430.62-3 in Lieu of 215.3

[fifty60]

Using 430.62-3 I can size a Feeder Circuit breaker smaller than what I can calculate in 215.3. For example. I have 2 motors branch circuits and 1 heater branch circuits. The FLA on the motors are 12 amps and 4 amps, and the FLA of the heater is 10amps.

Using 215.3 I get (12*1.25)+4+(10*1.25)= 31.5 so a 35A breaker

Using 430.63 I get (for a minimum) (12*1.25)+4+10= 29 so a 30A minimum breaker.

This is just an example, but this situation arrises when you use a time delay fuse that allows you to size the branch OCPD that allows you to size the largest motor at 125%. I know I use the actual breaker rating for 430.63, but in this case 12*1.25 is 15, which is what I use for the OCPD in this example.

So, can I use this smaller breaker or do I have to use the value from 214.3 first? In the above example, using 430.63 I would have a 30A breaker but a minimum circuit ampacity of 35A...so I would have a 30A breaker forced to protect 8AWG wire.

 

[augie47]

I see what I think are a few flaws. First, I don't see where you are getting your 1.25 for your motor in reference to 430.63.
430.63 is for sizing SC-GF devices and your reference is 430.62 which references 430.52. Your multiplier for your largest motor can be 2.5.
Secondly, IMO, the 1.25 on your heater applies to branch circuits. I don't follow why you would use it in your 215 application and not your 430 application.

 

[fifty60]

430.62 says "...rating or setting not greater than the largest rating or setting of the branch circuit...[based on the maximum permitted value for the specific type of protective device in accordance with 430.52]"

So this is saying that you HAVE to use the largest allowable rating, and cannot actually use the OCPD that is actually present. So the only multiplier I can use for 430.62 is the MAXIMUM rating allowed in 430.52?

430.63 reads "...not less than that required for the sum of the other loads" Which does not mention any multiplier. That is why I do not multiply by 125% for 430 calcs on non motor loads.

This problem here is that I am required to recommend a "Mains" service for our industrial machines. This is difficult and requires more variables than what I have at my disposable when these numbers are being calculated without the customer site info.

I believe the best I can do is give the minimum Feeder conductors and the minimum feeder OCPD. For me, the lowest rated "mains" is desirable. When first reading 430.63 I thought that it trumped 215.3 because of the motor loads. I also thought that the calculations were based off of the actual OCPD present, and not the maximum possible value. I thought that 430.63 allowed you to use a smaller OCPD for the feeder if you used Motor OCPD's that allowed you to size closer to the motor (125%)

 

[augie47]

You are correct that 430.63/430.52 does not require you to use the 2.5 multiplier but allows you to.
As was pointed out in a similar thread of yours, I see no way you can size the customers feeder without knowing all the variables.
I would think following 409.110 would be the most desirable route.

 

[fifty60]

Thanks Augie47. I agree with you there. I may try to push back on this "mains service" request.

...430.63/430.52 does not require you to use the 2.5 multiplier but allows you to

Does 430.63/430.52 allow you to use a lower multiplier than 2.5? Or is the maximum value (2.5 for a circuit breaker) the only multiplier 430.63 is allowing?

 

[jumper]

Thanks Augie47. I agree with you there. I may try to push back on this "mains service" request.

...430.63/430.52 does not require you to use the 2.5 multiplier but allows you to

Does 430.63/430.52 allow you to use a lower multiplier than 2.5? Or is the maximum value (2.5 for a circuit breaker) the only multiplier 430.63 is allowing?

You may use a lessor multiplier, that is the max for an IT breaker for some motors according to T430.52.

 

[fifty60]

Thanks Jumper. If I am using IT breakers, then 250% is the only value I can use? I have to use the maximum value given in table 430.52 for the given type of OCPD?

D-Curve breakers have similar characteristics to Dual element fuses. I can size them at 125% of my motor FLA. But I cannot use this 1.25 multiplier in accordance with 430.63, right?

 

[jumper]

Thanks Jumper. If I am using IT breakers, then 250% is the only value I can use? I have to use the maximum value given in table 430.52 for the given type of OCPD?

D-Curve breakers have similar characteristics to Dual element fuses. I can size them at 125% of my motor FLA. But I cannot use this 1.25 multiplier in accordance with 430.63, right?

You can always use an OCPD less than the maximum, but not less than the minimum.

430.52 Rating or Setting for Individual Motor Circuit.
(A) General. The motor branch-circuit short-circuit and
ground-fault protective device shall comply with 430.52(B)
and either 430.52(C) or (D), as applicable.

(B) All Motors. The motor branch-circuit short-circuit and
ground-fault protective device shall be capable of carrying
the starting current of the motor.

 

[fifty60]

and

and

Please correct me if I am wrong on any of the following:

That minimum (125%) is determined by 210.20A for branch circuits. This applies to fuses, circuit breakers...(not sure if that applies to motors with capacitors...but I will save that for a later post after I do more research)

The minimum feeder determined in 215.3 is the MINIMUM feeder for anything covered in 430..440.

No calculation from 430.63 can violate 215.3.

It is a little bit "up in the air" whether or not I have to use the maximum rating allowed for the particular OCPD from table 430.52, or if I can use the OCPD that is actually on the largest motor for this calculation, as long as that value is less than the maximum rating from 430.52 and greater than 210.20A. It is certain however that I can never size a feeder under any circumstance below the minimum in 215.3.

 

[jumper]

Here are graphics on how to size a multimoter feeder:

 

[fifty60]

Thanks, the illustrations are very clear. 430.62/430.63 are giving you the maximum OCPD for the minimum sized conductor. I can use any value below this maximum as long as it is above the minimum stated in 215.3.