Hi, I have a 10a MCB in my consumer unit for all the upstairs lights. The total load of all the lights commonly used at the same time is around 8 amps. The cables are 1.5mm for the main feed to the attic, and 1mm from light switches to individual sets of lights, clipped direct (attic). I'd like to keep it this way for simplicity if I can. My question is, I want to install some dedicated sockets for bedside lamps (with 2 way wall switches) from the lighting circuit. Can I use 2a or 5a sockets protected by a 10a mcb? I assume the MCB is only protecting the supply cable, not the individual sockets/light fittings. e.g. on a ring final, a 32a mcb is used but sockets are only rated at 13a because a maximum of 13a can be plugged into each individual socket. Is this correct? I guess the same could be said for lightswitches used for individual lights (rated at 5amps) but protected by a 10a mcb. As long as only a 40watt bedside lamp is plugged into the round pin socket, this is perfectly fine yes?
10a MCB lighting circuit and 2a sockets
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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
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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.
The same applies to ceiling roses which are used junction boxes and rated at 5A when used the supply needs protected by a 5A fuse/MCB/RCBO.
Although BS7671 states that you can go up to 16A for lighting circuits in real terms because the ceiling roses and other items used in lighting circuits are rated at 5A then in the main we are limited to using 5A fuse or 6A MCB.
This is why often the lighting circuits have been split upstairs and downstairs to reduce the circuit to 5A.
In practice I have found lamps fused to 16A when the lamps blow they often ionise and draw so much current that it welds the lamp to the lamp holder. So instead of changing a bulb one ends up changing the whole lamp fitting so I would never fuse to above 5A or use over a 6A MCB on a lighting circuit.
However today with the use of CFL and LED the current used by lighting has reduced and for your problem the first step would seem to be replace lamps with modern types until the current used drops below the 6A threshold.
One could use fuse connection units (FCU) or even switched FCU as light switch to supply socket or lamps but as we add RCD protection we then have a problem that if it trips we are in the dark. So today we will split both lights and sockets and in any area the lights and sockets will be on a different RCD so any standard lamps or table lamps plugged in will continue to work should a RCD trip.
With this in consideration I would not be connecting table and standard lights to the same lighting circuit as main lights as once the system is upgraded to have RCD's one would lose all lights in a room should a RCD trip.
So I would not use 2A plugs and sockets on a 10A supply without a FCU with 3A fuse but used on a 6A supply although not strictly correct I would not worry about. However step one is to ask is the lighting circuit OK on a 10A MCB to start with?
The same applies to ceiling roses which are used junction boxes and rated at 5A when used the supply needs protected by a 5A fuse/MCB/RCBO.
Although BS7671 states that you can go up to 16A for lighting circuits in real terms because the ceiling roses and other items used in lighting circuits are rated at 5A then in the main we are limited to using 5A fuse or 6A MCB.
This is why often the lighting circuits have been split upstairs and downstairs to reduce the circuit to 5A.
In practice I have found lamps fused to 16A when the lamps blow they often ionise and draw so much current that it welds the lamp to the lamp holder. So instead of changing a bulb one ends up changing the whole lamp fitting so I would never fuse to above 5A or use over a 6A MCB on a lighting circuit.
However today with the use of CFL and LED the current used by lighting has reduced and for your problem the first step would seem to be replace lamps with modern types until the current used drops below the 6A threshold.
One could use fuse connection units (FCU) or even switched FCU as light switch to supply socket or lamps but as we add RCD protection we then have a problem that if it trips we are in the dark. So today we will split both lights and sockets and in any area the lights and sockets will be on a different RCD so any standard lamps or table lamps plugged in will continue to work should a RCD trip.
With this in consideration I would not be connecting table and standard lights to the same lighting circuit as main lights as once the system is upgraded to have RCD's one would lose all lights in a room should a RCD trip.
