I have an old pump (Lotus "Little Gem") which is still working fine (so am loath to throw it away) but the cable is becoming very degraded: the outer rubber cover is cracking away in several places. As far as I can see the cable just disappears into a lump of resin(?) in the body of the pump. Any thoughts about digging this out and replacing it (with silicone?) -- or am I really onto a loser here?
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.
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.
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
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
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
*free* (but useless) pond pump? (But I would like to know whether the RCD might fail to function immediately the electrons begin to escape. What's the resistivity of pond-water?)
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.
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 !!
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?
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.
... 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 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.
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