Cable size to outbuilding with water pump.

[saveasteading]

Looking to seize an opportunity to put a cable from the plant room to an outbuilding. What size cable?

 

There will be a domestic water pump that will feed the large house. Plus workshop and who knows what else.

 I'm thinking the pump may be about 2kW but perhaps there is more to it.

No worse than a kettle? 

The cable length will be 30m. 

Pump will lift the water 4m max.

 

There will be advice taken from electrician and plumber but they are not fully engaged yet.

[markc]

I would go for a 4 or even 6mm cable, very little difference in price so might as well be over spec. To allow for extra sockets/lights etc to be added on later.

assuming you don’t have big machines in the workshop in which case 10mm.

Edited September 9, 2022 by markc

[Temp]

Calculator here..

https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

 

Suggests 4mm^2 SWA underground is OK for about 7KW and 6mm^2 about 9kW.

 

Main thing to check is the exact cable length. It's easy to forget you might need 4-5m each end. 

[Temp]

Just a heads up on earthing.. 

 

In many cases you shouldn't export the earth from the house to an outbuilding. There should be an earth rod at the outbuilding instead. A common set up involves:

 

A MCB is fitted in the House CU. Rating depends on the cable.

The cable braid is connected to earth at the house CU end only.

 

At the outbuilding a "Garage CU" is installed. These are typically supplied with an RCD and two MCB (lighting and power).

The Earth in the Garage CU is connected to an Earth rod hammered in the ground near the outbuilding.

 

Edit: Your water pump  could be plugged into a 13A socket on the power ring in the outbuilding. I think it may also be possible/better to wire it into an FSU.

 

Edited September 9, 2022 by Temp

[saveasteading]

Thanks both. From further discussion, there will be no heavy load tools in this outbuilding.

Yes I'm expecting another cu to be used and an earth. Not sure how good an earth spike will be in the hard but free draining sand here. 

In fact it is difficult to get a pinch bar into the ground...almost rock but then turns to soft sand when disturbed... maybe a long drill. But does dry sand conduct well enough for the earth?

 

4 to 5m each end noted. I would have underdone that, thinking just come up the wall 2m. So wall to wall route plus 10m. Looped up 5m each end ready for the electrician.

[JohnMo]

We put 12mm2 in.  Doing water pump treatment plant compressor, and discharge pump.  Since installing have taken a power supply to garage, and will possibly have a small ASHP connected also.