Sq 65 - undersized cable connecting generator to boat?

[MedMilo]

Anchored off the Amalfi coast in 30 deg heat last week with genny on all night when, at about 6am, aircon and all 240v systems stopped without warning. Assumed breaker problem but after an hour or so worked out that it was something in the large distribution / transformer unit. Not sure what it's actually called?! Anyway, on opening it up I saw that the cable leading from the generator into the transformer unit had entirely melted and virtually caught fire, scorching a few cables adjacent to it too.

Called in a large, reputable electrical services company who seem to think it's not too hard to fix but were amazed at the thin gauge of the cable used. To try to explain the problem to a relative luddite they made the seemingly very sensible point that the cable linking the generator to the boat (the one that melted) is about a third of the gauge of the boat's shore power cable yet is expected to carry the same current (albeit over a much shorter distance I guess). They're going to replace it with much thicker cable however this isn't entirely straightforward as the cable is loomed throughout this transformer box - but they seem to think they can sort it.

If their assessment is true I find this an extraordinary oversight / shortcut which might have had pretty disastrous consequences. In any case, am installing a fire alarm above that box (linked to the others on the boat)!!

Would be very interested to hear from anyone who knows more about electronics as I can't really believe a large builder like Fairline would do something as dumb as this...?!

 

[Portofino]

Perhaps the charger ( s) were working hard for a long time around early hours .Far harder demanding more juice
along with max demand for the Aircon ,as you say the output wire overheated cos it's too small .
There are simple calc s on wire Dia for the amps .
They know the Geny output , consuption /load of the chargers and airco .

I recall you have some Batt issues and other electrical issues and BUK had a look and did some remedial warranty work .
Can I ask if the chargers were changed ?

I,am no expert but has this type of demand been placed on the Geny before -- anchor off and all night airco?
It's just there's a remote possibility that a or some of the airco compressor motors are on the blink drawing more current than designed .
What airco system is it ?

Perhaps get BUK in agian ?

 

[volvopaul]

Two things here.

Check that the breaker from the generator to the boats supply panel is rated at the correct amperage to match the output of the generator , there should be one before it reaches the boats panel, most boats this size will have a supply cable for the domestic and another supply to the air con units, however when the Generator is run the whole demand for power comes from the one cable , I'd be making sure that the overload rating is correct and I doubt it is looking at how it's fried the cable.
I'd be updating the cable size and making sure or replacing the overload breaker with something that is the correct rating for it to do its job, you were very lucky not to have a fire.

 

[aquatom]

Is the cable melted along its full length? If it's just the first few centimetres where it meets the terminal then it could have just been a poor connection causing heat that travels up the cable. If it is melted all along it's length then the cable is overloaded.

 

[MedMilo]

No the chargers weren't changed, they're Mastervolt 100amp - two of them. And yes, we quite often run genny and aircon all night which draws around 50amps max but the genny puts out around 22kw which is around double that (I think!) so it shouldn't have been near to full capacity. Embarrassingly I can't remember what system the Aircon is!

BUK know about the problem but the boat is now on the west coast of Italy so not easy for them to sort. Will see how I get on with the local Italian outfit for the moment...

 

[MedMilo]

Perhaps the charger ( s) were working hard for a long time around early hours .Far harder demanding more juice
along with max demand for the Aircon ,as you say the output wire overheated cos it's too small .
There are simple calc s on wire Dia for the amps .
They know the Geny output , consuption /load of the chargers and airco .

I recall you have some Batt issues and other electrical issues and BUK had a look and did some remedial warranty work .
Can I ask if the chargers were changed ?

I,am no expert but has this type of demand been placed on the Geny before -- anchor off and all night airco?
It's just there's a remote possibility that a or some of the airco compressor motors are on the blink drawing more current than designed .
What airco system is it ?

Perhaps get BUK in agian ?

No the chargers weren't changed, they're Mastervolt 100amp - two of them. And yes, we quite often run genny and aircon all night which draws around 50amps max but the genny puts out around 22kw which is around double that (I think!) so it shouldn't have been near to full capacity. Embarrassingly I can't remember what system the Aircon is!

BUK know about the problem but the boat is now on the west coast of Italy so not easy for them to sort. Will see how I get on with the local Italian outfit for the moment...

 

[MedMilo]

Two things here.

Check that the breaker from the generator to the boats supply panel is rated at the correct amperage to match the output of the generator , there should be one before it reaches the boats panel, most boats this size will have a supply cable for the domestic and another supply to the air con units, however when the Generator is run the whole demand for power comes from the one cable , I'd be making sure that the overload rating is correct and I doubt it is looking at how it's fried the cable.
I'd be updating the cable size and making sure or replacing the overload breaker with something that is the correct rating for it to do its job, you were very lucky not to have a fire.

Thanks for this VP - v good point regarding breaker ratings, will communicate all of that to the electrician when I speak to him tomorrow. I think you're right about the fire risk, there was quite a smell of burning when I inspected the transformer box. I suspect this is an issue on quite a few boats - possibly whoever builds the transformer boxes is also to blame.

 

[MedMilo]

Is the cable melted along its full length? If it's just the first few centimetres where it meets the terminal then it could have just been a poor connection causing heat that travels up the cable. If it is melted all along it's length then the cable is overloaded.

