A few questions for a knowledgable electrician

[FunkyJive]

I'd be grateful if a practising electrician could help answer a few questions about wiring regulations, as I'm suspecting I've been considerably 'short-changed' on an electrical installation and want to get the facts straight before taking any action.

I have a large wooden outbuilding and recently had the domestic consumer unit upgraded as part of a professional installation to supply mains power to the outbuilding.

My original specifications for the installation were:

30A (min) supply, 40A if possible
Buried 10mm2 SWA twin and Earth
Total run from consumer unit to workshop termination: 15.5m

In-case it's relevant, I should add that the electricity meter is rated at 80A max.

I confirmed the specs with the engineer a couple of days before installation. However, he turned up with SWA cable clearly smaller than the 10mm2 we had agreed. I was informed that this was 4mm2 (passable I suppose for a 30A feed) but a visiting colleague reckons it is looks like 2.5mm2. Reluctantly, I accepted 4mm2 as I had booked a day off work and had further work scheduled the following day (requiring power to the workshop).

I was informed that it was not permitted for SWA cable to be routed into the house so conventional 2.5mm2 ring-mains cable was connected and routed inside wall-mounted PVC trunking the few metres from the outside wall to the CU in the kitchen cuppboard. Immediately I questioned this as I thought it was under-rated for 30A but was infomed that he could only give me a 16A-fused supply.

Question 1: Should approved SWA mains cables carry some BS or rating indication, as there's nothing on the black outer sleeve?

Question 2: As it is buried and routed in PVC conduit, what would be the maximum safe current for 2.5mm2 (assuming worst-case cable specs due to lack of type markings, etc).

Question 3: Is there some regulation limit on the maximum permissible supply current to wooden outbuildings, or could this be limited by the 80A-max electricity meter? Could the 16A fused supply have been to suit cheap/under-rated cable to the cost and convenience benefits of the installer - obviously at my cost?


Thanks in advance.

FJ

 

[ColJack]

yup, you've been fobbed off..
I hope you reduced the amount you paid to compensate for the less than quoted for materials? ( ie if he quoted £X for the spec you asked for and put in cheaper stuff then you only pay for the cheaper stuff not the original quote.. )

I'd have stood my ground and told him to either go get the stuff I asked for or to not bother comming back.. then re-scheduled the other works accordingly.. ( they either want the work or not.. )

he's bull****ing about the SWA not being allowed indoors.. he's just too lazy and / or incompetent to terminate it properly at the board..

 

[PrenticeBoyofDerry]

If you required 30A/32A supply to the outbuilding, over the distance of 15.5m.
If the cable was buried, using 3 core SWA cable 4.00mm will do that.
Why 10.0mm was originally decided I don't know and is that an issue?
You can route SWA internally, why 2.5mm has been jointed, heaven knows.
16A maximum supply total bollux!
Is the electrician registered with a scheme provider, what documents have you had, inspection, test, certification, building notice application?
Some cable will be marked but unfortunately not all is.

 

[sparkticus]

30A (min) supply, 40A if possible
Buried 10mm2 SWA twin and Earth
Total run from consumer unit to workshop termination: 15.5m

Not that there is anything wrong with your choice but what motivated your choices above?

I confirmed the specs with the engineer a couple of days before installation. However, he turned up with SWA cable clearly smaller than the 10mm2 we had agreed. I was informed that this was 4mm2 (passable I suppose for a 30A feed) but a visiting colleague reckons it is looks like 2.5mm2. Reluctantly, I accepted 4mm2 as I had booked a day off work and had further work scheduled the following day (requiring power to the workshop).

Understood but better nothing at all than something that is wrong.

I was informed that it was not permitted for SWA cable to be routed into the house so conventional 2.5mm2 ring-mains cable was connected and routed inside wall-mounted PVC trunking the few metres from the outside wall to the CU in the kitchen cuppboard. Immediately I questioned this as I thought it was under-rated for 30A but was infomed that he could only give me a 16A-fused supply.

-SWA cable can be used inside.
-2.4mm can not carry 30A
-Why did you accept 16A when you wanted more?

Question 1: Should approved SWA mains cables carry some BS or rating indication, as there's nothing on the black outer sleeve?

They do need to meet standards. Are you sure there is nothing at all on it? What about BS5467 or IEC 60502?

Question 2: As it is buried and routed in PVC conduit, what would be the maximum safe current for 2.5mm2 (assuming worst-case cable specs due to lack of type markings, etc).

Just over 20 amps.

Question 3: Is there some regulation limit on the maximum permissible supply current to wooden outbuildings, or could this be limited by the 80A-max electricity meter? Could the 16A fused supply have been to suit cheap/under-rated cable to the cost and convenience benefits of the installer - obviously at my cost?

