Fuses below (almost) every light switch in the house

[EFLImpudence]

However, for those who take the view that fuses/MCBs are there only to protect cables (not accessories or loads)

You rang, Sir?

Whilst the fuse/MBC is their to protect the cable I think it has been agreed in previous threads that the reason for 6A protection is because of the accessories.
Although, in this instant with apparently each room's lighting on a separate spur and therefore the likelihood of overload non-existant perhaps the 13A fuse could be omitted and it could be asked - is it a ligting circuit?

However, I am sure you will agree that 13A or 6A isn't much protection for the load which may be a 40W lamp.

 

[JohnW2]

However, for those who take the view that fuses/MCBs are there only to protect cables (not accessories or loads)

You rang, Sir? Whilst the fuse/MBC is their to protect the cable I think it has been agreed in previous threads that the reason for 6A protection is because of the accessories.

Indeed - it sure isn't necessary for the OPD to be anything like as low as 6A to protect a 1mm² or 1.5mm² cable. So, I presume that this is an exception which proves the rule?

... but, as they say, "hang on" Where exactly does this 6A actually come from? As I wrote earlier today, the best I could find in the regs was a requirement for the OPD of a lighting circuits (including the specified types of lampholders) to be no greater than 16A. Is it perhaps 'the voice of the OSG' again?

Although, in this instant with apparently each room's lighting on a separate spur and therefore the likelihood of overload non-existant perhaps the 13A fuse could be omitted and it could be asked - is it a lighting circuit?

... which would take us back to the top of this message, where you appeared to be saying that 6A protection was required (although I'm not sure by what regulation) 'to protect the accessories'. However, as you now say, if one assumes that overload is very unlikely, I'm not sure what we would be protecting the accessories from!

However, I am sure you will agree that 13A or 6A isn't much protection for the load which may be a 40W lamp.

Indeed so. I am perhaps one of the more loyal purchasers of 1A BS1362 fuses

Don't forget that, perhaps somewhat uncharacteristically, I got involved in this discussion by suggesting that a 13A fuse was probably compliant, even if much larger than 'necessary'.

Kind Regards, John

 

[EFLImpudence]

... but, as they say, "hang on" Where exactly does this 6A actually come from?

I thought, as in the above-mentioned previous thread (a while ago), that accessories (switches) and wiring in light fittings was only rated for 6A, therefore...

So unless 433.3 is employed for every situation then I presume the standard is accepted.

As I wrote earlier today, the best I could find in the regs was a requirement for the OPD of a lighting circuits (including the specified types of lampholders) to be no greater than 16A.

As also said - why?

Is it perhaps 'the voice of the OSG' again?

Not my area of expertise.

 

[JohnW2]

... but, as they say, "hang on" Where exactly does this 6A actually come from?

I thought, as in the above-mentioned previous thread (a while ago), that accessories (switches) and wiring in light fittings was only rated for 6A, therefore... So unless 433.3 is employed for every situation then I presume the standard is accepted.

But 433.3 is all about omission of overload protection for "conductors" which, in context, I take to refer to just fixed wiring cables, not to "accessories and wiring in light fittings". Apart from the rather weird 559.6.1.6, I haven't seen any thing in the regs about protecting anything other than cables against overload. Am I missing something?

As I wrote earlier today, the best I could find in the regs was a requirement for the OPD of a lighting circuits (including the specified types of lampholders) to be no greater than 16A.

As also said - why?

As above, goodness knows!

Kind Regards, John

 

[stillp]

In the 16th (1992) it was 6A for B15 or E14, unless the lampholders met ignitability class P of BS476.

And the logic there was.....?

Presumably that B15 and E14 were considered to need closer protection unless they had better flammability characteristics.

 

[mfarrow]

This is an interesting discussion, one for which I unfortunately have not hot an answer for.

The main reason I suspect for the regulation of 16A is, as ericmark has alluded to in a previous thread, that the longer the disconnection time, the more likely it is that the soldered base of the lamp will weld itself to the lampholder contacts. A rather expensive and inconvenient lamp replacement then ensues!

Quite why this is applied to ES and BC caps only, and not double-ended striplights to BSwhatever is a mystery. Perhaps is the fact that vertically mounted bulbs will quite often drop their filament onto the pins below allows more let-through than the striplights?

