Size of cable required

[billd766]

I am planning a small project to get a well dug on a neighbours land across the road from me up here in rural Khampaeng Phet.

1 I need to get a water finder and a well digger to see if there is water available before anything else and find the cost of digging the well.

2 If there is I need to get my wife to negotiate if we can but or rent a small plot of land to dig the well and also the right to run piping over the land that belongs to the neighbour.

3 The pipe run will be about 350 metres in total.

4 There is a klong but at the moment it has almost dried out.

5 The vertical lift from the klong is 8 metres and I would have to add to that the depth of the water in the well. The horizontal run would be about 350 metres in total running down my land, across another neighbours drive through a 6 inch drainpipe, along the front of his place on government land, through the 1 1/2 metre drainpipe under the road to the land on the other side and then to the well if we can get it done.

6 I saw a submersible 3/4 hp pump in the village with a 30 metre lift and a 2 inch pipe fitting. It is rated at 5 amps though I am not sure is that is the start up or the running current.

7 What size cable would I need for a 350 metre cable run. I am planning on 100 metre lengths running through 4 metre sections of 1/2 inch water pipe with a junction box every 100 metres where I will join the cables and seal them with a waterproof compound. The reason for that is that it will be hard enough to pull 100 metres at a time let alone 350 metres in one go.

If item 1 and/or 2 don't work

[Crossy]

5A would be the run current, start 3-4 x that, 15-20A.

Lets assume we can start on a 20% volt drop (180V) at the pump.

350m @ 20% is looking at 10mm² copper or 16mm² aluminium.

If your pump will withstand 23% drop you could get away with 6mm² copper or 10mm² aluminium but I would avoid unless the pump spec says it's ok and the budget is being stressed.

[billd766]

5A would be the run current, start 3-4 x that, 15-20A.

Lets assume we can start on a 20% volt drop (180V) at the pump.

350m @ 20% is looking at 10mm² copper or 16mm² aluminium.

If your pump will withstand 23% drop you could get away with 6mm² copper or 10mm² aluminium but I would avoid unless the pump spec says it's ok and the budget is being stressed.

Thank you for the information.

I was afraid you were going to say that.

The last time I pumped water from the klong a few years ago I used a 5.5 hp Honda engined water pump which worked fairly well apart from the fact that I had to go and refuel it every couple of hours. I still have the engine but it would need a new pump on it.

I can't remember the price of 10mm2 but I can probably get a small gen set cheaper and it would be far less hassle than a long cable run plus I would only need the 2 inch water pipe and not the extra 350m of 1/2 inch water pipe that I was going to run the power cable inside.

Have you any idea of the rough price of 10mm2 2 core cable? I haven't bought any for years.

I think that if I buy a small genny I will have to get a trolley to transport it to the well and I could then bring the well pump and genny back on a daily basis to save it from being stolen.

[Crocbait]

Is power available near the road ? If so what about putting up a pole and meter and run to a lockable switch box near the well. If you are renting the land I don't see they would object to a power supply.

[billd766]

Is power available near the road ? If so what about putting up a pole and meter and run to a lockable switch box near the well. If you are renting the land I don't see they would object to a power supply.

Thanks for the thought. It is something I hadn't considered.

This is one of the great things about TVF when you can ask some question and bounce ideas around that perhaps other people looking from a different viewpoint come up with.

There is power over there at a small shack belonging to the owner of the land and I may be able to use that in the way that you suggest.

OTOH having a wheeled genny would also come in useful when we have power outages so it is a trade off.

[impulse]

Franklin 50Hz AIM. Great source of info on motors for pumping water.

http://www.franklin-electric.com.au/aim-manual.aspx

P 11-12 discuss cable sizes...

http://www.franklin-electric.com.au/media/4746/50Hz_AIM_11.pdf

http://www.franklin-electric.com.au/media/4753/50Hz_AIM_12.pdf

[Crossy]

Good info Impulse.

If we use Table-11 our OP's 3/4 horse pump would just be ok on 350m of 6mm², it's right at the max cable length for 6mm².

[impulse]

Good info Impulse.

If we use Table-11 our OP's 3/4 horse pump would just be ok on 350m of 6mm², it's right at the max cable length for 6mm².

I always hate bumping up against the maximums. If the pump wears, or scales up slightly- starting problems will ensue. Besides, cable voltage losses cost utility $$$ that can often exceed the savings from buying smaller cable over the life of the project.

But sometimes, it is more cost effective to count a new pump/motor every few years than buy the bigger cable...

[Crossy]

Good info Impulse.

If we use Table-11 our OP's 3/4 horse pump would just be ok on 350m of 6mm², it's right at the max cable length for 6mm².

I always hate bumping up against the maximums. If the pump wears, or scales up slightly- starting problems will ensue. Besides, cable voltage losses cost utility $$$ that can often exceed the savings from buying smaller cable over the life of the project.

But sometimes, it is more cost effective to count a new pump/motor every few years than buy the bigger cable...

Agree 100%, so we're back at my original recommendation of 10mm² copper

[Forkinhades]

6mm is ok, but I'm with impulse on this one, especially here in Thailand where the supply voltage can drop 20% at certain times of the day, and for prolonged periods.

[Forkinhades]

Yeah back to 10mm Xy

[RichCor]

Step-up, then step-down transformers with selective tap?

I'd guess installing a heavier wire would be more cost efficient.

Another alternative could be a off-grid solar panel/batteries/inverter to run the pump.

[wayned]

6mm is ok, but I'm with impulse on this one, especially here in Thailand where the supply voltage can drop 20% at certain times of the day, and for prolonged periods.

Only 20%. For years I watched mine cycle from 210vac to 145vac at 10 second intervals for a couple of hours every afternoon. We , the village chief, and I , finally convinced PEA to change the transformer to three phase, only had one phase installed, and everybody was hooked to a different phase and the problem went away. PEA said that it was because of machinery at the gravel pit down the road and had known about it for years but just never did anything to fix it until I got Puyai involved.