Battery Charger cable type & size


I need to replace an original cables which are too short from an industrial generator (Stamford PI734D1)  to batteries Cummins 12V  1400A   220Ah  (0416-0439) connected in series so 24V

Sorry but my knowledge and experience on this subject is very limited. The cables supplied by the manufacturer are AWM 3340 or 3374 150degC 600V

My question is whether H07 or Coil and Lead could possibly be used as a replacement for the original ones? What size would be sufficient for this scenario?

The batteries will be standing about 4 meters away from the generator.

  • This really is not much more than a 12V lorry battery, albeit a rather heavy and in the UK at least a very pricey one.
    There will be a massive starting current for some seconds, maybe tens or so, while the engine is being cranked by the starter, and then it will sit idle, charged by more or less normal 12V alternator spun by a belt from the engine, not much different to a traditional car.

    Cable selection will be decided by the area of copper needed, and the environment  - heat. oil, fuel etc. And then finer stranded cable is used compared to normal fixed wiring, to resist vibration.

    The wire nos you mention cover a range of high temperature soft rubber covered (EDPM) cables . 'AWM 'just means Appliance wiring material and really does not say a lot - almost all 'wire' could be AWM unless it is specially something else.

    There may be an AWG code on there, but if not depending on the engine size, which is a proxy for starting current  we can probably assume we need the AWG equivalent of 25-35mm2  (AWG 4,2 or 1)

    Or measure the OD of the old cable and compare with the table here.

    So - why has the original cable failed ? (heat ? perished rubber? abrasion? )
    This is what needs to be guarded against, and it may be that like-for-like repair is not the brightest decision, if it fails again in the same way, and/or  that some sort of re-routing or mechanical protection is needed.

    If you can get a bit more detail about the cable and what has happened to it, we can point you at something suitable, that more helpfully will be readily available in the UK.

    The number you give for the alternator

    Tells us it is a 1,6 MVA unit at 50Hz, when spun synchonously, but not the engine size, so while we can guess a cranking current, it is a guess.

    Sanity check - battery is one of these ?


  • Are these cables to carry the engine starter current ?   If so then voltage drop under starting conditions is the main concern. In view of the extra length, I would use AT LEAST one size larger, than the original cables, two sizes larger might be better. 4M is rather long for an engine starter circuit.

    Very substantial currents are involved when starting a large diesel engine and voltage drop should be minimised by use of generous cable sizes. Tri rated pvc cables, or welding cable, or single core HOFR may be used.


    I think you are right. They need to be at least a size higher then original ones. My colleagues confirmed they used HO7 95mm2 before for similar application but end of they day I am the person to be blame of if something happens so I need to 100% Ho7 95mm2 would be good alternative to replace original AWM 3340/3374 which is probably 70mm2 equivalent.

  • ah you never mentioned four of the buggers. I'd like to increase my estimate of the cable size ;-)
    What has gone wrong with the original cable - i.e. why are you replacing it ?

  • I need to replace an original cables which are too short

    If you're extending the circuit length, be very careful of voltage drop - not just a matter of supplying enough cranking current, but charging systems can misbehave if they see a modestly different voltage than what's actually across the battery. Without any other information, to be safe, I'd probably calculate the resistance of the original leads and try not to exceed that with the new ones .... which depending on how much longer they are might mean going up considerably in c.s.a. (not just one size).

    Also consider faults - unless things are fused at the battery end (often not done, as you don't want arcs from fuses igniting evolved hydrogen) battery leads usually have to be reinforced (e.g. by a sheath as well as insulation).

       - Andy.

  • It was little surprise for me too :) The original cables supplied by manufacturer are very short less then a meter I would say.

    The problem is that the enclosure for the generator is very narrow and we have no room to connect these batteries as close to reach alternator connectors. According to that we are forced to fit them about 4 meters away. 

  • Or if they have to be 4 times longer you could I suppose you could use 4 in parallel to get back to the same resistance. suddenly its all a bit of a nightmare.

    Are the batteries in parallel or series (24 V system) The latter will be less freaked by voltage drops.

    PS whats it say after CSA on that cable ?


    Edit - Better if I read the original question. It is indeed 24V. In terms of Voltage drop, that  is something in your favour.

  • It is reported that two batteries are to be used in series for 24 volts, as is common practice for starter batteries for large engines.

    There is no indication that the original cables have failed, new cables are reported to be needed as the batteries are to be relocated further away 

    I therefore stand by my original suggestion that the new cables be AT LEAST one size larger, and that two sizes larger might be better.

    It is not common practice to provide any OCPD for engine starter circuits, and great care is therefore needed to reduce the risk of a short circuit to the absolute minimum. My usual approach is to place the positive and negative battery cables each in their own insulated conduit, pliable or rigid plastic as seems best.

    A few meters of such large single cable, and enclosure in insulating conduit is a trivial expense compared to the costs of failure to start the engine reliably when called upon. placing the batteries further away from the engine reduces failures resulting from heat and vibration, and eases future battery replacement in the event that new batteries are larger or of a different shape.

  • Agree - prompt starting is everything with a genset. Looking at likely engine sizes, I'd expect something about the size of the Cummins KTA50 GS8 though it may well be another engine maker's offering it will be a  similar horsepower, so about a 50 liter machine. Looking then at the installers spec

    (excerpt below)

    we see that we are allowed no more than 0.002 ohms in the cranking loop. (To put that into perspective, that's a couple of volts drop at 1000 amps, 1 volt at 500A so not so insane)

    Now we do not know the engine on this genset is the same, nor that the starter is the same, however  there are not many makers, I don't have a data sheet but the Perkins model P1650 GW would be similar,  (and I don't think Kubota make anything large enough) and the figures allow us to start to estimate.

    An 8m loop of cable there and back will be 16-18milliohms * 8 ~  0.15 ohms  per mm2 of cross-section, so 10mm2 is clearly too small at  0.015 ohms, (but we knew that, we are not starting a Mini !! ) and you are up to around 100mm2 before it feels sensible at 0.0015  ohms.

    So 95 to 120mm2 or bigger rubber covered welding style cable seems about the right sort of thing, to me at least, to be comfortable.

    Comfortable is relative - do you have a good hydraulic crimper to put lugs on ? Termination resistances will be critical.

    And, as per Broadgage, I'd be putting at least the long run parts of each wire  into some sort of tough plastic tube or flexi duct, and anchoring things well away from any possible chafing points.

    A fire at the sort of currents that this could deliver does not really bear thinking about.

    Thermal de-rating of the cable is not so relevant, as the starting duration is so short.