Wall Lights wired off Ring Final

[ADS]

Hi All,

Replacing two class 1 wall lights (lights only, not the circuit) for a customer.

They've been wired off the ring final via a switched fused spur.

It's a TN-C-S with final circuits protected by BS 3036s.

My question is this:

When measuring my Zs from the lighting points, do I compare it to the OSG figure for a 30A 3036 (which is 0.9, pg100) or do you take into account that the lighting spur is protected by a 5A 1362.

I haven't measured it yet, but I am just a bit worried that the 0.9 might not be achievable.

Thanks for your help.

 

[PC Electrics]

Compare it to the figure for a 13A 1362 (2.42ohms x80% = 1.94ohms).

Cos some dipstick could put a 13A in the holder.

 

[ADS]

Cos some dipstick could put a 13A in the holder.

You're right, didn't think of that - it's readilly accessible as well, right on the wall next to the telly.

So it's okay to base it on that figure as the 1362 is first in line (discrimination wise)?

If that's the case it gives me a bit more leeway.

Leads me to another question, though:

On the 'Minor Works' it asks for 'protective device for the modified circuit '- so do I put BS 1362 even though it's a spur and not a circuit in it's own right? - or do I go with the BS3036 30A?

Thanks.

 

[Lurch]

Cos some dipstick could put a 13A in the holder.

That is to some degree completely irrelevant. I don;t find the largest CPD that I can fit in a board and then put that down on the test cert when doing an EIC or any other cert.

 

[ADS]

That is to some degree completely irrelevant. I don;t find the largest CPD that I can fit in a board and then put that down on the test cert when doing an EIC or any other cert.

That's a good point - someone could swap out any protective device for a larger one.

I suppose he just means because of the ease with which 1362s can be swapped.

The regs only give Zs for two sizes of 1362 though, a 13A and a 3A, and there's quite a big difference in max Zs allowed -

I'll take the measurement and see - if it's less than 1.94 then happy days (if its less than 0.9 then even better)

Do I put BS1362 on the form though?

 

[PC Electrics]

An MCB just needs switching back on. A 1361 holder will only take the correct size fuse cos different ratings are different sizes. Your average Joe isn't very likely to delve into the board to swap them about.

A 1362 fuse needs replacing and a 13A is the same size as a 5A is the same size as a 3A. Easy done. You only need to think about how often you've come across the wrong wire rating in a 3036 holder for the proof.

Frankly, Lurch, I think your comment is unhelpful at best, puerile at worst.

What've I done to deserve such sniping?

ADS, you could label up the FCU as requiring a 3A fuse only and note this on your MWC (I do this for FCUs for heating systems).

 

[Lurch]

Frankly, Lurch, I think your comment is unhelpful at best, puerile at worst.What've I done to deserve such sniping?

It wasn;t sniping and I'm sorry you have taken offence. Clearly you've had a bad day and are taking it out on others.

I know why you said what you said, but that's not the way it works. I wouldn;t design a circuit on the assumption it will have an incorrect CPD on it, and neither would I test for such things.

 

[gselectrical]

Would agree with Lurch.

The size of fuse fitted at the time should be recorded on the cert. If somebody comes along and replaces it with a higher rating fuse, then that's not your problem.

Good point though, (about labeling the FCU.) Will do that in future with boilers!!

J

 

[tom1]

putting my head in the crossheirs but say its 1mm twin and earth from the fcu then does it matter if you put a 13 amp in

 

[androiduk2002]

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[Lurch]

putting my head in the crossheirs but say its 1mm twin and earth from the fcu then does it matter if you put a 13 amp in

It would depend on the rating of the connected equipment. The 1mm cable may well be fine, but the 3A connectors and .5mm flex may not. You would also need to check the manufacturers instructions as BS7671 says you need to follow these. Some will say they should be connected to 3A or 6A circuits only.

 

[tom1]

It would depend on the rating of the connected equipment. The 1mm cable may well be fine, but the 3A connectors and .5mm flex may not. You would also need to check the manufacturers instructions as BS7671 says you need to follow these. Some will say they should be connected to 3A or 6A circuits only.

yer i did think about the instructions.

it just got me thinkin as i have seen a few lights circuits on 10amp mcb