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Electric supply for log cabin


daiking

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Amongst the hundreds of other jobs involved I’m trying to get my head around this.

 

When we extended the house, I had the foresight to ask the electrician to put a 6mm2 cable on its own MCB and connect it to a weatherproof box on the outside of the house. It’s approx 7m cable length - through wall cavity/service gap/ceiling, it’s not running fully in insulation. 
 

Externally the new supply cable will need to run approx 25m, probably shorter. Size of that SWA cable to be determined by installer. As I understand it, my constraint is the 6mm2 cable from the CU in the house.

 

What I would like to understand is what sort of capacity I get in the log cabin based upon that constraint?

 

A few lights and sockets - obviously. We’ll be expecting to run a fridge and a heater as   Appliances needing more power

 

Inflatable hot tub ? - probably as this runs off a plug 

 

Proper permanent hot tub ? - don’t know? Unlikely? Are 13 Amp options any good?

 

I’ve seen that a 32 Amp hot tub requires 6mm2 and 40 Amp requires 10mm2 but don’t know how my distance affects that nor the additional load I require in the cabin

 

I’ll be getting an electrician to do the electrical work but I want a firm grip of what work is required and will probably be doing the layout stuff myself to make sure everything is exactly where I want it.

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Lets start by assuming you extend it in 6mm so the full run is probably 34m = 7+25+2. In which case an online calculator suggests the max power you should draw is about 9.5kW. Thats about 40-41A. 

 

I don't know if the regs allow you to extend the 6mm with 10mm but the voltage drop calculation would need to be done manually.

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I would have assumed that if I’ve started with a 6mm cable there’s no point increasing to 10mm for the SWA run but I have no idea really. Just trying to get a feel what is and isn’t possible.
 

Only 40A over 30m+ sounds touch and go for lights, power and a hot tub though. I’m not intending to get a big hot tub any time soon but just making sure what is feasible in the future. I suppose a 10mm2 cable from the CU would be possible but it would be a right PITA. 

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I think it will be fine, the important question is your supply earthing PME, as you don’t want to be exporting the earth if you are using it for a hot tub.

 

normally gland the swa as normal but don’t use a swa gland if it’s going into a metal box use a stuffing gland, so that the earth isn’t touching the metal box, then an earth rod in the ground  and a conductor up to the earth termination and connect that earth in.

 

so the DNO earth protects the swa uo to the point of termination and your earth rod takes over for the equipment such as hot tub, where bare feet, water and electrics and PME create a higher risk.

Edited by TonyT
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27 minutes ago, TonyT said:

I think it will be fine, the important question is your supply earthing PME, as you don’t want to be exporting the earth if you are using it for a hot tub.

 

normally gland the swa as normal but don’t use a swa gland if it’s going into a metal box use a stuffing gland, so that the earth isn’t touching the metal box, then an earth rod in the ground  and a conductor up to the earth termination and connect that earth in.

 

so the DNO earth protects the swa uo to the point of termination and your earth rod takes over for the equipment such as hot tub, where bare feet, water and electrics and PME create a higher risk.

From what I’ve read, I will probably need a local earth rod.

 

Gland terminations etc will be up to the sparky.

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+1

 

Its quite common to use a small  "Garage CU" with an earth rod for outbuildings. This typically has one RCD and two MCB one for lighting (6A) and the other for power (32A).

 

https://www.screwfix.com/p/british-general-5-module-3-way-populated-garage-consumer-unit/1926G?tc=IB6&ds_kid=92700055281954493&ds_rl=1249401&gclid=Cj0KCQiA3NX_BRDQARIsALA3fILaUGJznmB2qwdtKhJnHkYM3WQbCrPl4GQPowzJH7vT-UIHjQUQwPgaAie8EALw_wcB&gclsrc=aw.ds

 

Although something different might be needed for a hot tub. 

 

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  • 2 months later...

Latest fun quote has £150 to wire up a 2-way garage consumer unit and £300 to install 2 x 10m of LED strips.

 

Guys might be just using their house norms as he’s just multiplied his £30 per 2m strip x 10. I understand that a 12 way + household consumer unit would take a few hours but a simple garage one? 

 

still looking for an electrician obvs 

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4 minutes ago, daiking said:

Latest fun quote has £150 to wire up a 2-way garage consumer unit and £300 to install 2 x 10m of LED strips.

...

 

The consumer unit quote is a ' ...I don't want the job... ' statement perhaps?  @nod's right - there's too much work around. 

20 meters of LED strip - have you bought it already? There's huge variation in the price, quality, finish  and design of it, I think. If you have it in stock, the £300 appears excessive too.

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2 minutes ago, ToughButterCup said:

 

The consumer unit quote is a ' ...I don't want the job... ' statement perhaps?  @nod's right - there's too much work around. 

20 meters of LED strip - have you bought it already? There's huge variation in the price, quality, finish  and design of it, I think. If you have it in stock, the £300 appears excessive too.


I still have to supply the led strip and driver. That’s £300 just to install! What would be 2 connections. Same price as if I asked him to install 10 different strips 2m long ?‍♂️. Other pricing is broken down into norms, socket and light £40 each. 

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The consumer unit sounds fair.  I think you would be OK doing the strips yourself if they wire the switch(es) and the drivers.

 

He is probably charging a fair amount because he doesn't want to subsidise the use of a filthy sex pond hot tub.

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1 hour ago, ToughButterCup said:

 

 = I don't need the job

I disagree, this seems to be everybody’s pricing level and is clearly why these things normally come in at £15k+ As everyone is taking the piss now.

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40 minutes ago, Mr Punter said:

The consumer unit sounds fair.  I think you would be OK doing the strips yourself if they wire the switch(es) and the drivers.

 

He is probably charging a fair amount because he doesn't want to subsidise the use of a filthy sex pond hot tub.


I estimated 2 days labour at £250 per day to wire a log cabin. Thinking it was a simple discrete job that would fit in around larger jobs but was big enough itself to fill 2 days. 
 

Maybe I was a little low on my daily rate but am I wrong on the amount of work? 10 sockets, 4 lights + consumer unit?

 

Must take weeks to wire a house then...

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