As for the 6A thing, well I think it's probably again the rating of the accessories which gets people into a flap about it. What we should be looking at, and what we probably haven't got, is the short time withstand ratings of the contaccts for fault conditions. By matching this with the operating characteristic of our protective device, we can ensure adequate circuit design. Anyone got a light switch with a BS number on it?

 

[JohnW2]

The main reason I suspect for the regulation of 16A is, as ericmark has alluded to in a previous thread, that the longer the disconnection time, the more likely it is that the soldered base of the lamp will weld itself to the lampholder contacts.

Does that really hold water? Assuming that we're talking about a full-blown BS7671 (i.e. negligible impedance) fault, and proper circuit design, is there any reason why the disconnection time would be any longer with a 16A OPD than, say, a 6A one? Once one has enough fault current to get onto the magnetic part of a MCB's curve, I wouldn't expect the disconnection time to depend significantly on the rating of the MCB, would you? With a fuse, it would be a bit different.

Quite why this is applied to ES and BC caps only, and not double-ended striplights to BSwhatever is a mystery.

Indeed so,

As for the 6A thing, well I think it's probably again the rating of the accessories which gets people into a flap about it. What we should be looking at, and what we probably haven't got, is the short time withstand ratings of the contaccts for fault conditions. By matching this with the operating characteristic of our protective device, we can ensure adequate circuit design.

Indeed, but all we are usually told (if anything) is the 'rating' But, if we're talking up to 16A OPDs, it's probably not only short-term fault current tolerance we need to know about - goodness knows what lighting loads would actually achieve this but, at least in theory, one could have any load up 16A continuously on a '16A lighting circuit'.

Anyone got a light switch with a BS number on it?

Many (but not all) of those I have, both brand new and very old, bear BS3676 markings.

Kind Regards, John

 

[mfarrow]

The characteristics' differences between a 16A MCB and a 6A MCB below the vertical 'magnetic actuation' line, which finishes at 0.1s in BS 7671, can be seen clearly on manufacturers and other standard's data. Although the greatest difference will be noted when using fuses of course.

It still doesn't take us any further to confirming or understanding the reason for the regulation though. Perhaps there's another standard or avenue we're overlooking?

Flicking through the switch standards, they just give temperature withstand tests for rated load and up to 130% (depending on year and switch rating). There's nothing stipulating fault tolerance, which is probably why even modern switches are all rather too keen to weld themselves together if you close them onto a fault.

 

[JohnW2]

The characteristics' differences between a 16A MCB and a 6A MCB below the vertical 'magnetic actuation' line, which finishes at 0.1s in BS 7671, can be seen clearly on manufacturers and other standard's data.

Interesting. I was under the impression that once one had exceeded the current necessary to trigger the magnetic mechanism, the speed of disconnection would be a purely mechanical thing, not really related to the rating of the device (or the magnitude of the current which had triggered it).

It still doesn't take us any further to confirming or understanding the reason for the regulation though.

Indeed it doesn't. As you say, maybe we are missing or overlooking something.

Flicking through the switch standards, they just give temperature withstand tests for rated load and up to 130% (depending on year and switch rating). There's nothing stipulating fault tolerance, which is probably why even modern switches are all rather too keen to weld themselves together if you close them onto a fault.

To be honest, I doubt that it would be feasible to produce something like a light switch which could cope with a fault current maybe 100 times it's normal 'rated' current.

I also think that, in reality, many of the theoretical concerns being voiced in relation to accessories in lighting circuits are not really matters to lose any sleep about!

Kind Regards, John

 

[mfarrow]

Double posting.

 

[Philthy]

In response to maximjc's original post, have you had an electrician round or otherwise come up with a solution?

I'm in the exact same situation - just bought a house with fuses under every light switch, single plug sockets in every room and my main fuse box looks very similar to yours. My electricity meter also allows for dual tariff, although I won't be using this as the house is now gas-heated from a combi boiler.

Basically, I came here to ask exactly the same question as you! So if you've come up with a solution, please let me know what it was!!!

 

[knowall]

Hi, I have come across a similar installation, a 20a mcb on the off peak supply fed a wall mounted 20a room thermostat in the hall which fed 4x fcu's which supplied underfloor heating in each room rated at 500w !

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