So I would not use 2A plugs and sockets on a 10A supply without a FCU with 3A fuse but used on a 6A supply although not strictly correct I would not worry about. However step one is to ask is the lighting circuit OK on a 10A MCB to start with?
don't bother with FCU's, just fit 5a round pin sockets and use these
http://cpc.farnell.com/1/1/867-5a-fused-round-pin-plug-641whi-mk-electric.html
http://cpc.farnell.com/1/1/867-5a-fused-round-pin-plug-641whi-mk-electric.html
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Are your bedside table lamp flexes going to be adequately protected by the 10A circuit protection?
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I must say I have 4 x 2A sockets in my lounge on dimmers for table lamps (4 x 60W) on a 6A breaker. The flexes are all 0.75.
I ain't worried!
I ain't worried!
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A standard BA22d bulb holder is rated at 2A and there should be in every bulb a built in fuse so there is no real problem with a 6A supply the ceiling rose rated at 5A and again at 6A no real problem so using 2A rather than 5A plugs is not really a problem with a lighting circuit protected by a 6A MCB.
However the built in fuse in a bulb which should rupture if when the bulb blows one gets ionisation in the envelope is not always there often cheap china bulbs don't have them in and I found to my cost Ikea bulbs don't have it and where I powered an outside lamp with a 16A MCB when the bulb failed it welded the contacts of the bulb to the holder so instead of just changing a bulb I had to change fitting.
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 and I would always fit B type not a C type for same reason.
I was lucky the B16 MCB only feed the outside light but had it fed other lights I would have been without those lights until the fitting was changed so I would advise redressing the problem of a 10A MCB before adding any more lamps.
However the built in fuse in a bulb which should rupture if when the bulb blows one gets ionisation in the envelope is not always there often cheap china bulbs don't have them in and I found to my cost Ikea bulbs don't have it and where I powered an outside lamp with a 16A MCB when the bulb failed it welded the contacts of the bulb to the holder so instead of just changing a bulb I had to change fitting.
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 and I would always fit B type not a C type for same reason.
I was lucky the B16 MCB only feed the outside light but had it fed other lights I would have been without those lights until the fitting was changed so I would advise redressing the problem of a 10A MCB before adding any more lamps.
I wouldn't be happy without an isolator - at least single-pole switch - for an outside light for that very reason.
I'm assuming you had a PIR or PEC operated 'security' light otherwise you would've been able to switch it off.
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
... and nor would I be at all worried, for all sorts of reasons. Indeed, if you took the view that a table lamp cannot create an overload, you wouldn't even need 0.75mm² flex.
Kind Regards, John
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. I don't wish to use any CFL's or LED lamps because they're overpriced and I don't like the stark light they produce at all, and I have dimmers. With this load, would a 6a mcb be ok? I think I'll use 5a sockets as suggested. Out of interest, on 30a ring finals or 30a radials using 4mm cable, why is it ok to use sockets rated at 13amps then?-how is this any different? By this logic, 13a sockets would need to have a fuse in the actual socket to prevent the socket overheating and burning out if, say 2x13amp appliances were plugged into it at the same time (e.g. a washing machine and a dryer)
Things like this have been said a lot recently. However, unless the MIs of the accessory call for 5/6A protection, I'm not quite sure what regulation actually requires an OPD to have an In no greater than the 'rating' of accessories in the circuit. There are obviously a lot of regulations relating to the relationship of the In of the OPD to the CCC of cables, but I don't recall having seen any corresponding explict regs relating to the 'ratings' of accessories. What explicit reg(s) (i.e. excluding the very vague ones) am I missing?
Kind Regards, John
Theoretically, yes. By my reckoning, that lot (excluding fans) adds up to some 1690W, which translates to 7.34A at 230V. The guidance is that one can apply 66% 'diversity' to lighting circuits (on the basis that the lights will generally not all be on simutaneously, which leads to an after-diversity current demand of about 4.85A ... hence OK on a 6A MCB.
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).
Kind Regards, John
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.
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
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