armoured cable

[mikert]

Hello everybody,
Any help would be appreciated in letting me know what size cable to use for a 50m length for a filter/pump (300w ) and small water heater ( 3000W ), this is for a small swimming pool at the end of the garden which is being neglected as the kids say it's too cold. Both of these have a 13a plug fitted so I intend using an outdoor double socket at the end of it fitted to a post.
Thanks for any help, Mike.

 

[comms]

4mm swa would do it but is pretty near the limit on voltage drop.
If it were me i'd go for 10mm in case of any future additions.
don't forget the rcd protection.

 

[bathjobby]

Comms, I'm considering something similar; whats the maths for calculating size of cable, or is it in a table somewhere ?

 

[comms]

power/voltage = amps (this is design current so you can choose overcurrent device rating)

It= In / Ca x Ci x Cg x Cr

It = current carrying capacity of cable
In = overcurrent device
Ca = ambient temp
Ci = correction factor for thermal insulation.
Cg = correction factor for grouping
Cr = correction factor 0f 0.725 for semi enclosed fuses

then

voltage drop = (mV/A/M) x Ib x L / 1000

mV/A/M = milli volts per amp per meter
Ib= design current
L = length of conductor
1000 = to get answer in volts

But you do need a copy of the OSG or 7671 for the relivant tables.

Failing all that goto this calculator.
www.tlc-direct.co.uk/technical/charts/voltagedrop.html

 

[bathjobby]

Thank you comms, just the job.

 

[ban-all-sheds]

1) If you use that calculator for SWA, note the following:

a) Always specify PVC, or it'll assume the conductor temperature can reach 90°

b) Always specify 2-core cable, even if you are using 3 core (which you should be) or it will do 3-phase calculations.

2) Mikert - how long are the cables on the pump and the heater? The wiring regulations prohibit the use of 13A sockets within 2m of the edge of the pool.

3) You are aware of the regulations concerning RCD protection and supplementary equipotential bonding in the zones of a pool?

4) You are aware of the requirements to notify this work to LABC?