What the standard defines
There is no standard here, which is the point of the page. On low-voltage DC installations — vehicles, boats, solar — red is habitually positive and black negative, with yellow sometimes used for a switched or auxiliary positive. Solar cable is frequently sold in black for both poles, with the polarity marked at the connector instead.
What is defined, by national wiring rules rather than by this convention, are the colours used on mains installations. Those rules do not govern a battery lead.
What it does not promise
It does not promise that an unfamiliar cable is what its colour suggests. A previous owner, an imported accessory, or a single-colour extension can all break the habit, and the consequence of guessing wrong on a battery bank is a short circuit rather than a puzzle.
Nor does it apply across borders or trades consistently. The safest reading is that colour is a hint and a label or a meter is an answer.
What it works with
Colour comes up wherever cable is cut and terminated on this site: battery leads, solar runs, busbars and connector pairs. The practical companions are the label, the connector keying — an Anderson housing colour, an MC4 polarity — and a meter, which is why the DC clamp meter shelf sits close to these pages.
What people ask before they order
Is red always positive?
On most low-voltage DC installations sold for vehicles and solar, yes by habit. But the habit is not universal, extension cables are sometimes made in a single colour, and the only reliable answer on an unfamiliar installation is a meter.
What about the black used for negative and for mains live?
That overlap is exactly why the convention is not a standard. Mains colour codes are defined by national wiring rules; the DC habit is separate and has no such authority behind it.
Last reviewed 16 September 2026