Help with a 170 volt pushpit!

silver-fox

silver-fox

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I could do with a bit of help in tracing a wiring fault. We are currently out of the water having a cutles bearing replaced and are connected to Spanish 220v supply via a 16 amp socket in the cockpit which feeds : -

1. A ring main of 6 sockets
2. An immersion heater
3 A sterling batter charger.

Everything works OK. My polarity light indicates polarity is OK and the supply is shown at 220v at the panel voltmeter.

Imagine my surprise when SWMBO went to get off the boat this morning immediately after heavy rain and got a significant jolt the moment she touched the aluminium ladder whilst still holding onto the pushpit.

I checked out the situation and the it is unpleasant. I got my meter out and measured 170volts between ladder and pushpit.

I then went through a testing process which involved progressively switching off circuits at the main control panel.

With everything (all AC as listed above) switched off at the boat control panel, the pulpit was still live!

I then switched off the mains supply at the main boat panel and it was still live. Only by disconnecting the feed to the cockpit socket could I stop this problem.

I then put my meter across the supply terminals and everything was as expected: -

live to neutral 220v
live to earth 220v
neutral to earth 0v

I then checked the wiring for the socket and that was correct in that the socket wiring was consistant with the supply-side wiring so when connected it was live to live, neutral to neutral, and earth to earth.

At this point I could do with some help as I don't know how best to trace this fault.

Two other bits of info that might help the experts..

1.The boat is a Moody 425
2. It is not just the pulpit that is live, pretty much everything is including the rigging and the engine.

Any help on how best to find this fault would be gratefully received.
 
I remember there was a similar issue with a certain Trader boat some time ago. It was traced to a faulty earth in the boatyard's electrical system.

Sounds as if the boat is OK but there's a stray connection somewhere ashore side.

170v doesn't sound like a phase issue.
 
Don't know whether its any help but 170V is near halfway between 110V and 220V, incorrectly wired/damaged site transformer somewhere?
 
Check the input side of the switch panel. If there has been no major changes, the reverse polarity warning light is wired before the RCD ( assumming you have one ), this could give you a fault with power turned off at the panel.

Brian
 
Is your boat metalwork low impedance to the earth terminal on the incoming mains socket?
If so, I suspect that the earth you are importing is broken, floating up towards mains. Luckily it seems to be highish impedance.
Otherwise the earth on your boat is not connected to the metalwork.
 
Thanks for our feedback guys. Work has been halted by more heavy rain.

I think I am right in saying my earlier checks have eliminated both reverse polarity and a faulty earth from the supply side, so I shall be checking out what's happening behind my main panel in particular the switch as suggested.

Am I right in assuming the most likely problem is a connection somewhere where earth and neutral have been reversed? Or will I get these symptoms with live and neutral reversed as well?

Cheers
 
It might be worth seeing if adjacent boats have the same problem. If they do, then it may well be a marina/boatyard fault, and worth notifying the operator to sort it out...
 
When you say the pulpit is still live. You might think of it the opposite way in that the ladder is live.

When you disconnected the feed you lost the earth and so you boat became part of the fault.

Spain has many power supply standards from history. There is a yard with three phase 120/210v plugs and another marina next door who uses 240/415 sockets of the same colour.



The only solution is to go out and buy an industrial isolation transformer and supply your boat from it. With an isolation transformer you decide what is earth.

Then put a wire from the pushpit to the a lump of metal on the ground and that will stop static and charge differences building up.

HOWEVER do NOT do that without the ISOLATION transformer in the circuit first.

Edit: see next post
 
Proof of the above theory would be to measure between the supply socket earth and the ladder.

If the Earth wire vs. the local puddles/concrete IS at, or near 0v, ignore the above.
 
Why not check for any connection between your pushpit/rigging etc and the live/ neutral on your 220v system with the shore power disconnected.

This should let you know if the fault is yours or the yards.

If it is yours i suggest you start disconnecting the feeds to the various circuits ( both live and neutral) until you find the culprit.

hope this helps.
 
Why should the rigging be live ? or the pushpit, it's not bonded ? also aluminium ladders normally have rubber / plastic feet, so are effectively insulated from ground. Have we static, as in a shock from a car.
From first post the supply sounds reasonable.
What voltage is there between 12 volt neg / bonding system and pushpit / rigging ?
Is the battery charger through the AC switch panel, or direct to mains ?

Brian
 
Re: Help with a 170 volt pushpit! -Problem Solved

Problem solved ... I think...

I started trying to trace what was going on behind my control panel and learned a lot in the process about what cables come from where and why.

For those of an inquisitive frame of mind the cause is described below.

