A few questions for a knowledgable electrician

[martinxxxxxx]

I am pleased to read it is routed in conduit, he can take the effin stuff away and give you what you spec'd.

Forget the other avenues this is one for Trading Standards. BTW did you sign a right to cancel form as part of the contract (or any contract) if not then he is in very poor shape to defend your claim indeed.

I hate this sort of thing, gives all tradesman a bad name.

If you ask for 10mm2, and it meets or exceeds what you need. Then that it is what you should get. It is your money and if you want to add future proofing that is your call (with the way copper is going up in price) it could be a good investment to do it now.

Get back to him first, if he is not willing to put things right the plough on to Trading standard

 

[sparkticus]

Looks like 2.5mm2 SWA is confirmed

Doing the figures with loop resistance:

3.5m of 2.5mm2 = 0.047R
15m of 4mm2 should give me 0.126R

Had he installed 4mm2 SWA then I calculate the expected loop resistance (ignoring contact resistance, etc) to be 0.126 + 0.047 = 0.173R total.

Quite a way off for supposed 4mm2 unless my numbers are way out?

Yes very unlikely you have 4mm CSA cable in the 15m run.

 

[sparkticus]

Get back to him first, if he is not willing to put things right the plough on to Trading standard

Yes that might be the more appropriate rout.

 

[JohnW2]

R1+R2 = 0.43
... 3.5m of 2.5mm2 inside the house, and 15m of SWA mm2
Zs = 0.45 Ze quoted at "0.80 max" Ohms

Looks like 2.5mm2 SWA is confirmed
Doing the figures with loop resistance:
3.5m of 2.5mm2 = 0.047R
15m of 4mm2 should give me 0.126R
Had he installed 4mm2 SWA then I calculate the expected loop resistance (ignoring contact resistance, etc) to be 0.126 + 0.047 = 0.173R total.
Quite a way off for supposed 4mm2 unless my numbers are way out?

Hmmm. I'm not sure that you can rely on those figures. That (R1+R2) of 0.43Ω seems rather high (and therefore perhaps not trustworthy), even if he used 2.5mm² SWA and even if (fairly unlikley) he did not use the armour as well as third core (assuming their was one) as CPC. By my quick reckoning (always very fallable!), 3.5m of 2.5mm² T&E (with 1.5mm² CPC) plus 15m of 2.5mm² SWA (using just a core as CPC), ought to give an (R1+R2) of around 0.35Ω; if (as is most commonly the case) the armour was used as well, it would be a fair bit lower.

A Zs of 0.45Ω is also pretty unlikely if (R1+R2) really were 0.43Ω, since it seems to imply a Ze no greater than 0.02Ω. I therefore again 'wonder' about the reliability of the figures you've been given!

You say your colleague thought that the SWA looked more like 2.5mm² than 4mm. He may, of course, be right, but one needs a fairly good eye to tell the differeence - 3-core 2.5mm² SWA has a diameter of about 13.8mm and 4mm² about 14.9mm.

Kind Regards, John.

 

[FunkyJive]

Many many thanks guys - Whilst sadly confirming my suspicions, your informed comments and suggestions have truly been invaluable.

It is a real shame that occasions like this cast doubt on all diligent and trustworthy professionals. It's that "one bad apple in a barrel" thing.

Incidentally Martinxxxxxx - No contract of any kind (including a right-to-cancel) was ever signed. The only thing detailing the actual specifications was on MyHammer, and the specification and price agreed by the engineer via the same site. The Emailed quotation confirmed the price, but merely stated "SWA cable" (not the size or current) although everything else was correct. I missed that one, but certainly doesn't state 2.5mm


EDIT: Thank you John for your thoughts and comments. My colleague (a former industrial electrician) was observing the insulation and bared/visible cable terminated at the Neutral bus bar in the workshop CU. i.e. 7 strands of something thinner than expected


Thank you again.

FJ

 

[sparkticus]

3.5m of 2.5mm² T&E (with A Zs of 0.45Ω is also pretty unlikely if (R1+R2) really were 0.43Ω, since it seems to imply a Ze no greater than 0.02Ω. I

Yes I also noticed the Zs slightly higher than R1+R2 and the Ze possibly at 0.02 which is unlikely on a TN-S supply which I assume it is from the 0.8 by enquiry.

Of course, he may not have a well calibrated instrument and/or took no care over measurements - hard to tell. If there is an RCD at the source then he may have optained Zs on low current which may account for a less than accurate reading.

