Cable Rating

[joinerjoe]

I currently have a radial circuit from the house to the garage consumer unit. It feeds a single socket and the lighting. As it's only 1.5mm and I want to add more sockets, I'm considering adding a second radial. Looking at the existing 1.5mm installation, a twin and earth runs from the house consumer unit up into the loft space, across the loft from the front to the rear of the bungalow where it connects to the armoured cable via a junction box. The armoured cable from the junction box to the garage is about 8 metres.
At this point in time, I'm just weighing it all up and would appreciate your advice. The total distance from the house consumer unit to the garage is about 20m. Was thinking of replicating the installation method used for the current installation, that is, twin and earth from the consumer unit into the loft space junction box connected to the armoured cable running to the garage.
As regards what would be used off this circuit, this would be a table saw at 1850 watts, track saw at 1200 watts, a router table at 2000 watts and a mitre saw at 1600 watts. As I would be the only one using this equipment, only one machine would be used at any given time, except for a 1400 watt dust extractor which would be activated when these are used.
Given this, what would be the most suitable size of cable to use from the house consumer unit to the loft junction box, armoured cable and cabling from the garage consumer unit to the individual sockets?

 

[SUNRAY]

Is the SWA (armoured cable) also 1.5mm²? 11-12mm diameter. the size may be embossed along its length something like 2x2.5mm

 

[joinerjoe]

Is the SWA (armoured cable) also 1.5mm²? 11-12mm diameter. the size may be embossed along its length something like 2x2.5mm

Hi,
The outside diameter is 15mm. The only thing that I can see embossed on the surface is 'electric cable 600/1000v delta Enfield'.
It is not a recent installation

 

[SUNRAY]

Hi,
The outside diameter is 15mm. The only thing that I can see embossed on the surface is 'electric cable 600/1000v delta Enfield'.
It is not a recent installation

Asuming it's 2 or 3 core, 15mm external diameter is bigger than 1.5mm². It's more likely to be 4mm² for an older cable or 6mm² for more recent. What are the external dimensions of the twin and earth cable?

Looking at your other posts we don't know your electrical skills, is this the sort of work you'd be experienced in?

 

[markyd1]

Get a sparky

 

[joinerjoe]

Asuming it's 2 or 3 core, 15mm external diameter is bigger than 1.5mm². It's more likely to be 4mm² for an older cable or 6mm² for more recent. What are the external dimensions of the twin and earth cable?

Looking at your other posts we don't know your electrical skills, is this the sort of work you'd be experienced in?

Yes I am experienced.

 

[joinerjoe]

Get a sparky

I intend doing just that. I intend doing bulk of the work and get someone qualified to connect and test as. I usually do.

 

[ericmark]

There are four considerations:-
1) Earthing system and system to disconnect supply if earth fails.
2) Heat generated in the cable, is it likely to melt, thermal plastic or thermal setting makes a diffrence.
3) Short circuit protection, is the loop impedance low enough?
4) Volt drop, at the load enviguaged will it exceed the permitted valve.

The volt drop may not matter, but selecting cable size will impact on it. In the main we use experience rather than sit with a calculator working it out. And we measure once complete to ensure no errors, but by that time a bit late.

Personally I would use 4 or 6 mm, more likely 6 mm in case I want to charge a car latter.

 

[Harry Bloomfield]

Personally I would use 4 or 6 mm, more likely 6 mm in case I want to charge a car latter.

I would suggest replacing the existing completely, with the new installation, so there is just one isolation point at the supply end, one in the garage.

 

[joinerjoe]

There are four considerations:-
1) Earthing system and system to disconnect supply if earth fails.
2) Heat generated in the cable, is it likely to melt, thermal plastic or thermal setting makes a diffrence.
3) Short circuit protection, is the loop impedance low enough?
4) Volt drop, at the load enviguaged will it exceed the permitted valve.

The volt drop may not matter, but selecting cable size will impact on it. In the main we use experience rather than sit with a calculator working it out. And we measure once complete to ensure no errors, but by that time a bit late.

Personally I would use 4 or 6 mm, more likely 6 mm in case I want to charge a car latter.

Thanks for your advice, it's appreciated. I was considering 6mm but wanted confirmation (and reassurance)

 

[joinerjoe]

I would suggest replacing the existing completely, with the new installation, so there is just one isolation point at the supply end, one in the garage.

Yes, that's good thinking that can actually be used to my advantage. Feeding from the loft to the cu could be difficult due to location. I could when pulling the 1.5mm out attach the new 6mm to it and pull it up that way. Thanks

 

[joinerjoe]

Asuming it's 2 or 3 core, 15mm external diameter is bigger than 1.5mm². It's more likely to be 4mm² for an older cable or 6mm² for more recent. What are the external dimensions of the twin and earth cable?

Looking at your other posts we don't know your electrical skills, is this the sort of work you'd be experienced in?

Hi,
Finally got around to checking this cable and you are correct, it's 4mm. 7 strands at .78 .83mm.

 

[SUNRAY]

And the size of the T&E? external dimensions will be fine

 

[joinerjoe]

2.5mm

 

[SUNRAY]

20m of 2.5mm² is likely to be suitable for a 20A overcurrent protection device which will allow 4.5KW and possibly 25A/5.7KW. I haven't done the cable calculations though.

What fuse/MCB do you currently have in the house CU?