Battery cable rating

[Mr Flibble]

I'm planning to dispense with the battery box at the transom and resite the batteries into the Jockey console. Just need to get the correct rating of cable.
Distance from transom to inside of console is approx 4.5m - 5m.
Engine is a Tohatsu 115hp tldi. Anyone any idea what rating/diameter of cable I'd need? I can find virtually no info regarding the starting draw etc for this engine. Only stuff I can find is for alternator output = 12V, 490W, 40A.

Any help greatly appreciated.

[falcon0310]

16 mm tryrated pm me if you need know more adrian

[Daniel]

16mm no where near enough.

When starting you'll be drawing 80 if not 100A I expect. Plus longer run = voltage drop if undersized cable.

You want 25 or 35 sq mm cable, local battery shop will carry it. Dont be tempted to join onto exsisting cables to extend them, strongly suggest spend the extra few quid and run new the whole length.

Or ASAP supplies Tinned Battery Cable, Red 35mm

TriRated is indeed good stuff but you'll most likely have to buy a 50m drum.

[falcon0310]

16 mm can be bought per meter, so can 25, on 4/5 run 16 mm trirated is 80 amps
ive only been electrician for 22 years

[Dirk Diggler]

Originally Posted by falcon0310

16 mm can be bought per meter, so can 25, on 4/5 run 16 mm trirated is 80 amps
ive only been electrician for 22 years

Auto electrician?


I'd reccommend at least 25mm (170 amp) cable for a run that long. Tinned would be nice, but multi strand will do the job.

[Daniel]

Volt drop at 230 or 400v is a lot less important than down at 12v.

Lets say (I dont have info to hand, but its a rough figure) 3mV/A/mtr for 16mm cable. @ 100A, over only 5m thats a 1.5v drop, which will upset an ECU and prevent an engine from starting.

[Erin]

Daniel is right on this, and it has been discussed here many times before. You cannot state a particular cable will have a particular current carrying capacity unless you know its length. It is generally accepted that 3% voltage drop is the max accepted for critical marine equipment and 10% for all other. There are simple tables in various marine cable websites which allow you to work out what cable to use based on the complete length of the circuit i.e. battery to engine and back again, and current draw.

Any electrician worth his salt will know about hysteresis losses and I2R which is greater the lower the voltage. Likewise a household cable is rated differently whether it is open or enclosed. Perhaps we need a sticky about marine wiring?

[PeterM]

Are you confusing diameter with cross section in this thread?

[Daniel]

when talking about cable people (including me) often omit the "sq" from the end of the description.

In my experience we always refer to "mm sq", IE C.S.A., even if we write, or say "10 mm cable".

Standard sizes are 10, 16, 25, 35 all is "mm sq".

[Downhilldai]

Originally Posted by Dirk Diggler

Auto electrician?

I'd reccommend at least 25mm (170 amp) cable for a run that long. Tinned would be nice, but multi strand will do the job.

[Mr Flibble]

Cheers guys,
All very valuable input. I'll get the 35mm2 ordered up as it's better to be a little over spec'd. Just didn't want to order something online and end up with something you could have used to moor the Titannic with.
Thanks all again.

[simsy]

35mm will be the best, 25mm will do it, 16mm is a bit poor to say the least. (25years experience as an electrical engineer, at all sorts of voltages and frequencies)....as said, volt drop at 230v is not such an issue as with 12v.........