RFI to Ground-Fault Circuit Interrupters
Ground-Fault Circuit Interrupters (GFCI) circuit breakers are occasionally reported to “trip” (open the circuit) when a strong RF signal is present, usually a ham’s HF transmissions. GFCI circuit-breakers operate by sensing unbalanced currents in the hot and neutral conductors of an ac circuit. In the absence of RF interference such an imbalance indicates the presence of a fault somewhere in the circuit, creating a shock hazard. The breaker then trips (opens) to remove the shock hazard.
An Arc Fault Circuit Interrupter (AFCI) circuit breaker is similar in that it monitors current to watch for a fault condition. Instead of current imbalances, the AFCI detects patterns of current that indicate an arc – one of the leading causes of home fires. The AFCI is not supposed to trip because of “normal” arcs that occur when a switch is opened or a plug is removed.
Under current codes, GFCI protection is required for all basement outlets, outdoor outlets, and for outlets in kitchens and bathrooms. AFCI protection required for all circuits that supply bedrooms.
RF interference to GFCI breakers is caused by RF current or voltage upsetting normal operation of the imbalance detection circuit, resulting in the false detection of a fault. Similarly, RF current or voltage could upset the arc detection circuitry of an AFCI breaker.
Some early GFCI breakers were susceptible to RFI but as the technology has improved, fewer and fewer such reports have been received. While it is possible to add filtering or RF suppression to the breaker wiring, a simpler and less expensive solution is to simply replace the GFCI breaker with a new unit less susceptible to RF.
The ARRL Lab has received favorable reports on the following GFCI products:
· Leviton GFCI outlets which are available in both 15 and 20 amp versions for 117 VAC circuits as well as cord sets and user-attachable plugs and receptacles.
· Bryant Ground Fault receptacles which feature published 0.5-volt immunity from 150 kHz to 230 MHz.
Reports have not yet been received on AFCI products.