Meter stack with 3 tier rating all equal AIC

[hhsting]

Attached sketch has 1000A feeder from switchboard feeding meter stack that has 27 feeder breakers. Each feeder breakers feed one dwelling unit apartment panelboard.

Meter stacks is 22kA. The meter stack main breaker is 22kA and the meter stacks feeder breakers are 22kA. The meter stack is 3 tier series rating.

The unit panelboards are 22kA so all breakers in the unit panelboard are 22kA.

Each unit panelboard is MLO and has HVAC motor loads from one of the branch circuit breakers 30A.

In the sketch meter stack main breaker is labeled 1, one of the meter stack feeder breakers is labeled 2 and panelboard one of the branch circuit breakers is labeled 3.

I am trying to see if 3 tier series rating can be used or not between bkrs labeled 1,2 and 3 in sketch by using NEC 2017 section 240.86(C) however I do not know how to apply that since all those breakers are 22kA. Which one is higher rated overcurrent device and which one would be lower rated device?

 

[electrofelon]

I don't think much can be said without knowing the available fault current at each of the OCPD's.

 

[hhsting]

I don't think much can be said without knowing the available fault current at each of the OCPD's.

Ok but you are missing the point of question or maybe I dont follow you.
The question is Not about 240.86(c)(2) where you actually look at the fault current

The question is about nec 2017 section 240.86(c)(1). Note all breakers are 22kA. They are all equal. Which overcurrent device is higher rated and which lower rated in sketch as stated in 240.86(c)(1)? What does code mean by higher rated overcurrent device and lower rated overcurrent device? Current rating, interrupting rating, voltage rating or something else? Where does available fault current coming from in the equation here


240.86(C) Motor Contribution. Series ratings shall not be used where

(1) Motors are connected on the load side of the higher rated overcurrent device and on the line side of the lower-rated overcurrent device

 

[xptpcrewx]

Ok but you are missing the point of question or maybe I dont follow you.
The question is Not about 240.86(c)(2) where you actually look at the fault current

First, 250.86(C)(2) isn’t about fault current.

The question is about nec 2017 section 240.86(c)(1).

Second, you can’t even get to 240.86(C)(1) without getting past the main text. The parent text requires having an available fault current higher than the marked interrupting rating.

Note all breakers are 22kA. They are all equal.

Third, the parent text requires having two devices one of which must have a higher interrupting rating than the device you want to series rate with.

Which overcurrent device is higher rated and which lower rated in sketch as stated in 240.86(c)(1)?

None. You told us all the breakers are rated the same (22-kAIC). Series ratings do not apply in you example.

What does code mean by higher rated overcurrent device and lower rated overcurrent device? Current rating, interrupting rating, voltage rating or something else?

The interrupting rating.

Where does available fault current coming from in the equation here


240.86(C) Motor Contribution. Series ratings shall not be used where

(1) Motors are connected on the load side of the higher rated overcurrent device and on the line side of the lower-rated overcurrent device

What equation?

If you want to determine the prospective fault current, you need to perform a power system study short-circuit analysis.

If you want to address 240.86(C)(2), you would take the sum of the motor FLC’s and this total would need to be no more than 1% of the lower interrupting rating. In your example, 1% of 22-kAIC is 220 FLC amperes.

 

[hhsting]

I don't think much can be said without knowing the available fault current at each of the OCPD's.

True

 

[augie47]

See the answer in your other thread....

Fault currents motor contribution

In the attached sketch their are fault current locations labeled F1,F2,F3,F4,F5 and F6. I am wondering at location F1, F2,F3,F4,F5,F6 does the motor contributions of M1,M2,M3,M4 need to be taken into account or not? If not then which motors’ motor contribution would need to be taken into...

forums.mikeholt.com

 

[jim dungar]

Why is this a concern of the plan reviewer?

Every project I have worked on this issue is the responsibility of the electrical contractor, electrical inspector, and the equipment vendor. Many, if not most, of the specific details required to confirm Series Ratings are not available until construction is started.