Rewiring garden pond pump?

On Mon, 07 Aug 2006 13:54:03 +0100 someone who may be Douglas de Lacey wrote this:-

Throw it in the bin. Replace with another pump.

I assume that the circuit is RCD protected. Do you really want to trust your life (and the lives of family and friends) to a piece of mechanical equipment that is not 100% reliable? All for the sake of a few pounds.

How is anyone going to get killed (or even injured) by it? One's life doesn't depend on the operation of a pond pump usually.

The pond pumps I've seen have mains cables going underwater. Seems like they rely very much on maintaining the insulation and seals. Replacing the cable will inevitably disturb these, and if you do get it wrong, then it's not the operation of the pump which you're worried about, it's the elecric water feature you now have.

clive

You would have to repace only the cable outside the water and weatherproof the splice in some way. Less effort to get a new pump TBH.

On 07 Aug 2006 15:46:21 GMT someone who may be snipped-for-privacy@isbd.co.uk wrote this:-

That should be fairly obvious. If they are in contact with the water when the electricity finally escapes from the cable then they might be killed.

Replacement is the logical option. If for reasons unknown youre determined to use it for another 20 years, theres always...

a) running it off isolation transformer and rcd b) coat the cable with a mixture of silicone gloop and plastic fibres c) or fit a new cable and epoxy waterproof the connection d) fit earthed gauze round the lead and add rcd e) dangle the pump just above the water so the inlet just touches the surface but the cable doesnt

and various other equally unlikely options.

NT

Replacement is the logical option. If for reasons unknown youre determined to use it for another 20 years, theres always...

a) running it off isolation transformer and rcd b) coat the cable with a mixture of silicone gloop and plastic fibres c) or fit a new cable and epoxy waterproof the connection d) fit earthed gauze round the lead and add rcd e) dangle the pump just above the water so the inlet just touches the surface but the cable doesnt f) fit deioniser to water feature

and various other equally unlikely options.

NT

Nononono! It's for the sake of d-i-y!

I admit I was puzzled too; you mean "when the bodge funally breaks down", right? I do have an RCD on the circuit; would that not immediately trip? In which case only the fish are likely to be in any danger.

No, Clive is right, the mains cable goes right into the pump, and has degraded along the whole of the underwater length.

snipped-for-privacy@care2.com then added:

Hey, it's barely ten years old so far:-)

That's more-or-less what I thought of

Ooh, yes that could be fun!

Yes, I get the impression that "unlikely" is the key term. Anyone want a

Thanks, all, for your comments.

Douglas de Lacey

On Tue, 08 Aug 2006 08:10:45 +0100 someone who may be Douglas de Lacey wrote this:-

When the existing cable breaks down.

That depends on the fault. It should do, but like any mechanical device it may not operate properly. There are also electrical faults that such devices don't detect. As a result relying on one to save one's life is foolish. Far better to avoid the possibility, by getting a new pump with a new cable.

. What's the resistivity of

There's a fair number of 'impurities' abour so I imagine it is fairly low.

My rather complex pond system has a number of points where there is seepage loss and I installed an automatic 'topper-up' - initially the sensor was two bits of stainless steel with dc passing through them - two reasons lead me to work out a very low voltge / high impedance ac system. One was the plating effect of what looked like lime on one electrode, the other was, that although I was only using a few volts, and possibly because it wasn't an isolated supply, it killed frogs !!

Rob

That still doesn't explain how I (or anyone else) gets killed by it, how does the 'electric water' get to you?

When the electricity 'escapes'?

How will a person touching any part of this offer a lower impedance to earth than the water itself? Or, on the other hand, how will any part that can be touched have a significant voltage on it?

Maybe because the water is insulated by a Butyl pond liner.

MBQ

condensation that cause my RCD to trip I have absolute confidence that water ingress into a pump would give the RCD no problems with detection. Having said that I wish I could more than ten years out of a submersible pump. I have just had to chuck a 3000 gallon per hour pump away that tripped the RCD due to very slight water ingress through a worn cable. The pump ran quite happliy on an unprotected circuit. This was a =A3200 pump. It was repairable but coming close to =A3200 to repair it was it worth it. It was 10 years old so time for the dump. If the RCD were to go while on holiday the ruined contents of your freezer are more than the replacement cost of the pump.

Kevin

One is standing in the garden and dangles ones fingers in the pretty waterfall. Or similar.

(isn't that _really_ obvious?)

clive

... and how do you thereby get a voltage between your fingers and the ground? It just doesn't add up, the water (which the pump is immersed in) is sitting in a hole in the ground, it would need a fair amount of current before that could be at any significant potential above that of the earth in general.

I doubt very much if the pond liner means that the water is insulated from the surrounding earth. Either the ground around will be dry (and thus non conductive and won't offer a 'path to earth' that I'm standing on) or it will be wet and so will the edge of the pond so the pond will be at earth potential.

On 08 Aug 2006 08:25:32 GMT someone who may be snipped-for-privacy@isbd.co.uk wrote this:-

Feel free to experiment, at your own risk.

You may only get a mild electric shock, I didn't say you would certainly die.

On 8 Aug 2006 03:53:22 -0700 someone who may be "Kev" wrote this:-

It should do and in nearly all cases will. However, the question is whether the small risk that it will not trip is worth it considering that the pump would cost little to replace.

I can see why the manufacturers encapsulate the stator and the cable leading to it in resin. Less to manufacture and less to go wrong after it is sold, including less for people to fiddle with. Watertight connections that will last for decades under water are a difficult thing to make and usually involve encapsulation of the joint.

Is long life not one of the things surface pumps are for?

Indeed, if the house electrical system is designed that way.