Recessed Lighting: Fire Rated Or Not?

[JohnW2]

Another possible cause of a "too low" reading (compared to the expected value for a ring wired in T&E with no paralell paths) would be if parts of the ring were wired in something other than T&E. For example flex has a "full size" CPC and I think NYY-J does too. 3 core SWA with a core used as CPC ends up with a "full-size" CPC and then the Armour on top of that.

That's true - but again, I would have thought, fairly unlikely.

Secure has, unfortunately, seemingly forgotten the actual numbers but, as I asked earlier, it would be helpful to know "how low" this resistance measurement is, and how the CPC resistance compared with that for L and N, since that might give us some idea of "what we are looking for". That information might address the suggestion you've made - in that if the CPC resistance was even lower than that for L and N, I don't think that could be explained by any cable type.

Kind Regards, John

 

[securespark]

Keep us posted!

As I said, it will probably be a good while, but I shall do my best to remember!

 

[plugwash]

Another one to add to the list of possibilities for unexpectedly low end to end earth readings.

Someone has moved the CU and used din rail terminals to extend the circuits.

 

[JohnW2]

Another one to add to the list of possibilities for unexpectedly low end to end earth readings. Someone has moved the CU and used din rail terminals to extend the circuits.

Maybe I'm being dim, but I think I need a bit to help in understanding what is in your mind!

Kind Regards, John

 

[TimboTwo]

Maybe I'm being dim, but I think I need a bit to help in understanding what is in your mind!

Kind Regards, John

I think he means earth DIN rail terminals connect to the rail and hence each other.

 

[JohnW2]

I think he means earth DIN rail terminals connect to the rail and hence each other.

He might - but I wouldn't have thought one would be trying to measure end-to-end resistance whilst the conductors were connected to anything, would one?

Kind Regards, John

 

[plugwash]

When a CU is moved, the circuits need to be extended somehow. Some electricians use a box containing din rail terminals for this.

Din rail earth terminals connect the earth conductor to the din rail, so this can end up commoning all the earths that pass through the extension box. If the next guy doesn't realise the extension box exists or doesn't realise that din rail earth terminals connect the earth conductors to the din rail they are likely to be left scratching their head as to why the end to end earth resistances for the circuits are so low.

 

[JohnW2]

When a CU is moved, the circuits need to be extended somehow. Some electricians use a box containing din rail terminals for this. .... Din rail earth terminals connect the earth conductor to the din rail, so this can end up commoning all the earths that pass through the extension box. If the next guy doesn't realise the extension box exists or doesn't realise that din rail earth terminals connect the earth conductors to the din rail they are likely to be left scratching their head as to why the end to end earth resistances for the circuits are so low.

Thanks. I understand now.

I remember that one of the first questions i ever asked ion an 'Electrics' forum was about extending all the circuits when moving a CU, and one of the things I recall being told was to be very careful not to do it in a way which would result in the CPCs of different circuits becoming inter-connected "because that would make subsequent testing a nightmare" - which advice sounded very sensible to me. However, it sounds as if your DIN rail earth terminals would create that very nightmare

Kind Regards, John