430.52 - Several Motors or Loads on One Branch Circuit | 1/8hp, 208-2P VAVs

[ElectrifiedClimber]

This discussion came up among a few Engineers in my company. On projects where our Mechanical Engineers provide hydronic VAVS with small fan motors (1/8 HP), we typically circuit multiple 120V VAVs on a single 120V,20A branch circuit. Providing a Cooper Bussman Type "STY" fused @15 or similar. This conforms with 430.53(A) Not Over 1 Horsepower and (1), (2), and (3) listed in that section.

Our Mechanicals provided 208V-2P VAVs that are 1/8 HP on another project and when I brought it up, other EEs has said to use the same approach on a 20A circuit and 15A fused STY type switch. There are a few issues with this since the STY is rated at 125V and Part (A) applies to 120V circuits. Since Part (A) no longer applies, are 208V-2P, 1/8HP VAVs able to be circuited together on a 208V,15A circuit with a non-fused motor rated switch at each unit under Part (B) If Smallest Rated Motor Protected?

1/8HP is not listed in table 320.248 so I cannot verify that the 15A Inverse Time Circuit Breaker is <800% of the rating per 430.52. Calculating the value, it seems that 15A would exceed 800% of the FLA of the motor which would not follow the first sentence of Part (B) "If the branch-circuit short-circuit and ground-fault protective device is selected not to exceed that allowed by 430.52 for the smallest rated motor". Is a smaller fused switch needed at each motor to comply?

 

[don_resqcapt19]

....

1/8HP is not listed in table 320.248 so I cannot verify that the 15A Inverse Time Circuit Breaker is <800% of the rating per 430.52. Calculating the value, it seems that 15A would exceed 800% of the FLA of the motor which would not follow the first sentence of Part (B) "If the branch-circuit short-circuit and ground-fault protective device is selected not to exceed that allowed by 430.52 for the smallest rated motor". Is a smaller fused switch needed at each motor to comply?

The 800% only applies to instantaneous trip breakers, and not to inverse time breakers. It is 250% for inverse time breakers.

 

[ElectrifiedClimber]

The 800% only applies to instantaneous trip breakers, and not to inverse time breakers. It is 250% for inverse time breakers.

Thanks for the correction, I was referencing the wrong column. I just reread Exception No. 1 of 430.52 which is next size up since we do not fall on a standard size. That would seem to allow a 15A circuit breaker to protect it subsequently following 430.53(B) without a smaller fuse.

 

[don_resqcapt19]

Thanks for the correction, I was referencing the wrong column. I just reread Exception No. 1 of 430.52 which is next size up since we do not fall on a standard size. That would seem to allow a 15A circuit breaker to protect it subsequently following 430.53(B) without a smaller fuse.

If you are on the 2023 code that might be a 10 amp breaker, as that size has been added to 240.6 in the 2023 code.

 

[ElectrifiedClimber]

That is good to know. I just moved states recently from Iowa (NEC 2020 adopted) to MN (NEC 2023 adopted). I am familiar a few changes but wasn't one of them. Thanks again!

 

[LarryFine]

If you are on the 2023 code that might be a 10 amp breaker, as that size has been added to 240.6 in the 2023 code.

Will they be making #16cu NM to go with it?

 

[don_resqcapt19]

Will they be making #16cu NM to go with it?

The reason it was added in the 2023 was for 14 AWG copper-clad-aluminum, but that still has limited uses in the. However I have heard both 14 AWG CCA and 16 AWG copper were approved for 10 amp branch circuits in the first draft meetings for the 2026 code.

 

[LarryFine]

The reason it was added in the 2023 was for 14 AWG copper-clad-aluminum . . .

I know, which is why I added 'cu' to my question.

 

[don_resqcapt19]

I know, which is why I added 'cu' to my question.

I am surprised that the first draft meeting accepted 16 AWG copper because of the higher risk of physical damage for conductors smaller than 14 AWG. Of course to pass at the meeting, the PI only needed a 50% +1 majority. The PIs that got that majority are "balloted" where it must receive a 2/3s majority to become a first revision that will be published in the First Draft Report to be published on 7/10/24.

 

[tortuga]

1/8HP is not listed in table

I often extrapolate the tables into a VA/HP X HP plot for custom motor sizes and voltages not in the tables.
For a 1/8 HP 200V motor (208V single phase service) I get 1.87 Amps

 

[AC\DC]

Is price saving that substantial from 14 to 16 cu??? Seems dump. I get it for copper clad

 

[tortuga]

We used to have spools of 16 AWG stranded speaker wire from back when builders wanted to pre wire new spec homes with those Bose whole house speaker systems . For a audio cable 16 stranded is decent stuff just like NM I could see them adding 16AWG stranded to the listing for NM (with THHN or TFFN). Solid no way that would be nuts.
I only see 10A breakers come up with commercial/industrial work like small motors.
The gotchya about the new 10 A 'standard size' is you cant have receptacles on the circuit, OK makes sense,
but we now have a floor for de-rating for pipe fill if a 14 AWG gets de rated below 10 amps (>9 CC in a pipe) and 10 is a standard size, you can't round back up to 15.