It's shocking .... My boats melting

[Nostrodamus]

Twice in the last year I have found melted wires on my boat.

On the first occasion during last winter I had heaters and a dehumidifier on. Putting the electric kettle on at the same day just finished it off.

The problem came about in a wire which had been added at a later date by someone to run additional items on th boat. It was not big enough to handle the load and therefor melted it and a small terminal block and if I had not smelt it things could have been far worse.

An electrician told me it is a common problem as boats are designed with a certain electrical system that works. Over the years people upgrade and add various items often using any old wiring they have to hand or not upgrading the existing wiring to cope with the extras.

On the second occasion it was the external shore power cable leading into the boat. That too stopped working and began to melt at the pins connecting it to the boat. Apparently over time the pins can get corroded or pitted setting up a resistance which can heat up under load as it did in my case.

I am not an electrician alhough I have now learnt the hard way of how important it is to use the correctly rated wires.

Has anyone else had similar problems, is this a problem of our own making with boats and hopefully it may make you all have a look and save yourself some danger or work in the future.

 

[VicS]

Overheating due to corroded pins etc on connectors can really only be avoided by keeping the pins etc clean.

Overheating wires due to overload can be avoided by ensuing that no wire has a current carrying rating ( for the conditions in which it is installed) less than rating of the fuse or mcb which supplies it.

 

[sarabande]

and to add to VicS comment, many additional installations fail to include the length of the 'return' cable in the calculations for cable cross-section.

 

[ProDave]

I strongly suggest to the OP you get the mains installation ripped out and started from scratch. It's clearly not up to standard.

The maximum current available from a shore hookup is 16A, usually less, so that's what your wiring should be rated for. Clearly it's not.

Usually 2.5mm cable throughout is all you need. What's yours wired with, bell wire?

 

[stuhaynes]

Usually 2.5mm cable throughout is all you need. What's yours wired with, bell wire?

2.5mm flex, not the flat grey twin and earth used in a house, it must be multi-stranded to cope with vibration.

 

[pvb]

and to add to VicS comment, many additional installations fail to include the length of the 'return' cable in the calculations for cable cross-section.

That's true for crucial voltage drop calculations for DC cables, but the OP is surely talking about his AC installation?

 

[sarabande]

yes indeed, he notes an issue with mains wiring, but my comments - perhaps out of context - was primarily about DC. Apologies if it obfuscated.

 

[VicS]

and to add to VicS comment, many additional installations fail to include the length of the 'return' cable in the calculations for cable cross-section.

In mains power installations like the OP was describing enhanced cross-sectional area to limit volts drop is not likely to be necessary. It is adequate the X-sectional area for safe current carrying capacity that is important.

Once you come down to 12 volt installations the loss of much more than say half a volt starts to be come significant. If cable runs exceed very roughly about a metre or so then it becomes the overriding consideration as cable simply sized for safe current carrying capacity will not be heavy enough to carry the current without significant volts loss.

As you say when sizing cable to avoid volts drop on long runs the total length of both positive and negative conductors must be taken into consideration.
Some on-line calculators take this into account automatically but some, the majority perhaps, do not.

 

[Blueboatman]

When I installed a 1200w windlass, even by the received and written electrical recommendations plus the 30% extra cross section, I still went a tad over the top. Fit and forget ( apart from the corrosion, condensation, aging, vibration, fatigue, aging of the batteries and charging system, regulator, er er) Sigh.

Perhaps we should fit smaller fuses as the years roll by in lieu of rewiring?

 

[Beadle]

"Perhaps we should fit smaller fuses as the years roll by in lieu of rewiring?"

I'm not convinced this is a good idea.

The fuse will have to be of an adequate capacity to take the load current. A fault in the wiring will not increase this current, it will actually reduce it. The danger is voltage drop across the faulty bit of cable or connector.

This causes power to be dissipated at the faulty point by voltage drop across it. The power being equal to the voltage drop X the current

A smaller fuse will not reduce the current. It will only "blow" if the current increases above the rating of the fuse - which will have to be adequate to take the normal load current.

If the wiring is faulty the answer, the only answer, is to repair or replace it.

 

[Nostrodamus]

The problem I had was with someone who took a short cut prior to me owning the boat. In effect a 3 inch piece of wire was put in so the reverse cycle air conditioning could be run from shore power. The wire used and the associated joining box were far too small for the load that went through it. I have consequently gone through all the other wiring and I am as happy as I can be.
I was supprised by the shore power lead though as it was something I was unaware of and I wonder how may boats may have the same problem?

I am no expert as I say but it makes me wonder how may changes on oldr boats are made without concidering the original wiring ie, new and additional instruments, auto pilots, light changes, running tv's, stereos, computers, and a lot of other things. I was also supprised at the initial power draw of an electical kettle which is huge. I still have so much to learn but by putting something like this up and your comments I and others may learn more and think before other electrical items are added to the boat. If it saves damage or lives so much the better.

 

[[2574]]

Mike,

I've been in a number of Marinas where there is a 32a shoreside supply. The danger is that boats tend to be rated for 16a supply. Consequently it is perfectly possible to overload the shore power lead without the trip on the pontoon supply tripping. I protected for this eventuality by fitting a 16a supply trip directly after the inboard shore power supply socket. When we accidentally demand too much power, (heater, dehumidifier, 70a charger, 3kw kettle) and it is easy to forget, the 16a trip on the boat trips out. Since instalation this system has protected us on a couple of occasions, well worth the cost. The same trip device is also a polarity checker, two birds with one stone.

