Fusless Current Limiter in Breaker 1

[cherry2000]

Does anybody know how the Current limiter in a breaker works? Typically a breaker has 25kA interrupting capacity which goes upto 100kA with this fuseless current limiter which sits at the load end of the breaker.

 

[davidbeach]

It uses the magnetic forces of the fault current to "blow open" the contacts. Manufacturer's literature should be able to provide many details.

 

[dpc]

You might want to double-check the breaker you're looking at. There are two approaches:

The breaker with a current-limiter - the current-limiter is a fuse that is integrally mounted on the breaker.

A current-limiting circuit breaker. As David mentioned, if the breaker can open fast enough, it becomes current-limiting because the current is interrupted before it reaches a maximum peak current in the first-half cycle. Specially designed and tested breakers can achieve this by having contacts that are forced open before the breaker actually trips.

 

[LionelHutz]

To add to dpc's post - I doubt that you can bolt on a fuseless current limiter. From what I have seen, that type of block is just a set of fuses, often sealed inside the block so you can't see what it is.

 

[cherry2000]

David..You are absolutely right ..see the attached literature which I had missed. Thanks to you all.

 

[xxjohnh]

Depends on the voltage. With low voltage you can get a current limiting molded case circuit breaker or an air circuit breaker wuth current limiting fuses. For medium voltage you can get current limiting fuses or a high current fault limiting device, which is a one time operation, where a chemical explosion blows out the arc.

 

[busbar]

One caveat—I understand that you give up selective coordination with other overcurrent devices when you apply current-limiting circuit breakers.

 

[sibeen]

busbar, in the IEC world we call the use of a current limiting circuit breaker upstream to reinforce the breaking capacity of a downstream circuit breaker, cascading.

If you use this to 'increase' the downstream breaking capacity then you will lose discrimination between the circuit breakers.

This doesn't mean that using a current limiting CB in a circuit precludes full discrimination being available. If the downstream breakers are fully rated for the prospective kA there is no problems (as long as the manufacturer shows discrimination between the CBs).