Plain Copper Battery Cable 25mm² 170A

Plain copper flexible battery cable, 25mm², rated 170A. The same fine-stranded flexible construction as our tinned range, with an untinned copper conductor. Correct and cheaper for dry indoor runs. Not the right choice anywhere it may see damp.

When plain is the right call, and when it is not

Plain copper is fine inside a sealed, dry campervan cabin or an indoor battery cabinet. It is the wrong choice in a bilge, an engine bay, a wheel arch, an outdoor shed or anywhere exposed to salt air, because corrosion wicks up the strands under the lug where you cannot see it.

We are straight about this because the price difference is small. At 25mm² the tinned version costs only a little more, and at 50mm² and above the difference from our supplier is between 4% and 8%, which is why we do not stock plain copper in the larger sizes at all. If you are anywhere near water, buy tinned.

Specification

• Conductor: plain (untinned) copper to BS EN 60228 Class 5 (flexible), 196/0.40 stranding
• Cross sectional area: 25mm² (nearest AWG equivalent 4)
• Current rating: 170A nominal, conditions not stated by the manufacturer
• Overall diameter: 9.7mm
• Conductor resistance: 0.80 mΩ/m at 20°C
• Weight: approximately 0.3kg per metre
• Colours: red and black

This is not welding cable

A lot of what is sold as battery cable in this country is welding cable, or unspecified PVC single core sold under both names at once. The honest arguments against using it are these. Genuine welding cable to H01N2-D is rated 100V, not 600/1000V. Its current ratings are quoted on duty cycle rather than continuously, so a 25mm² cable advertised at 300A is a 35% duty cycle figure and only 180A continuous. It is plain copper. Its insulation is rated 85°C rather than 105°C, and UV resistance is not specified.

What we will not tell you is that welding cable is not oil resistant, because it is: the H01N2-D specification explicitly covers resistance to oils, acids, fats and petrols. That claim is repeated all over the internet and it is wrong.

Typical applications

The highest volume size across all three markets. 1200 to 1500W inverter at 12V, 50 to 60A DC-DC chargers, battery to busbar on 100 to 200Ah banks, engine starting on small diesels, 3000W at 24V, 5000W at 48V.

Current rating: what the manufacturer actually says

AMC publish 170A for this cable as a nominal current rating, and they publish no conditions alongside it. Their datasheet says, in full: "Nominal current amperage ratings are provided as a guide only, and can vary depending on the application, condition and environmental factors." There is no stated ambient temperature, no installation method and no bundling basis, on any size in the range.

We say so because the same number is quoted all over this market as though it were a rated ampacity, and it is not. The datasheet is linked at the foot of this page if you want to check us.

So the derating below is ours, not AMC's. We treat their figure as a single unbundled cable in open air, because that is the usual convention for a table of this kind, and we apply bundling factors following ABYC E-11 practice, which is the most widely used published basis for DC conductor derating in small craft. It is engineering judgement applied to a guide figure, and we would rather show you the judgement than hide it.

These ratings are considerably higher than BS 7671 would permit for the same conductor, because BS 7671 assumes a lower permitted conductor temperature and different installation methods. BS 7671 does not apply to small craft in any case: Regulation 110.2 excludes vessels covered by BS 8450. It is the right reference for a caravan or motor caravan, through Section 721. If you are used to BS 7671 tables, the difference is worth understanding rather than being surprised by.

Volt drop is usually what decides the size, not current

At 12V a 3% volt drop budget is 0.36V in total, there and back. That almost always calls for a larger cable than the current rating alone would suggest. BS EN ISO 13297 permits up to 10% for general circuits and 3% for equipment vital to safety.

Work it out properly with our cable size calculator, which checks current rating and volt drop independently and hands you a configured assembly at the end.

What goes with it

• Copper tube terminals: 25mm² in M6, M8, M10
• Adhesive lined heat shrink: 19mm

Datasheet

Every cable specification on this page comes from the manufacturer datasheet, and you can read it yourself: download AMC PVC flexible battery and starter cable (PDF). We host the file here rather than link to the manufacturer, so it stays available and stays the version our figures were taken from. The derating factors above are ours, not the manufacturer's.