Double Pole Breaker — One Side Hot, One Side Not

How a 240V Circuit Works

A 240V circuit uses two hot wires, each carrying 120V but 180 degrees out of phase with each other. The voltage between the two hots is 240V. A double-pole breaker connects to both hot legs simultaneously — when it trips, it disconnects both legs at the same time.

Cause 1: Lost Leg from the Utility

The utility company delivers power to your home on two hot legs (L1 and L2). If one leg is lost due to a downed power line, a blown transformer fuse, or a utility fault, half your panel will have no power.

Signs: multiple 240V appliances stop working at the same time, some 120V circuits work and others don't, lights may be dim on some circuits.

Fix: call your utility company — this is their problem to fix.

Cause 2: Faulty Double-Pole Breaker

A double-pole breaker with a failed internal connection on one pole will show voltage on one side but not the other. The breaker may appear to be ON but one pole is not conducting.

Test: with the breaker ON and the circuit loaded, measure voltage between each hot terminal and neutral. You should read approximately 120V on each side. If one side reads 0V, the breaker is faulty.

Fix: replace the double-pole breaker with the same brand, amperage, and type.

Cause 3: Loose Bus Bar Connection

The breaker connects to the panel's bus bars. If the bus bar connection is loose or corroded on one side, that pole will have no voltage.

Fix: have an electrician inspect the bus bar connections and tighten or clean as needed.

Safety Warning

Never work inside an energized electrical panel. Even with the main breaker OFF, the main lugs (the large wires entering the top of the panel from the utility) remain energized. Only a licensed electrician should work on the main lugs or bus bars.