Motor molded-case circuit breaker chart

[Rson]

Hi,

I almost always use a fused disconnect for enclosures, usually class J and rely on the Bussman SPD publication to help with sizing the appropriate fuses for the disconnect sizes, since I mostly (99% of the time) deal with motor control.

Is there a trusted publication for Molded-case circuit breakers that is similar or a sizing chart? We have a customer that is requiring a circuit breaker for the main disconnect rather than fuses.

I've found this schneider electric one:
https://www.se.com/us/en/faqs/FA239478/

but it seems to be all I've found thus far. If anyone has a great resource, please share!

 

[Aabeck]

Personally I would consider rather using a properly sized manual motor overload

This one from FactoryMation.com is $32 and they have a range of settings from 0.1 to 65 amps.

 

[Rson]

I didn't find a better table, but I guess I should have looked closer at the NEC.

NEC 430.52 has the inverse time circuit breaker % at 250% with the time-delay fuses at 175%. Doing the math, the numbers all add up to on the above chart.

It appears NEC 670.4(c) mentions the size could be for fuse OR circuit breaker, so the main disconnect size would use the same calculation as the fuse.

 

[jraef]

Years ago most of the motor control mfrs gave away (for free!) what were called "slide charts" where you slid a center core chart to the appropriate motor HP, picked out your voltage, and the chart displayed the motor starter, breaker, fuses and OL heater elements for you. haven't seen one of those in years now though...

But apparently you can BUY one on Amazon...

What a world...