HVAC experience? / AC questions

2com

Well-Known Member
Hi,

I don't know exactly what make/model of AC I'll be picking up, so I'm wondering if I should just run 3 wire + ground, or 2 wire + ground? Some of these units use a neutral, right? Maybe it'd be best to run the 3 wire + ground, just in case, so it's there.

I'm thinking of/looking for 24000 BTU at most, 240V, Inverter (mini split or window/through wall design) and would also like to know, what sort of amperage these units *actually draw* - as I'm getting some mixed info that isn't adding up or making sense to me.
 

kingromano

Well-Known Member
do you have 3 phase current at your home ?
splits units always use single phase current. then the machine convert it to 3 phase current to make the compressor rotate.
to wire it, you just need 1 hot wire+1 neutral+ground wire

choose one of your 3 phases and wire the AC on it

i'm in 240v too
 

2com

Well-Known Member
All I'm asking there is "do some of the 240V ACs use a neutral, which would require 10/3 instead of 10/2" (for example).
Apparently, some of'em need a four conductor cable, not a three conductor cable (including the ground).

(Like for example is some other function no the device uses 120V, there might be the need to run a 10/3 cable, versus only needing a 10/2 cable.)

I'm not talking about 3P.
 

rkymtnman

Well-Known Member
All I'm asking there is "do some of the 240V ACs use a neutral, which would require 10/3 instead of 10/2" (for example).
Apparently, some of'em need a four conductor cable, not a three conductor cable (including the ground).

(Like for example is some other function no the device uses 120V, there might be the need to run a 10/3 cable, versus only needing a 10/2 cable.)

I'm not talking about 3P.
i "think" the 240V AC's use 2 hot wires, no neutral.
 

getogrow

Well-Known Member
All I'm asking there is "do some of the 240V ACs use a neutral, which would require 10/3 instead of 10/2" (for example).
Apparently, some of'em need a four conductor cable, not a three conductor cable (including the ground).

(Like for example is some other function no the device uses 120V, there might be the need to run a 10/3 cable, versus only needing a 10/2 cable.)

I'm not talking about 3P.
95% of the time you are going to be fine with 2 wire but go ahead and wire with 3 just in case. (unless its a huge money deal or something) Like i said , most units are going to only use 2 wires and a ground but its always good to run the extra wire just in case.
 

getogrow

Well-Known Member
I'm thinking of/looking for 24000 BTU at most, 240V, Inverter (mini split or window/through wall design) and would also like to know, what sort of amperage these units *actually draw* - as I'm getting some mixed info that isn't adding up or making sense to me.
from a quick read , it appears you will be no where near 20 amps with a unit that big. I dont know exactly how it adds up but it wont be more then 12/2 is rated for.
From experience , i cant see it drawing more then about 10 amps while running. Thats not counting startup current. Im sure herb and suds is right in saying 12 is overkill but safe.
 

kingromano

Well-Known Member
All I'm asking there is "do some of the 240V ACs use a neutral, which would require 10/3 instead of 10/2" (for example).
Apparently, some of'em need a four conductor cable, not a three conductor cable (including the ground).

(Like for example is some other function no the device uses 120V, there might be the need to run a 10/3 cable, versus only needing a 10/2 cable.)

I'm not talking about 3P.
ah ... you're speaking of the interconnexion cable

sorry i initially read too fast

on every monosplit you have a indoor unit and a outdoor unit.
they are linked by a cable, the interconnexion, maybe it has another name in english i don't know

so you have :

-power supply cable, 3 wires , hot wire,neutral and ground

-interconnexion cable, this cable is here to allow both units to communicate ,4 wires (3 wires and a ground)

read the notice to know what cable section size you need to buy
 

2com

Well-Known Member
95% of the time you are going to be fine with 2 wire but go ahead and wire with 3 just in case. (unless its a huge money deal or something) Like i said , most units are going to only use 2 wires and a ground but its always good to run the extra wire just in case.
This is basically what I was thinking. For the price difference, might as well run the 3 wire, in case some oddball ac needs neutral/120V for something.
Thanks dude.
Just buy 12/2 with ground a little overkill on wire size but safe
There's already a 12/2 ran for 240V HVAC in the room. I had originally thought it would certainly be enough for the AC needs alone (and maybe even a small dehu, but not alongside a 24000btu ac probably - I wasn't thinking I'd need 24kbtu).
There's a dedicated 240V circuit for lighting. And another 12/2 circuit for whatever (120V equipment, or another 240V circuit, depending what's needed).

I started looking for/at Amperate ratings of 24kbtu split ACs and seeing "30A breaker recommended", and "18A disconnect", and hearing the commonly ran wire gauge being 10awg...
...I was ready to seal things up until this.
from a quick read , it appears you will be no where near 20 amps with a unit that big. I dont know exactly how it adds up but it wont be more then 12/2 is rated for.
From experience , i cant see it drawing more then about 10 amps while running. Thats not counting startup current. Im sure herb and suds is right in saying 12 is overkill but safe.
See, this is closer to what I was thinking.

