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Topic Title: BS 546 Circuit Accessories used on Ring Final Circuit
Topic Summary: Is it allowed to use BS 546 circuit accessories on a ring final circuit?
Created On: 11 October 2017 02:24 PM
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 11 October 2017 02:24 PM
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moss@info.bw

Posts: 3
Joined: 25 July 2008

A little bit of background first. I have a small consultancy business in Gaborone, Botswana that provides various services to the locally based Construction Industry. These services include, amongst others, Services Coordination. When examine the distribution board schematics in preparation for dry testing of the electrical installation I noticed that the final circuits for essential socket outlet circuits are ring mains protected by a 30A RCD. However, I am also aware that the type of sockets connected to these circuits are 15A Round Pin Outlets (BS 546) that accept an unfused plug with a shaved earth pin. My understanding is that only circuit accessories complying to BS 1363 are allowed by the regulations to connected in a ring final circuit. Could anybody confirm that this is the case or tell me that I am barking-up the wrong tree.
 11 October 2017 05:20 PM
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Nesspark

Posts: 10
Joined: 01 September 2006

I don't know what wiring regulations apply in Botswana, but BS 546 unfused plugs would not be acceptable on a 30/32A ring circuit in UK.
A couple of possible solutions would be to place fused connection units adjacent to each socket or downgrade the circuit protective device to 16A. It may be necessary to split the circuit into smaller radial circuits with appropriate overcurrent protection depending on the anticipated load.
 11 October 2017 08:46 PM
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geoffsd

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You say 30A RCD; do you mean 30mA RCD or 30A MCB?

If the former, what is the rating of the OPD - and, in either case, what is the csa of the conductors?
 11 October 2017 08:51 PM
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AJJewsbury

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Are the plugs used definitely unfused? In the UK fused (as well as unfused) variants are available (e.g. MK 643 WHI - see http://www.mkelectric.com/Docu...s%20and%20Adaptors.pdf ). If fused ones are used then it's not a lot different to the BS 1363 system (other than the risk of using an unfused plug by mistake of course).
- Andy.
 12 October 2017 05:45 AM
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ebee

Posts: 6347
Joined: 02 December 2004

'Tis a poor advert from a manufacturer of plugtops to show wiring of a flex to a plug top so badly done , look at length of E compared to L & N ??

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 12 October 2017 08:25 AM
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moss@info.bw

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Thanks everybody for your responses, much appreciated. With regard to Nesspark's query; the contract documents states that this work will be carried out strictly in accordance with the "IEE Wiring Regulations - Seventeenth Edition (BS 7671) including latest amendments" so I believe I am correct that this would be BS7671:2008+A3:2015. With regard to geoffsd's query: the circuit protection is a 30A 30mA RCD. With regard to AJJJewsbury query: the plugs are definitely unfused and what I am saying to the Consultant Electrical Engineer, for this project is, that because the plugs are unfused in the event of an overload at a particular socket, whether intentional or accidental, that does not cause an imbalance in the live/neutral current, it is possible that the socket and plug can be subjected to a current equal to or more than twice their rated capacity for a long period without tripping the circuit breaker. As a result excessive heat can be generated which could lead to a fire. What do you think, am I correct or not?
 12 October 2017 09:45 AM
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broadgage

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If compliance with UK regulations is required, then 15 amp sockets that accept unfused 15 amp plugs should not be installed on a 30/32 amp ring final circuit, not indeed on a 30/32 radial circuit.

Even if compliance with UK regulations was not required, it would still be very poor practice to install unfused 15 amp outlets on a 30/32 amp circuit.
The risk is not just the potential overloading of the plug/socket but also the increased risk of an appliance or flex thereto catching fire.
If an appliance fitted with relatively small flex develops an internal fault, then fire may occur before a 30/32 amp MCB trips.

I would consider the following alternatives.

1) use sockets designed for UK type 13 amp fused plugs

2)use the proposed 15 amp sockets, but on 15/16 amp radial circuits.

3)retain the proposed UK style ring circuit, but connect the 15 amp outlets via UK style fused connection units that incorporate a 13 amp fuse.

Do please check that the circuit is properly protected against overcurrent ! Here in the UK, a "30 amp RCD" Is understood to mean a device that protects against earth leakage but NOT against overload. The "30 amps" indicates the maximum current that the RCD can handle, it DOES NOT mean that it trips on more than 30 amps.
To protect against earth leakage AND against overload you need either an RCBO, or an RCD and a separate fuse or circuit breaker.

Overseas terminology may vary, but do please double check that the circuit is protected against both overload and earth leakage.
 12 October 2017 09:53 AM
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potential

Posts: 1642
Joined: 01 February 2007

Originally posted by: ebee

'Tis a poor advert from a manufacturer of plugtops to show wiring of a flex to a plug top so badly done , look at length of E compared to L & N ??


I agree with you about the length of the earth wire but IF you must insist on using the word plug "top" surely the diagram must show a plug bottom?
 12 October 2017 10:36 AM
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moss@info.bw

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Thanks to all and particularly broadgage for the comprehensive response. Just a quick comment about the plug top issue. When I was a boy, which was a some while ago we called sockets, plugs and plugs, plug tops to differentiate between the two.
 12 October 2017 01:30 PM
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geoffsd

Posts: 1786
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Originally posted by: moss@info.bw
When I was a boy, which was a some while ago we called sockets, plugs and plugs, plug tops to differentiate between the two.

That may be a reason -

but it makes even less sense.
 12 October 2017 01:33 PM
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ectophile

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Originally posted by: broadgage

3)retain the proposed UK style ring circuit, but connect the 15 amp outlets via UK style fused connection units that incorporate a 13 amp fuse.


That might not be so good if someone plugs in a high power appliance that actually draws 15A. The 13A fuse won't blow in any reasonable time, but it would get seriously hot.

-------------------------
S P Barker BSc PhD IEng MIET
 12 October 2017 05:19 PM
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AJJewsbury

Posts: 16114
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When I was a boy, which was a some while ago we called sockets, plugs and plugs, plug tops to differentiate between the two.

It wasn't just you either - the 4th Ed of the regs themselves referred to "wall and floor plugs" (in a context where they clearly mean what we'd call sockets today) - by the 6th Ed they were "plug connectors", not till the 7th Ed did the term "socket" appear.

So, officially old, rather than irrational terminology I think.

- Andy.
 12 October 2017 05:32 PM
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mapj1

Posts: 9707
Joined: 22 July 2004

It is possible to be both old and irrational, as others on here will no doubt testify.

There is a general change of language, as a similar problem occurs with Jacks, and Jack plugs, and Jack sockets in the world of audio.
In today's world, more sensitive to gender balance, you need to be careful to have similar numbers of each.

In any case,unless its just one round pin socket and the rest are square pin, I'd suggest more circuits on 16A RCBOs giving combined RCD (earth fault) and MCB (overload) protection, or an RCD and many 16A MCBs, rather than lots of extra boxes and fused spurs

In places where materials are expensive, I think you will find any blown fuses likely to be by passed with cigarette foil and similar, and wires stuck into the socket sans plug at all, as we, oops, sorry "some people", used to do in the past. Ahem


Thanks to flameport website for the pic.
It's not quite as I remember it, as the old flex colours were red and black, and you just left the green one off to one side as usually it still worked without it. When I last visited South America, a couple of years ago, this sort of bodge was still commonly the case there. I am less sure about standards in Botswana.

-------------------------
regards Mike
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