Pond electrics

[FireFury]

This might be completely the wrong place to ask, but I'm hoping some of you have a bit of experience of installing duck ponds and can offer some advice.

At the moment, the ducks are making great use of a washing up bowl full of water, but we're going to be digging them a small pond soon. Pond water will be pumped through a biological filter and through a hydroponic garden to keep it clean (this is a bit of an experiment, so time will tell how well it works!).

We need a dirty water pond pump (i.e. one that can handle solids) - there are plenty available, but all of them seem to run on 240 volts, which means laying mains electricity cabling under the lawn. I was hoping to get hold of a low voltage dirty water pump - does anyone have any ideas? (All the low voltage pumps I've found are "water feature pumps" - i.e. clean water only).

It looks like the (UK) electrical regs require armoured mains cables to be buried quite deep, and the ground is so stony that's going to require serious pickaxing, which I was hoping to avoid.

 

[Marigold]

I'm not sure about the UK regs - a couple of years ago, a professional electrician ran an armoured cable down to the quail shed at the bottom of our garden, on the ground surface and under the hedge. He provided a certificate of electrical compliance, and everything has been fine so far. Obviously, if going over the lawn it would have to be buried out of the way of mowers etc, but should be possible?

 

[rick]

Depending on the power needed - inverters are fairly cheap these days. Trouble is how to charge the battery.
Or were you thinking of running a 12V supply up the garden so it's safer?
I have a 240V extention on an RCD - If it got wet inside or I hit it with a shovel it would trip without doing any harm but it is on show along the fence line.

 

[FireFury]

Or were you thinking of running a 12V supply up the garden so it's safer?

I was thinking a 12 or 24v supply would be easier as it wouldn't be governed by electrical regs, so I could easily bury a cable myself without needing to dig deep trenches.

but it is on show along the fence line.

Unfortunately the cable has to cross a gate in the fence, otherwise I'd just clip it to the fence and it wouldn't need to be buried.

 

[rick]

What wattage of pump would you want to run if it was 240V? (just to get an idea of the amount of power you need to run)

 

[FireFury]

What wattage of pump would you want to run if it was 240V? (just to get an idea of the amount of power you need to run)

Probably under 25W, so 2A on 12v. Its not going to be a big pond so I think the pump probably needs to do around 250 litres / hour.

 

[rick]

Probably under 25W, so 2A on 12v. Its not going to be a big pond so I think the pump probably needs to do around 250 litres / hour.

I used to have a boat with a bilge pump that drew a couple of amps on 12V. Moved a lot of water too so maybe a chandlers would be worth checking out. Only thing though - I don't think they are rated or built for continuous use and you might wear out bearings/bushes.
2A (DC) over any distance needs some hefty wire or will lose several volts from end to end. That might not be a problem (pump runs a bit slower.)
I bought a 100W car inverter (12V DC to 240V AC) from Asda a while back for about £15 I think. You would have to put it in its own little 'shed' to keep the weather off and allow ventilation and would allow you to run a mains pump but run a low voltage supply.
An RCD would still be a good idea at the pond end for the sake of the ducks and yourself just in case anything gets leaky (current wise)
I don't think you would need any compliance cert for a 12V supply running a DC supply to inverter as long as it plugged into a standard outlet. The re-inverted 240 end would be no less capable of delivering a shock so reasonable care required.
Hope that helps.

An afterthought - while a DC pump will run slower on a DC line with voltage drop, an inverter will need it's operating voltage to be pretty stable. It then just comes down to how far you have to go.