AC and DC circuit breakers may look similar, but their arc-interruption requirements are different. Using an AC-only breaker on a DC circuit can be unsafe.
Why DC arcs are harder to interrupt
AC current naturally crosses zero many times per second, helping extinguish the arc. DC current does not have a natural zero crossing, so DC breakers use specific contact spacing, arc chutes, polarity arrangements and series poles.
| Feature | AC breaker | DC breaker |
|---|---|---|
| Current waveform | Alternating | Direct |
| Arc extinction | Assisted by zero crossing | Requires stronger arc control |
| Polarity | Usually not polarity-sensitive | May be polarity-sensitive |
| Typical use | Utility mains and AC loads | Solar PV, batteries, DC control |
How to select a DC breaker
- Confirm maximum DC voltage.
- Check current rating and cable capacity.
- Follow polarity markings where present.
- Use the required number of poles in series.
- Verify breaking capacity at the system voltage.
Solar PV considerations
PV array voltage rises in cold conditions. Use the maximum calculated open-circuit voltage, not only nominal operating voltage. Consider reverse current and string configuration.
Frequently asked questions
Can I use a DC breaker on AC?
Only when the manufacturer provides an AC rating and the device is approved for that use.
Why are some DC breakers polarity marked?
Internal magnetic arc control may depend on current direction. Incorrect polarity can reduce interruption performance.
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