Power supply to large HVAC Air Handlers

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Dchaisson

New member
Location
Boston Ma USA
We sell large air handling equipment.
the unit have Ul labeled control panels
and the entire unit has an ETL listed.

typically there is a single point 480 volt
power connection and a separate 120 volt power connection for
convenience outlets and lighting. This allows service
people to have plugs and lighting while they work on the equipment with the 480 power lovked
off.

The is fed into a generic 100 amp max load center with two or three 20 amp breakers
for the lighting and plugs. Plugs are GFCI.

What size wire and 120 volt breaker has to feed this from the building panel?
Two duplex plugs on one twenty amp breaker
minimal amperage drawn on lighting 10 amps or less.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Sadly, your description is neither complete nor clear. If you have a 100 amp load center, it will not be served at 120 volts. It will either have 120/240 volt single phase or 120/208 volt three phase, depending on what is available from the building's electrical distribution system. Even though that load center may be rated for 100 amps, there is no requirement to bring 100 amps of capacity to it (i.e., the ratings of the upstream breaker and the intervening wires). That breaker and those wires will be based on the total load, which you have not given us.

I am curious as to why you are asking these questions. If you sell the equipment, it will be some other company (i.e., the electrical contractor) who will be installing it. There may also be an engineering company involved in the overall building design. These people will be making the decisions on the breaker and wire sizes. What then is your intended role here?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Not sure what you are asking. Is there a feeder that you need to run to this panel that is 120/208? If so then it could be 20 amp or more depending on what the panel may be used for later. 20 amp would be the smallest size in a commercial building although 15 amp may be allowed.

I am not quite clear of the setup
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The is fed into a generic 100 amp max load center with two or three 20 amp breakers
for the lighting and plugs. Plugs are GFCI.

What size wire and 120 volt breaker has to feed this from the building panel?
Two duplex plugs on one twenty amp breaker
minimal amperage drawn on lighting 10 amps or less.

It's really a design issue, you said that the 100 amp panel has 2 or 3 circuits so it really depends on what you anticipate the load to be. A single 20 amp circuit is probably all that you'll need for the two receptacles and the lighting. Typically we feed units like these with a single 120 volt, 20 amp circuit for lights and power. The 100 amp panel is overkill. :)
 

kwired

Electron manager
Location
NE Nebraska
It's really a design issue, you said that the 100 amp panel has 2 or 3 circuits so it really depends on what you anticipate the load to be. A single 20 amp circuit is probably all that you'll need for the two receptacles and the lighting. Typically we feed units like these with a single 120 volt, 20 amp circuit for lights and power. The 100 amp panel is overkill. :)
I mostly agree here.

What load is expected to be supplied by the receptacle circuits? Good chance a single 120 volt 20 amp supply never gets overloaded if it is only used for servicing this equipment.

100 amp panel is overkill, but unless you only go with say a two space loadcenter you probably don't find many rated less than 100 amps. QO has a 30 space indoor and 40 space 3R version with only two spaces, and I believe a three pole 60 amp three phase version, most everything else they have jumps to 100 amp main lugs/bus.
 

priyankasethi

Member
Location
New Delhi
Occupation
Student
Air dissemination considers ventilation work that conveys the molded air to the ideal territory in an immediate, calm, and efficient route as could be expected under the circumstances. Air appropriation incorporates air terminal units, for example, grilles and diffusers to convey gracefully air into a space at low speed; fan-controlled terminal units, which utilizes an indispensable fan to guarantee the flexibly air to the space; variable air volume terminal units, which convey variable measure of air into the space; all-air acceptance terminal units, which controls the essential air, instigates return air, and circulates the blended air into a space; and air-water enlistment terminal units, which contains a curl in the enlistment air stream. All the ventilation work and channeling ought to be protected to forestall heat misfortune and spare structure energy. It is additionally suggested that structures ought to have enough roof spaces to have ventilation work in the suspended roof and floor piece, and can be utilized as a return air plenum to lessen the return ventilation work.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
What size wire and 120 volt breaker has to feed this from the building panel?
Two duplex plugs on one twenty amp breaker
minimal amperage drawn on lighting 10 amps or less.
As stated above, you could use a single 20a 120v circuit to supply this panel, or go as high up as a 100a feeder if you want. It all depends on the maximum total simultaneous load you want to be able to provide.

Options are 120/208 1ph or 120/240v 1ph or 120/208 3ph (depending on your 120v source), meaning more wires and more expensive breakers, but the advantage is that a tool malfunction won't kill the lights.

In any case, the breaker must be sized to suit the wire, or vice versa, depending on your perspective. If a single 120v 20a circuit is enough for the feeder, it's enough for the circuit; you don't need the 100a panel at all.
 
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