Reverse polarity LED glowing dimly

superheat6k

superheat6k

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I have noticed the reverse shore power polarity LED is glowing, indicating the neutral is at some voltage above earth.

The LED glow is quite dim, and goes off entirely when I knock off one particular MCB to a socket ring.

I have been around and unplugged each socket in turn, but can't isolate why this is glowing. The only item I cannot switch off locally is the fridge.

Is some potential difference between earth and neutral acceptable. Tomorrow I am going to investigate what the voltage level is.

However, any pointers here would be appreciated.
 
superheat6k said:
I have noticed the reverse shore power polarity LED is glowing, indicating the neutral is at some voltage above earth...
Click to expand...

I doubt that many people have such a device, do you mean something like this:
IN0526707-40.jpg


Surely the "reverse shore power polarity" LED indicates reverse shore power polarity. A neutral to earth fault would be indicated by a "neutral to earth fault" LED.
 
Does it only glow when the fridge is actually running? Does glow when that mcb is open but with a similar load on another circuit. If so maybe a poor connection on the neutral upstream of the warning indicator ...... that could include the pontoon supply :(
 
superheat6k said:
I have noticed the reverse shore power polarity LED is glowing, indicating the neutral is at some voltage above earth.

The LED glow is quite dim, and goes off entirely when I knock off one particular MCB to a socket ring.

I have been around and unplugged each socket in turn, but can't isolate why this is glowing. The only item I cannot switch off locally is the fridge.

Is some potential difference between earth and neutral acceptable. Tomorrow I am going to investigate what the voltage level is.
Click to expand...

When you say LED, is that actually a neon ?

Does the fridge have a off switch inside?

It can be a high voltage on earth, as well as neutral, but not likely confined to one circuit, as neutral and earth are common to all AC circuits, normally reverse polarity neon is between incoming neutral and earth.

So first job is to sort out circuit, and were reverse polarity neon is located.

Mains is dangerous, be careful.

Brian
 
This is a very common problem and is probably caused by the shore supply cabling. A simple test is to get the boat next door, or on the same pontoon, to put a large load on their boat. If they run a kettle and fire and your Reverse Polarity LED lights gets brighter then the fault is the pontoon AC supply.

This may not be an actually fault, but the result of lots of boats on the pontoon using lots of amps and causing a voltage drop along the cables feeding the pontoon. If you've not noticed this before in your marina it could be caused by a lose connection somewhere on the neutral cable feeding your pontoon. It may take the marina a long time to admit to any fault!!!!!

At the marina transformer the Neutral and Earth are bonded together. With large currents down the cables there will be a voltage drop along the neutral wire which may get up to 5 volts or more by the time it gets to your boat. There will be no voltage drop on the earth cable as there is no current flowing, so there is now 5 volts between the Neutral and Earth which makes the LED glow. This can cause earth leakage breakers to trip so you will keep losing power.

You should measure the voltage between the neutral and the earth cable. It shouldn't go above 5 volts AC. When there is a full reverse polarity it will have 240 volts across it and shine brightly.
 
The indicator is a 240v LED. When I bought the boat I found this was missing. It is connected between Neutral and earth at the incoming connection to the distribution panel after the RCD.

Not on my normal mooring, but on the visitors at the Cove in Weymouth. Only around four boats here.

If it is shore side I would not expect the LED to go out when I open a particular MCB, so most likely candidate is the fridge, which on this boat the plug is inaccessible. Can't even cut the supply to put it on permanent 12v - so another job to do here.

I will switch off the boat at the RCD and see what the shore power Earth - Neutral potential is, and if more than a few volts I will inform the HM.

I will monitor it for now, and will see if same thing happens tomorrow in Poole or back on my home mooring.

I do appreciate the safety advice, but I should be ok - I design and install 400vac industrial control systems in my day job, just this one has got me a bit foxed for now.
 
superheat6k said:
....,If it is shore side I would not expect the LED to go out when I open a particular MCB,....
Click to expand...
But that's exactly the point - the more amps you take, or the boat next door, the more the neutral/earth volts go up. Switch all AC off and measure the N/E volts. As you turn on your AC outlets one by one then the N/E volts will go up.
 
Measured 3v N - E AC, but also 2.4 v DC across the galvanic isolator, so reckon this is the cause. Doesn't light at all on the genny. I am surprised a 240v LED would detect such a small PD to make it glow dimly.

I wonder if this LED is defeating the purpose of the galvanic isolator, as the neutral line could be providing a secondary galvanic leakage path. This would explain the continued wear on my anodes since I fitted the GI. Looks like the LED is going in favour of a Neon.

Views please !
 
superheat6k said:
Measured 3v N - E AC, but also 2.4 v DC across the galvanic isolator, so reckon this is the cause. Doesn't light at all on the genny. I am surprised a 240v LED would detect such a small PD to make it glow dimly...
Click to expand...

You need to sort out why there is a voltage across your GI.

There is no such thing as a 240V LED, or even a 12V one. It will have a resistor in series to limit the current at the expected voltage. Personally I would remove it, and just check the AC with a test plug on occasion: http://www.amazon.co.uk/exec/obidos/ASIN/B003337BLM/dolcetto-21
 
nigelmercier said:
But still check the voltage across your GI.
Click to expand...

