AHU disconnect

[hhsting]

I have AHU which has MCA of 29A and MOCP of 42A.

The breaker provided panelboard is 35A. The AHU has integral disconnect which is rated at 30A and its non fused. Would not 60A non fused disconnect be required?

 

[david luchini]

Would not 60A non fused disconnect be required?

No

 

[hhsting]

No

Is it in code? How can 30A non fuse disco be protected by 35A breaker?

 

[petersonra]

Is it in code? How can 30A non fuse disco be protected by 35A breaker?

where does it require that in the code?

 

[Rock86]

Is it in code? How can 30A non fuse disco be protected by 35A breaker?

To answer your question I will ask you this... How can a 20A circuit breaker be protected by a 200A circuit breaker?

 

[hhsting]

To answer your question I will ask you this... How can a 20A circuit breaker be protected by a 200A circuit breaker?

20A breaker would trip parts made by 20A breaker listed capable of handling 20A

Note in my case disconnect is 30A non fused while breaker is 35A. Different

 

[EC Dan]

It's a fair question, but I don't see anything in Article 404 that requires the disconnect to be protected at it's rating, which is the maximum interruptible load, not it's ampacity. Since the MCA is 29 A, 30 A would be an appropriate size for the unit.

 

[LarryFine]

MCA means that the "weakest link" in the circuit must have at least a 29a capacity, not 35a.

The MOCP of 42a is there to allow for momentary starting current.

Remember that, for motor and HVAC loads, the breaker does not provide overload protection.

 

[hhsting]

MCA means that the "weakest link" in the circuit must have at least a 29a capacity, not 35a.

The MOCP of 42a is there to allow for momentary starting current.

Remember that, for motor and HVAC loads, the breaker does not provide overload protection.

The question is regarding 30A non fuse disconnect AHU integral and up stream breaker is 35A. Post #1

 

[david luchini]

The question is regarding 30A non fuse disconnect AHU integral and up stream breaker is 35A. Post #1

The answer is still no.

 

[wwhitney]

The question is regarding 30A non fuse disconnect AHU integral and up stream breaker is 35A. Post #1

And the answer has been given: the required rating of a non-fused disconnect is based only on the load characteristics, and not on the supply characteristics (e.g. the upstream breaker size). The configuration in the OP is analogous to a 15A rated snap switch on a 20A lighting branch circuit, which is also fine, as long as the switch is controlling <= 15A of load.

Cheers, Wayne

 

[LarryFine]

The question is regarding 30A non fuse disconnect AHU integral and up stream breaker is 35A. Post #1

I got that. The disco is rated for its interrupting capacity, not its current-carrying capacity.

Otherwise, it would be labeled to never open unless the supply is deenergized first, IMO.

 

[Greentagger]

I have AHU which has MCA of 29A and MOCP of 42A.

The breaker provided panelboard is 35A. The AHU has integral disconnect which is rated at 30A and its non fused. Would not 60A non fused disconnect be required?

MOCP 42A?

 

[LarryFine]

I have AHU which has MCA of 29A and MOCP of 42A.

MOCP 42A?

Which translates to 40a breaker or fuses. The numbers are calculation results, so they won't necessarily match standard rating numbers.

Why not also question the 29a?

 

[Greentagger]

Which translates to 40a breaker or fuses. The numbers are calculation results, so they won't necessarily match standard rating numbers.

Why not also question the 29a?

Never saw the MOCP designated as a non srandard value. No problem with the MCA at 29A

 

[don_resqcapt19]

I have AHU which has MCA of 29A and MOCP of 42A.

The breaker provided panelboard is 35A. The AHU has integral disconnect which is rated at 30A and its non fused. Would not 60A non fused disconnect be required?

This is part of the listed equipment and does not need to be looked at by you or anyone else. The NEC does not apply to factory installed parts of listed equipment.