supply cable sizing

[ronky]

Hi ,I have a wood cabin outside 70mtrs from house incoming supply, I was thinking of using a 35mm 2core pvc/swa, as I think a TT system would be appropriate for the cabin, owing to the distance away from house load would be allowing for diversity would be 51amps, seems a lot but it will be a live in dwelling with all requirements for cooking heating etc,am i correct with supply size Thanks ron

 

[Strima]

What's your installation method, earthing arrangement, bonding requirements?

 

[Spoon]

Why not 25mm on 50A.

 

[ronky]

What's your installation method, earthing arrangement, bonding requirements?

Earthing wood be as TT supply, ie stake in the ground at hut position' bonding as regs, sub circuits would be 6242y and sized, appropriate for circuits suplied

 

[ronky]

Earthing wood be as TT supply, ie stake in the ground at hut position' bonding as regs, sub circuits would be 6242y and sized, appropriate for circuits suplied

PVC/SWA would be buried in the earth at appropriate at depth

 

[telectrix]

Why not 25mm on 50A.

volt drop.is OK on 25mm ( about 4V @ 50A). 25mm on a 63A MCB would be my choice.

 

[Wilko]

Why not 25mm on 50A.

Agree, 25mm SWA is 1.75mV per A per m, so for 70m at 50A I get 6.1V, or 2.7%...

 

[telectrix]

soz. misread the table as 1.65mV

 

[ronky]

PVC/SWA would be buried in the earth at appropriate at depth

my calcs as follows , volt drop table 4E4B 1.85mv/a/mt 35mm =1.35 x50ampsx70mtrs =4.72 volts . 25mm = 1.85mv/a/mt x50amp x70mtr= 6.47volts so not much lighting load so 5% of 230volt=11.5volts allowed and 3% of 230volt =6.9 volts so would the calc with 5% be okay which is 11.5 volts am I getting to tied up ronky

 

[ronky]

volt drop.is OK on 25mm ( about 4V @ 50A). 25mm on a 63A MCB would be my choice.

I make it as table 4D4B 1.75mv x 50 x 70 = 6.12volts drop am I doing something wrong Thanks for reply Ronky

 

[Leesparkykent]

volt drop.is OK on 25mm ( about 4V @ 50A). 25mm on a 63A MCB would be my choice.

Switch fuse would be better than an MCB.

 

[westward10]

35mm gives you 2% vd which allows 1% in the cabin for the lighting.

 

[Strima]

Your volt drop needs to take into account the circuits within the cabin not just the distribution circuit.

 

[Deleted account]

What’s your current load in the main property.

 

[Toneyz]

Whilst cable size has been worked out to 25 or 35 due thought needs to be given to the terminal sizes and termination practicalities.

 

[Bobster]

Whilst cable size has been worked out to 25 or 35 due thought needs to be given to the terminal sizes and termination practicalities.

You can buy pin lugs to reduce 35mm to 25mm, since the 35mm size is only required for VD an not load, there is no issue in this solution.

Don't see why at that size you can't use the house's earthing system. Utilizing the armor of the SWA as a CPC. Unless you have extraneous services entering the outbuilding.

A switch fuse would be more ideal to provide protection for this cable, purely to meet discrimination with MCB's that I presume are going to be installed in the outbuilding.

 

[bill01803]

You would need to have an 300mA rcd not a switch at the origin

 

[Leesparkykent]

You would need to have an 300mA rcd not a switch at the origin

Where did that ball hang come from?

 

[bill01803]

Where did that ball hang come from?

Someone said you should use a switch fuse

 

[Midwest]

Think the OP is going to use swa cable.