10a MCB lighting circuit and 2a sockets

[tew1]

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There are discussions/uncertainties about how much total current a double 13A socket can supply (many believe that it is 20A). However, if you forget that complication and think just of single 13A sockets on a 32A ring, the fuse in the plug obviously provides the necessary protection (just as would a 5A fused plug in your situation).
[/quote]

The UK is the only country in the world as far as I'm aware that uses 30a protection for power socket circuits. The ring final was a hashup method used during the war to either convert 15a radials or use less copper cable. The rest of the world uses individual 15/20a radial circuits (many putting lights on the same circuits as sockets using the same gauge cable and no added protection). It's very common to see twin 13a sockets with scorch marks around the terminals where two heavy current appliances have been plugged in at the same time for a long period of time (e.g. in a kitchen, a dishwasher and a tumble dryer). brick-type Multiway adaptors are also unfused and allow up to 3 13a appliances to be plugged into one socket. Try plugging two 2kw fan heaters into the same twin socket, and feel how hot the socket gets!

 

[riveralt]

ok thanks. There are 17x50w recessed lights, 4x60w recessed lights, a chandelier with 8x40w lamps, two 40w wall sconces, one 40w pendant, 2 extractor fans and 4 more 40w lights.

This statement simply reflects your general lack of knowledge, understanding or appreciation of lighting and circuit design.

By the way, hiding your previous misdemeanors behind the privacy block doesn't mean your electrical work, stupid statements and even worse advice simple goes away. You are after all, just a search away.
Your comments then and here continue to inspire no confidence in your work.

 

[JohnW2]

The way I see it, the MCB only needs to be rated to protect the parts of the circuit which draw the full current of the circuit. e.g. the cables themselves. For example, on a lighting circuit, there may be 2kw of lights. They all draw current from the same supply cable no problem. In a ceiling rose, the wires are connected in the same terminal (no current actually goes 'through' the ceiling rose' e.g. the 0.75mm flex. However, if all 2kw of lamps were connected through one single lightswitch rated at 5 amps, you'd more than likely get arcing and overheating in the lightswitch. I guess you just have to design the circuit so that no individual accessories are able to draw more current than they are capable of

I don't disagree with the common sense of any of that. However, as I said, I've yet to find any explicit regulations which relate to the protection of anything other than cables.

Kind Regards, John

 

[JohnW2]

It's very common to see twin 13a sockets with scorch marks around the terminals where two heavy current appliances have been plugged in at the same time for a long period of time (e.g. in a kitchen, a dishwasher and a tumble dryer).

I agree - but, IMO, that is a situation which should never have been allowed to arise. Given that, for better or for worse, we do have 30/32A circuits, and given that the vast majority of the general public have no reason to believe that they cannot plug two 13A loads into a double socket, it seems crazy to me that BS1363 did not insist that double sockets had to be able to safely provide 2 x 13A continuously.

Kind Regards, John

 

[ban-all-sheds]

ok thanks. There are 17x50w recessed lights,

Mad.

 

[JohnW2]

ok thanks. There are 17x50w recessed lights,

Mad.

For once, I find it difficult to disagree with you...

Goodness - nearly 2kW of lighting 'upstairs'?! Are you using them for heating, or is it just that you 'grow things' in your bedrooms ... or is this perhaps something very different from a 'regular house'?

Kind Regards, John

 

[RF Lighting]

Some 5A plugs have fuses fitted. Not sure about 2A plugs though . . . I think they should - after all, the old type of clock plugs (that you hardly see anymore) had/have fuses in them.

MK 639 WHI

2A fused plug.

 

[plugwash]

MK 639 WHI

Mk list it but does anyone actually sell it?

 

[JohnW2]

MK 639 WHI

Mk list it but does anyone actually sell it?

First hit on Google - click here ...but it does say "2-3 weeks delivery". When Amazon say that, they mean 'never', but I don't know about Rapid! It sure ain't cheap for a tiny little plug - but I guess that reflects the volume of the market!

Kind Regards. John

 

[Risteard]

In theory if we use a 2A plug and socket then we need to fuse to 2A and the same with a 5A plug and socket we are limited to 5A fuse or MCB.

I don't agree. The socket won't have more than its rated current running through it unless you plug something ludicrous in.