I have three AC functions only as previously described
Immersion heater
Battery charger
Ring main for appliances

As I started to try to chase the fault I noticed that if I switched on either the charger or the heater it would "appear to short out and the panel AC voltmeter would drop to zero. If I then switched off the supply at the panel waited a few seconds then the supply would return at a full 220v.

I (wrongly) concluded that I had a common short on these circuits and if I could find it then problem solved. In fact what was happening was any serious demand was dragging the voltage down to zero.

Then in a moment of (for me ) great lateral thinking I realised that whilst the ring main appeared to be working OK, it actually wasn't doing anything. I tried to find something cheap and cheerful to plug in and used my inspection lamp which has a 20 watt bulb. Result was it dragged the voltage down to around a 100volts at the panel. Clearly a supply problem.

I decided to move the borrowed extension cable to another shore feed and only to find that it had fried and whole lengths of cable had burned insulation. Clearly it had been shorting out under load but looked good when I measured voltages

I then made an additional extension to my existing lead and "Voila", everything works fine, I even have zero volts on the pushpit etc when compared to the ground peg I had driven in earlier.

Just to compound things we have just had a thunderstorm with overhead lightning and torrential rain and I have lost shore power altogether, but I am not even going to investigate that till it stops hailstoning...

Finally I have to figure out why the pushpit went live and how to prevent that happening again. It really doesn't seem failsafe to me

A big thanks to you all for your help and suggestions.

Onwards and Upwards!
 
Re: Help with a 170 volt pushpit! -Problem Solved

[ QUOTE ]
Finally I have to figure out why the pushpit went live

[/ QUOTE ] maybe your pushpit is connected to the ships internal earth system and the damaged cable made the whole earth system live but not connected to the shore earth.

Too late to test the theory now but if you had put 1 foot on the ladder and the other on the engine you would have got a shock. So would any one watching I guess!
/forums/images/graemlins/laugh.gif It sounds as though the RCD on the shore power is not working you should not have got a shock no matter what the fault was. You should endeavour to test it then if it doesn't work complain loudly.
 
Re: Help with a 170 volt pushpit! -Problem Solved

I promise you we did get a belt ... that's how we discovered the problem. It very near sent SWMBO off the top of the ladder.

Like Queen Victoria she was "not amused" As chief mechanic I am held personally responsible.

I suspect you are right about the grounding. Most things are bonded -ultimately to the anodes to stop corrosion. What I have to get my head around is how the AC fits into all this!

A salutary lesson about the dangers of AC on a boat.

Still SWMBO always wanted blue eyes and for a moment this morining she did.
 
Re: Help with a 170 volt pushpit! -Problem Solved

This sounds like an induced current in the earth. If the electrical earth is not properly bonded it can float and can, under certain circumstances, create a high potential. I've inadvertantly created a 70V potential in an unbonded earth by leaving the extension cable coiled up. This acted like a transformer and induced a voltage in the earth and I only had a 30W soldering iron running.

Make sure that your earth is fully bonded, that the supply wiring is not coiled and that no appliances have faults which create currents in the earth circuit.
 
Re: Help with a 170 volt pushpit! -Problem Solved

Just one point regarding using a digital voltmeter for testing voltage.
The DVM has a very high input impedance that means it takes virtually no current from the source you are testing. This is great for electronic circuits but has a disadvantage when checking things like 12 v or 240 volt circuits which are low impedance and use lots of current.

The high impedance of the DVM can be demonstrated if you insert a wet finger in the circuit between one probe and your 12v battery. The current flows theough your finger to give a significant reading.

Now even more so with 240v power the meter can almost smell Ac even if it coming via a very high resistance circuit. Now clearly the power leaking to the pulpit was significant if gave a shock to SWMBO but your actual voltage reading may not mean much.
If you connect a resistor across the terminals of the DVM you can measure the power in more like real terms. So for 12v system measuring 1000ohms means that the meter draws 12 miliamps at 12 volts which while not a lot of drain will check to make sure they are "real" volts you are measuring. For 240v systems a resistor of 20K ohms will do the same thing. It might have been interesting to see what voltage was on the pulpit with a 12ma load.

Anyway I am glad you have fixed the problem. Yes it is very concerning it could have caused a nasty accident. olewill
 
Re: Help with a 170 volt pushpit! -Problem Solved

[ QUOTE ]
This sounds like an induced current in the earth. If the electrical earth is not properly bonded it can float and can, under certain circumstances, create a high potential. I've inadvertantly created a 70V potential in an unbonded earth by leaving the extension cable coiled up. This acted like a transformer and induced a voltage in the earth and I only had a 30W soldering iron running.



[/ QUOTE ]

I think you have hit the nail on the head. Foolishly I did leave part of the extension lead in a coil and it did fry! OOps. The earth here is renowned for being unreliable.
 
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