Pretty sure my cps assessor was wrong

[AndyL]

So I had my yearly assessment today with my friendly local engineer. He was fair enough but there was 2 points he pulled me on that have niggled me because I am sure I was right.
Would like some other opinions please.

Firstly a 60 Amp TN-S supply to a domestic property. ... what is the minimum size tails?
Secondly do you guys tick the double insulated box in S.O.I because of the meter tails?

I'll let you know who was in each corner after a few replies so as not to sway your decision ( as if it could)

 

[Leesparkykent]

They are insulated and sheathed not double insulated so I wouldn't tick double insulated box and 16mm tails would be fine. What's your thoughts?

 

[ImpededLoop]

First one depends on the load that you have calculated for the installation.

Second one I don't agree with. Tails are insulated and sheathed, same as twin and earth...

Edit: Speedy Lee beat me to it!

 

[AndyL]

They are insulated and sheathed not double insulated so I wouldn't tick double insulated box and 16mm tails would be fine. What's your thoughts?

My thoughts exactly

 

[Ian1981]

Did the assessor say you had to install 25mm tails by any chance?

 

[Leesparkykent]

What scheme was it?

 

[AndyL]

Yes he said 25mm and was quoting on site guide, I was pretty dumbfounded

 

[buzzlightyear]

double installation means class 2 fittings

 

[Ian1981]

I installed 25mm tails to a db in the garage around 1 meter from meter/cut out.
Was told the db could be hit by a larger car (whatever that means) and I should have moved the db with a switch fuse isolator and coming out to other side of garage with a 35mm swa 2core and 16mm cpc.
I asked my QS why 35mm as volt drop wasn't an issue, he said had better mechanical strength haha!!

 

[Richard Burns]

Theoretically the minimum size tails for a 60A fuse would be 10mm² as this can take 64A when clipped direct (and tails are often in free air). I would tend to use 16mm² as the fuse may often be 60/80A labelled so I could not be sure of the protective rating.

For the schedule of inspections the protective measure for meter tails is ADS, by chance the cable could be classified as equivalent to double insulated, but the sole protective measure is not double insulation, it is ADS. If if it were double insulation then there would be no fuse required and no earthing required.

Now worried about the quality of the assessors if their reference books are just the OSG.

 

[westward10]

Double insulation means TWO layers of insulation or a single layer of reinforced insulation so in your case it doesn't apply. Those conductors have one layer of insulation and an overall sheath for mechanical protection.
Need to stand your ground with these people.

 

[Octopus]

16mm tails on existing install... 25mm tails on a new install (both with 60A main fuse)

i.e. I wouldn't upgrade the 16mm tails to 25mm on an existing install with a 60A fuse.

 

[Leesparkykent]

what CPS was it?

 

[westward10]

My thoughts on clipped direct is that it may apply between the head and meter where there is no enclosure, enter them into a board they are no longer clipped direct and should be down rated.

 

[AndyL]

Thanks for all the responses, it was an niceic domestic installers assessment

 

[Ian1981]

My thoughts on clipped direct is that it may apply between the head and meter where there is no enclosure, enter them into a board they are no longer clipped direct and should be down rated.

What reference method would you use for down rating them?

 

[AndyL]

My thoughts on clipped direct is that it may apply between the head and meter where there is no enclosure, enter them into a board they are no longer clipped direct and should be down rated.

But surely all clipped direct cables eventually go in to an enclosure

 

[westward10]

What reference method would you use for down rating them?

I would use the column from 4D1A for cables contained in conduit or trunking, Reference B.

 

[westward10]

But surely all clipped direct cables eventually go in to an enclosure

Not between the head and meter they don't.

 

[Dave OCD]

25mm tails, what's the point when the incoming supply is 16mm.