Electrical problem

[oldsaltoz]

Connecting shower pump, soldering the joints with a 240 volt iron, noticed a small spark on the negative terminal, and pump runs when soldering contacts the positive terminal, 12 volt power turned on at the time, float switch is in line before the pump connection.

Put a meter between the 240 volt iron and the positive side of the pump and got 12vDC. but nothing with the iron turned off.

We have a 3 stage battery charging and battery monitoring systems on board as well as shore power and 3 solar panels, also twin engines.

Any idea what we should be looking for?

 

[Gunfleet]

Double insulation isn't, er double insulating? I think I'd buy another iron.

 

[William_H]

No I find it common certainly with my home soldering iron where the body is connected to the mains earth. I think that a safety feature. ie blow a fuse if you touch a live wire with it.

So if the iron causes a spark to the negative of the pump then clearly the ships negative is connected to the mains earth. Perhaps back through the marina power supply earth.

This then begs the question is that intended? It may be via a deliberate connection mains earth to ships earth. Or even deliberate via a galvanic isolator. However it may be inadvertent via your battery charger negative being connected to the case and mains earth. Disconnect the battery charger -ve and +ve to check that out.
Or it could be via a 240V fridge body or similar.

If it were me I would want to know the nature of the connection. You can use a multimeter to check continuity (mains earth to ships negative) with the mains disconnected. The stray earths and currents can give horrible electrolysis damage if power is left connected long term.
Incidentally the pump is switched in the negative to minimise power at the switch which may be under water (hence corrosion). However ensure as far as possiblle that all wiring and connections stay out of the water as far as possible. good luck olewill

 

[oldsaltoz]

No galvanic isolator on board and sparking only hapens when supply is turned on to the shower pump?

 

[VicS]

I would expect the soldering iron to be earthed. That's easy enough to check with a meter on a low ohms range. I would expect the negative side of the ships 12 V supply to be earthed (unless it has a positive earth system)

If the float switch is in the negative side of the supply to the pump as William _H suggests I would expect a big spark when the soldering iron contacts the positive terminal of the pump with the power on. In fact I would expect it to blow the fuse/ trip the circuit breaker on the pump supply. With the fuse replaced or cb reset I would expect a small spark when contacting the negative terminal and the pump to run.

If however the float switch is in the positive feed to the pump I would expect nothing to happen when touching either the pump terminals unless the float switch was in the "ON" position, in which case I would expect a large spark when touching the positive terminal and for the fuse to blow or breaker to trip.

If the negative side of the 12v system is not connected to the ships mains voltage earth there will still most likely be a connection to earth via the stern gear or anodes and the water. That may explain why you are not blowing the fuse or tripping the circuit breaker on those occasions when I said that would happen.

Even so I cannot explain what you are observing unless the +ve and -ve in the supply to the pump have become swapped.

IMHO pretty stupid to go soldering wires onto the pump with the supply turned on!

 

[oldsaltoz]

Quote:
IMHO pretty stupid to go soldering wires onto the pump with the supply turned on!
End Quote.

I can only agree with that. No doubt 'someone' thought it was off.

 

[William_H]

OK Brian my guess is that the negative of the battery goes to ships ground and to the sea. The soldering iron body is going to the sea via the earth wire on the soldering iron then back through the marina wiring to the earth stake probably at the meter box for the marina.
This assumes that your 240V electric system does not take the earth wire to any earth on the boat but simply by the earth that comes with the power cord. That is all OK to a point. It relies on the integrity of the earth wire in your power cord to the marina to provide a safety earth.

It is sometimes considered inadequate when you consider how much metal work in the boat is electrically connected to the sea. In which case the mains earth in coming into the boat is also bonded to the ships earth. So if the power cord/marina earth fails you still have good earthing.

Good earthing is vital in devices which have a metal case. So if an active wire falls off or shorts to the case (often happens in emersion heaters) the case is connected to earth and the fuse is blown. If you don't have an adequate earth then the case simply becomes 240V live waiting for someone to touch it while the other hand is electrically connected to the sea,-ve etc. Devices which don't have a metal case are called double insulated and are essentially safe cos there is no case to become alive. When you get to a battery charger you have both the case which may or may not be metal and the terminals and wiring.

To connect the negative to the case and the mains earth will provide extra safety.

However your local earth connected to the mains earth can provide an additional path for any stray currents from the marina. Indeed you could in a fault condition become the only safety earth for all the consumers in the marina.
A galvanic isolator will stop the small (corrosion) currents and only conduct with a fault current ie when saving lives. However it won't work if it is bypassed by any other appliance case being connected to the mains eath and ships earth. Hence my suggesting you identify just what is earthed and how.

So as far as I can tell it a matter of safety level demanded by marina local supply and good sense (earthing at the ship) versus safety from corrosion and simplicity usually being adequate. ie an extension cord over the rail to a jug or heater or battery charger is not seen as needing a full installation with local earthing. But check that charger if you leave it on 24/7 good luck olewill

 

[oldsaltoz]

Thanks OleWill,

All a bit second hand, my Son is on board and I'm a 2 hour flight away with a mobile that will not stop ringing.

I have him looking for other faults now that we seem to have put that one to bed.

Thanks again all.

Avagoodweekend......