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Worksheets3005 419 21 MCB Curve Types
Total questions: 13
Worksheet time: 7mins
This is an MCB (Miniature Circuit Breaker).
What current can run through it continuously forever?
4A
6A
12A
24A
48A
This is an MCB (Miniature Circuit Breaker).
What curve type rating is it?
A
B
C
D
E
This is an MCB (Miniature Circuit Breaker).
If I put 24 Amps through it, what would happen?
It will trip at anything over 6 amps
It will trip at exactly 6 amps
It will allow 24 amps for a short period of time, maybe a few seconds, and then trip
It will allow about 24 amps for about 4 minutes and then trip
It will allow 24 amps for up to 4 1/2 hours
This is the trip curve graph of a C curve MCB (Miniature circuit breaker).
If the MCB is marked at 6 amps, and 24 amps runs through it for half a second, would it trip?
Yes, it is rated at 6A
No, it is rated at 6A, and must trip at 6A, not more
Yes, there is enough current at the rating of the C Curve MCB
No, there is not enough current at the rating of the C Curve MCB
This is the trip curve graph of a C curve MCB (Miniature circuit breaker).
If the MCB is marked at 6 amps, and 35 amps runs through it for half a second, would it trip?
Yes, it is rated at 6A
No, it is rated at 6A, and must trip at 6A, not more
Yes, there is enough current at the rating of the C Curve MCB
No, there is not enough current at the rating of the C Curve MCB
This is the trip curve graph of a C curve MCB (Miniature circuit breaker).
If the MCB is marked at 6 amps, and 24 amps runs through it for 5 seconds, would it trip?
Yes, it is rated at 6A
No, it is rated at 6A, and must trip at 6A, not more
Yes, there is enough current at the rating of the C Curve MCB
No, there is not enough current at the rating of the C Curve MCB
This is the trip curve graph of a C curve MCB (Miniature circuit breaker).
If the MCB is marked at 6 amps, and 12 amps runs through it for 1 minute, would it trip?
Yes, it is rated at 6A
No, it is rated at 6A, and must trip at 6A, not more
Yes, there is enough current at the rating of the C Curve MCB
No, there is not enough current at the rating of the C Curve MCB
This is the trip curve graph of a C curve MCB (Miniature circuit breaker).
What would a C Curve MCB normally be used for?
Normal domestic operations
Motors and coils
Hospitals and medical centres
Lighting systems
This is the trip curve graph of a C curve MCB (Miniature circuit breaker).
Based on the C Curve characteristics, would we consider this MCB to generally trip at 7.5 times it's current value?
No, it must be exactly 10 minus 5 equals 5 x Current value
Yes, it is 7.5 x Current for under 1 second
Yes, 7.5 is centre of 5 and 10 for any current no matter how long
No, It will only trip at exactly 5 x Current rating, and not go higjher
If this MCB is marked C 20, then what is the 6 KA marking for?
That is manufacture model number
It can handle 6KA for a very short time, so it will not accidentally switch off if there is an electrical spike
This figure represents its breaking capacity, also known as interrupting rating.
This is an indicator of the wire size that must be used
If this MCB is marked C 20, then what is the 6 KA marking for?
That is manufacture model number
It can handle 6KA for a very short time, so it will not accidentally switch off if there is an electrical spike
The MCB will safely isolate currents below 6 KA without breaking or causing a fire, in fault current or short-circuit current conditions
This is an indicator of the wire size that must be used
This is a D Curve MCB and operates around 12 x Current rating. Where would this possibly be used.
Light systems
Car starter motors
Stoves
Electric motors
On the main input MCB of a house
This is a graph of multiple Curve type MCB's. If we look at the curve for Z, where would it likely be used?
Motors and drills, to activate quickly
Mainly on motors where it activates slowly, allowing start-up currents of motors
On purely resistive loads where accuracy is needed
For military purposes where current must be precise
Hospitals and elevators where fast response is needed.
