Why a GFCI breaker trips on an old dryer circuit but holds on a two-wire cooktop

The electrician raised the question on Reddit's r/electricians forum, and it comes up more often as GFCI rules reach 240-volt equipment. Since the 2020 NEC, dwelling GFCI requirements cover receptacles up to 250 volts in listed locations such as laundry areas, and section 210.8(D) of the 2023 code lists appliances whose outlets need Class A protection, among them clothes dryers, electric ranges, wall ovens and counter-mounted cooking units.

A two-pole GFCI breaker compares the current leaving through its sensor with the current coming back. A pure 240-volt load such as an induction cooktop sends current out on one hot and back on the other, so the two cancel. Schneider Electric's guidance for its QO and Homeline GFCI breakers says to land the two hots, leave the load neutral lug empty and still connect the breaker's pigtail to the panel neutral bar, because the electronics need it for power.

An old three-wire dryer circuit has no separate ground. Under the NEC rule for existing circuits, now 250.140(B), the neutral also bonds the dryer's frame, and the drum motor, controls and light run at 120 volts on that neutral. If the frame touches anything else that is grounded, the washer for example, part of the neutral current returns outside the breaker and the breaker counts it as a ground fault. A participant on Mike Holt's code forum summed it up: "this setup will always trip a GFCI."

The fix is a four-wire circuit with an equipment grounding conductor and the dryer's neutral-to-frame jumper removed. The 2023 NEC requires that ground on new circuits, and a jumper left in place on a four-wire hookup causes nuisance trips. The cooktop has its own issue: 250.140 requires the frame of a counter-mounted cooking unit to be connected to an equipment ground, and the neutral-bonding allowance covers only 120/240-volt three-wire circuits, so an old two-conductor run needs checking for a ground before sign-off.