For all said I have to say I would lean towards the SWA being 2.5mm rather than 4mm.

 

[JohnW2]

EDIT: Thank you John for your thoughts and comments. My colleague (a former industrial electrician) was observing the insulation and bared/visible cable terminated at the Neutral bus bar in the workshop CU. i.e. 7 strands of something thinner than expected

Ah, right - yes, it's fairly easy to distinguish 2.5mm² from 4mm² if one is actually looking at the cores - even I could probably get that right, but I would have no confidence in my view on 2.5 vs 4 based on the overall diameter of the cable alone - which is obviously what I thought you meant.

The figures you've presented are certainly too high for 4mm² SWA - but, as I said, they also seem too high for 2.5mm² - so I wonder if you can trust them at all!

Kind Regards, John.

 

[PrenticeBoyofDerry]

If we started looking at the given resistance of the readings of R1+R2 and calculated them assuming that part of the installation was 3.5m of 2.5mm T&E, the tabulated calculation from the reading could well leave you with 1.5mm cores for the SWA. Makes me now wonder is that why 16A device was installed.

 

[sparkticus]

If we started looking at the given resistance of the readings of R1=R2 and calculated them assuming that part of the installation was 3.5m of 2.5mm T&E, the tabulated calculation from the reading could well leave you with 1.5mm cores for the SWA. Makes me now wonder is that why 16A device was installed.

Good point.

 

[JohnW2]

If we started looking at the given resistance of the readings of R1+R2 and calculated them assuming that part of the installation was 3.5m of 2.5mm T&E, the tabulated calculation from the reading could well leave you with 1.5mm cores for the SWA.

Indeed, although I didn't go quite as far as saying that, as I said the (R1+R2) is even too high for 2.5mm² SWA, so that's certainly a possibility. However, given the reported (R1+R2) and Zs, I really don't think I have much confidence in the reliability of any of the figures we're being shown. If the Zs were correct (but the (R1+R2) wrong) then 2.5mm² SWA, or even 4mm² SWA, could be credible.

Kind Regards, John.

 

[riveralt]

Many many thanks guys - Whilst sadly confirming my suspicions, your informed comments and suggestions have truly been invaluable.

It is a real shame that occasions like this cast doubt on all diligent and trustworthy professionals. It's that "one bad apple in a barrel" thing.

As a NAPIT member myself - I too am appalled. I take it you have checked that he is still a member of the scheme here. http://www.napit.org.uk/fastSearch.asp
Trading Standards will require that you have gone down this route...
Contact the Electrician - highlight the discrepancies and ask him to put them right. If that fails..
Contact NAPIT here: http://www.napit.org.uk/consumerComplaints.asp

Incidentally Martinxxxxxx - No contract of any kind (including a right-to-cancel) was ever signed. The only thing detailing the actual specifications was on MyHammer, and the specification and price agreed by the engineer via the same site. The Emailed quotation confirmed the price, but merely stated "SWA cable" (not the size or current) although everything else was correct. I missed that one, but certainly doesn't state 2.5mm

NAPIT require Cancellation rights be given to customers for any job over £35. In failing to do so he has broken the criminal law....

Cancellation Rights
31.For all work over the value of £35.00 completed in the
domestic market, members must provide the
householder with a seven working day ‘cooling off
period’ form, as required by The Cancellation of
Contracts made in a Consumer's home or place of
work etc Regulations (2008). The cooling off period
form must provide details of how the contract can be
cancelled, together with name and address of the
person to contact.

 

[sparkticus]

Yes, going on just the readings from the cert to verify cable CSA is always a bit hit & miss. If the Zs and indeed the R1+R2 where taken with a socket adapter (very typical to do so) then you may or may not have the socket switch and other contact resistance issues clouding the picture. The main goal of the cert (for what we are looking at) is to ensure limits are not breached. There are times when you can nail down the actual CSA from the cert with some accuracy but not on this occasion.

The final confirmation should be easy to determine from looking at the bare ends at the shed end of the circuit and/or performing an R2 measurement with a descent wonder lead (nulled out of course)

 

[sparkticus]

As a NAPIT member

So you are the one NAPIT member

 

[SimonH2]

Just one other point. If the electrician got the OP to accept the changes by stating "that's what the regs say" then he can't use customer acceptance of the changes as a get out. It sound very much like he's lied to the customer and you can't expect a non-qualified customer to know the details of all the regs.

 

[riveralt]

As a NAPIT member

So you are the one NAPIT member

Yep my £400 yearly subscription is going to be stretched on this one