I’m an RV Technician and enjoy reading your articles. I went to Amazon to look at the Extech CT70 and it asked me if I wanted the GFCI or the AFCI/GFCI version (CT80). Not being familiar with the AFCI, I did some light reading on arcing. So, now I’m wondering – can we use AFCI in an RV? And if so, would you recommend it on all circuits, outlets only, or some other configuration (kitchens, bathrooms and bedrooms)? If we use AFCI and I connect the Neutral to the AFCI circuit breaker, and non-AFCI circuits use the Neutral bar, will this work OK? Thanks. —Derek
Thanks for the great question. To answer it we first need a short lesson on the difference between a standard circuit breaker, a GFCI breaker, and an AFCI breaker.
A standard circuit breaker is actually called an Over-Current Protection Device (OCPD) and it has only one job, to monitor the amount of load current going though it to protect the wiring from current overload. It’s that overload that will cause overheating of the wires and eventually a fire. So a 15-amp circuit breaker trips with currents above 15 amp, a 20-amp breaker trips above 20 amps, etc. But it does ZERO to protect a human from getting shocked. If you accidentally touch a live 120-volt wire with wet hands while your feet are also wet, you might draw around 20 to 30 mA (milliamperes) of current, which is 0.030 amperes. That tiny amount of fault current is way below the 20-amp trip threshold of a typical circuit breaker, so it won’t even know its shocking you and will do nothing to protect you from electrocution. Basically it’s just a reset-able fuse.
Next up is a Ground Fault Circuit Interrupter (or GFCI). A GFCI receptacle like the one on the right doesn’t do over-current protection at all. That is, it expects a standard OCPD circuit breaker upstream of it in the panel to take care of any currents over 20 amperes. But a GFCI circuit serves the very important function of monitoring the outgoing current and comparing it to the return current. So if the hot wire is sending out 7.000 amps of current to an appliance, and only 6.995 amps are coming back through the neutral wire, then that 0.005 amps (or 5 milliamps) of current is unaccounted for and MUST be going somewhere or through someone. And that someone could be you touching a live wire while grounding yourself. Since a GFCI is set to trip at around 5 or 6 mA, that’s below the 10 mA of current that’s dangerous to your heart, and below the 20mA threshold of not being able to let go of a live wire. This is why GFCI-protected receptacles are now required in all places where you could come in contact with something grounded, such as your bathroom or kitchen sink, or on the outside of your RV.
You also need to know that a GFCI circuit breaker like the one on the left combines the function of a GFCI receptacle along with Over Current Protection, so it not only monitors for the 5 mA imbalance of the human getting shocked, it also monitors for too many space heaters on the circuit exceeding 20 amps of current that could overheat the wire.
Everyone with me so far? Good.
An AFCI (Arc Fault Circuit Interrupt) breaker (like the one on the right) includes the function of a standard Over Current Protection Device with Arc Fault Protection, and it may also be a combo AFCI/GFCI breaker that includes a Ground Fault Circuit Interrupter which is required in bathrooms and kitchens. What an AFCI circuit does is listen for the sound of electricity arcing in the wiring, and trip if it hears something it interprets as arcing.
Here’s why this is an important function. If the insulation in a wire breaks down for any reason, say by a nail through the wall piercing the insulation, or too much flexing of a cable carrying 120 volts, then the wires can begin to arc internally. The same thing can happen with the contacts in a switch that are worn or oxidized which cause them to arc. And this internal arcing will create carbon and copper oxide, which creates even more arcing and more heating. And that overheating can eventually lead to a fire inside of the walls. Modern electrical code calls for AFCI protection in places where occupants are sleeping, such as bedrooms. And that’s because the fire can start inside of the walls and not release enough smoke to set off a smoke detector until the inside of the walls are on fire. At that point you might have seconds to escape safely, which is why these types of fires tend to be so deadly. So the most important function of an AFCI is to monitor the circuit for any arcing that can cause a hidden fire and stop it BEFORE the fire starts.
Finally, to answer your question. Yes, an AFCI can be installed in the same circuit panel as all the other breakers, and as long as you connect the AFCI (or GFCI) separate neutral wire to the neutral bus bar, it shouldn’t get confused and trip without a good reason. But know that you can’t use a AFCI or GFCI breaker on a shared neutral wiring run like you typically find in a home, but maybe not an RV. So I think that installing AFCI protection in RV bedroom outlets is a great idea, simply because any in-wall fire in an RV will be in close proximity to the sleeping area. But if you add an AFCI breaker to a bathroom, kitchen or outside outlet on your RV, it needs to be a combo unit which also includes the GFCI function in order to meet code for usage in those areas.
Let me know if any of you would like to take this discussion to a higher level and I’ll set up an area to talk about AFCI protection in RVs.
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.
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