HVAC Nameplate
- Thread starter barclayd
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes and Yes, IMO
- Location
- Logan, Utah
Actually the disconnecting means needs to have an ampere rating of 115% of the nameplate rated current or branch circuit selection current, whichever is greater.
So a 30 amp disconnecting means is not large enough for this install.
Take a look at 440.12(A)(1).
Chris
So a 30 amp disconnecting means is not large enough for this install.
Take a look at 440.12(A)(1).
Chris
- Location
- Massachusetts
I will have to be a PITA and say yes and no.
I believe the disconnect must be rated 115% of the MCA.
I believe the disconnect must be rated 115% of the MCA.
shamsdebout
Senior Member
- Location
- Macon,GA
The MCA is not the rated current. The MCA value is the ampere rating, at least that is what I thought. This can work as the info is from the manufacture but I would size my conductors to the MOCP. I would not terminate at a 30/3 safety switch.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
That's why you guys are the mods 
. Thanks for the correction. Interesting that it needs to be 115% of the nameplate esp. since the nameplate has 125% already in it.
. Thanks for the correction. Interesting that it needs to be 115% of the nameplate esp. since the nameplate has 125% already in it.
- Location
- Logan, Utah
The minimum circuit ampacity (MCA) is also known as the branch circuit selection current.
The branch circuit selection current can be used to size the branch circuit conductors.
Sizing the branch circuit conductors using the maximum overcurrent protection device rating is way overkill.
For example in the original post, using the MOCP to size the branch circuit you would need to use #8 THHN conductors.
Chris
Do we also have to be sure the disconnect has the proper HP rating?
440.12 (A) 2
440.12 (B) 1
Or if there is no AC involved 430.110 (C) 1
IMO these would be combination loads and I thought they had LRC on name plate which could reference to 430.251 (A), 430.251 (B)
Please correct me if I've missed something
shamsdebout
Senior Member
- Location
- Macon,GA
Thank for the info, as you can tell I haven't used this section of the NEC. I didn't think this applied to air handlers. I hadn't heard about the branch circuit selection current.
- Location
- Logan, Utah
My understanding is that you can either use an ampere rated disconnect in accordance with 440.12(A)(1) OR a HP rated disconnect in accordance with 440.12(A)(2), but you are not required to meet both.
Also a single air handling unit IMHO would not be a combination load and 440.12(B) would not apply.
Chris
- Location
- Logan, Utah
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I have wired air handlers that are marked with MCA and MOC numbers just like A/C units.
shamsdebout
Senior Member
- Location
- Macon,GA
Ok I am officially
I did a surface reading of some parts of Article 440, someone help.
1.) Air Handler to my knowledge does not have a motor compressor apparatus, so it wouldn't apply to this section, is that correct?
2.) From what I read MCA is not the same as the branch circuit selection current, my rational for saying that is in 440.11(A)(1) it speaks about the Ampere Rating shall be at least 115% of the nameplate rated-load current (FLA in my mind) or branch-circuit selection current. The MCA has already include all the loads so no calcuation is needed to size conductors. Is that correct?
I did a surface reading of some parts of Article 440, someone help.
1.) Air Handler to my knowledge does not have a motor compressor apparatus, so it wouldn't apply to this section, is that correct?
2.) From what I read MCA is not the same as the branch circuit selection current, my rational for saying that is in 440.11(A)(1) it speaks about the Ampere Rating shall be at least 115% of the nameplate rated-load current (FLA in my mind) or branch-circuit selection current. The MCA has already include all the loads so no calcuation is needed to size conductors. Is that correct?
One-eyed Jack
Senior Member
- Location
- Scotland Neck, NC
Ok I am officially
I did a surface reading of some parts of Article 440, someone help.
1.) Air Handler to my knowledge does not have a motor compressor apparatus, so it wouldn't apply to this section, is that correct?
2.) From what I read MCA is not the same as the branch circuit selection current, my rational for saying that is in 440.11(A)(1) it speaks about the Ampere Rating shall be at least 115% of the nameplate rated-load current (FLA in my mind) or branch-circuit selection current. The MCA has already include all the loads so no calcuation is needed to size conductors. Is that correct?
Self contained outdoor heating systems are also considered air handlers and they contain compressors.
The MCA is greater than the nameplate so you must use that value even tho it has 125% added to it. The MCA is the branch circuit selection current.
Last edited:
shamsdebout
Senior Member
- Location
- Macon,GA
I agree with your first point.
I think the second is where I am having some trouble. Per NEC 440.32 speaks about determining conductor ampacity from the branch-circuit selection current. (They are actually determining the MCA by 1.25 of the Branch-circuit selection current). Am I just really missing it?
- Location
- Logan, Utah
I believe that you are mis-reading that section. The motor-compressor rated-load current is NOT the same as the minimum circuit ampacity (MCA)
The motor-compressor rated load current is the current marked on the compressor motor itself without the 125% added on.
The branch circuit selection current is sonomous with minimum circuit ampacity.
So 440.32 allows you to size the branch circuit conductors 1 of 2 ways
1st, 125% of the motor-compressor rated-lozd current OR
2nd in accordance with the minimum circuit ampacity.
Hope this helps.
Chris
shamsdebout
Senior Member
- Location
- Macon,GA
It says "Branch-circuit conductors shall have an ampacity not less than 125 percent of either the motor compressor rated-load current or the branch-circuit selection current, which is greater"
My interpretation is that 125% (motor compressor rated-load current) or 125% (branch circuit selection current) The either is throwing me off
Back to square 1 for a second. The thread is entitled "HVAC" but the OP states air handler. Is some of this load compressor ?
If not, don't we need to be in 424 rather than 440.
Barclayd: Compressor or not ?
If not, don't we need to be in 424 rather than 440.
Barclayd: Compressor or not ?
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