Cluttered!

[JohnW2]

3 pages of arguing about the regs and no one has complimented the OP on his fairy lights!!

Even though not explicitly, you seem to have just done that

Kind Regards, John

 

[JohnW2]

It is very difficult to measure something that happens "instantaneously" at some point whenm the fault current is rapidly increasing.

We're not really interested in the precise speed of tripping. We're talking about the difference between magnetic tripping (milliseconds), if one is over the threshold for that to happen, and thermal tripping (which, as discussed, will take at least ~12 secs at currents just below the magnetic tripping threshold). That is a 'gross' difference, which does not require any fancy equipment to detect.

Kind Regards, John

 

[EFLImpudence]

I think you are missing the point.

They are required to trip at 3 to 5 times Ia.
I do not know what the manufacturer does; they may all make them to trip at 4 x.
That is, although we are not allowed to consider it, for a B32, a Zs of (230 / 128) x 0.95 = 1.71Ω will be satisfactory.

The same as RCDs must trip at 30mA, although they may trip at anything between 16 and 30mA and
within 300ms, although they may trip at 25ms.


Anyway, in domestic premises, how often is the Zs right on, or anywhere near, the limit?

 

[JohnW2]

I think you are missing the point. .... They are required to trip at 3 to 5 times Ia.

I'm not missing anything - but if you know for certain that that is what the Standard requires, then my question is answered.

Anyway, in domestic premises, how often is the Zs right on, or anywhere near, the limit?

Sure, and how often is (since Amd3) the supply voltage as low as 218.5V? However, that is not really the point, at least as far as regs are concerned. No matter how unlikely, the regs should be such that a magnetic trip will occur in response to a 'negligible impedance' L-CPC fault, even if the supply voltage is 218.5V and the Zs is 'right on the limit' (and "hard luck" to anyone whose supply voltage is 216.2V, as far as Amd3 is concerned ), shouldn't they?

Edit: Something relevant to this discussion which I've never thought of before has just occurred to me, so I'm going to start a new thread to discuss it.

Kind Regards, John

 

[SimonH2]

I did a job with those knock out hole joists. The Bulgarian chippies threw up the joists, not knowing about the importance of the knock out holes. So they did not line up.

Funnily enough there was an electrician at Mum's house to check on the electrics for the buyers. I decided to be there in case he started asking questions or looked like he was "making a job for himself". As it was he was a really nice chap, and as we chatted that very subject came up - how these are often installed in new builds without the holes lining up.