EICR For Dad's Widow

[JohnW2]

It would be interesting to know where the "conventional" sizes for CPCs in UK T&E come from. Are they just a de-facto thing? or are they mentioned in some standard (perhaps BS 6004)?

Good question. As I said, there certainly seems to be no mention of it in BS7671 - such that, as I said, any CPC size which satisfies the two requirements I mentioned should be compliant with BS7671. However, as you imply, .cable Standards' may well mandate the CPC size, and therefore restrict what is actually available.

I would assume that the sizes on offer were originally decided upon on the basis that they usually resulted in 'the two requirements of BS7671' being satisfied. They obviously 'got it wrong' with 2.5/1.0 mm² (in the context of BS3036 fuses), and therefore had to make the change.

Kind Regards, John

 

[securespark]

Yes, 1.0mm² CPC on a ring final is OK with circuit breakers, but not with 3036 fuses.

I think the sizes were already pretty much sorted when the imperial cables were formulated. They just chose the metric equivalent. But in the case of the size used for ring finals, I believe the CPC was equivalent to 1.29mm². I guess they swung the wrong way.

 

[JohnW2]

Yes, 1.0mm² CPC on a ring final is OK with circuit breakers, but not with 3036 fuses.

Indeed - and, as I said, BS7671 does not seem concerned about the actual CSA of the CPC (and probably never has done), provided only that it satisfies the Zs and adiabatic requirements.

I think the sizes were already pretty much sorted when the imperial cables were formulated. They just chose the metric equivalent. But in the case of the size used for ring finals, I believe the CPC was equivalent to 1.29mm². I guess they swung the wrong way.

Indeed.

Kind Regards, John

 

[securespark]

I think Flame has gone on holiday.....!

 

[JohnW2]

I think the sizes were already pretty much sorted when the imperial cables were formulated. They just chose the metric equivalent. But in the case of the size used for ring finals, I believe the CPC was equivalent to 1.29mm². I guess they swung the wrong way.

Thinking about it, that was perhaps a little silly (as they subsequently realised!). Since 'the next (metric) size up' was 1.5mm² then one would have expected them to 'round up' (to 1.5mm²) any 'converted figure' that was 1.25mm² or greater!

Kind Regards, John

 

[securespark]

According to a post in another leccy forum, 2.5/1.0mm² went out with the 14th Edition.

So now we're in that strange time-warp that is the "extended" 14th Edition where it was agreed that due to the complexity of the 15th Edition, published 1981, its mandatory use could be delayed until 1 January 1985, before which time use of the 14th Edition was allowed.

So I guess in theory, 2.5/1.0mm² could have been in use up to the end of 1984.

But the reality is that manufacturers would have known about the proposed change and all the "old" 2.5 cable would have been sold off years before that date.

 

[securespark]

I have contacted the IET to see if they can shed some light on this for us.

 

[securespark]

I have a couple of IR readings that pretty much prove he just Meggered stuff without unplugging appliances or lamps or disconnecting at the board.

Got a 250 Meg IR reading L-E on downstairs sockets. NE is very low but the fusebox is a wooden Standard Wylex and absolutely stuffed so it's a mare.

The GF sockets (at least those in the kitchen) are wired in 2.5/ 1.0.
Got 0.39 , 0.40 and 0.86 end to end so doesn't quite add up.

Tried mocking something up with spare cable at home, but have not got enough to glean meaningful readings.


The number for 1.5 CPC is 1.67 X that of the line conductors. Should be 2.5 X for 1 Milli.

 

[JohnW2]

Got a 250 Meg IR reading L-E on downstairs sockets. NE is very low but the fusebox is a wooden Standard Wylex and absolutely stuffed so it's a mare.

Fair enough, but you surely need an explanation for the very low N-E figure - a stuffed wooden fusebox is obviously not, in itself, an explanation

The GF sockets (at least those in the kitchen) are wired in 2.5/ 1.0. .... Got 0.39 , 0.40 and 0.86 end to end so doesn't quite add up.

As you say, those figures don't really add up - your readings are almost exactly half-way between what one would expect of 2.5/1.0 and 2.5/1.5. Are you absolutely certain that it is 2.5/1.0? Have you perhaps discovered a hitherto unknown 2.5/1.25?

Kind Regards, John

 

[securespark]

It is definitely a 1 Milli CPC.

I can only think the circuit is made up of mixed cable sizes.

 

[JohnW2]

It is definitely a 1 Milli CPC. I can only think the circuit is made up of mixed cable sizes.

Indeed - if about half were 2.5/1.0 and the other half were 2.5/1.5, then the results you got would be exactly 'as expected'.

... but what about that 'very low' N-E IR - that surely needs to be investigated/explained, doesn't it?

Kind Regards, John

 

[securespark]

The stuffed fuse ox was not an explanation for the low IR, but a reason why I didn't want to get involved in pulling it to bits in order to find the right neutrals.

 

[JohnW2]

The stuffed fuse ox was not an explanation for the low IR, but a reason why I didn't want to get involved in pulling it to bits in order to find the right neutrals.

Fair enough!

Kind Regards, John

 

[securespark]

OK.

Was there when he came back today.

Bit embarrassing.

Last time, I checked many roses/ fittings and switches for earth and they all had one.

He found two switches (controlling roses I checked had an earth) that did not.

He got some improvements in IR.

I shall await his new cert.

 

[securespark]