Air Handler Unit with Electric Heat

[Electriman]

Good morning,

I am working to provide power for a Air Handler Unit (AHU) that is equipped with an electric heater. I was wondering if I need to provide one feeder that feeds both AHU and heater or two feeders one for each one.

On AHU, the maximum fuse/ HACR breaker size is 15 A. But the electric heater is requiring to have a 50A MOCP.

Regards,

 

[kwired]

Are these separate units or is it an air handler listed to install specific heat coils within? The latter typically has the air handler circuit supplied by one of the heater circuits when heat is installed, and is listed to be installed that way.

 

[Electriman]

Are these separate units or is it an air handler listed to install specific heat coils within? The latter typically has the air handler circuit supplied by one of the heater circuits when heat is installed, and is listed to be installed that way.

They are two separate units attached together. The AHU is Carrier unit 480V and the electric heater is CAELHEAT 20kW. But the they will be attached together.

 

[kwired]

Unless you have instructions that say otherwise, you need separate branch circuit for each unit then.

A feeder to nearby and then short branch circuits is one option that may be favorable, this can also be easy method to gain a local disconnecting means.

 

[Sahib]

Unless you have instructions that say otherwise, you need separate branch circuit for each unit then..

You mean tap rules are not applicable here?

 

[Mgraw]

They are two separate units attached together. The AHU is Carrier unit 480V and the electric heater is CAELHEAT 20kW. But the they will be attached together.

Those heaters sit on top of the air handler. Bring power to the heater and there is usually a knockout in the air handler to bring power from the heater.

 

[Mgraw]

Caelheat 20kw

 

[kwired]

You mean tap rules are not applicable here?

On AHU, the maximum fuse/ HACR breaker size is 15 A.

Tap can supply the 15 amp overcurrent device but not directly supply the AHU. Load side of overcurrent device is the branch circuit.

 

[Electriman]

Caelheat 20kw

So I only need to bring a 50 A over-current protected power feeder for the unit.

Should I be concern about 15 A maximum over current of the AHU since it is being fed from a 50A breaker.

 

[Mgraw]

So I only need to bring a 50 A over-current protected power feeder for the unit.

Should I be concern about 15 A maximum over current of the AHU since it is being fed from a 50A breaker.

The unit is designed to work with that heater. 50 amp circuit is all you need.

 

[kwired]

So I only need to bring a 50 A over-current protected power feeder for the unit.

Should I be concern about 15 A maximum over current of the AHU since it is being fed from a 50A breaker.

Yes, because you said: On AHU, the maximum fuse/ HACR breaker size is 15 A.

You may or may not be able to tap off the 50 amp circuit though.

20 kW is 83.3 amps @ 240 volts - this is likely split into two ~10 kW circuits.

10 kW is 41.6 amps x 1.25 = needing a 60 amp overcurrent device, but most of what we call 10 kW is actually rated 9.6 kW which comes out right at 40 amps. Experience says it will work fine to have 9.6 kW and the blower on a 50 amp breaker, but to strictly follow NEC you need 50 amps plus whatever blower unit rating is, usually only about another 2 amps max, for supply circuit conductors and overcurrent protection.

 

[Mgraw]

Yes, because you said: On AHU, the maximum fuse/ HACR breaker size is 15 A.

You may or may not be able to tap off the 50 amp circuit though.

20 kW is 83.3 amps @ 240 volts - this is likely split into two ~10 kW circuits.

10 kW is 41.6 amps x 1.25 = needing a 60 amp overcurrent device, but most of what we call 10 kW is actually rated 9.6 kW which comes out right at 40 amps. Experience says it will work fine to have 9.6 kW and the blower on a 50 amp breaker, but to strictly follow NEC you need 50 amps plus whatever blower unit rating is, usually only about another 2 amps max, for supply circuit conductors and overcurrent protection.

You can wire the air handler to the heater. The heater is matched by the manufacturer of the air handler to be wired together. The unit is 480v.

 

[kwired]

You can wire the air handler to the heater. The heater is matched by the manufacturer of the air handler to be wired together. The unit is 480v.

I wasn't aware we were dealing with a 480 volt unit. 50 amps is a little overkill if it is three phase, is still just a little undersized if it is single phase.

 

[Mgraw]

I wasn't aware we were dealing with a 480 volt unit. 50 amps is a little overkill if it is three phase, is still just a little undersized if it is single phase.

50 amps is what is called for by the manufacturer.

 

[Smart $]

50 amps is what is called for by the manufacturer.

OP'er didn't furnish model number but basing an analysis on this document (http://dms.hvacpartners.com/docs/1009/public/03/iik-caelheat-01.pdf) you are correct. For others, note especially the asterisked footnote after the tables.

 

[ramsy]

..For others, note especially the asterisked footnote after the tables.

* Values shown are for single---point connection of electric heat accessory and air handler.

Heater may have 15A Breaker or fuse block for air handler. I doubt its impedance protected?

 

[Mgraw]

* Values shown are for single---point connection of electric heat accessory and air handler.

Heater may have 15A Breaker or fuse block for air handler. I doubt its impedance protected?

If there is a breaker it is usually in the air handler.

 

[kwired]

* Values shown are for single---point connection of electric heat accessory and air handler.

Heater may have 15A Breaker or fuse block for air handler. I doubt its impedance protected?

Blower motor can have thermal protector. Impedance protected is mostly going to be a shaded pole motor only. 20 kW of heat is probably going to need large enough blower that one will be getting on upper end of what is common for shaded pole motors, and a PSC or three phase motor will be more likely.