When I should use a type B or type C MCB
MCB
- Thread starter carys43
- Start date
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Always stick to type B for domestic. Type C have larger surge current rating and are used more in industrial installs with more inductive loads eg. motors and many fluorescents
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Type / Curve : B / 2
Short Circuit response : 3-5 times current rating
Applications : Circuits with moderate inrush, mixed lighting heaters and other resistive loads
Type / Curve : C / 3
Short Circuit response : 5-10 times current rating
Applications : Higher inrush mildly inductive loads, motor drives, ballast lamps or large amounts of switching
Type / Curve : D / 4
Short Circuit response : 10-20 times current rating
Applications : Abnormally high inrush due to highly inductive loads, transformers, motors and non power factor corrected thyristor drives
MORE INFO
Type / Curve : B / 2
Short Circuit response : 3-5 times current rating
Applications : Circuits with moderate inrush, mixed lighting heaters and other resistive loads
Type / Curve : C / 3
Short Circuit response : 5-10 times current rating
Applications : Higher inrush mildly inductive loads, motor drives, ballast lamps or large amounts of switching
Type / Curve : D / 4
Short Circuit response : 10-20 times current rating
Applications : Abnormally high inrush due to highly inductive loads, transformers, motors and non power factor corrected thyristor drives
I've bought MCB type C 6A, would it be OK for me to use them in a garage consumer unit providing external lighting (max 500W per circuit) and sockets
If you can guarantee the circuit impedance is low enough to trip the breaker rapidly in the event of a fault, yes, it is OK.
In practice, this will be true if the wire length is less than ~ 40m to the furthest point ( assuming wired in 1mm sq), or more like 60m if the cable is 1.5mm sq, assuming your supply to the main board is not already breaking the earth resistance rules when it supplies the socket circuits.
You do not need to worry about that length limit if the circuit is also protected by an RCD.
PS although BJS suggestion that only B types are needed for domestic installtions is generally right, #I would add that C16s can be good for small load radial power circuits for garges and workshops etc, as occasional use of high surge, but low running current loads like welding gear, compressors etc can often trip a B16 but not really justify the laying in of a B-32 radial. The same arguement is also true for some larger fridge/freezer combinations.
In practice, this will be true if the wire length is less than ~ 40m to the furthest point ( assuming wired in 1mm sq), or more like 60m if the cable is 1.5mm sq, assuming your supply to the main board is not already breaking the earth resistance rules when it supplies the socket circuits.
You do not need to worry about that length limit if the circuit is also protected by an RCD.
PS although BJS suggestion that only B types are needed for domestic installtions is generally right, #I would add that C16s can be good for small load radial power circuits for garges and workshops etc, as occasional use of high surge, but low running current loads like welding gear, compressors etc can often trip a B16 but not really justify the laying in of a B-32 radial. The same arguement is also true for some larger fridge/freezer combinations.
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Thanks both for the advice
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