Electrical issues - outdoor cable & isolator switch

[RickS]

Evening

I have a couple of questions that are both electrical in nature - if a moderator wishes me to make that two separate questions then i will.

First question - my external mains hook-up cable, which is attached to a short metered cable from the marina, was decidedly warm with a melting plastic smell, which I knew was bad news. I unplugged and took it apart - one of the wires was coming loose but just looked a mess, and the plastic housing had started to melt slightly.

I think I have to own up and admit that it looks like it was my fault but would like it confirmed so i don't make the same mistake again. I was testing the immersion heater and started using the hoover at the same time - I haven't adjusted from being in a house with unlimited LX. I suspect I was drawing too much current without thinking and the already dodgy cable took the brunt rather than tripping the electric supply bollard. Does this sound the right diagnosis? (hands up for being a wally!)

Second question - I only seem to have one isolator switch which is really difficult to get to - I can get my hand on it but have to turn it by feel rather than seeing what I am doing. I turned it to the only other position it would go to and the bedroom lights (at the stern) dimmed but did not go out, and the saloon lights came on as normal.

Is there another position I am missing on the switch or is there something funny going on?

As always, thanks in advance for the all the helpful advice I know i will get (having got lots of help on my other questions)

Rick

[WotEver]

Q1: The bollard is probably fitted with a 16A breaker (MCB).  It is possible that you exceeded that, but an immersion and hoover shouldn't have done.  If you DID exceed 16A then the MCB is faulty. If you DIDN'T exceed that then it's just a poor connection in the plug. I'd suspect the poor connection first - they're the most common cause pf electrical fires.

 

Q2: Not enough info I'm afraid.

[RickS]

Thanks for the reply WotEver. A chap at the marina spoke about 10A at some point but Im not sure in what context.

 

Im not sure how much more info I can give about the isolator switch Im  afraid - it turned from its 'on' position to the only other position I could turn it to (but thats possibly because it was awkward to get to) and some lights dimmed, others weren't affected  When i go back to the boat I can try and get more info if you let me know what you need to get a better picture of the situation. I'll try and take a photo of the switch

[ditchcrawler]

29 minutes ago, Rick Savery said:

Thanks for the reply WotEver. A chap at the marina spoke about 10A at some point but Im not sure in what context.

 

Im not sure how much more info I can give about the isolator switch Im  afraid - it turned from its 'on' position to the only other position I could turn it to (but thats possibly because it was awkward to get to) and some lights dimmed, others weren't affected  When i go back to the boat I can try and get more info if you let me know what you need to get a better picture of the situation. I'll try and take a photo of the switch

If that is your main DC isolation it needs investigating

[GUMPY]

36 minutes ago, Rick Savery said:

Im not sure how much more info I can give about the isolator switch Im  afraid - it turned from its 'on' position to the only other position I could turn it to (but thats possibly because it was awkward to get to) and some lights dimmed, others weren't affected  When i go back to the boat I can try and get more info if you let me know what you need to get a better picture of the situation. I'll try and take a photo of the switch

 

Random thought, its a 1/2/both switch and the other battery is flat

 

[RickS]

I would agree 100% with that ditchcrawler - provided Im not doing something stupid (real possibility) then it doesn't feel right. I would also ideally like 2 isolator switches rather than just the one - maybe time to get a sparks in

 

Thanks for the thought Loddon. To be honest, I don't know enough about these systems to be able to comment, but all taken on board.

 

Incidentally, I am looking at a new mains cable - really don't trust the old one - and some say 1.5mm cable and some 2.5mm cable (I assume this is the measurement of the individual cores) -  which one should I be going for please?

[ditchcrawler]

I am starting to suspect the isolator is in the negative line and you are getting some sort of earth path return. How old is the boat. Our share boat only had one isolator in the negative return cutting off both batteries. Its OK if no one modifies or adds things

[RickS]

That's possible, the boat is 22 years old - I will see if I can follow the cables when i get back to the boat. It does sound like I need an electrician to look over this, and probably the whole electrics - whilst I kind of get what you are saying, it certainly isn't my field. Thanks again

[Paul Gwilliams]

18 minutes ago, ditchcrawler said:

I am starting to suspect the isolator is in the negative line and you are getting some sort of earth path return. How old is the boat. Our share boat only had one isolator in the negative return cutting off both batteries. Its OK if no one modifies or adds things

That's the problem with our installation. Switched negative. Currently rewiring

[ditchcrawler]

4 minutes ago, Paul Gwilliams said:

That's the problem with our installation. Switched negative. Currently rewiring

Its OK until some one does something and runs both cables back to the battery bypassing the isolator in the negative line and making an earth connection like a car radio and aerial 

[WotEver]

34 minutes ago, Rick Savery said:

some say 1.5mm cable and some 2.5mm cable

2.5

[RickS]

Thanks Wotever, I assume that 2.5 is better for longer lengths and higher loads - Im going to get a 14m one.

 

Paul, ditchcrawler - thanks, I suspect you are right. There are more sockets than you can shake a stick at in this boat - I have found 2 RCD units (one in the engine room, one in the saloon) with at least three car radios around the place. Everywhere you look there are cables, in cupboards, under cupboards etc.

I think I will get an electrician to have a good look at the whole installation. 

[WotEver]

26 minutes ago, Rick Savery said:

Thanks Wotever, I assume that 2.5 is better for longer lengths and higher loads - Im going to get a 14m one.

Not really. 2.5 is the minimum for a 16A hookup, even if your current mooring offers less. Voltage drop is irrelevant for mains cables. 

