live' thereafter flowing the entire way round the ring to the other fuse/feed-point whereas the neutral current would still have two paths to follow....

Could you perhaps be confusing things with the old DC mains where both L and N were fused? I did come across some legacy installations [old 1940s/1950s metalclad fuseboxes with ceramic rewireable fuses] that had live-and-neutral fusing on circuits feeding 5/15A BS546-type outlets but they were installations originally put in place for DC mains.

[dave walsh]

That's certainly a possibility Tanuki as I do have a few old electrical engineering books. I've only ever used the single feed point myself though when putting in a ring! That air conditioner job seemed like someone who just couldn't be bothered to run a suitable cable from the right source.

Dave

Erratum-When I said SNAP [post 107*] I was referring 104* not 212 of course!