Building Standards; Getting It Right!
Dec 14, 2019 2:47 pm
I have just had the main over head cable to the house replaced after a tree kindly took them all out.
New poles, and for the hell of it, a new 3 phase distribution board.
I also have an air cooled semi-commercial 7kva single phase 220V diesel generator, which I asked them to put in a transfer switch and plug to connect. We've put the genny in a shed adjacent to the distribution board (which is around 10m from the house, on a pole) and will connect via plug/sockets and orange cable.
Now, the 3 phase in has been split at the distribution board into 3 separate single phase lines; one for the house, one for a dam circuit, and one for future connection to the shed.
On the side of the distribution board they put in a 5 pin 32A plug setup, and gave me a cable which will eventually terminate in a 3 pin 32A plug into the genny.
My understanding is, when the transfer switch (a 3 phase switch) is changed over to run from the genny, all 3 phase circuits will be joined at the 3 pin 32A plug into the genny, so all 3 circuits will run from the genny simultaneously, as a single phase system.
Yes, I know it will be load limited, as the genny will output 32A across the 32A cables, which won't necessarily power everything in the house simultaneously. Where I’m struggling to determine if it’s OK they have used 5 core 2.5mm cable on the transfer cable between genny and dist board.
So, if all 3 phases are made a single phase, this would suggest there is 3x2.5mm active lines (all 3 joined at the genny plug), but a single 2.5mm neutral line. Wouldn’t this then suggest the maximum amp that can be ran across the cable is around 20A (max for 2.5mm cable), due to the single neutral being the limiting factor, just as if you were running it as a single phase circuit?
I would have thought they’d be better using 4mm2 cable minimum, as then the neutral alone could handle the 32A load at least, and it'd be equivalent to a single phase transfer line at 32A.
So, is the cable used, for this situation, too light? Should it be 4mm2 not 2.5mm?
Appreciate any suggestions…
Re: Question on cable size ataching a generator to house2
Dec 14, 2019 3:36 pm
In hindsight, I don't need to run either the dam pump or shed if the power is out. Not a priority.
I think I'll bugger off their 5 core 2.5mm cable and use 3 core 6mm orange cable, and run it to the single house phase. Solves a whole lot of hassles.
But still, open to opinions
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