HVAC Air Handling Unit

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charlie b

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Lockport, IL
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All electrical loads on all power distribution systems are connected in parallel. I cannot think of a single exception (well, maybe I could if I had my second cup of coffee).
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
Are the Motor & Heater inside AHU are supplied by single branch circuit or 2 branch circuit for each motor and heater?
Depends on a few factors such as the manufacturer, the size heat load.
With the units in this area, they are often served by one branch circuit. 424.22 limits the size of overcurrent protection on any one set of heaters so you may find internal supplemental overcurrent protection dividing the heating load or you may find the air handler is designed for more than one branch circuit.
Generally the units I see are one circuit for 10kw or less and two or more circuits for over 10kw.
(That has been true for all US mfg units i have encountered,, unsure what you may find in your area)
 

Dennis Alwon

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Chapel Hill, NC
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I agree with Gus and Charlie. It used to be any unit with more than 15kw would have 2 circuits but now a 15 kw unit may have 2 circuits. Sometimes you can feed the unit with one circuit and the unit has 2 breakers inside and other instances you need 2 separate circuits from the panel.
 

Dennis Alwon

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Ok 10kw or 15kw, but what does it mean?? Total load for units (motor+heater)?

Those terms are very loose. A 10kw unit may have a 9.6kw element and with the motor it may be 10 kw. It is not exact you need to look at the nameplate
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
Those terms are very loose. A 10kw unit may have a 9.6kw element and with the motor it may be 10 kw. It is not exact you need to look at the nameplate

ditto: The "10kw, 15kw" references are somwehat generic. Actual heater loads will be close to that number and the motor load is added to that.
Note that the units are often 208/240 rated with a proportional reduction in heater wattage.
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
what size fuses are usually on those 10kw heat kits

Most of the 10kw air handlers I see have a MCA between 54 and 58 (an interesting scenario for the folks that habitually install #6NM) and a MOCP of 60.
 
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