3 phase loading question

[Steve2381]

Hello all
I am working for a company and we are installing supplies to some industrial 3 phase heaters in a factory in Devon.
I am questioning the maths used by my boss to arrive at the SWA size to supply these heaters.

Seeing as I am not a wiz with 3 phase stuff (only just started working for this firm), can someone give me some pointers on calculating the load?
I know the basics, but would like to make sure I am right before rocking the boat!

We are supplying 4x 15000kw heaters - 3 phase.
What load is that going to be per phase, per heater? He has basically divided the 15000kw into 3 - therefore 5kw per phase, then divided it by 230v.
Arriving at 21.7A per phase.

That means with 4x 3 phase heaters on the distribution board, we are looking at around 88A per phase load.
That's a huge 348A load.

He has 'guessed' at a 35mm 4 core SWA for the 50M run. Not convinced any calcs have gone into that decision.

Thanks!

 

[Lucien Nunes]

Or get yerself one of these. Ex power station control room mid 1960s., changed one duff valve and a leaky capacitor and up it came within 0.01 Hz of my bench FG. Trouble is, if you want to wake up in the morning knowing whether your clock is running at the right speed, you've got to be able to sleep through the funny little noises it makes - the pointer is driven by a servomotor so it whirrs and hums all the time as the frequency changes. You also need a strong wall to put it on! Note the red marks on the dial - load shed is at 48.50Hz and island mode on the 132kV at 47.6.

Flicking back through the thread, the reference to the current being wrong 'because the OP hadn't built in a factor of sqrt(3)' - he had, you just didn't see him do it. He used the line current but the L-N voltage, which includes the division by sqrt(3). Saves space on the envelope.

 

[DPG]

Excellent! That's not your average car-boot sale find! Daz