Cable size for 30m run

[regedit]

Will be run in pcv conduit below ground from MCB to an outbuilding.

I was thinking 2.5mm will be enough to power a couple of sockets (for light power tools) and lights.

If I want to future proof for potential additional small aircon unit (< 9,000 BTU) do I need to use 4mm ?

Thanks. 

[Crossy]

Ok, let's assume you will load up your outlet / lighting to 10A or so (some of my tools are pretty Ampy).

 

Baby aircon 900W = 4A (double it for start current).

 

From Doncaster Cables calculator http://www.doncastercables.com/technical-help/ you could just do it on 2.5mm² (5% drop) but going up to 4mm² is probably wise if the budget allows.

 

Are you going underground or aerial?

 

[Sophon]

56 minutes ago, Crossy said:

Ok, let's assume you will load up your outlet / lighting to 10A or so (some of my tools are pretty Ampy).

 

Baby aircon 900W = 4A (double it for start current).

 

From Doncaster Cables calculator http://www.doncastercables.com/technical-help/ you could just do it on 2.5mm² (5% drop) but going up to 4mm² is probably wise if the budget allows.

 

Are you going underground or aerial?

 

From the OP:

Quote

Will be run in pcv conduit below ground from MCB to an outbuilding.

Sophon

[Crossy]

@Sophon that will teach me to speed-read posts ????

 

Anyway, for underground runs, even in conduit our OP will be looking at NYY cable (smaller sizes are available). 

http://www.bangkokcable.com/product/backoffice/file_upload/131007_34-450!750V 70C NYY-2C.pdf

 

NYY can actually be buried direct thus saving the cost of putting in a conduit.

 

Money could be saved by running 2-core and providing a local ground rod at the shed (RCD protection needed).

 

[regedit]

Thanks for the replies !

[thaibeachlovers]

On 3/18/2019 at 9:06 PM, Crossy said:

Money could be saved by running 2-core and providing a local ground rod at the shed (RCD protection needed).

 

I guess that answers part of my question, thanks. Does the RCD need to be at the supply end of the cable, or at the user end? The cable will be buried. For that matter, should the breaker box be at the supply end or the user end?

[Crossy]

8 minutes ago, thaibeachlovers said:

I guess that answers part of my question, thanks. Does the RCD need to be at the supply end of the cable, or at the user end? The cable will be buried. For that matter, should the breaker box be at the supply end or the user end?

 

RCD/RCBO should be at the supply end.

 

If you are feeding several circuits (shed/workshop) as small consumer unit/distribution box in the shed would be wise.

[thaibeachlovers]

Just now, Crossy said:

 

RCD/RCBO should be at the supply end.

 

If you are feeding several circuits (shed/workshop) as small consumer unit/distribution box in the shed would be wise.

Thanks Crossy.

I have a consumer unit to use at shed end ( bought in Thailand ), but it doesn't have an RCD in it, so that makes it easier. Get a stand alone RCD for the supply end.

 

I was thinking of using 12 mm cable, but is that over doing it?

 

So, from your posts, an RCD at supply end, buried 2 core cable of needed size, consumer unit with an earth rod at shed end.

 

Thanks.

[Crossy]

Sounds good.

 

You can use this cable calculator https://www.doncastercables.com/technical-help/

 

As noted in the other thread, do NOT provide a N-E link at the shed, you are making a "TT island".