WiremanWireman · Electric heat strips not working: troubleshooting for electricians · 2023 NEC ·
Electric heat strips not working
Breakers, the W call, amps on each element, then elements, limits and sequencers.
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How it works
Electric heat in an air handler is a set of resistance elements, commonly 5 kW each, switched on by sequencers or relays when the thermostat sends W (or W2 or E). Each element has an automatic-reset limit and a one-time fusible link or thermal cutoff that opens if it overheats. Larger kits are split into two or more circuits, each with its own breaker in the air handler and at the panel. Strips must have airflow: the blower has to run whenever they’re on.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What’s happening with the electric heat?
- No heat from the strips at allAre all the heat breakers on, at the panel and in the air handler?
- One was tripped or offA heat circuit breaker was off or tripped
- All onTest: Check the heat callExpect: About 24 V AC.
- 0 VThe thermostat isn’t calling for strip heat
- 24 VTest: Clamp each element circuitExpect: Close to W ÷ V for each element: a 5 kW element draws about 21 A at 240 V, or about 18 A at 208 V.
- One or more read 0 ATest: Test the element, limit and linkExpect: Element near R = V² ÷ W (about 11.5 Ω for 5 kW at 240 V). Limit and link near 0 Ω.
- Element reads OLBurned-open element
- Limit or link reads openOpen limit or fusible link
- All goodFailed sequencer or heat relay
- All draw about rated ampsThe strips are working
- One or more read 0 ATest: Test the element, limit and linkExpect: Element near R = V² ÷ W (about 11.5 Ω for 5 kW at 240 V). Limit and link near 0 Ω.
- Some heat, but not enoughTest: Clamp each element circuitExpect: Close to W ÷ V for each element: a 5 kW element draws about 21 A at 240 V, or about 18 A at 208 V.
- One or more read 0 ATest: Test the element, limit and linkExpect: Element near R = V² ÷ W (about 11.5 Ω for 5 kW at 240 V). Limit and link near 0 Ω.
- Element reads OLBurned-open element
- Limit or link reads openOpen limit or fusible link
- All goodFailed sequencer or heat relay
- All draw about rated ampsThe strips are working
- One or more read 0 ATest: Test the element, limit and linkExpect: Element near R = V² ÷ W (about 11.5 Ω for 5 kW at 240 V). Limit and link near 0 Ω.
- The heat breaker tripsTest: Test the elements to the cabinetExpect: OL on every terminal.
- Reads to the cabinetElement shorted to the cabinet
- OL everywhereOverheating connection or breaker
- Strips heat but the blower doesn’t runHeat strips running without airflow
- No heat from the strips at allAre all the heat breakers on, at the panel and in the air handler?