Fire due to loss of earth path

[Paul Linford]

Hi troops I am a new LAA member and will soon be owning an LAA machine.
Something to be aware of with electric carb heat (and any other earthed carb) is that the carb body has to be connected to the battery negative (return path) to complete its electrical circuit. Carbs are usually on rubber mountings so an earth lead has to go from the carb to a good negative connection i.e. engine block or airframe (on earth return systems).The engine has to have an earth cable of large cross sectional area to cope with the high (100 Amps plus) starter motor current. If the carb is earthed to the engine and the engine earth cable becomes open circuit the starter return current will travel from the engine block down the carb earth lead (which is a much smaller cross sectional area and will get hot) to the carb body. It will then go down the choke / mixture cable and throttle cable and they will melt with the associated fire risk. I have seen this happen on older cars which have an all metal throttle or choke cable design.