24-07-2014, 12:05 AM
All very interesting, the question came about when I was asked to explain how to work out what cross sectional area conductor would be needed when adding auxiliary stuff to a vehicle, nothing specific was specified but I used a 100 watt load as an example for a nominal 12 v system, that would be a current draw of 8.3 amps, a 1 mm cross sectional area conductor (standard PVC auto cable) would just about cope with that but the voltage drop over say 3 metres or so would be around 0.45 volts, the general consensus for voltage drop in vehicles for auxiliary stuff seems to be a maximum drop of 3% of the supply voltage if possible so although a 1 mm cross sectional area conductor would probably just about pass from a safety aspect it wouldn't pass from a voltage drop aspect so I mentioned a general rule of thumb that I have used in the past, choose a conductor that has a cross sectional area that's double that of a conductor that has a current rating the same as the load current or near to it as possible.
The question then came up about working out the voltage drop more precisely for a couple of different supply voltages and could it be done without a test meter, nothing load specific apart from the fact it would be a filament bulb, the parameters used in my earlier posts were chosen at will to illustrate the problem.
Lawrence.
The question then came up about working out the voltage drop more precisely for a couple of different supply voltages and could it be done without a test meter, nothing load specific apart from the fact it would be a filament bulb, the parameters used in my earlier posts were chosen at will to illustrate the problem.
Lawrence.
