EICR For Dad's Widow

[securespark]

Cabling is not rubber.

Did a quick IR at ceiling rose and got a squeak over 1Meg.

I suspect he has:

tested the fixing screws at the hall switch and got nothing, so assumed no earth.

tested the IR without unplugging appliances or removing lamps and got low readings (which you would expect) and called it faulty wiring.

He apparently took less than an hour and charged a ton fifty.

 

[securespark]

I know the area well and it will most likely be stripped after sale for complete renovation.

But it just annoys me that the EICR does not reflect the true condition.

 

[scousespark]

Looks a typical drive-by. First impression is the installation has passed its use by date. Couple of quick tests (probably done as you suspect) to back up this belief. Decides not worth much more effort than to fill in report. See what he comes back with when he replies to your email.

 

[securespark]

Cheers.

 

[securespark]

Just researching BS67. It was around in 1955, at least, as it appears in the 13th Edition.

But then I have found references to BS67: 1969 and BS67: 1987.

I am wondering if previous incarnations of BS67 had the same 16A standard?

 

[flameport]

First version was in 1914, then 1929, 1938, 1969 and 1987.
1987 is the current version.

I don't have access to any of the older ones, so their contents remain a mystery.

 

[securespark]

This has rumbled on a bit. I went back to check the hall light switch (which I think he tested for an impedance reading) and found it was a pre 14th Edition back box with Nylon screw lugs. Got a decent reading off the box.

Going back again as I forgot (brain is really shot!) to do some more IR testing.

When was 1.5 CPC introduced in 2.5 T&E?

 

[JohnW2]

... When was 1.5 CPC introduced in 2.5 T&E?

We've discussed that before, and I think the consensus belief was that the answer was "early 70s" - but, having just had a quick look around, it's not as easy as I would have expected to find a definitive answer.

Kind Regards, John

 

[Adam_151]

When was 1.5 CPC introduced in 2.5 T&E?

From about 1980 onwards. It had been 2.5/1 since things went metric in 1971 then went up in size in 1980
Looking at a school built in '71 at the moment, one leg of a ring from board is 7/029 with 3/036 cpc, the other is 2.5/1

 

[securespark]

Thanks, John/ Adam.

John: I'm sorry, I forgot there had been a discussion about it.

I too have looked extensively on the interwebby and have not found anything definitive yet.

My only two points of reference are these:

1. The 15th Edition regs I got issued in College says (of the 14th Edition) "Reprinted in Metric units 1970."

2. My Mum's house was rewired in 1982 (neither of us can remember what month) and the guy used 2.5mm²/1.0mm².

These dates are not quite as helpful as would first appear;

I don't know when in 1970 the Metric edition was published (it could have been 31/12/70). Added to that, there would have been a changeover period (You can use Imperial up to NN/NN/NN but thereafter must use Metric).

But at least we know that Metric cable can't have been installed before 1970 at the very earliest.

There would have been a similar period for the changeover from 2.5mm²/1.0mm² to 2.5mm²/1.5mm². Judging by later changes, that changeover period could be as much as 2 years.

My first work as an apprentice was in the Summer of 1983, under the "extended" 14th Edition and I did drag in an awful lot of 2.5 T&E, but it was first fix only and I didn't know what size the CPC was.

 

[securespark]

I found this tucked away in a drawer of my filing cabinet under "Narnia"....

 

[securespark]

I'm not sure 1975 is accurate.

Assuming the spark that rewired Ma's gaff was installing the "old" 2.5 within the allowed timeframe, 1980 sounds like it could be right.

There must be reference to the CPC size in the regs, I shall continue looking......

Flameport, we may need your assistance!

 

[JohnW2]

There must be reference to the CPC size in the regs, I shall continue looking......

On reflection, I think that we are probably all being a bit silly in thinking this is a regulatory matter, because, having thought, I don't think it is.

To the best of my knowledge, nothing in BS7671 (either now or ever) says what size of CPC should be in any particular size of T+E.

The only requirements are (a) that Zs of a circuit is sufficiently low for ADS (and even that is essentially irrelevant in a TT installation), and (b) that the CPC is of adequate size to withstand the PFC until the fault is cleared - determined either by adiabatic calculation (per 543.1.3) or, for the lazy, Table 54.7 (although the latter would lead to 2.5mm² T+E having to have a 2.5mm² CPC).

So, unless I'm missing something, I think that, provided only that those two requirements were satisfied, the use of 2.5/1.0 mm² T+E would be compliant with BS7671, even today.

Kind Regards, John

 

[JohnW2]

.... The only requirements are (a) that Zs of a circuit is sufficiently low for ADS (and even that is essentially irrelevant in a TT installation), and (b) that the CPC is of adequate size to withstand the PFC until the fault is cleared - determined either by adiabatic calculation (per 543.1.3) or, for the lazy, Table 54.7 (although the latter would lead to 2.5mm² T+E having to have a 2.5mm² CPC).

On further reflection, unless I'm doing something wrong, it would seem that in the case of a TT installation, the minimum required (per BS7671) CPC size for any size of T+E would be tiny.

Any credible size of CPC would satisfy requirement (a) - since, even taking regard of "Cmin", Zs only has to be below about 7,283Ω for a 30 mA RCD to operate. As for requirement (b), if one assumes the worst case of a supply voltage of 253V and an unusually low (for TT) Zs of 10Ω (hence PEFC of 25.3A) and an RCD disconnection time of 40 ms (for PEFC = 5*In=150mA), then, with k=115, an adiabatic calculation seems to indicate that the minimum CPC size would be about 0.044mm².

Is there something wrong with my calculation/reasoning?

Kind Regards, John

 

[plugwash]

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)?