How is SCCR rating used to deterine PPE?

[Sclark]

Giving that you have a electrical enclosure labled with the SCCR, how do you use that number to determine the Personal Protective Equipment required?:-?

 

[charlie b]

You don?t. The PPE requirements are based on the amount of energy that the system, as installed, could release into a short circuit, not the amount of fault current a component is able to handle. You would need to do an Arc Flash Evaluation of the power distribution system into which a component would be installed, in order to determine the PPE required to work on that component.

Welcome to the forum.

 

[jim dungar]

There are a lot of acronyms, commonly/universally used ones are:

AIC - Amps Interrupting Capacity - this only applies to overcurrent protective devices. It is the amount of fault current a device can "break" (see NEC 110.9).

SCCR - Short Circuit Current Rating - this only applies to 'static' devices like conductors and panels. It is the amount of fault current a device can "withstand" for a specified time frame (see NEC 110.10).

SCA - Short Circuit Amps (or Short Circuit, Available) - this is the amount of fault current available at a point in the electrical system. This is the value used to check if the appropriate AIC and SCCR have been applied. It is sometimes called the "bolted fault current".

 

[Sclark]

Thanks for the replies.

So I need to determine the available bolted fault current where the control panel would be installed. In our building, for instance, there is a transformer that supplies the Circuit breakers for the building. So am I right in saying that the fault current available would be based on the transformer and the circuit breaker rating?

 

[weressl]

Giving that you have a electrical enclosure labled with the SCCR, how do you use that number to determine the Personal Protective Equipment required?:-?

The total heat energy is expressed in cal/sqin. The available heat is determined by the magnitude of the current AND the duration of the fault, eg. the action of the protective device that interrupts the fault, be it fuse or CB.

 

[jim dungar]

Thanks for the replies.

So I need to determine the available bolted fault current where the control panel would be installed. In our building, for instance, there is a transformer that supplies the Circuit breakers for the building. So am I right in saying that the fault current available would be based on the transformer and the circuit breaker rating?

Almost.

The fault current available would be based on the transformer and all of the 'conductors' to the control panel. Effectively the only impact the circuit breakers have, is the amount of time it takes them to sense a fault and then clear that fault current.