12 Volt Frequently Asked Questions (FAQs)

In this section are answers to many of the commonly asked technical questions related to 12 volt wiring. We hope you find this useful as a quick reference to save you time when deciding which parts to select for your project.


Cables & Wiring

Q Is your cable specified by the outside diameter of the cable, including insulation?

No, all our cable is specified by the cross-sectional area of the copper conductor (in mm2) which is related to the current carrying capacity. Cable insulation thickness changes by manufacturer and cable type so you should never rely on outside diameter alone.

Q What do the red / blue / yellow colours of pre-insulated crimp terminals mean?

This relates to the cable size that should be used with them.  Red suits 0.5-1.5mm2 cable, blue suits 1.5-2.5mm2 cable, yellow suits 3.0-6.0mm2 cable.

Q I have cable larger than 6mm2 so what terminals should I use for the ends?

For cable over 6mm2 you will need to use copper tube terminals.

Q How do I fit copper tube terminals to larger cable?

You will need to use a heavier duty crimping tool such as this one (10mm2 max cable.) or this one (120mm2 max. cable).

Q Can I solder copper tube terminals rather than crimp them?

You can, but it is not recommended in automotive applications due to potential cracking of the solder with vibrations over time. Crimping is also neater, cleaner and less risky than soldering (care must be taken when soldering not to set the insulation alight when heating the terminal).

Q My inverter is rated at 1000W but I how do I know what cable size to use to connect it to the battery?
A For a 12V system divide 1000 (W) by 12(V) to give you 83 (A) (Current = Power/Volts). Now choose a cable that is rated to at least this, plus a margin of safety  - we would recommend 16mm2 (110A) in this case.

Q I have heard the voltage drop also needs to be taken into account when selecting cable, but how do you calculate this?

See our voltage drop calculator

Q My battery is 120Ah, so do I need a 120A cable to connect it?

No. The capacity of a battery in Ah is unrelated to the cable size you need to use to connect it to a charging source or load. You should rate the cable based upon the maximum charge or discharge current that you expect to put through the cable, plus a margin of safety. This also applies to cables used to inter-connect batteries.

Q How do I connect two 12V batteries in parallel?

Connect the positive terminals together and the negative terminals together. This keeps the system voltage at 12V but doubles the capacity in Ah.

Q How do I wire my lighting circuit so that I can switch it on and off from 2 different locations

For a 2-way lighting circuit you will need 2x On/On switches. Each switch has a common terminal (normally the centre terminal) and 2 switched terminals (normally the outside terminals).  Connect your +12V supply to the common terminal of one of the switches, then connect the common terminal of the other switch to the +12V input to your lights.  You then connect the switched terminals of the switches together (imagine a train track running between the terminals).



Q Should I fuse my circuits and, if so, which cable should I fuse?

Yes, we would always recommend fusing the positive cable of each circuit. The fuse should be located as close to the power source (e.g. battery) as possible.

Q How do I know what value fuse to use?

You should protect a cable with a fuse that is lower than the cable's rated value in Amps (A). We recommend fusing at around 70-80% of the cable's rating.


LED Lighting

Q Can I dim LED lights?

Some can be and some can't be. If we have tested a particular light for dimming compatibility it will be mentioned in the product specification.

Q Which wire is positive and which is negative?

If it's not clear which is positive and which is negative try connecting both ways around. You can't damage the lights as they are all protected against reverse polarity.

Q How can I tell how bright an LED light will be?

LED lights cannot be compared directly with traditional incandescent bulbs (which are described as having an outputs in Watts) because they draw so little power in comparison. Their output is normally specified in 'effective lumens' and we have created a guide to allow you to compare this with the outputs of other types of incandescent bulbs.