[nicknorman]

Regarding the isolator, it is a battery isolator and thus its purpose is to disconnect the batteries from the cabin services (lights etc). But not necessarily to remove all sources of power from the cabin services. So you might have a battery charger, solar controller, alternator  etc connected directly to the cabin services and one of these sorts of items might be providing power to the cabin services even with the isolator off.

[Higgs]

 

Think about relocating the isolator switch. You seem to have poor access to the switch, it really should be in a handier place; for use and inspection. 

 

 

 

Edited September 5, 2020 by Higgs

[RickS]

Wotever - thanks for that, although I'm now slightly confused - if no voltage drop then is 2.5 for larger loads / current draws? 

 

Nickorman - thank you - I have a inverter/charger which seems to still be live when I turn the isolator, but no solar and the engine isn't used at present, so not sure what is powering everything when the isolator is switched off - except it must still be the batteries so the isolator clearly isn't doing what it's supposed to.

 

Higgs - thanks. will definitely look at relocating the switch - I can get my hand on it, just, but can't see what I am doing at the same time - doesn't feel very safe 

[WotEver]

9 minutes ago, Rick Savery said:

Wotever - thanks for that, although I'm now slightly confused - if no voltage drop then is 2.5 for larger loads / current draws? 

A shoreline cable has a 16A plug on one end, and a 16A socket on the other.  It can be plugged into a bollard capable of supplying 16A.  Therefore the cable should be rated for 16A, and that's 2.5mm²

[RickS]

Makes sense - you'll have to allow for my ignorance I'm afraid ? I only ask as I have seen 16A shoreline cables saying they are 1.5mm cables, hence my confusion - although I will be taking your advice and going for 2.5mm one.

[WotEver]

11 minutes ago, Rick Savery said:

Makes sense - you'll have to allow for my ignorance I'm afraid ? I only ask as I have seen 16A shoreline cables saying they are 1.5mm cables, hence my confusion - although I will be taking your advice and going for 2.5mm one.

1.5mm² flex is right on its upper limit at 16A. So it can legally be sold but it will get warm, and there’s no margin for error if it ends up in coils. 2.5mm² on the other hand will be well within its rating and is overall a tougher cable, physically as well as electrically. 

[KenK]

Rick, You need to understand what the isolator actually does, given that you only have one it should remove all battery power from the domestic bank to the boat, clearly if the lights are staying on it is not working correctly. It should removing the positive pole of the battery not the negative (0V) because as has already been said it is possible to achieve a return via the hull of the boat.

The external mains cable 230 V AC needs to be capable of carrying more current than is available from the shore supply, generally a maximum of 16 amps although it could be less, so 2.5 mm per core and ideally flexible cable. Voltage drop of an AC mains supply will be virtually nothing over a short distance, it is the current capacity of the cable which is important. In addition do not coil any excess mains cable that can create an inductance and generate heat.

Voltage drop can be an issue with the 12 V DC supply from the batteries, again the size of the cables is important too small and they could overheat.

[RickS]

Thanks KenK . .  it should remove all battery power from the domestic bank to the boat . .  that was my thinking and the fact that it is called an isolator was what I was expecting it to do - but you're right, if lights etc are still on, then either i have done something odd with the switch and not turned it off properly - difficult to be 100% sure as I can't see what I am doing - or, as you say, something is not correct.

it has been suggested by others that it is erroneously connected in the negative line - which I shall check when I am back at the boat - but either way, I shall be getting an electrician to look at the whole installation and make appropriate changes.

I have just ordered a 14m 16A cable with 2.5mm cores so thanks to you and Wotever for that advice.

When the electrician has a look hopefully he/she will spot any undersized cables

[IanD]

5 hours ago, KenK said:

Rick, You need to understand what the isolator actually does, given that you only have one it should remove all battery power from the domestic bank to the boat, clearly if the lights are staying on it is not working correctly. It should removing the positive pole of the battery not the negative (0V) because as has already been said it is possible to achieve a return via the hull of the boat.

The external mains cable 230 V AC needs to be capable of carrying more current than is available from the shore supply, generally a maximum of 16 amps although it could be less, so 2.5 mm per core and ideally flexible cable. Voltage drop of an AC mains supply will be virtually nothing over a short distance, it is the current capacity of the cable which is important. In addition do not coil any excess mains cable that can create an inductance and generate heat.

Voltage drop can be an issue with the 12 V DC supply from the batteries, again the size of the cables is important too small and they could overheat.

Coiling up a mains cable doesn't cause any inductance problem because the current return path is back down the same cable. It does cause a heat problem because cable current ratings are for straight uncoiled cables where the heat can escape -- same thing applies to those extension cables on reels, they can only carry the rated current when fully unwound.

[WotEver]

4 hours ago, Rick Savery said:

either way, I shall be getting an electrician to look at the whole installation and make appropriate changes.

Just do yourself a favour and ensure that he’s an experienced boat electrician and not a land-based sparky. 

[RickS]

Good point Wotever - I suppose land-based electricians won't have the 12V experience if nothing else.

[Keeping Up]

Assuming that it is correctly connected (ie so that it disconnects the battery terminal from absolutely everything) then having the isolator switch in the negative lead CANNOT cause a spurious return path via the hull, even if various things that shouldn't connect to the hull do in fact do so (such as a car radio aerial outer). Actually I prefer it being in the negative because having switched it off results in the safe situation that when working on the battery connections it doesn't matter if any one cable should happen to drop and land on the hull; if the switch is in the positive and you should happen to accidentally drop the positive cable on to the hull there will be sparks. In fact the only convincing argument I've seen for it being in the positive is because that is where you would expect to find it! And yes I am a qualified electrical engineer (or was until I retired).