Battery leads

[LadyPatricia]

Hi all

Quick question.

The battery leads currently fitted on lady Patricia are fairly thin. I would have thought for marine use they should really have the same thickness cable as you would find on a car and also be tinned to help prevent corrosion.

Can anyone confirm please?

Steve

[Guest]

It all depends on the maximum possible discharge and charging amperage.

 

I believe your boat is powered by an outboard motor, so the charging alternator is going to be a maximum of about 10 amps, compared to 50 amps or more for an inboard engine or a car engine.

 

Likewise, your highest discharge rate is likely to be the starter motor, if your outboard has one. That will be quite low in comparison to an inboard motor or car engine starter which could be more than a 100 amps.

 

So if your battery is only supplying things like lighting etc., then it's quite safe to have much thinner cables than those seen on a car battery, as long as they are still fused correctly.

 

 

..and yes, you're quite right about them needing to be tinned as well.  

[LadyPatricia]

Morning Strowager,

She is fitted with an inboard volvo penta engine. I'm assuming this being a Diesel engine will require the same type of heavy duty battery as a car diesel would.

We also have 2 leisure batteries but I was informed, by another boat owner at our mooring so it could be incorrect, that for the BSC the cables from the batteries to the cut off switches and also to the engine need to be the thicker 'car type' leads.

Apparently this applies to leisure batteries as well as the engine one.

Do you know if this is correct?

Steve

[Guest]

It does seem strange as your engine is an inboard, with the associated higher output alternator and higher cranking current starter motor.

 

It's not just a question of a possible BSS failure, if the cables are thinner than the minimum required then they must be running hot and be over fused, which is very dangerous, as you fear.

 

The electrical safety rules and BSS requirements are quite straightforward though. Any section of cable must be thick enough for the maximum power transmitted, and also be fused below it's safe carrying capacity.

 

In the case of an outboard powered boat, those cables could quite safely be much thinner, even the connections between the isolating switches and the batteries, and pass the BSS, as long as the potential current is within their limits and the fuses backing them.

 

As yours is inboard powered, you need to find out the amperage of your alternator and your starter motor. The correct cable size can then be calculated, to check whether your existing wiring is safe. 

 

The left hand column shows dc rating for typical sizes.

 

25 sq mm is fairly thick, and can carry 146 amps DC, but even 10 sq mm can carry 85 amps.

[Guest]

Here's a better guide of cable sizes, specifically drawn up for low voltage DC boat wiring, with multi stranded flex.

 

It's on the ASAP supplies (of Beccles)  web page:

 

http://www.asap-supplies.com/marine/useful-wiring-specifications-and-information

 

That shows 10sq mm cable as being 70 amps, and 25 sq mm cable being 170 amps, for example.

[JawsOrca]

Steve, I'm no expert with cables (My mate is the electrical one).. the best advise I would give . is that if you are not an electrician then consult a qualified marine engineer before doing anything with electrical bits.. changing anything around battery leads can be very dangerous.. google isn't really the place to be going for this. 

 

(To reassure, if you boat has a recent BSC then I would suspect these battery cables are thick enough).

[Guest]

Steve, I'm no expert with cables (My mate is the electrical one).. the best advise I would give . is that if you are not an electrician then consult a qualified marine engineer before doing anything with electrical bits.. changing anything around battery leads can be very dangerous.. google isn't really the place to be going for this. 

 

(To reassure, if you boat has a recent BSC then I would suspect these battery cables are thick enough).

 

A very good point from Alan there, I swung straight into "advice mode" there without thinking about mentioning electrical competence.

 

Giving DIY advice on a forum is always very tricky, not knowing how comfortable or competent anyone is with certain technical aspects.

 

I wouldn't be complacent about it already having passed a BSS test though. Mistakes can be made even by testers, or the owner could have even modified things since the the last test....

[JawsOrca]

 

I wouldn't be complacent about it already having passed a BSS test though. Mistakes can be made even by testers, or the owner could have even modified things since the the last test....

 

Totally agree.. A BSC just like an MOT is only as valid for that split second when the examiner was there.. boat owners can make changes as soon as they left... Although I would suspect the examiner would look closely at these as it really is one of the most dangerous parts of the boat... and therefore owners (you hope) wouldn't touch, but certainly anything posible!  

[BroadScot]

As a retired sparky, dinny muck about with cables. Seek proper electrical knowledge advice IMHO. It will be safer and less risk in the long term. If you wish to put your mind at ease Steve.

 

 

 

Iain.

[MauriceMynah]

My rules of thumb when working with electrics...

 

Try it.

If it gets hot, try something else.

If it gets VERY hot, try something else quickly

If it doesn't work but doesn't get hot try it with a bigger fuse. Still no luck, use a nail.

If it still doesn't work, doesn't get hot and you're using a really big nail, you didn't want one anyway!

[grendel]

MM one of my Bosses (an electrical engineer and senior authorised person for HV cable installations), managed to nearly lose his finger when working on his car, the screwdriver he was working on one battery terminal with, shorted to the other via his wedding ring, very rapidly the ring got very hot. it had to be cut off (the ring) and he was lucky that he hadn't cauterised every blood vessel to the end of his finger or he would have lost it.