2.4 volts is certainly a puzzle unless the GI is defective although some GIs do go to a higher voltage that the usual 1.2 ish before conducting. I think it and its installation should be checked esp if the rate of anode loss has increased since it was fitted .
 
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superheat6k said:
Coming out tomorrow.
Click to expand...
I would remove the Galvanic isolator not the LED. The Amazon plug will do a similar job and is simple to fit in any socket on the boat, but the intensity of an LED (Neon) light does tell you the severity of the problem.

An AC voltage across the GI suggests it doesn't have a capacitor to pass the AC, or the capacitor has failed. A DC voltage suggests other problems and nothing to do with a Reverse Polarity light in circuit. This is a very complicated subject - with different ideas about how GIs should be fitted. See this link from Nigel Calder and read his Mech & Elec manual for correct fitting instructions:

http://www.yachtingmonthly.com/plus/409969/non-isolating-isolator
 
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sailinglegend420 said:
I would remove the Galvanic isolator not the LED. The Amazon plug will do a similar job and is simple to fit in any socket on the boat, but the intensity of an LED (Neon) light does tell you the severity of the problem.

An AC voltage across the GI suggests it doesn't have a capacitor to pass the AC, or the capacitor has failed. A DC voltage suggests other problems and nothing to do with a Reverse Polarity light in circuit. This is a very complicated subject - with different ideas about how GIs should be fitted. See this link from Nigel Calder and read his Mech & Elec manual for correct fitting instructions:

http://www.yachtingmonthly.com/plus/409969/non-isolating-isolator
Click to expand...

If the boat is normally/often left plugged into a shorepower supply and the earth is bonded , as is recommended, to the boats own ground/DC negative removal of the GI and directly connecting the earth would very likely lead to a high rate of loss of metal from the anodes. Its purpose is to prevent that.

A GI is normally fitted in series with the incoming shore power earth.
Fig1 in the diagram below

Galvanicisolator.jpg
 
VicS said:
If the boat is normally/often left plugged into a shorepower supply and the earth is bonded , as is recommended, to the boats own ground/DC negative removal of the GI and directly connecting the earth would very likely lead to a high rate of loss of metal from the anodes. Its purpose is to prevent that...
Click to expand...

Indeed, I would not remove the GI, just find out where the earth leakage is coming from. Do you have a RCD / ELCB?

On my boat the GI is the first thing that terminates the earth, as in Vic's figure 1, but it does not connect to the "Earthing point, anodes etc." There have been dozens (if not hundreds) of discussions on this latter point. I think the conclusion is that this connection is only mandatory on steel boats, but I would resist fitting it unless compelled to do so: it's like earthing the vice in your tool-shed!
 
nigelmercier said:
Indeed, I would not remove the GI, just find out where the earth leakage is coming from. Do you have a RCD / ELCB?
Click to expand...
Which is what NC says in the final paragraph of the link in #13

On my boat the GI is the first thing that terminates the earth, as in Vic's figure 1, but it does not connect to the "Earthing point, anodes etc." There have been dozens (if not hundreds) of discussions on this latter point. I think the conclusion is that this connection is only mandatory on steel boats, but I would resist fitting it unless compelled to do so: it's like earthing the vice in your tool-shed!
Click to expand...

It may be that it is mandatory for all in the latest edition of ISO 13297.

earthing your stainless steel kitchen sink might be a better parallel
 
VicS said:
It may be that it is mandatory for all in the latest edition of ISO 13297... earthing your stainless steel kitchen sink might be a better parallel
Click to expand...

Presumably ISO 13297 is not retrospective?

I found it hard to come up with an analogy, the vice was the first I thought of. However, I do see a purpose in earthing a metal sink: in case a live wire contacts a water pipe. I don't see any point at all in earthing seacocks or anodes, and a questionable safety benefit in earthing the low-voltage installation.
 
nigelmercier said:
Indeed, I would not remove the GI, just find out where the earth leakage is coming from...!
Click to expand...
I do agree - I didn't make it clear that I would remove the GI to try and isolate the fault and make sure it is installed correctly. Every boat that connects to AC shorepower should have one - or better still an isolation transformer.
 
I installed the GI due to heavy wear of the anodes on the Hamble, a common problem I am advised. However, by installing an led rather than a neon indicator I may have defeated the whole point if fitting it, the led with its voltage dropping resistor effectively allowing a short circuit straight past the thing. The AC PD is virtually nil, but I am seeing nearly 3 vdc across the GI, designed to stop Galvanic DC voltages below 6v, so seems to me the GI is trying to do its job, just that LED short is allowing the upstream shoreside connection for neutral to earth to effectively completely bypass the GI, which would explain why I saw little benefit for having it last season.

As for pros and cons of having the AC earth connected / bonded to the DC negative plus engine block, grounding CCT etc, I am satisfied the correct mode here is that the bond should remain. Not least of all to protect anyone in the water near the boat, should a fault current arise. To this end I have read both Calder, Ed Sherman and Charlie Wing.

The point I have learnt here is that an LED will provide continuity via its voltage dropping resistor, which I had not realised. I should be using a Neon with virtually infinite resistance.
 
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