3Kw-9KW Water Heater Cable size ?

[Robinson]

Hi Got situation with one of these heaters. pretty juicy. It does heating & Water. 3-9kw

http://accl.onwirral.net/Downloads/Heatrae_Amptec_Installation_Guide.pdf

Its going to be wired Y Plan but issue is that its being asked of me to put 10mm cable in. Which i would agree on is suitable
BUT what i suggested is that it could be possible to use 6mm.

The cable run is no more than 4 metres from board. there large boxing for cable to lay in. no insulation So by OSG this is fine YES NO?
I mean the cable can take what 46/47 Amps Clipped Direct the max load of the unit would be 37.5 amps.

I recent saw the post on showers with this in mind but thought this could be a different beast as it could be on for long periods of time at max power. So issue is Would a large plastered board boxing in count as Ref B or Ref C. If C then surly 10 amps head room is ample.


I know would be easy to put a 10mm in and be done with it. but there a new 6mm in there already for the original spec asked for. So way i see it is money is money and if we can save SAFELY then why not.

 

[Richard Burns]

For a 4m cable in a large box run it will take 5 minutes to use the existing 6mm to pull a 10mm in so total extra cost would be about £10 and you are then covered for future changes.
A plasterboard box I think would class as ref method B as there is not free air circulation and no easy heat conductive path.

 

[Robinson]

For a 4m cable in a large box run it will take 5 minutes to use the existing 6mm to pull a 10mm in so total extra cost would be about £10 and you are then covered for future changes.
A plasterboard box I think would class as ref method B as there is not free air circulation and no easy heat conductive path.

Thanks for reply. Yeah air circulation was a consideration. there is a fair bit both end s of boxing but i do see the point.


Not sure i get the £10 part. its say 5 m with connections thats waste of old cable going to buy new cost of new, time getting it. etc etc. i know it sounds tight. But It all add's up. It just annoy's me when people change the goal posts at last minute and expect things for free....... As for future proof. Its domestic and really cannot see them getting anything bigger than this for small flat..

Thanks

 

[Richard Burns]

Ahh, if you have to pay for it then this is different, I would be adding to the invoice for late changes outside of the estimate.
I was assuming you would have 10mm cable, and would be using the existing connections so just cost of cable ~£8 and a couple of quid for installation time.
If you look at installation methods 40 to 56 they are all roughly what you have and are installation method B, however 6mm cable on installation method B can take 38 amps and you are drawing 37.5 amps possibly only 35 at 230V, you can do this in compliance with the regs, however if you can get payment for the change then up it to 10mm and charge more!

 

[Robinson]

Yeah Had chance to have good look and yes its tight and could get it through the regs but i have now gone down route you suggested, Went and bought 10mm and billing . if i had more headroom than an 1amp then maybe but not really happy with it being so close to mark and as you rightly pointed out it is Ref B

Ta