Breaker vs Cable

[Hameedulla-Ekhlas]

Greeting all,

Does a breaker trip when the a feeder heats up or it trips due to ampere increase more than braker capacity.


Suppose, we have a breaker with 100 ampere and is connected to a feeder with 60 ampere capacity and if 100 ampere load is connected to this feeder.

Will this feeder burn first or as soon as this feeder heats up befor burning the breaker will trip

Please advise me.

 

[Dennis Alwon]

The insulation on your feeder will get very hot and start to melt. The breaker won't trip under those circumstances at least until some damage is done.

 

[Hameedulla-Ekhlas]

Is the breaker not sensible against the heat which produces in a feeder.

 

[jwjrw]

The insulation on your feeder will get very hot and start to melt. The breaker won't trip under those circumstances at least until some damage is done.

I thought the breaker was designed to prevent the insulation from damage from heat and short circuits.

 

[brian john]

Depends on the type of circuit breaker and the condition causing the heat. Circuit breakers utilizing static trip/electronic OCP work purely on amps and time.

Common molded case circuit breakers inverse time current are thermal magnetic devices, long time over current s is in the thermal range for overloads, instantaneous operation due typically to faults or inrush currents exceeding the circuit breaker ratings based once again on current and time ratings are in the magnetic portion of the device protection.

 

[jim dungar]

Is the breaker not sensible against the heat which produces in a feeder.

No, the breaker responds to the current flowing through it.

The internal parts of the breaker are designed to heat up at the same rate as a cable of equal size for an equal amount of current.

Because a breaker does operate based on heat, its behavior is slightly modified by the amount of heat absorbed or dissipated at its terminals, but it does not sense the temperature of conductors.

 

[Jraef]

No, the breaker responds to the current flowing through it.

The internal parts of the breaker are designed to heat up at the same rate as a cable of equal size for an equal amount of current.

Because a breaker does operate based on heat, its behavior is slightly modified by the amount of heat absorbed or dissipated at its terminals, but it does not sense the temperature of conductors.

That sums it up for you. I'll only reemphasize that since the breaker is not sensing heat directly, but rather current and thus the indirect effects of current at a given level, you cannot protect a cable rated for 60A with a breaker set to trip at 100A (which is what was alluded to in the earlier posts as well).

 

[Hameedulla-Ekhlas]

Thanks all guys I really appreciate your idea, information and response. It is really helpful for me.

 

[glene77is]

Thanks all guys I really appreciate your idea, information and response. It is really helpful for me.

So,
It sounds like you will use a 60A breaker on 60A cable for a <=60A load.
Right? :smile:

 

[Hameedulla-Ekhlas]

Yes, you are right cable ampere capacity must be >=breaker current capacity and not less than breaker current capacity.