6mm2 for 8.5 kw shower

[scott g]

can i fitt 8.5 kw shower using 6 mm2 cable 3m from mains board
only thing is its going through loft insulation more than 100mm
would it be ok to use trunking with insulation on top would this effect cable calculations

 

[KFORDHUNTER]

3 metres of cable, just put 10mm in mate, never know in future they could want 10.5 kw shower.

 

[Spudnik]

Def use 10mm with 32A MCB.

Peace of mind as its only 3 meters!!!

 

[simopesh]

Hi Scott
Yes, you can use 6.0mm twin and earth cable for 8.5Kw shower. (8.5 multiply by 4.2 equals 35.7 current) 6.0mm cable will be just about enough for 11.5Kw shower if cable ends are crimped or welded for a better and stronger contact. (48.3Amps)
6.0mm cable in wall or trunking ~52 Amps!

can i fitt 8.5 kw shower using 6 mm2 cable 3m from mains board
only thing is its going through loft insulation more than 100mm
would it be ok to use trunking with insulation on top would this effect cable calculations

 

[12345aob]

8500/230 =36.9

Table 6E1 in the onsite guide states that a 6mm in an insulated wall has the current carrying capacity of 32 amperes.

I would put in 7.2 shower. (or 10mm cable)

 

[simopesh]

I’m using some old fashion maths! Coefficient for single phase (4.2) and for tree face (2.8) done enough showers with 6.0mm cable – no problems so far!

8500/230 =36.9

Table 6E1 in the onsite guide states that a 6mm in an insulated wall has the current carrying capacity of 32 amperes.

I would put in 7.2 shower. (or 10mm cable)

 

[Spudnik]

6mm will be fine, but for the sake of 3 meters, and easy access, id put in 10.

But thats me.

 

[flukey]

put in 10mm and youve covered all bases.
wouldnt scrimp on such a short distance

 

[DanBrown]

Hiya Guys!,
I must be missing something here!

I did the calculation 8500/230 = 37amps

cable current capacities table 6e1 on-site guide -
6mm2 in thermal insulation etc = 32amps
10mm2 in thermal insulation etc = 43amps

Isnt 6mm2 too small and require 10mm2? or does diversity come onto this?
According to diversity table,
1,water heaters (instantaneous) = 100% f.l.
2, water heaters (thermostatically controlled) = no diversity allowable.

What's missing??
Thanks

 

[flukey]

hi dan,
scott is asking for ways to install the cable so that he can use 6mm even though its borderline.
putting it in conduit would help with the thermal insulation problem but for the sake of a few extra quid he needs to do the job right and install 10mm.
you are quite right with your cable calcs but he is looking for the thumbs up to use what he has got which must be 6mm

 

[scott g]

• ze 0.17 60898 type b 32 6mm2 cable clipped direct with loft insulation on top
• protected by 30 mamp rcd x1 69 ms
• thank you for eny feed back
• its an old lady 87 just had bathroom dones not wont damage to tilles
• i know it would be ok but boss insists shoud be 10mm
• im in two minds regs say 10mm common sence says leave it for what she is going to use
• what would you recommend
• think boss is thinking of money

 

[flukey]

Once again scott, whatever the big red book says is the way to go
little old ladies shouldnt cloud your judgement

 

[eskimo39]

I'm with the guys on this one. The big red book is king!!

Have you thought about installing a smaller Kw shower to be compatable with 6mm cable?

If she doesn't want that, I am sure after telling the old dear what a mess an electrical fire can cause, she will be pulling the tiles off for you.

 

[simopesh]

I don't think that that would suffice on an EIC.

How are you going to claim that you've complied with BS 7671 if you've got a load greater than the tabulated current carrying capacity of the cable and a protective device rated higher than the tabulated current carrying capacity of the cable?

Very simple and I will certify it too. You’ve got free metres run that means voltage drop will be almost non existent. It will simply allow for a much higher current.
The big red book is a guide only. (Non statutory)
Where is the usual cable burns, is it at the beginning, in the end or in the middle?
According to any physical laws if your connection is good the cable caring capacity does increase. That is one of the main reasons why in other western European countries crimping or soldering the cable ends is absolutely compulsory!

 

[flukey]

you are quite right, the red book isnt statutory but i find that by abiding by it on simple things like cable selection i sleep better at night
the fact that the customer is a little old lady with new tiles is irrelevant and not a viable defence when it all goes wrong
each to their own i suppose but i will be sticking with the regs safe in the knowledge my install is 100% correct