When I went shopping for a 50-amp extension cord for our 5th wheel, I was surprised (shocked?) to find that they seem to all contain three #6 gauge conductors and one #8 gauge conductor.
I’m assuming that the #8 gauge line is the ground. But whether it is ground or neutral, I’m surprised that one of the leads can be seemingly underrated (the common rating for #8 gauge I’ve seen is 40 amps, although I’ve seen higher and lower for special uses). How can this be safe?
Thanks, and thank you for all your contributions to the RV community. —Al
Actually, code only calls for a #8 gauge grounding conductor for this type of circuit. That’s because the ground wire should never have to carry any of the neutral return current. The reason that the neutral needs to be the same size as the hot wires is that it’s possible for all the loads to occur on one side of the 120/240-volt supply. In that case the neutral could carry up to 50 amps of current for a sustained amount of time.
However, in the event of a short circuit to chassis, the equipment grounding conductor (EGC) only needs to carry a few hundred amperes of peak current to trip the circuit breaker quickly, not carry a sustained load. And a #8 gauge conductor can easily do that.
So a ground wire really only has two jobs to do:
#1) Keep the overall voltage of any conductive surfaces in your RV close to actual earth potential (grounding).
#2) Provide a fault current path back to the neutral-ground bonding point at the incoming service panel in the event of a line-to-chassis short circuit (bonding), which will trip the circuit breaker quickly.
In both cases, a #8 conductor can easily handle the current of grounding and bonding, so that’s why it’s allowed to be undersized compared to the neutral and hot wires.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.