Does this comply.... thinker of the day!

[Darkwood]

Im bored so I thought Id get your heads thinking and take note who's posting this so Im not after a straight answer yes or no! Back your comments up please with regulations.

I have a small house and they complain when a lamp blows the bs3036 5amp wire blows and they have to replace it (nuisance tripping/blowing), the lighting is on 1 circuit and covers 5 fittings - kitchen, room, stairwell, bathroom and bedroom.. they are adamant to keep using their stock of filament lamps so for the sake of this debate we are not replacing the style of lighting nor upgrading the board or fuses...

Can i fit a 15amp or 30amp fuse wire in the lighting fuse carrier noting that under the circumstances the Zs is still in compliance and still be within BS7671 and not breaching any regs.

Remember alternative solution are off the table this is theoretical to test your understanding of the regs.

 

[SJD]

What size cable is the lighting wired in, and what reference method?

 

[Richard Burns]

Hmm I would say that without any reference that you would not be able to get a fully compliant system there.
The 30A fuse wire is out because the maximum for ES/BC is 16A.
I will leave it at that for the moment.

 

[NickD]

Just for clarity, you are asking if you can put 15A / 30A fuse wire in the existing carrier? You're not asking if you can change the carrier and if necessary the receptacle to a 15A / 30A rated/labelled one?

 

[Darkwood]

To rid the idea the carrier will be undersized which isn't the aim of my question you can exchange the carrier to meet the rating of the fuse wire but this wouldn't be an issue either way tbh.

 

[NickD]

OK, I was just thinking if you put 15A / 30A fuse wire in a carrier probably labelled and colour-dotted for 5A, you'd probably get off with crucifixion. For a first offence, anyway. The switches are, surprisingly, rated to 15A / 30A I take it?

 

[Darkwood]

The rating of the accessories and carriers is irrelevant as will be made clear later...

Ill drop in a key point that has not been asked .. the lighting is the original cable which is tested fine and is 1mm t&e.

 

[nickblake]

this all depends on a few factors cable size factors installation methods etc now if its a 1.5mm cable clipped direct maximum cable rating is 20 amps so 15amps mmm looks ok but there is the correction factor for bs3036 fuse of 0.725 so if you take it with out any other factors it would be 15 / .725 = 20.69 so over the maximum rated now if you add say 3 cables you have a grouping factor of 0.70 that would then become 15/.70 x .725 = 29.42 so my answer would be no

 

[Richard Burns]

Without going too far into it to have a lighting circuit as you describe, assuming it was correctly wired at the time of installation, and making an alteration by changing the rating of a BS3036 fuse to 15A you would not be able to comply fully with the 17th edition of the wiring regulations (as amended).
There are considerations of full compliance and partial compliance and also considerations of what is excepted and what is permitted.
I am also not certain that this would definitely resolve the problem, although it should alleviate it to a very large extent.
I will put a reg number in for the 30A fuse wire as 559.6.1.6.

 

[Redvanman]

I could have misunderstood but here goes.
if you have fully tested circuit and Zs is under the new rated fuse, the earth arrangement ok, the switches and light fittings rated to the new fuse rating then I'd say you could possibly do it with a note on the board explaining what you've done as the circuit wouldn't pull more than the cable rating
but personnally I won't but it's abit like a bussbar arrangement
Have I got what your on about?

 

[Richard Burns]

For fault current on a 15A BS3036 I calculate the csa for adiabatic compliance would be ~0.5mm² or less, so that would be covered (543.1.3)

 

[Octopus]

What cu is it? Could you try a 10a mcb?

 

[spark 68]

this all depends on a few factors cable size factors installation methods etc now if its a 1.5mm cable clipped direct maximum cable rating is 20 amps so 15amps mmm looks ok but there is the correction factor for bs3036 fuse of 0.725 so if you take it with out any other factors it would be 15 / .725 = 20.69 so over the maximum rated now if you add say 3 cables you have a grouping factor of 0.70 that would then become 15/.70 x .725 = 29.42 so my answer would be no

Knowing DWs 'penchant' (lol) for overload protection may be omitted due to the nature of the load, I would say that 15A would be permitted due, as RB pointed out earlier, 16A being the max for BC/ES fittings, provided the Zs complied of course.
I would have to look deeper though to give a definitive answer.

 

[Darkwood]

Hmm I would say that without any reference that you would not be able to get a fully compliant system there.
The 30A fuse wire is out because the maximum for ES/BC is 16A.
I will leave it at that for the moment.

First point to Mr Burns - now lets just say then following this reg' (559.6.1.6) you derated the 30amp to 15amp would we now comply...

As said in the OP Murdoch - all alternatives for the theoretical point of the question are off the table.

 

[Richard Burns]

OK next consideration which I think is outside of what you are meaning since spark 68 has gone for 433.3.1 (ii), is later modification to the regs that make the existing circuit non compliant anyway, but I may not have been told about other protective devices!

 

[Richard Burns]

What cu is it? Could you try a 10a mcb?

If we could use MCBs then I would be aiming for a different solution that would meet more of the regulations, but would be no more compliant than the suggested modification.

 

[NickD]

For fault current on a 15A BS3036 I calculate the csa for adiabatic compliance would be ~0.5mm² or less, so that would be covered (543.1.3)

Based on what fault current have you calculated that, please? Needs to be the PFC at the origin doesn't it (neglecting any resistance within the CU)? To handle worst-case of a screw going through the cable within a foot of the board? And we don't know the PFC.

30A does not protect the cable from overload, nor does 15A unless entire run is reference method C, so we would be reliant on downstream overcurrent protection of which there is none unless you count the lamps, and there is nothing to stop someone adding a ton more light fittings, so it doesn't comply....?

<Edit: question is only about whether existing installation strictly complies with regs so scratch the bit about extra fittings....mea culpa...>

 

[Darkwood]

Various points to look at here....

Mr Burns saw the fact that id specified incandescent lamps and your typical lamp in domestic of this nature will be subject to regulation 559.6.1.6 so a 30amp wire is out of the window and won't comply.

Thus we drop down to 15amp with the same question ...

Note rating of switches etc are only subject to the load they are switching and not the fuse that covers them or we would have a lot of non compliant installs out there.

Install is your basic drilled through joists buried in plaster and insulation in loft - just to clarify although it changes little.

Nick your last sentence is key to part of it...

and there is nothing to stop someone adding a ton more light fittings, so it doesn't comply....?

 

[Richard Burns]

Based on what fault current have you calculated that, please? Needs to be the PFC at the origin doesn't it (neglecting any resistance within the CU)? To handle worst-case of a screw going through the cable within a foot of the board? And we don't know the PFC.

...>

I did the pathetic calculation of 15A BS3036 will blow in 0.1s with a fault current of 180A from the time current graphs. Based on that the minimum csa is 0.49mm². However even if the fault current is higher, as one would hope it would be, the time decreases (but is off those graphs) and should make it a lower csa, if I have it right!

 

[nickblake]

it could boil down to junction boxes if the fuses are BS3036 then you could well have an abundance of 5 amp junction boxes up in the loft so the first one could have the complete load on it