# Mini Split Systems



## cctracy1978 (Sep 11, 2015)

I know you have to take a 100%of nameplate rating to figure in an AC unit. But is there a derating to use when figuring a service load while adding up to 10 Mini splits to an office building?


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## Drsparky14 (Oct 22, 2016)

I really do not think so. Because they can all be used at the same time. 


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## cctracy1978 (Sep 11, 2015)

Thanks, that what I was thinking but I can't find anywhere in the code book that addresses multiple units, I'm doing 100% for all to be safe.


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## Drsparky14 (Oct 22, 2016)

In the office just out of curiosity what is your largest motor? The AC Split?


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## cctracy1978 (Sep 11, 2015)

I have 5 units that are rated for 50 amp and 2 that are 20 amp, all 240 volt


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## splatz (May 23, 2015)

I never really checked but it doesn't seem unusual to be on a roof and seems like every unit is running. 

With programmable thermostats all set to kick in at the same time, I'd bet there's probably a couple times a day when they're all running, every day. I don't know if the bigger building controls systems coordinate this to stagger things.


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## oliquir (Jan 13, 2011)

50A mini split?? how much btu is that unit?


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## cctracy1978 (Sep 11, 2015)

They are capable of 5 indoor heads off of one outdoor unit --62000 -68,000 BTU


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## telsa (May 22, 2015)

You can bank on the fact that they will all kick on at the same time... because they are weather dependent.

It's not at all like a bunch of residential: washing machines, ovens, dryers....


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## cctracy1978 (Sep 11, 2015)

yep, 100% name plate


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## Drsparky14 (Oct 22, 2016)

Do these mini splits provide heat? If so what percent of the unit amperage is heat/blower and what percent is the actual ac unit?


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## cctracy1978 (Sep 11, 2015)

Yes they act as a heat pump, as far as percentages go I have no idea. I don't install or sell them, just hook them up for a HVAC company. They are designed to be used as an individual room heat or AC source Perfect for office environments or the cold or hot room in a home


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## Dennis Alwon (May 9, 2009)

I have no idea what you are asking. Are you wanting to know how to wire each unit or do you want to calculate a feeder or service load.


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## Dennis Alwon (May 9, 2009)

If these are heat pumps with an indoor unit that has auxiliary heat strips then you need to feed both units based on the nameplate minimum circuit ampacity for the heat pump and then calculate the load for the heat strips - if there is a nameplate on the indoor unit you usually have to multiply by 1.25 (125%) for the conductor size


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## Drsparky14 (Oct 22, 2016)

cctracy1978 said:


> Yes they act as a heat pump, as far as percentages go I have no idea. I don't install or sell them, just hook them up for a HVAC company. They are designed to be used as an individual room heat or AC source Perfect for office environments or the cold or hot room in a home




C) Heating and Air-Conditioning Load. The largest of the following six selections (load in kVA) shall be included:
(1) 100 percent of the nameplate rating(s) of the air conditioning and cooling.
(2) 100 percent of the nameplate ratings of the heat pump compressors and supplemental heating unless the controller prevents the compressor and supplemental heating from operating at the same time.
(3) 100 percent of the nameplate ratings of electric thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value. Systems qualifying under this selection shall not be calculated under any other selection in 220.30(C).
(4) 65 percent of the nameplate rating(s) of the central electric space heating, including integral supplemental heating in heat pumps where the controller prevents the compressor and supplemental heating from operating at the same time.
(5) 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.
(6) 40 percent of the nameplate rating(s) of electric space heating if four or more separately controlled units.


Section 220.21 states that for loads that do not operate simultaneously, the largest load being
considered is used. In concert with 220.21
,
220.30(C) requires that only the largest of the six
choices needs to be included in the feeder or service calculation. Examples of calculations
using air conditioning and heating are found in Annex D, Examples D2(b) and D3(c).




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## Drsparky14 (Oct 22, 2016)

Does the unit have backup heat in this 50 amps? I assume no since it has multiple satellite units. 


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## MDShunk (Jan 7, 2007)

I've never actually seen a mini split that had electric backup heat. Just straight heat pumps. Do they even make such a thing with electric backup heat? Maybe a larger cassette unit?


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## Dennis Alwon (May 9, 2009)

MDShunk said:


> I've never actually seen a mini split that had electric backup heat. Just straight heat pumps. Do they even make such a thing with electric backup heat? Maybe a larger cassette unit?


Yeah, we used to see them with a 5 kw strip but we haven't wired one of those in years


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## MDShunk (Jan 7, 2007)

Dennis Alwon said:


> Yeah, we used to see them with a 5 kw strip but we haven't wired one of those in years


Ok, cool. I've seen plenty of heat pump PTAC's with backup heat, but I never saw a mini split with electric backup heat.


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