AHU with dual circuit indoor

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DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
I don't know. I dont even know what is single circuit module? But whats more confusing is two disconnects at the unit according to Section 440, 422 would be required or not? And which section?
I looked up the papers on your AHU and it's listed as an optional accessory.

Like I said, I don't know if two disconnects would be required within sight but I say it would be bad practice, safety wise.

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hhsting

Senior Member
I looked up the papers on your AHU and it's listed as an optional accessory.

Like I said, I don't know if two disconnects would be required within sight but I say it would be bad practice, safety wise.

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Right but now that we know blower and heaters are shared between 4 lines then how could it not be required? That is like all four lines are for heating (HVAC) so would note Section 422 come into play?
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
Right but now that we know blower and heaters are shared between 4 lines then how could it not be required? That is like all four lines are for heating (HVAC) so would note Section 440 come into play?
Yes, if that's the case then yes. You could use a 4 pole switch but they are super expensive. I don't see why you couldn't use 2 AC pullout disconnects. Cheap as dirt.

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hhsting

Senior Member
Yes, if that's the case then yes. You could use a 4 pole switch but they are super expensive. I don't see why you couldn't use 2 AC pullout disconnects. Cheap as dirt.

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Its not me I am just plan reviewer. I don't decide 4 pole switch or 2-2pole switches. I have never seen 4 pole disconnect 240V. not on single plan. What would be the amps rating of the disconnect be 60+25=85 which is 100A? Instruction calls for two EGCs and if their is one 4 poles disco then both EGC from branch circuit breaker go to one ground lug in the disco and from disco provide two separate ones to the ground lugs on the unit? My question was along the lines of should not 2-2 poles disconnect switch be required at the hvac unit instead on one disconnect

I think in this case NEC 2017 Section 424.19(A) applies as it is heater with motors in it and heater has breakers in it with unit. Regardless that says disconnect needs to be within sight of the equipment.
 
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DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
Also I just read in the manual that the single circuit kit is only to be used with 15 and 20kW fuses heater units. All th thing is is a jumper basically to bridge L1 and L2 to L3 and L4.
12e196d801c6bfae80fbe12260b13e30.jpg


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DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
Its not me I am just plan reviewer. I don't decide 4 pole switch or 2-2pole switches. I have never seen 4 pole disconnect 240V. not on single plan. What would be the amps rating of the disconnect be? Instruction calls for two EGCs and if their is one 4 poles disco then both EGC from branch circuit breaker go to one ground lug in the disco and from disco provide two separate ones to the ground lugs on the unit? My question was along the lines of should not 2-2 poles disconnect switch be required at the hvac unit instead on one disconnect

I think in this case NEC 2017 Section 424.19(A) applies as it is heater with motors in it. Regardless that says disconnect needs to be within sight of the equipment.
Well the 4 pole, if you went that route would be 60 amp rated. Each circuit is not more than 60 amps. It would be a non fusible unit. I don't see why you couldn't use 2 standard 60 amp 2 pole non fusible AC disconnects.

I would still post a sign warning about multiple power sources though.

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hhsting

Senior Member
Well the 4 pole, if you went that route would be 60 amp rated. Each circuit is not more than 60 amps. It would be a non fusible unit. I don't see why you couldn't use 2 standard 60 amp 2 pole non fusible AC disconnects.

I would still post a sign warning about multiple power sources though.

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post a sign where at the panelboard or at the unit? Also looks like engineer is using 4 pole disco. Do you have link to any nema 3R?
 

hhsting

Senior Member
Also I just read in the manual that the single circuit kit is only to be used with 15 and 20kW fuses heater units. All th thing is is a jumper basically to bridge L1 and L2 to L3 and L4.
12e196d801c6bfae80fbe12260b13e30.jpg


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Would not the kit then override the max 60A breaker allowed? How is that safe then?
 

Tulsa Electrician

Senior Member
Location
Tulsa
Occupation
Electrician
I would say two disc.
I do this all the time.
1- 60 amp set next to 1-30 amp.
Lable the disconnects and unit correctly. Send bill for additional disc and work. Check panel schedule to be sure correct breakers are installed. Some times the OCD in unit if supplied can have the tie bar removed on the line side ( input) and two circuits ran in lieu of one. The tie bar cab be factory installed tie bar or a set of wires from each OCD (line in) to a lug kit. I always thought the tie bar (old school) was considered double lugging.

For a single circuit the OCD's are in the unit doing the subdivision required.
 

brantmacga

Señor Member
Location
Georgia
Occupation
Electrical Monke
It’s two disconnects. The EE would show one on the floorplan for simplicity; they’ve identified there are two circuits. Likely a note or detail somewhere either in the drawings for spec book. This isn’t unusual.


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Tulsa Electrician

Senior Member
Location
Tulsa
Occupation
Electrician
Sure can use a four pole disc.
I would not want to buy one.
If a spec job I would look at the spec for that ahu and see if it specs four pole. If not well some one has a choice to make.
Either way code compliant.
A warning lable on disc for sure required since feed with two circuits.
When in dout, maybe an RFI for clarity.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
I’ve seen one feeder sized for the entire load, then the factory has two individual breakers in the AHU to split the load. The breakers are accessible externally, so they qualify as the disconnecting means. The smaller breaker runs the fans, and one stage of heat, while the other runs the larger heat strips. Done quite often in residential. I have also seen two branch circuits run, with two disconnects external of the unit. Never seen an AHJ have an issue with that set up either.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Hillbilly sums it up well in Post #35. You plans vary from the "norm" in that when you have (2) circuits it's normally (2) disconnects. If you have a gear submital it might clarify but if left up to the installer most lilely you would have (2) pullouts at the unit unless it has accessible disconnects built in. Both methods are common. I don't know how deeply you wish to get involved but I would let it be decided in the field.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
I’ve seen one feeder sized for the entire load, then the factory has two individual breakers in the AHU to split the load. The breakers are accessible externally, so they qualify as the disconnecting means.

I was going to say the same thing. Done all the time in commercial HVAC and refrigeration where there is a condensing unit on the roof or outside and an evaporator with fans inside.

-Hal
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The units I have seen like this were usually a 60 amp cir and a 30 amp circuit or for larger units 2- 60 amp circuits. The code does not allow the heating element circuit to be larger than 60 amps so that is why it is supplied by 2 circuits.
 
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