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Topic Title: 32-amp IEC60309 sockets on a radial circuit
Topic Summary: must they be individually supplied from the DB
Created On: 13 June 2013 07:44 PM
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 13 June 2013 07:44 PM
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burke3

Posts: 24
Joined: 12 January 2006

Many thanks to those who responded to a query I had about this same question regarding ring-maining a group of 16-amp 60309 sockets.

This time I have a set of 2-off 32-amp IEC60309 sockets to be mounted adjacently on an enclosure. the circuits are 1PN+E. The sum of the loads across the pair of sockets will be less than 32A, and I would like to run a radial supply to the pair together from a 32A MCB on 4mm2 cable.
However, I have seen something on the internet that this idea of a radial supply to 60309 style sockets is only allowed for 16A models.

Would I be transgressing BS7671 if I were to implement this format of distribution.?

I cannot see why it would be unreasonable in this case where the protection rating is no more than any individual outlet.

Once again your comments would be most valued.


thank you,
Joey
 13 June 2013 07:48 PM
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jamieblatant

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Just treat them like any other socket outlet providing the items connected have protective devices providing downstream protection

Maybe throw in an rcd if you like

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 13 June 2013 07:54 PM
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perspicacious

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"The sum of the loads across the pair of sockets will be less than 32A, and I would like to run a radial supply to the pair together from a 32A MCB on 4mm2 cable."

If each socket-outlet is going to supply less than 16 A, is there any reason why the items that will be plugged in, can't use 16 A plugs?

Secondly, is there a possibility that someone could plug in two fully rated 32 A items?

Regards

BOD
 13 June 2013 08:01 PM
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OMS

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In the absense of knowledge of the internal protection arrangements of the connected loads, I certainly wouldn't put 2 x 32A BS EN 60309 sockets on a single 32A radial circuit.

Even with knowledge of the connected equipment, I wouldn't do it unless I was absolutely certain that the arrangements would remain in place - ie what control is there over what's plugged in. If it's certain the client can manage that, then OK - but if not, then I wouldn't do it.

With appropriate cable sizing, then the cable's not at particular risk (use a cable that can carry 47A though) - but the terminals of the first socket of the pair are certainly at risk - and using an MCB as a load limiting device is simply p**s poor design

If found on a EICR I would give it an unsatisfactory label

Regards

OMS

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 13 June 2013 08:57 PM
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broadgage

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Agree, a 32 amp socket might be reasonably expected to be loaded to 32 amps, or at least to significantly more than 16 amps, the next lowest size.

In all COMMON circumstances I would expect that a 32 amp socket would be on its own 32 amp circuit.

The only likely exception would be premises with a single, large, portable load such as a large welding set that they wish to use in multiple locations. And even then I am not keen on the arrangement lest they aquire more large loading appliances with 32 amp plugs.

If multiple 32 amp sockets must be connected to a single 32 amp circuit, then I would consider it advisable to use cable one size larger than normal practice, perhaps 6.0mm on a 32 amp circuit, this to allow an extra margin in case multiple appliances load the 32 amp circuit to say 40 amps, which the MCB will probably pass for days.
 13 June 2013 09:58 PM
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leckie

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Although its a deviation, and a carp design, is it dangerous? I mean, you do have overload protection. So how can it be code 1 or 2 on an EICR? I.e. dangerous or potentially dangerous?
 14 June 2013 07:23 AM
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zeeper

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talking about the bs4343 16a socket ring reminded me of this I come across the other day.

Adaptor

And going back to the 16A radial what if you have a 32A ring final circuit .And you had say 4 points of utilisation and each point was fitted with one of these outlet and a 16A rcbo fitted to each outlet enclosure.

I think that would be ok ?
 14 June 2013 08:28 AM
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leckie

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Well look at this, now that could cause a few problems I would think. To be used with care.

http://uk.rs-online.com/web/p/...?origin=PSF_435731|cav
 14 June 2013 11:36 AM
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OMS

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Originally posted by: leckie

Although its a deviation, and a carp design, is it dangerous? I mean, you do have overload protection. So how can it be code 1 or 2 on an EICR? I.e. dangerous or potentially dangerous?


I very much doubt you have overload protection and you are certainly not dealing with the thermal effects.

Take that 32A MCB - if I'm loading it to say 40A, it's going to take a fair bit of time to operate - and it's going to get hot and the terminals are getting hot - way beyond 70C realistically.

Then consider the first socket - the terminals are also carrying 40A - way beyond thier 32A 70C rating - so they are getting hot as well.

If the cable has only been sized on In of 32A then that's a risk as well

It's a classic overload becoming fire risk scenario - of course it's unsatisfactory - as it fails to meet at least one of the objectives of BS 7671 in addressing the risks of shock, fire and burns.

Regards

OMS

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 14 June 2013 12:07 PM
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Parsley

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I've often wondered about the twin socket in this note in appendix 5. Difficult to quess what some people are likely to plug in.

An unfused spur should feed one single or one twin socket-outlet only. An unfused spur may be connected to the origin of the circuit in the distribution board.

