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Posted By Topic: long LV run

Nov 20 2019 13:30

Hi all.

have been asked to quote running a cable to a pump shed, it's 1800m from nearest SWBD. I've inquired about getting HV closer, but the Network's quote is $60k+.
The pump is a tiny 3 phase submersible, 0.37kW (1A). A 70mm 4C Al will provide 6A over this run with allowable volt drop.
It seems "wrong" to run a cable that can only supply such a small load, but I can't find anything wrong with this in 3000. Any thoughts?

Nov 20 2019 15:00

Voltage drop only needs to be calculated on the actual load current. 3.6.2
So at say 2A, you could go down to 25mm2 Al, and still be under 2% VD as a balanced load.

The issue you might have is the earth loop impedance. But if you run it on an RCD, it shouldn't be a problem?

Nov 20 2019 15:22

Surely there's a way of doing it with solar for a helluva lot less. A 3 phase pissy wee motor could be swapped for single phase.
A couple or 300 for solar, maybe a bit more for a decent inverter and Bobs your uncle!

Nov 20 2019 15:28

Dougs idea is good for 1.8km easy. Is it just a water pump? You can get solar submersible water pumps nowadays . Because that’s a huge amount of work for a little pump

Nov 20 2019 16:56

Thanks. Yes, I'm quoting a solar option too, but they want a cost comparison, hence the grid fed option.

Nov 20 2019 20:34

FTR; we have to comply with EFLI / earth continuity regardless of whether RCD or not.
The requirements are separate & independent; and just 'cos an EFLI test may not be req'd, and an RCd will provide fault protection within time doesn't let us off keeping PEC continuity down.


Nov 21 2019 22:13

Smaller breakers (e.g. 2A) are available easily enough.