Air handler nameplate requirements

[Riograndeelectric]

We all agree you must use the manufacturers nameplate but it seems like something is in error.

if the AHU or HVAC indicates the minimum and maximum fuse size I take this to mean the unit has have a fused disconnect switch.

what is in error?

 

[Mgraw]

There is nothing in this thread to indicate only fuses can be used. We are waiting for Dennis to tell us what the error is.

 

[Dennis Alwon]

I was just insinuating that we are missing something as nothing seems to be calculating. In the past I was always able to use 1.25 and get the nameplate but for some reason it is off but regardless we must use the nameplate. I am just confused why it doesn't add up

 

[mivey]

We are waiting for Dennis to tell us what the error is.

Again?

 

[mivey]

I am just confused why it doesn't add up

My guess is that the data is not quite right.

 

[GUNNING]

Greener

Greener

My guess is the mfg wants larger wire size, but likes the amperage rating given so it looks greener.

 

[Mgraw]

Dennis this might help. It is from a manufacturer.

"Minimum Circuit Ampacity (MCA) for both fan-powered and heater-only products is calculated with the following equation:

MCA = 1.25 x [Motor Rated Current + Heater Current]

The ?Motor Rated Current? is sometimes referred to as the FLA (full load amps) of the unit. This can be a source of confusion because this rated current is not the same as the motor FLA shown on the nameplate of the motor itself. Our ?Motor Rated Current? is determined during worst-case, high-current test conditions of the complete terminal unit, in accordance with UL1995. The FLA on the motor nameplate is a rating from the motor manufacturer and is of no use in our calculations."

 

[Dennis Alwon]

Dennis this might help. It is from a manufacturer.

"Minimum Circuit Ampacity (MCA) for both fan-powered and heater-only products is calculated with the following equation:

MCA = 1.25 x [Motor Rated Current + Heater Current]

The ?Motor Rated Current? is sometimes referred to as the FLA (full load amps) of the unit. This can be a source of confusion because this rated current is not the same as the motor FLA shown on the nameplate of the motor itself. Our ?Motor Rated Current? is determined during worst-case, high-current test conditions of the complete terminal unit, in accordance with UL1995. The FLA on the motor nameplate is a rating from the motor manufacturer and is of no use in our calculations."

Thank you. If this is the case for all units then there will be many EC's in the same boat as the OP. I have never installed a 5KW unit that demanded more than a 30 amp circuit.

With the price of copper soaring, the 60C rating of se and NM, and the manufacturers playing with the traditional ratings of these units I see alot of unhappy EC's esp. with contracts on the job.

The last few years we have seen the 10kw units go from 52 amps to now over 55 amps which in NM cable demands the next size also. Yikes. Big difference in price from #6 NM to #4 SEU or NM if the suppliers have it.

 

[DaveBowden]

While we were on this job running the 8/2 RX today, I copied everything I thought might be relevent.
From the air handler nameplte:
Volts 208/230
Motor HP 1/2
Motor FLA 4.3 Amps
From the stick on label supplied with the heat strip and placed on the nameplate of the AHU:
208Volts 230Volts
Heater Watts 3750 4600
Heater Amps 18 20
Minimum Circuit Ampacity 31.2 33.6
Maximum OCP 35 35

I don't know if this info will help or make things worse as far as figuring out the manufacturer's math, but its all we have to go by.
On a side note, it was cheaper to buy 125 foot roll of 8/2 for $129 than have them cut an 80 foot piece @ $1.72 per foot. The cost of wire has gotten ridiculous - it might as well be gas.

 

[LarryFine]

On a side note, it was cheaper to buy 125 foot roll of 8/2 for $129 than have them cut an 80 foot piece @ $1.72 per foot.

Absolutely. Have you ever looked at the price of a 100' roll of NM? It's almost as much as a 250' roll. :roll:

 

[Mgraw]

If this is the case for all units then there will be many EC's in the same boat as the OP.

The higher numbers appear to be the result of "worst case" test required by UL 1955.