There is no limit to wooden buildings in the context of your question.

Without knowing a lot more about your installation I would only be guessing on the rest of your questions. What is true is that the electrician should have consulted with you first before supplying less than you had apparently agreed with him.

Did you receive and electrical installation certificate from him and a building control compliance document in the post within 2/3 weeks after the work was complete?

 

[holmslaw]

..

 

[FunkyJive]

Thanks gentlemen for your replies.

I was led to believe that the 16A limit was due to regulations, and the reason why I didn't insist on giving me what I had asked for. I'm technically savvy, but electrical wiring regulations are a different matter. Regrettably, I had to trust to what he told me and advised - the down-side of trusting "professionals".

He is a registered electrician, and I have since received the relevant certification. It mentions 2.5mm cable (this I suspected was the internal/lowest spec'd part of the wiring running in the internal trunking), although the original job post remains on MyHammer.

My particular field is electronics, and the workshop office will not only have heater/air conditioner, but also test instruments and computing equipment, so just a small step to avoid the depths of dips and spikes during working switching surges (etc). I also took the view that the installation should be future-proofed as-well, hence the oversized cable.


All the best,
FJ

 

[holmslaw]

..

 

[sparkticus]

Did you have a written agreement with him that he would provide more than he actually delivered?

These sites such as myhammer are awful in my opinion. They encourage quoting without actually seeing the details which will always go wrong. They play lip service only to actually making a proper site visit before quoting.
They also promote cowboys despite the fact that they "check" qualifications.

If you have a heater, lighting, sensitive test equipment and computing equipment on the end of that 2.5mm cable then then expect some voltage drop plus possible trouble with harmonics from the PC power supply.

 

[FunkyJive]

Thanks for your reply.

Regrettably, the 16A compromise was simply because that's what I was told was all I could have - from a "trained professional".

The cable size however was an agreed compromise because I was told it was 4mm2 - sufficient for the pseudo-16A regulation limit.

I guess the biggest mistake I made was not to question this so-called professional every step of the way, and inspect the cable with calipers against sizing charts before installation.

As the job is still up on MyHammer, perhaps this will give me recourse?


All the best,
FJ

 

[sparkticus]

As the job is still up on MyHammer, perhaps this will give me recourse?

Contact the electrician. Tell him that after research what he provided does not meet your original expectations and agreement. Ask him to put it right.

If he refuses then provide him with an appropriate review via the myhammer site then contact his registration body and ask them to review the design for compliance with the application.

 

[PrenticeBoyofDerry]

Plus if the SWA cable is 4.00mm there is no reason why the 2.5mm cable jointing this to the CU, can not be changed to the 4.00mm it should be, then your protective device rating can be upgraded.
What scheme are they a member of? there is a complaints procedure.

 

[FunkyJive]

The installer is a member of NAPIT.

I'm certainly going to check that cable for size with my verniers (once I can find them).

Definitely no markings of any kind anywhere on the outer sleeve of the SWA cable, which would surprise me if allowed in this age of strict safety regulations and compliance

Perhaps that's the first thing I could focus on should I need to complain to NAPIT - If non-compliant it'll HAVE to be replaced then


All the best,
Brendan

 

[sparkticus]

The installer is a member of NAPIT.

I'm certainly going to check that cable for size with my verniers (once I can find them).

Definitely no markings of any kind anywhere on the outer sleeve of the SWA cable, which would surprise me if allowed in this age of strict safety regulations and compliance

Perhaps that's the first thing I could focus on should I need to complain to NAPIT - If non-compliant it'll HAVE to be replaced then

Look at your electrical certificate. You should see the R1+R2 resistance value on the cert. This will be the live & earth conductor DC resistance in series (linked at one end for the sake of the test)

You could just post the result here or look up the expected resistance based upon length of cable & CSA. You will soon know if it's 2.5mm or 4mm in a significant part of the cable run. If he has used the SWA outer armour as an additional earthing conductor (which he should have done) then the readings will take a bit more interpretation but still possible.

Also, have a look at the Zs reading for the circuit and subtract the external Ze from it.

 

[FunkyJive]

Thanks Sparkticus - good idea
Sorry - didn't pick up on this before my last post.

Here's the quoted stats...

R1+R2 = 0.43

Allowing for the buried drop (approx 2 x 0.5m) and the spare cable inside the workshop, this would make the total lengths...

3.5m of 2.5mm2 inside the house, and 15m of SWA mm2

Zs = 0.45
Ze quoted at "0.80 max" Ohms


All the best,
FJ

 

[FunkyJive]

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?


All the best,

FJ