 

[ericmark]

With this in mind I would not fit anything over 6A to protect lighting using BS22d, E27 or E14 light bulbs it's not to comply with regulations (although since the rose is rated at 5A or 6A you do need to use a 6A MCB to comply) but I limit it to a 6A MCB to avoid the problems with welded contacts on bulbs ...

As I've just written/asked in another thread, does it actually work like that? The magnitude of the fault current will be the same, regardless of the MCB rating and, if it is a fault of 'negligible impedance' (low enough to get onto the magnetic part of the MCB's curve) then the duration of that fault current (i.e. MCB disconnection time) also ought to be much the same, regardless of the MCB rating. ... or am I missing something?

Kind Regards, John

I see your point that current will be the same for the fraction of a second before the protective device opens if there is a short circuit. However the bulb was a CFL and I would guess to start with it was not a direct short circuit and a more sensitive device would have opened quicker. There is a big difference between 30A of a B6 MCB and the 80A of a B16 MCB before it trips.

I will admit I did not check the loop impedance line - neutral but so close to the consumer unit unlikely it would have been greater than 1 ohm however the poster here is talking about a large radial system and clearly he would need to test to see if below 4.6 ohms (assuming a B10) before extending.

Also of course since using a socket it will need RCD protection.

 

[JohnW2]

I see your point that current will be the same for the fraction of a second before the protective device opens if there is a short circuit. However the bulb was a CFL and I would guess to start with it was not a direct short circuit and a more sensitive device would have opened quicker. There is a big difference between 30A of a B6 MCB and the 80A of a B16 MCB before it trips.

Sure, as I wrote, everything I said was assuming that we were talking about a fault of negligible impedance. If that isn't the case then yes, a B6 might operate 'immediately' when a B16 didn't. However, in general, the regs only think in terms of faults of negligible impedance (i.e. 'dead shorts' / 'bolted faults') - since, otherwise, it would be effectively impossible to ever meet disconnection time requirements (for any impedance of fault).

Kind Regards, John

 

[ericmark]

In theory if we use a 2A plug and socket then we need to fuse to 2A and the same with a 5A plug and socket we are limited to 5A fuse or MCB.

I don't agree. The socket won't have more than its rated current running through it unless you plug something ludicrous in.

I would hope one not connect a pair of 500W halogen lamps, but the fuse is not there to stop you using large loads it is to open the circuit in the event of a fault. From dog chewing the cable to cable crushed in a door it may not always be a direct short circuit.

Personally I think the 2A plug and socket will take far in excess of 2A before any problem exists assuming one is not disconnecting and reconnecting under load.

I have bought quite a few items with 5 and 15 amp plugs fitted when working in Hong Kong although not bought any with 2 amp plugs however there is always the possibility that items which are not lights are plugged in and as far as stickers saying lights only goes I would not consider a general label lights really is what is mean when it says "a specific labelled or otherwise suitably identified socket-outlet provided for connection of a particular item of equipment." I would consider "particular item of equipment" would need to be labelled as "Standard Lamp only" not just lights.

Clearly if not surface wiring will need RCD protection anyway.

 

[plugwash]

First hit on Google - click here

Ahh you searched without a space.

And when I do that it seems I get a hit for MK, a hit for rapid and then a pagefilled with a mixture of price comparision sites listing rapid and copies of the MK catalogue.

...but it does say "2-3 weeks delivery". When Amazon say that, they mean 'never', but I don't know about Rapid!

I suspect it means that they don't hold stock of them so they have to order them from MK when a customer wants one.

 

[JohnW2]

First hit on Google - click here

Ahh you searched without a space.

Actually, I didn't. I literally copied and pasted "MK 639 WHI", with both the spaces, from RF's post into Google and 'hit Return' - and what I posted here was the very first hit!

...but it does say "2-3 weeks delivery". When Amazon say that, they mean 'never', but I don't know about Rapid!

I suspect it means that they don't hold stock of them so they have to order them from MK when a customer wants one.

One would hope that's what it means, but by experience with some suppliers makes me nervous. "ordered on demand" or something like that is more reassuring. As I said, over the years, I've learned Amazon's 'code'. "5-6 days" usually means 'you might get it this year', and anything measured in weeks seems to mean 'forget it' - every few weeks, until they get fed up, one gets an e-mail saying that it has been 'further delayed' ... but maybe I've just been unlucky!

Kind Regards, John