A HVAC person is providing a 3 head ductless heat pump system, where 3 indoor units are wired to one outdoor unit which has a nameplate that states Maximum Overcurrent Protective Device (MOPD) 25 Amps, Minimum Circuit Ampacity (MCA)18.1 Amps, and 3 indoor units will be powered from this outdoor unit does the manufacturer figure that load into the MCA? It seems 440.4(B) would require that. Its just a little close to the 20A ampacity a 12/2 NM cable and I am wondering if they figure every combination of indoor unit and use the 3 largest ones. It's probably worth calling the manufacturer but curious what you all do.
Multi head ductless unit; nameplate marking 440.4(B)
- Thread starter tortuga
- Start date
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Likely yes. I just connected one about the same thing as you described not long ago. Same MCA and MOCP and three indoor units. The outdoor unit had three sets of ports for refrigerant lines so I would assume it was intended to support three indoor units, I think it also had three sets of terminals for wiring to indoor units as well.
That said those indoor units are typically very minimal load wise, often less than 50 VA each, so they wouldn't need to factor much extra in over the compressor load to be able to handle them in the MCA
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
Interesting thank you for the quick response, we ended up just running a 10/2 to be safe. If it was not NM cable I be inclined to run 12's.
On residential I often have no idea what a HVAC person is installing, they speak in 'tons' as if that means something to me, or if they send a cut sheet something different shows up in the van so I usually provide a 30A disconnect with 10/2.
But lately these 1-head units have stickers like 9 - 12 amps so I am like OK I guess I'll notch down a size.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
That often helps me more then whey they say it needs 30 amps. Most the time they only talking breaker size when they say that, and sometimes they still are not correct with that. When they say it needs 30 amps it very well may say MOCP of 25 on nameplate.
If I am doing rough install of the main supply long before the unit will arrive, I may end up running 10 AWG if they can't give me good enough information, especially if it is 2.5 to 3.5 ton. Modern units under 2.5 generally are fine on 12 AWG, even @ 60C. Units over 3.5 ton have some chance of needing more than 10 AWG. This all for typical single phase 208-240 volt rated units.
Thanks this installer also uses Daikin, but you did not answer my question;
Does the sticker on the outdoor unit include the maximum indoor units loads with all features added in the MCA or do they need to be added up separately?
(my conclusion is no and it does not matter unless you start adding more than one indoor unit)
For example this is the unit a 3MXS24WMVJU9, its a 2 Ton.
The nameplate seems to be taking the input of the Fan motor drive + The compressor drive and adding 15% to the compressor drive;
So there appears to be no accounting for say the three indoor units, with optional condensate pumps, and a drain pan heater in that 18.1A MCA.
I realize this is probably a dumb question to a HVAC person like yourself.
Fan Motor Drive | 0.34 |
Compressor Drive | 15.5 |
Add 115% to Compressor Drive | 2.3 |
Minimum circuit Ampacity | 18.1 |
12 AWG NM cable ok
However with 3 indoor units fed from this, each having a condensate pump, and the optional drain pan heater on the outside unit:
| Amps Each | qty | Extended |
Drain pan heater | 1.10 | 1 | 1.1 |
FDMQ09WVJU9 Indoor unit | 0.40 | 3 | 1.2 |
DACA-CP4-1 External Condensate Pump each indoor unit | 0.07 | 3 | 0.21 |
Fan Motor Drive | 0.34 | 1 | 0.34 |
Compressor Drive | 15.5 | 1 | 15.5 |
Add 115% to Compressor Drive | 2.3 | 1 | 2.3 |
Minimum circuit Ampacity | | 1 | 20.65 |
10/2 NM cable required.
Last edited:
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
YES, YES, YES! My head hurts. All you need to look at is the MOP and MCA on the label. Use #12 and a 25A 2 pole breaker and call it a day. If you don't have that information because the unit isn't available, do what kwired said and run #10.
-Hal
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
This is the combination of all the inside units that can be connected to the outside units.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
But the indoor units don't seem to be on the data plate. Where are they accounted for?
I called their tech support and got thru to someone who then had to call me back and yeah the indoor units are not accounted for in the MCA.But the indoor units don't seem to be on the data plate. Where are they accounted for?
The MCA is just the outdoor unit,115% of the compressor VFD and the fan motor / electronics.
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
Daikin has already determined the inside units that will work with the outside units. They have done the work for you, just follow their requirements. The outside and inside units work on D.C. and the system is monitoring many different complex levels. Any slight change will quickly turn the system off and will require turning the A.C. off to reset. See Post #9 attachment.
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electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Have they? If that information on the compressor does not include the indoor units then no, that would not be the number you would use for your circuit sizing. Of course the value is quite small and this is probably just an academic question but it is interesting, it never occurred to me.
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
Is it because all the Daikin units internally are direct currant and don't need to be listed on the label. Not to mention the size of the label would be overwilling to list all the combinations listed in Post #9.
AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
It does not matter if it’s dc it’s still not an additional load .if tortuga is correct it’s only outside unit on nameplate that dc is an additional unknown load
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Another rocket scientist.
It's a complete system. Why wouldn't the three indoor units it uses be included in the total load??
-Hal
AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
name plate says it all heat pump (outdoor section)
So there in indoor section and that’s not on the name plate
I never paid attention to it still won’t but it’s there
So there in indoor section and that’s not on the name plate
I never paid attention to it still won’t but it’s there
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Perhaps @mtnelect can confirm, but I believe you may not use all of the available indoor unit provisions.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Seems like they should be required to list the indoor units(s) values as an option, much like they do with heat strips.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Then someone would be wasting a lot of money when they could buy a system with the number of indoor units they actually need.
-Hal