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536.5.1 A switching device shall be protected against overcurrent......

This is hypothetical situation which has some barring on a condition that I have !!

So a 10Amp MCB protects the whole lighting circuit on the ground floor of a small office total load with all lights on 7.5A.
The building is maintained by qualified electricians and the occupier does no maintenance .

Each light switch is rated for 6A is this a FAIL as the maximum load through each light switch is less than 1A ?

What is your interpretation of this reg?

Could you argue that the designer has taken the max load into account per room and as it is looked after by qualified electricians there is no need to interoperate this regulation and up-grade each light switch?
 
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I too say not a fail, however, I was really hoping for a reference from the BGB to counter this claim.... or example where this would be allowed.
Common sense approach doesn’t work here!
Lights kick in = 1.1A, all lights running 0.9A, Switch-6A - to me system safe. Then you have regulation 536 given to you saying it’s not compliant!
 
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You design the switch for the FLc of what it is switching not the MCB rating , if you think about it under normal running conditions only the load on that switch is to be accounted for, how would you have an overload of the switch within that design excluding fault conditions?

This fully satisfies the regulation as the load Max demand is fixed and can't exceed the switch rating (induction taken into account if needed).....the switch rating has no relation to the circuit breaker size only what it its switching load is.
 
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Just to add a bit.

6amp is the switch rating or maximum normal operating current, they don't fail at 7amp, the manufacturer has allowed for fault overcurrent when designing the switch.
 
Similar issue with the use of 0.75mm flex in pendant drops or 2.5mm fed spur from RFC - Not a fail
 
Don't go there Hawkmoon,

I've had fights with the 'inspectors' pulling up and documenting Fluro lights, because from the ballast to the tube, the cable wasn't ----- 1.5mm because the MCB was 10A !!!
Same as them pulling manufactures wiring inside (yes inside the AC) and manufactures lead from the isolators for the AC units as being 'undersized' for 20A MCB (AC unit internally fused to 3.5A with thermal trips) !!
But because they are 'inspectors' they are always correct (seen some good people get sacked because of these idiots).
I could be sacked soon for using the Adiabatic equation instead of table 54.7 to OK a building feed as the 'inspector' can't do the maths ! He's a C#*@ !
 
Most devices for switching have 2 capacities their rating for resistive loads and the rating for inductive loads.

Where a switch has only one rating printed on it you can for this particular case assume its an inductive rating as the switch will be designed to handle both scenarios. The inductive rating when given separately will always be less than the resistive rating because the inrush on SW made and and the back EMF on SW break can cause arcing and will quickly damage the contact points if the switch isn't rated.

For your average domestic or small commercial you can take the switch will do the value stated for both resistive and inductive loads, when you get to larger installs careful design has to be done to ensure switching devices are correct for the job and will last ... their are contactors that are specifically designed to be used with inductive lighting and differ from other contacts you may use to run a motor etc by the nature of the size and resilience of the contact plates.

To note the above comment ...factory wiring internal of light fittings etc is out of the scope of the BS7671 and follow their own BS standards and due to the nature of the fixed load they control they will not overload . The supply wiring you bring into the fitting is subject to BS7671 and i can't believe an inspector would not know the difference now if you had 1mm lighting cables on a 10amp mcb it is quite likely the comment was aimed at your cabling needing to be 1.5mm.
 
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Just to add here and stir the pot with a tin hat on!

Most household circuits can be wired without overload protection of the cable been supplied by the mcb due to the nature of the loads can be calculated for max demand thus can use a clever regulation regarding the omitting of overload protection for fixed load equipment.

This wouldn't cover socket circuits but even though lighting loads can change depending what lamp is fitted and how many lights are switched on - if you calculated the max ratings that can be fitted and the max load if all were on then this can be seen as your fixed load value and you could in a sense have a higher rated MCB than the cable rating as long as short circuit protection is met with Zs values.

Having said this it is a practice not usually done within the domestic realm as it is simple enough to afford the extra protection of the cable at no extra cost, ill also stress i wouldn't like to see this practice used in domestic either, i have designed circuits where the OCPD exceeds the rating of the cable but due to the nature of the load and the fact that i have met S/C requirements this is deemed within regulation. The circuits i relate to are supplying motors (fixed load) where the inrush trips lower rated MCB's if the were fitted to protect the cable for overload. If omitting O/L protection of the cable is used with careful design while staying within the reg's it can save a lot of money as smaller cables can be used.

Ill reiterate though its really not a regulation that should be practiced within the domestic realm but from a point of arguing an inspector down it could be brought into conversation on a therectical point..... trust me ive done it :) but commands a very good understanding of all the regulations that ask for the cable to be protected and those that allow you to omit it.
 
Pretty much the exact point I wanted to make when I read this thread last night DW, but then I decided I couldn't be ar$ed lol. Too much writing and too many ill educated people looking at it going "WTF????".
 
I bet if you ask the switch manufacturers they will state a maximum protective device rating for which the switch is designed and a fault current rating with that protection, or a let-through value that it must not exceed. They will certainly have values for making capacity and breaking capacity. All of these will be higher than the switching rating given on the switch itself, which is the current it is designed to make and break x thousand times before it wears out (subject to constraints e.g. X-rating for fluorescents as explained by DW above)

There is nonetheless a limit, because if you have a hard fault downstream of the switch, obviously its contacts will be subjected to the full fault current and if high enough the contacts might arc and self destruct, opening the circuit before the protective device has time to act and or ejecting arc flash from the switch faceplate. Simply because you can get a certain gauge of cable into the terminals, does not necessarily mean you may protect the switch with the largest rating of device permissible under any circumstances for that cable, on account of that switch having a fixed load below 6A. For unusually highly rated circuits it might be sensible to check it's still within the making capacity etc. recommended by the manufacturer.

I would tend to ignore any such issues with MCBs up to 16A (for which most lighting equipment is designed) above which I would be inclined to check the specs. With something like MK Logic Plus which has a 20A non-inductive rating, obviously proportionally higher.
 
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OK, slightly garbled explanation requiring a backwards step of inference - I've edited it! Thanks.
 
Just an observation....Most switches are rated at 10 amps anyway.....

I was going to say the same thing last night Guitarist, but wasn't sure if this was always the case as I can remember buying uprated ones for fluoros a couple of years ago.
 
From DW .... The supply wiring you bring into the fitting is subject to BS7671 and i can't believe an inspector (*) would not know the difference now if you had 1mm lighting cables on a 10amp mcb it is quite likely the comment was aimed at your cabling needing to be 1.5mm. NOPE!!

Afraid not DW, the design was for ALL wiring to be 2.5 in the building. I kid-you-not they have pulled up internal wiring (the manufactures wiring) for being to small to tubes.
A few months ago you kindly answered my question on internal wiring which was based on these idiots interpertation of the Regs.

(*) one inspector turned out to be a cable TV installer. HR accepted his 'card' as it had the word electrical on it, so he became a company electrical 'inspector' !!
 

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