I mentioned it in some other thread, and linked to growmau5 video where he planned his latest growroom (I'll link again if any wants to see) and talks for a min or two about this specifically. And his example lines up with my limited personal experience.
I have a 12kbtu portable, it's 120V, it's not a new 'inverter' style, and it draws just about 12A max (not including inrush/startup, never measured that). So, I duno why a similar, 12kbtu AC unit, running at 240V wouldn't draw *approximately* half that current - i.e.: about 6A.
So, what's said in the video sounds logical to me, almost a guideline of 12A per tonne (12kbtu) at 120V, or 6A per tonne (12kbtu) at 240V. Inversely proportion.

From what I've been able to find video of, these inverter mini split units, even the "mid range"(?) and DIY style units have soft starts, very gradual amperage draw and I didn't see an huge inrush spike at all (and most if not all I saw were 120V though), definitely not a spike larger than the actual max running current draw like plain old compressor style units - correct me if I'm wrong there.

Does this make sense to you lot?
A cust. service guy I called at an ac company earlier said 12awg was "on the cusp" (haha). But I think he said the max running draw was like 12A, maybe - maybe less, he didn't sound 100% and it wasn't too clear.

Thanks guys.
 

2com

Well-Known Member
if you had a dedicated run for a 240v A/C, wouldn't it be on a 30a breaker? which would be 10g wire right?
By "dedicated run" I just mean a circuit that was run only for the purpose of powering the AC and/or Dehu equipment on it.
It's whatever gauge wire it needs to be, based off the required amps, and the breaker is sized to protect the wire.

And in this case, I thought a 20A circuit (or 16A at 80%) would be more than sufficient for the needs of the room - especially at 240v - where the amperage should be half what it is at 120V - and at 120V a 12kbtu is basically sized to just barely "fit" on a 15A circuit (15A x 80% = 12A, and 12A is what that AC draws) if it's the only thing on that circuit.
 

rkymtnman

Well-Known Member
By "dedicated run" I just mean a circuit that was run only for the purpose of powering the AC and/or Dehu equipment on it.
It's whatever gauge wire it needs to be, based off the required amps, and the breaker is sized to protect the wire.

And in this case, I thought a 20A circuit (or 16A at 80%) would be more than sufficient for the needs of the room - especially at 240v - where the amperage should be half what it is at 120V - and at 120V a 12kbtu is basically sized to just barely "fit" on a 15A circuit (15A x 80% = 12A, and 12A is what that AC draws) if it's the only thing on that circuit.
that's kinda what i meant. i have a 30 a run for my well pump which is about the same draw as a mid sized A/c. and it is 10/2. i thought that was kinda a "normal" set up? 30a is 10, 40a is 8g, 50a is 6g, etc. don't quote me on that
 

2com

Well-Known Member
that's kinda what i meant. i have a 30 a run for my well pump which is about the same draw as a mid sized A/c. and it is 10/2. i thought that was kinda a "normal" set up? 30a is 10, 40a is 8g, 50a is 6g, etc. don't quote me on that
Yea, that part is all good. The general conventions (and approximate/actual limits by code etc) and such.
What I'm saying, is the AC (or ACs) in question do not draw 30A, so they don't need 10awg wire. They don't draw 24A either, from what I'm kinda hearing is they might draw around 12A give or take and that is max.

If the ACs only draw a maximum of, for example 15A, then 12awg wire should be fine as it's good for up to 20A ("20a is 12g", conventionally), and even at 80% of 20A (rated for "continuous loads") it'd still be under the 16A limit by 1A.

Btw, did any of your buddy's here start calling you rickymartinman? I was hoping it might stick. @kovidkough ?
 

Nizza

Well-Known Member
this 2 ton mitsubishi takes 20 amps @ 240v
keep in mind a lot of states codes require an outlet within 25' of the unit for service
also if you get a heat pump model you may want to get a stand for it if you expect snow
 

2com

Well-Known Member
this 2 ton mitsubishi takes 20 amps @ 240v
keep in mind a lot of states codes require an outlet within 25' of the unit for service
also if you get a heat pump model you may want to get a stand for it if you expect snow
I remember finding that page because I remember seeing the 17.1 min. breaker size and laughing. I think I have a few 17.3A breakers kicking around, but no 17.1A at the moment...jokes.

But yea, these numbers still left me guessing:
Max Breaker Size20
Min. Breaker Size17.1
Amperage Requirement20

So the thing requires 20A (max? avg?), but that's also the "max" breaker size they advise? ..Huh?
And the "min" breaker size is... 17.1A, say what?
The "Amperage Requirement" says 20A (again; max? avg?) If that's the case I would immediately think it needs 10awg wire, because it'd be at the literal limit of 12awg (and well beyond the 16A at 80%), but then the appropriate size breaker for the 10awg wire would be 30A.

I duno if this is just the way hvac equip/industry/trade specs or "labels" stuff - I don't think it is; at least that is - when I see the actual information sticker on the unit it gives specs that make fucking sense to me, haha. Like any other specs sticker on any other electrical device.

"Spec sticker"? What the fuck is the name of that area on a piece of electrical equipment? 'Something' plate?
 
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