Regards
 14 June 2013 12:20 PM
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OMS

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Originally posted by: Parsley

I've often wondered about the twin socket in this note in appendix 5. Difficult to quess what some people are likely to plug in.



An unfused spur should feed one single or one twin socket-outlet only. An unfused spur may be connected to the origin of the circuit in the distribution board.



Regards


Look at the product standards - a 13A socket is only required to carry 17A - ie 13A one side and 5A the other side - that's what it's tested for

Well within the current rating of a minimum 20A cable in the installed condition.

Regards

OMS

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 14 June 2013 12:33 PM
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Parsley

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Originally posted by: OMS

Originally posted by: Parsley



I've often wondered about the twin socket in this note in appendix 5. Difficult to quess what some people are likely to plug in.

Regards



An unfused spur should feed one single or one twin socket-outlet only. An unfused spur may be connected to the origin of the circuit in the distribution board.







Regards




Look at the product standards - a 13A socket is only required to carry 17A - ie 13A one side and 5A the other side - that's what it's tested for



Well within the current rating of a minimum 20A cable in the installed condition.



Regards



OMS


Yes agreed, but what prevents 2 x 3 KW loads being plugged in by some numbty?

Regards
 14 June 2013 12:58 PM
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OMS

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Nothing - but 2 x 3kW are going to thermally cycle (and not in synch usually).

Remember we are not designing to make risk as low as possible, only as low as practicable (take diversity as an example).

So yes, there is no doubt some numpty is plugging in 2 x 3KW appliances in a dual socket outlet as we speak - but they are idiots - and BS 7671 doesn't (yet) require us to address the actions of every idiot in every circumstance - we've drawn the line at RCD's for the moment.

Plugging in 2 x 32A loads into 2 x 32A socket outlets though, is entirely credible.

Regards

OMS

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 14 June 2013 01:24 PM
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Parsley

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Good points OMS

Regards
 14 June 2013 01:30 PM
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broadgage

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A twin socket as a spur from a ring final might well be subjected to a couple of 3KW loads, but even that is probably just about within the cable rating, though not the socket.
I thought the test condition for twin 13 amp sockets was 14 amps on one side, a slight overload, and 6 amps on the other for a total load of 20 amps.


To return to the question of multiple 32 amp sockets on the same 32 amp circuit, I dont much like the idea, and if I reluctantly installed such would probably use 6.00mm cable to give an extra margin.

That said though, if a cable is selected in accordance with regs, surely it should be protected against long term small overloads, short term heavy overloads, and short circuits by the correct size fuse or MCB.

If a cable is correctly selected (probably 4.0mm in practice for a 32 amp circuit) then it should be safe from damage.
I would expect that cable correctly selected for a 32 amp MCB should be safe regardless of the load current being 33 amps, 40 amps or 2,000 amps. The trip times being likely never, a few hours, and almost instant for the three currents given, but in each case I would expect that the MCB would trip before the cable became dangerously heated.
 14 June 2013 01:56 PM
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AJJewsbury

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13A socket is only required to carry 17A - ie 13A one side and 5A the other side

I'm not sure I agree with the maths....
- Andy.
 14 June 2013 02:37 PM
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OMS

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Ahem -

That'll teach me to rely on memory and multi task.

Ignore the above numbers, what the standard requires is:

BS1363-2:1995 requires for double socket outlets that both socket outlets have loads applied via test plugs, 1 test plug having a load of 14 amps whilst the other has a load of 6 amps, making a total load of 20 amps on the cable supplying the double socket outlet. The double socket outlet is then subjected to this loading for a minimum continuous period of 4 hours or longer until stability is reached with a maximum duration of 8 hours (stability being taken as less than 1 degC rise within 1 h). The test is passed if neither the terminals / terminations, nor the accessible external surface, increase in temperature by more than 52 degC.


The figure of 17A comes from a well known socket manufacturer as being the continuous current the socket can carry beyond the 8 hour period.

Broadgage and Andy - have cakes on me

Regards


OMS

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 14 June 2013 02:39 PM
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OMS

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but in each case I would expect that the MCB would trip before the cable became dangerously heated.


agreed - my point ws regarding the MCB temperature and the socket outlet terminal temperature - and consequent physical damage and fire risk.

Regards

OMS

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 14 June 2013 10:39 PM
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leckie

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Back on 32A sockets....Well while I bow to the genius that is OMS...
you will have to teach me a bit more.

The amount of overload a socket can take, thermal effects, etc.

What difference does one or two or three sockets make to what an individual socket can take? Not much I don't think, but I'm bound to be corrected!

If you have one socket it can still be overloaded. Either the mcb works or it doesn't. So when you say consider a load of 40amps to the first 32a socket that can be the same for an individual radial socket. What difference does it make for additional sockets? I m of course assuming a suitable sized cable.

Edited: 15 June 2013 at 06:05 AM by leckie
 15 June 2013 07:32 AM
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perspicacious

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"Either the mcb works or it doesn't."

Within the constraints of 433.1.........

Regards

BOD
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