is a standard breaker (sq.D FAL) instantaneous trip?

[biofueler]

I am considering using a breaker for a motor short-circuit and ground-fault protection (standard thermal-magnetic sq.d FAL series) as per NEC 430.52.

I'm not sure if this is classified as an instantaneous trip or an inverse-time breaker. I downloaded the trip curves, but its not clear exactly what category it would fall into.

thanks in advance! Its for determining the current rating based on 250%/800% of motor FLA.

 

[dpc]

A thermal-mag breaker has both inverse time and instantaneous trip.

A "mag-only" or motor-circuit protector is a molded-case breaker with no thermal (inverse time) trip.

 

[biofueler]

well, I guess my question is, how is it classified as per code?

 

[rbulsara]

bio:

Both. Since it has inverse time (thermal) characteristics which comes in play during motor starting current, its rating shall be selected as permitted for inverse time breakers. It is this characteristics that permit a smaller size (ampere rating) breaker for a motor breakr compared to one with only instaneous (magnetic) element. Make sure If adjustable, the instantaneous trip is set to high,

The instaneous (magentic) part provides short circuit protection as required by code.

Speaking of plotting curves, you make sure that you also load the motor curve. The breaker curve shall remain to right and above the motor current curve and the breaker rating shall not exceed what Code permits. That is all you need to confirm.

Beyond that sit down with an electrical engineer friend who knows the subject.

 

[jraef]

Careful, the FAL can come in either format, depending on the catalog number.

The only caveat to all this is that the Mag (Instantaneous) trips on a Thermal-Mag breaker are fixed at the factory in that frame size, not adjustable. It's sometimes tricky to get the right continuous amp rating while still staying within the allowable limits of the NEC 430.52 sizing (including exceptions). In some motor applications, especially when starting ATL (DOL), the magnetization inrush may exceed that fixed rating and cause nuisance tripping. That's why MCPs are used in motor circuits as a rule, they have higher trip ranges and adjustability to avoid nuisance tripping on motor inrush.

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