Overcurrent protection (ii)

[DWCOCKBURN]

How do we protect an electrical circuit from 'a large overload of a short duration'?

 

[mainline]

With an overload protection device.

Some circuits can be very well protected by using an electronic circuit protection device, which would drive a mosfet.

The trip current, trip delay time and auto-reset period are
programmable over a wide range to accommodate a
variety of load impedances. An active high shutdown input
is also provided and interfaces directly to a PTC thermistor
for thermal circuit breaking. An open-drain output is
provided to report breaker status to the µP

Hope that helps with your obvious dilemma.

 

[DWCOCKBURN]

If we were to use a 'C' Type or a 'D' Type circuit breaker; given that the I2 values of all 'Types' of circuit breaker of the same nominal current value are identical, could we then claim to have also fulfilled our primary objective of protecting an electrical circuit from 'a small overload of a long duration'?

 

[mainline]

If we were to use a 'C' Type or a 'D' Type circuit breaker; given that the I2 values of all 'Types' of circuit breaker of the same nominal current value are identical, could we then claim to have also fulfilled our primary objective of protecting an electrical circuit from 'a small overload of a long duration'?

No they are relevant to inrush currents in inductive loads, not sustained overloads

 

[DWCOCKBURN]

Take a closer look at your time current characteristics graphs.

If we were to use an overcurrent protective device of a larger nominal current rating by employing a 'fusing factor' of 1.45, could we then claim to have also fulfilled our primary objective of protecting the circuit against 'a small overload of a long duration' by adding an amp-meter to the circuit and permanently monitoring current flow?

 

[Brother Blue]

We do not normally apply the 1.45 factor to the nominal current, In, of the protective device.

The 1.45 factor is applicable to I2, which is the current causing effective operation.

Could you clarify exactly what you want to ask about in this thread, you started the thread asking about large overloads of short duration but have now switched over to small overloads of long duration?

 

[DWCOCKBURN]

All circuits must be protected against 'a small overload of a long duration'.

 

[mainline]

All circuits must be protected against 'a small overload of a long duration'.

Not all need to have a device providing protection against overload.

 

[Risteard]

All circuits must be protected against 'a small overload of a long duration'.

Through correct design...

 

[DWCOCKBURN]

First; you will need to provide an example of an electrical circuit that apparently does not need to be protected against 'a small overload of a long duration'.
Second; you will need to explain to all of the technical boffins at every circuit breaker manufacturer, why their 'C' Type and 'D' Type circuit breakers fail to protect an electrical circuit from 'a small overload of a long duration' and therefore aren't fit for purpose.

 

[Brother Blue]

First; you will need to provide an example of an electrical circuit that apparently does not need to be protected against 'a small overload of a long duration'.

Any circuit feeding a fixed load which is not susceptible to overload or incorporates its own fine overload protection.
For example a circuit feeding and immersion heater or a circuit feeding and electric motor with it's associated motor starter.

Second; you will need to explain to all of the technical boffins at every circuit breaker manufacturer, why their 'C' Type and 'D' Type circuit breakers fail to protect an electrical circuit from 'a small overload of a long duration' and therefore aren't fit for purpose.

No need at all, circuit breaker manufacturers are already fully aware of the limitations of thermal-magnetic circuit breakers and furthermore would be able to advise you on suitable devices to provide such protection if you have an application which needs it.

MCBs are fit for their purpose, none of us are suggesting otherwise.

 

[DWCOCKBURN]

You are protecting the circuit not the load.

By 10, 000 seconds all I2 values have been achieved, therefore all types of circuit breaker are capable of protecting any electrical circuit against 'a small overload of a long duration'; as long as the current carrying capacity of the smallest conductor within that circuit exceeds the I2 value of the chosen overcurrent protective device.

 

[newfutile]

The type of circuit breaker is not applicable to a small overload,it just determines the amount of current required to trip Instantaneously.
The best way as stated is to design the circuit correctly

 

[DWCOCKBURN]

The type of circuit breaker is not applicable to a small overload,it just determines the amount of current required to trip Instantaneously.
The best way as stated is to design the circuit correctly

All circuits need to be protected from 'a small overload of a long duration'.

 

[Brother Blue]

All circuits need to be protected from 'a small overload of a long duration'.

No they don't, as been previously established in both of these threads.

 

[DWCOCKBURN]

Where exactly did you establish that?

 

[Brother Blue]

Where exactly did you establish that?

Read both of these threads and you will see.

 

[DWCOCKBURN]

Everybody is reading them.