electrical academy · lesson 5 · about 8 minutes
Fitting circuit breakers: keep the vents clear
When a breaker clears a big fault, hot gas escapes through vents. This lesson shows why those vents must stay open and what to fit around them.
Learning material, not a design or safety instruction. Electrical work must be done by qualified people following the maker's instructions and local rules.
What happens in a fault
Opening a large fault current creates an arc inside the breaker. The arc heats the air and makes hot, ionised gas and metal vapour.
Vents let that gas out, away from live parts, so the arc does not restart outside the breaker.
Rules to follow
- Do not block the vents with barriers, panels or neighbouring devices.
- Fit phase separators or terminal covers where the maker requires them. They keep phases apart and leave the vents free.
- Use insulated bars or cables to connect the breaker.
- Follow the maker's installation sheet for each fixing style, whether fixed, plug-in or withdrawable.
Alternatives need proof
If you want a different layout from the maker's, it must be checked by test, not by opinion.
check yourself
Three quick questions
Think of your answer first, then open the question.
Why do breakers have vents?
To let hot arc gas escape away from live parts.
Name two things you must not do.
Block the vents, or use bare conductors where insulated ones are required.
Who must prove an alternative layout?
The installer, by test.
Learning material, not a design or safety instruction. Electrical work must be done by qualified people following the maker's instructions and local rules.