That said - one I learnt last night - don't trust anyone who tells you that a battery terminal  is either positive or negative - always check, I went out late last night to help a mate who had broken down, when connecting the jump leads I connected negative to the one he told me was negative, and positive to my car battery, then to the other terminal, cue big fat yellow sparks, no I wont connect there - checked terminals, and yes he had told me the wrong way round, reconnected correctly, ah yes little blue sparks as I connect - that's better, much more what I expected.- yes He got home safely.

Grendel

[grendel]

oh and while I remember, if you have longer runs of battery cable, you may need a thicker wire than specified to cope with the resistance losses in the cable. You really want your battery connectors as short as possible.

Grendel

[VetChugger]

Unfortunately "Marine Electricians" are not exactly ten a penny on the Broads. I had great difficulty in finding one to investigate wiring problems I had on "Glenmore" and never did satisfactorily resolve this. If anyone has knowledge of Marine Electricians who are able to work on the Southern Broads I'd love to know as I have a bit of work to offer!

[quo vadis]

L E C Marine in Lowestoft have some excellent marine electricians

[Oddfellow]

I hold a BMET certificate for Marine Electrical installations. 

 

Starter cable for an inboard would generally be at least 25mm. Do not used braided cables as is common on cars. 

 

It is poor practice to connect multiple small wires to a domestic battery terminal. Take a large cable capable of carrying all the current you will ever need and wire it to  a power distribution post or busbar and take your individual feeds from that.  This will make the wiring much tidier and reduce movement on countless connections which is generally the biggest cause of failure in cables. 

[Guest]

......It is poor practice to connect multiple small wires to a domestic battery terminal. Take a large cable capable of carrying all the current you will ever need and wire it to  a power distribution post or busbar and take your individual feeds from that.  This will make the wiring much tidier and reduce movement on countless connections which is generally the biggest cause of failure in cables. ....

 

Good advice from Andy there, and surprising how many boats are wired badly in that respect. 

 

Every boat I've ever bought (all second-hand), has had a mish-mash of wiring that I've totally replaced, with hardly a bus-bar or connection post in sight. 

 

...and going by the usual provenance of old receipts etc., many had got into that state even with some professional installations, adding to the hap hazard layout.

 

Here's a photo showing the main negative bus-bar in my boat. All of the distribution negative leads come back to that, and then a single heavier gauge wire to the battery post, (except the much heavier starter motor and alternator negs, which also go direct to the battery post).

[Oddfellow]

Often, a professional installer will have to work with what's there already as the customer will not stump up the cost of ripping things out to do the job properly. 

 

Strowager's pic also shows another pet hate of mine (sorry, Strow), Mismatched cable colouring. The Windlass fuse has a Red cable in and a black cable out (with a red heatshrink shroud). Anywhere else down that cable run, this now looks like a negative cable (I assume a red headshrink shroud is used at the other end). 

[MauriceMynah]

I too try to avoid mismatch colours on cables, but to be fair, Strows photo looks to me like Brown not black cable coming out. Whilst understanding the difference between Live and Positive in wiring, I would accept this as a compromise as long as there is some sort of notation of this coding somewhere.

[Guest]

Often, a professional installer will have to work with what's there already as the customer will not stump up the cost of ripping things out to do the job properly. 

 

Strowager's pic also shows another pet hate of mine (sorry, Strow), Mismatched cable colouring. The Windlass fuse has a Red cable in and a black cable out (with a red heatshrink shroud). Anywhere else down that cable run, this now looks like a negative cable (I assume a red headshrink shroud is used at the other end). 

 

Not only a red heatshrink shroud at the other end Andy, but a red insulating tape band every 6" along it as well, which can't be seen in that photo because it then enters the flexible plastic trunking.

 

I'm well aware of the need for polarity identification along it's entire length.

[MBA Marine]

Thought I would pop back to the forum for this one.

 

Along with a mis-mash of cable colours my pet hate are fuses, safe when the correct size are fitted but a pain in the butt when one pops, whenever the customer will pay I will happily remove the mess of old fuse blocks and fit breaker panels.

 

I once came across a leccy toilet fitted by a popular boat yard (not southen, not in stalham or wroxham) and the loo had been wired to the nearest wire they could find behind it, I rewired the boat to find it was wired to a bit off 2mm (17.5A ish) cable that went around the boat powering water pump and shower pump as well, then to top it off as the toilet needs to be fused at 25a the fuse had been up rated to cope, sadly this then makes the wire thats supplying more of a fuse than the fuse!! 

 

Thought i might get in on the photo act, here is a panel designed by myself and the customer produced by Brian Wards, fitted out and wired by me. I also knocked up the plinth that the bulkhead light is mounted on to cover some scars on the GRP, I have many pics of this boat and she is far from the hirecraft it was a year ago, but as Andy has more than alluded to, it comes down to what the customer is prepared to pay.

 

For what its worth I never used tinned cable for starter cables and neither do any boat buiders that I have worked for or along side, I am currently using 10mm tinned red sheaved to supply up to your average domestic distribution panel, its a nice high flex cable that easy to work with.

 

 

 

 

[Samuel]

As well as the expert advice given here so far the BSS is specific about battery cables:

 

http://www.boatsafetyscheme.org/media/194782/2013ecp_private%20_boats_ed3_public_final.pdf

 

see sections 3.2.2 and 3.4.1

 

I took a lot of care about getting this right on my boat and therefore was somewhat dismayed when the examiner rather casually passed over them without proper examination!