18kw heater - 45m cable run - 3 phase - rewireable fuses. . . . Fuse size ????

Eric-George · Jul 9, 2012

Hi Guys,

Firstly, this is my own project and I have no 3ph supply in my own unit and have to take a supply from neighbors unit who has an old 3ph rewireable board with plenty of spare spaces.

I cant upgrade neighbors board and have to run a cable 35- 45m to supply a 18kw heater and fans.

My question is what size fuses do I need ??

The total current works out to be 43 amps with a 3.3% volt drop.

This gives me a minimum cable size of 6mm 4 core swa.

The question is . . . . . Do I try to source 45a fuse wire to cover the total current load or is the total current (43a) divided by the 3 phases making the fuse sizes smaller ???

Appreciate all your suggestions.

malcolmsanford · Jul 9, 2012

Not sure where you got that 43amps from as an 18kw load over 3 phase would be 26amps per phase

telectrix · Jul 9, 2012

is the heater and fans single phase or 3 phase?

Eric-George · Jul 9, 2012

malcolmsanford said:
Not sure where you got that 43amps from as an 18kw load over 3 phase would be 26amps per phase

Malcolm, you may have just answered my question. I got the 43a from dividing power by voltage (18000 / 410). I'm sure there a square root of 3in the calculation that I've missed?

43/ sqrt 3 (1.73) = 26 !!

Telectrix - Fans and heater are all 1 unit with 3 ph supply.

telectrix · Jul 9, 2012

think the way forward is to split the tails to the neighbour's DB, install a 40A 3 phase MCB to feed your installation, add a meter if required so neighbour can charge for what you use. 6mm SWA if it meets VD limits beats 3 rusty nails in his DB.