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Electric leak, advice needed


Hannah Jones McVey

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Hi,

 

A few weeks ago our boat came out for survey and the blacking job done since months earlier looked like it had seen better days. During investigations since the man responsible for the blacking has done an electrical leakage test and sent us this outcome

 

'

basically I don’t think there was anything switched on on the boat because the current draw was 71 milliamps and at that current the imbalance between live and neutral was 0.3 mA  . the earth wire had zero current.

This means that the imbalance current is flowing out thru your hull

Although small at this quiescent state it would likely rise when other units are switched on'

 

I am no electrician and this means nothing to me. Can someone explain it in a dummy's guide style. The boat is being sold at the end of the week and I need to know what I should do.

 

Many thanks

 

 

Edited by Hannah Jones McVey
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The report means that 71 thousandths of an amp was going into the boat down the live wire and 70.7 thousandths of an amp was coming out again down the neutral wire.  The remaining 0.3 thousandths of an amp was going out of your hull into the water and then through the earth back to the sub station.

The stray current is probably getting out through the interference filters in equipment  power supplies which are only switched in the live wire or as Wotever says through dampness.  It will leak out through power supplies even when they are off.

Not much you can do about it and I don't think it is a big enough problem to cause your blacking to come off.  That is more likely to be poor application.  Any current  leak will tend to take the easy routes through anodes or the prop and shaft.

Let the next owner think about it.

N

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The buyers survey didn't pick it up.

 

The explanation is really useful thank you. Is that a significant amount?

 

I am saddened you think it's poor application, I agree but the bloke who did it doesn't, have already lost £700 off the negotiations as a result. 

 

No neon lights that I know of. 

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Innisfree's blacking was applied nearly 2 years before launch, done immediately the shell was completed and after it was degreased, but it started to peel off within weeks after launch. Decided blacking hadn't adhered to shiny millscale so grit blasting removed blacking rust and millscale and then reblacked, no problem from then on. 

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27 minutes ago, Hannah Jones McVey said:

Can you explain what you mean? Do you feel he tested it incorrectly?

Yes. With the shore power disconnected he should have checked the wiring with an insulation tester, taking resistance measurements and more if he’s going to give any meaningful reports. 0.3mA ‘leakage’ (if correct) must be caused by something, but without the correct tests we don’t know if it’s from RF circuitry in some piece of equipment or a bit of damp somewhere. Either way in my opinion it’s best simply ignored. 

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If the wiring is going to be checked with an insulation resiatance tester it is important to ensure that nothing is plugged in inside the boat and that any permanently wired equipment is switched off.  A resistance tester can put over 4 times the normal voltage  on the wires and anything connected may not like that.

Do you have an immersion heater? These are a not infrequent source of current leaks.

N

Edited by BEngo
speelinge
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Hmmm my concerns exactly

Just now, BEngo said:

If the wiring is going to be checked with an insulation resiatance tester it is important to ensure that nothing is plugged in inside the boat and that any permanently wired equipment is switched off.  A resistance tester can put over 4 times the normal voltage  on the wires and anything connected may not like that.

Do you have an immersipn heater? These are a not infrequent source of current leaks.

N

No. No imersion

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55 minutes ago, BEngo said:

If the wiring is going to be checked with an insulation resiatance tester it is important to ensure that nothing is plugged in inside the boat and that any permanently wired equipment is switched off.  A resistance tester can put over 4 times the normal voltage  on the wires and anything connected may not like that.

Well yes of course. As anyone doing such testing would know. 

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I’m sceptical that the boat blacker has equipment accurate enough to detect 0.3 mA difference. He’s probably assuming his Digital multimeter is 100% accurate !

 

I’m also not sure how there can be any earth leakage if the GI is properly installed and working. This suggests to me that there is a fair degree of BS baffling brains going on.

 

i be inclined to treat it as a red Harding for the time being

 

 

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1 minute ago, jonathanA said:

I’m sceptical that the boat blacker has equipment accurate enough to detect 0.3 mA difference. He’s probably assuming his Digital multimeter is 100% accurate !

 

I’m also not sure how there can be any earth leakage if the GI is properly installed and working. This suggests to me that there is a fair degree of BS baffling brains going on.

 

i be inclined to treat it as a red Harding for the time being

  

 

Wot is this red Harding please?

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2 minutes ago, jonathanA said:

I’m sceptical that the boat blacker has equipment accurate enough to detect 0.3 mA difference.

Hmm, or would know how to use it if he did.  I'm not knocking the knowledge of folk who black boats as the bloke who did mine was  Chartered Engineer, but I suspect very few folk slapping bitumen on narrowboat bottoms are the right ones to make such an assessment. Boat electrics, particularly where stray currents are concerned, are a pretty tricky subject even for the otherwise well qualified: some folk here have a good depth of understanding, but for the rest of us it's a limitation worth bearing in mind.

 

  • Greenie 1
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The guy is talking rubbish. Apart from the fact that the current discrepancy is tiny and probably the result of measurement inaccuracy, the whole point of blacking is to insulate/isolate the hull from the water. So it is not feasible to suggest that this (probably imaginary) tiny current is in any way responsible for the blacking degrading. There will still be plenty of exposed metal (the baseplate, the propeller etc) which would conduct away any current much more easily than blacking (if the current wasn't imaginary!). He is simply making up an excuse for the blacking issue and probably thinks that with you being a girly he can bamboozle you with fake science. Fortunately you are sensible enough to seek advice and not take his mansplaining at face value!

  • Greenie 2
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12 hours ago, BEngo said:

If the wiring is going to be checked with an insulation resiatance tester it is important to ensure that nothing is plugged in inside the boat and that any permanently wired equipment is switched off.  A resistance tester can put over 4 times the normal voltage  on the wires and anything connected may not like that.

Do you have an immersion heater? These are a not infrequent source of current leaks.

N

It should be twice the operating voltage so the 500V range. A neon indicator light will show a .2 meg fault which is a giveaway that a spur has been left on.

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