Rob

 

[OldBawley]

Last summer. Sailing single-handed to Dokos Greece. Black smoke comes out of the cabin. A no longer in use power cable to a 12V LCD colour TV burns . I cut the cable and throw it in the cockpit.
See pic.
We do not use the tele any more, the cable was not connected to the TV, just stowed away, power on it, coiled neatly. Very thin cable, an 8'' LCD colour TV uses very little power. Had noticed that the cable was brittle, the outer plastic was broken on several places. Chinese junk.
I think that the isolation of the inner cores has broken also, the copper strands made a short and started glowing. The fuse protecting the galley power block did not blow, it is 8 A since a water pump is on it. A CD holder touching the cable melted also. Must have had about 14 Volt on the system, windgen and solar panels charging.
Had it happened while I was playing with the dingy, who knows.

 

[pvb]

I think that the isolation of the inner cores has broken also, the copper strands made a short and started glowing. The fuse protecting the galley power block did not blow, it is 8 A since a water pump is on it.

You were lucky! But it's worth remembering that the purpose of fuses is to protect the wiring, and fuse values must match the wire connected to them. If you connect power to a very thin wire, you have to use a correspondingly low-rated fuse.

 

[oldharry]

Twice in the last year I have found melted wires on my boat.

On the first occasion during last winter I had heaters and a dehumidifier on. Putting the electric kettle on at the same day just finished it off.

Has anyone else had similar problems, is this a problem of our own making with boats and hopefully it may make you all have a look and save yourself some danger or work in the future.

Hold on a minute: 2 heaters, a humidifier AND and electric kettle? At least 200% overload, possibly more for a standrad 16a marina supply surely?

Caravanners with the same 16a hookup, know well that they can only run 1x 3kw appliance at a time in their vans, and popularity plummets when they blow the trips and plunge the whole caravan site into darkness if they forget to switch off heaters before boiling the electric kettle.

Chances are your boat was wired to carry the standard 16amp maximum load - small wonder things started to melt if you overloaded 2-300%! Fuses? Yes if the marina supply was 32 amps feeding a 16a circuit there would have been no overall overload protection for your boat unless it has a main fuse.

Old plugs and sockets with dirty or tarnished contacts rapidly overheat in use, and are a very common cause of household fires.

 

[savageseadog]

I took over a boat where the shorepower connector (both halves) had melted pins. I think it was caused by the cockpit filling up in the yard when the cockpit drains blocked. Moral of the story is perhaps not to have the connector in the cockpit? perhaps on the transom?

Remember that even at currents below the fusing level considerable power can burn out faulty wiring and connections. I'm not sure if ring mains are appropriate for boat power systems, individual breakers on all circuits must surely be better but I've no idea what the recommendations are.

 

[mitiempo]

I'm not sure about the shorepower connectors used in the EU, but the ones in North America, typically 30 amp 120 volts rated, are designed for only 80% continuous load - 24 amps.

Like these:

 

[Burnham Bob]

interesting thread - can anyone tell me the current (volts and amps) of the nmea output of a gps? the connections on my boat are quite lightweight as I've assumed that in fact very little power was being sent down them.

 

[mcframe]

interesting thread - can anyone tell me the current (volts and amps) of the nmea output of a gps? the connections on my boat are quite lightweight as I've assumed that in fact very little power was being sent down them.

A quick google confirm my guess of 5V at max 20mA, ('tho I see references to 3A for NMEA 2000/CAN bus) so my shielded telephone extension (or alarm - I can't remember what I had lying aout in the garage at the time) wiring is quite safe.

 

[Nostrodamus]

Hold on a minute: 2 heaters, a humidifier AND and electric kettle? At least 200% overload, possibly more for a standrad 16a marina supply surely?

Caravanners with the same 16a hookup, know well that they can only run 1x 3kw appliance at a time in their vans, and popularity plummets when they blow the trips and plunge the whole caravan site into darkness if they forget to switch off heaters before boiling the electric kettle.

Chances are your boat was wired to carry the standard 16amp maximum load - small wonder things started to melt if you overloaded 2-300%! Fuses? Yes if the marina supply was 32 amps feeding a 16a circuit there would have been no overall overload protection for your boat unless it has a main fuse.

Old plugs and sockets with dirty or tarnished contacts rapidly overheat in use, and are a very common cause of household fires.

I should imagine that like a lot of boat people I know the rudiments of electricity but the posts on here have shown there is a lot more too it and a little knowledge can be worse thn no knowledge at all.

I have RCD's on the main components and previously they or the shore power have tripped if there is too much load. The marina I am at now is use for the bigger boats and boat shows and never once has the shore power terminal tripped no matter what I have on. W do try and limit the major things on at one time but occsionally you forget as you switch the kettle, or water heater on.

The post was intended to show that fires from electrical circuits can be easily started and if the boat is not new you may not be aware of bodged electrical work. Your boat may also have been upgraded with additional items that the original wiring was not designed for. If one person eads this and by so doing prevent a fire aboard it is worth it.