TBH it's quite hard to tell how far along the cable it was melted but it definitely wasn't just a couple of cms near to the connector. BUK's initial thought was that it's a poor connection but the massive difference in size between the shore power cable and this cabling makes me think the cabling in the transformer box is way underrated for up to 22kw of current.

 

[aquatom]

Is the blue neutral cable the same size as the burnt one. This cable will have exactly the same amps going through it and it looks ok. I'm not saying that the cable is not the wrong size but if it was overloaded and both live and neutral cables are the same size then both cables should be melted over their length. Looks like a poor connection getting hot to me.

 

[jfm]

Miles I'm with a/tom - you have a bad connection. Otherwise as he says you woyld see a charred neutral and even charring along the length. And it would have happened a while ago; something has changed recently.

Porto's talk of chargers etc is red herring. Your genset makes 100amps nominal, 85 real in hot weather, and its cable needs to be sized for that (and all the other factors you use for cable sizing, like grouping). so it likely needs 16 or 25mm sq cable (I think - you can look it up). Comparing with shorepower is barmy- that has 3 insulated cores plus an outer sheath so of course it is going to look thicker. Furthermore its capacity is reduced because it is multi core cable with touching cores so it needs more copper than the cable in your picture aotbe. I bet you have the black shore power cable and a glendinning-same as my boat each side.

In summary that's a bad joint not an undersized cable.

 

[jfm]

Two things here.

Check that the breaker from the generator to the boats supply panel is rated at the correct amperage to match the output of the generator , there should be one before it reaches the boats panel, most boats this size will have a supply cable for the domestic and another supply to the air con units, however when the Generator is run the whole demand for power comes from the one cable , I'd be making sure that the overload rating is correct and I doubt it is looking at how it's fried the cable.
I'd be updating the cable size and making sure or replacing the overload breaker with something that is the correct rating for it to do its job, you were very lucky not to have a fire.

That breaker is supplied pre installed in the genset. Left side, on the end of the gen, as you look at the thing (it's an MDKBT gendset). It will therefore be the right size.

 

[MedMilo]

Miles I'm with a/tom - you have a bad connection. Otherwise as he says you woyld see a charred neutral and even charring along the length. And it would have happened a while ago; something has changed recently.

Porto's talk of chargers etc is red herring. Your genset makes 100amps nominal, 85 real in hot weather, and its cable needs to be sized for that (and all the other factors you use for cable sizing, like grouping). so it likely needs 16 or 25mm sq cable (I think - you can look it up). Comparing with shorepower is barmy- that has 3 insulated cores plus an outer sheath so of course it is going to look thicker. Furthermore its capacity is reduced because it is multi core cable with touching cores so it needs more copper than the cable in your picture aotbe. I bet you have the black shore power cable and a glendinning-same as my boat each side.

In summary that's a bad joint not an undersized cable.

Thanks John, v helpful, as ever! That makes perfect sense, esp re the variance in cable thickness. And, on the basis that you're correct, I have to say that's more in keeping with my general experience with the boat, which seems to be very 'over-engineered' in most respects, especially re all the technical installations. (especially in the battery department )

 

[BartW]

the heating up and cooling down of electric connections, combined with vibrations
can cause electric connections to become insufficient / bad,
one should have a rountine to check / re tighten electric connections every few years,
I was shocked a few years ago how much and how many electric connections / screws I could tighten in the electric switch board.

MedMilo,
may I asc where you stay with the boat ? do you have there a (temporary?) permanent berth?
we are on our way to the Amalfi region ETA around 12 july,
and will stay there for the rest of the summer. (most probably in Salerno)
at the moment boat is in Polignano (east coats)

 

[MedMilo]

the heating up and cooling down of electric connections, combined with vibrations
can cause electric connections to become insufficient / bad,
one should have a rountine to check / re tighten electric connections every few years,
I was shocked a few years ago how much and how many electric connections / screws I could tighten in the electric switch board.

MedMilo,
may I asc where you stay with the boat ? do you have there a (temporary?) permanent berth?
we are on our way to the Amalfi region ETA around 12 july,
and will stay there for the rest of the summer. (most probably in Salerno)
at the moment boat is in Polignano (east coats)

Hi Bart
Thanks for this. TBH it hadn't ever occurred to me to check the connection buried deep in the transformer but following last week's episode I will do from now on for sure!
We've taken a berth for a year at Marina D'Arechi, Salerno, from June 1st. So far it seems incredibly well organised and functional - plenty of electrical power and all very new though only one or two restaurants and no supermarket or shop yet in the marina, so not quite Porto Montenegro! Though, by the look of it, all coming soon. Our main objectives were to have a safe base, easily accessible all year round and well placed to see the Amalfi area as well as Sicily. I spent last week there with friends, spending nights at Amalfi, Positano and Capri - simply stunning coastline and the furthest point (Capri) only 30nm away. Three weeks in July will be spent in Sicily and two weeks in August cruising to Ischia, Procida, Isola di Ponza etc
The team there are very helpful indeed - if you'd like to get a deal done for the summer then PM either me or the resident expert, MAFWeiss of this parish, and we can put you in touch with the right people to talk to about rates and, indeed, to help with cleaners and technical people.