Electrical rough-in for mini-split

[Skyman]

Hi, all.

Looking at future installation of a mini-split to heat/cool my attached garage that's roughly 750 s.f. I don't yet know enough about the existing insulation, but would like to get the electrical rough-in done prior to installing the unit. I also don't know much about the electrical requirements, and would welcome insights about this, as well as recommendations for how best to do the rough-in.

Many thanks in advance for any advice and info.

 

[rlitman]

The rough-in is a disconnect on the wall, and a GFCI protected outlet within 25' of it.
Not knowing the size, you could run 10AWG wire from the panel to the disconnect and figure out the breaker later.

 

[dcg9381]

You need 2 wires + ground wire. Depending on the size of your unit, either 10 gauge or 12 gauge. Wire type depends on how you are going to run it.. Through wall - romex. Through conduit THHN or THWN (individual wires).

If you're uncomfortable putting the wires in, use 3/4" electrical conduit to the right spots and an electrican can run the wire for you.

Your unit will be 120V or 240V, both can be done by 2 wires (and a ground).

As mentioned, there needs to be an external "disconnect" (these are cheap) and a 120V outlet near the compressor (assuming there is not one in the area from another HVAC already).

The "control" for these units is a set of wires that runs from the head unit, usually through the path of the coolant/drain line cover to the compressor. Most units come with control wire.

Personally, I set the head unit first, then determine the placement of the compressor based on the existing line length.

If you've got open walls, you might want to install a separate drain line... I use 3/4 PVC. Beats the plastic tubes that these things come with. This assumes you have a "gravity" path for the drain.

 

[wyliesdiesels]

Hi, all.

Looking at future installation of a mini-split to heat/cool my attached garage that's roughly 750 s.f. I don't yet know enough about the existing insulation, but would like to get the electrical rough-in done prior to installing the unit. I also don't know much about the electrical requirements, and would welcome insights about this, as well as recommendations for how best to do the rough-in.

Many thanks in advance for any advice and info.

without knowing the specs on the unit, its impossible to say what the requirements are.

how about a pic of the nameplate on the unit or a brand and model # so we can look it up?

 

[mm08822]

without knowing the specs on the unit, its impossible to say what the requirements are.

how about a pic of the nameplate on the unit or a brand and model # so we can look it up?

10 copper will provide an mca of 30a. That provides a lot of headroom.

 

[Steve W.]

I pre-wired my shop, knowing that I wanted a mini-split, but it's taken 10 years to finally install it.

My 24k Pioneer is scheduled for install this weekend.

The 10ga I pulled proves to be more than adequate, I'm not disappointed with my choice of over-kill on the wire size.

.

 

[Skyman]

Thanks for the replies, all. I won't be DIY-ing this work. I have an electrician lined up to come in and set a sub-panel in the garage and distribute from there to the mini-split, and to other devices. I haven't selected the unit yet, so the recommendation for 10 AWG makes good sense to me. I presume the breaker in the sub-panel would satisfy the requirement for a disconnect - is this correct?

 

[mm08822]

The ac unit needs a disconnect in-site of it and less than 50'. Otherwise, the cb must be lockable.

However, for troubleshooting and general maintenance, at the unit is best.

Also need a gfci recept within 25'.

 

[mike93lx]

Thanks for the replies, all. I won't be DIY-ing this work. I have an electrician lined up to come in and set a sub-panel in the garage and distribute from there to the mini-split, and to other devices. I haven't selected the unit yet, so the recommendation for 10 AWG makes good sense to me. I presume the breaker in the sub-panel would satisfy the requirement for a disconnect - is this correct?

A disconnect is about $20 and has the added benefits of being a good place to connect up the unit, plus a good spot to put a surge protector.

Any electrician will know what to use

 

[rlitman]

... I presume the breaker in the sub-panel would satisfy the requirement for a disconnect - is this correct?

Let's just say no. An exterior disconnect mounted on the wall nearest where the AC unit will be located is going to be the cheapest option, and likely the ONLY method accepted by both the AHJ as well as any HVAC contractor. Also, your electrician will not know what breaker to install without the specs from the mini split, so at best, you can run the wire, but not power it yet.

 

[dscheidt]

Let's just say no. An exterior disconnect mounted on the wall nearest where the AC unit will be located is going to be the cheapest option, and likely the ONLY method accepted by both the AHJ as well as any HVAC contractor. Also, your electrician will not know what breaker to install without the specs from the mini split, so at best, you can run the wire, but not power it yet.

If you install a fusible disconnect, it can be fed from a 30a breaker, and fuses fitted to suit the machine. A surprising number of mini splits require fuses, so it's probably best to install one. A lot have manuals that are wrong, they say X amps OCP, but the name plate says 'max fuse'. Nameplate is controlling, so until you have the machine you can't be sure you don't need a fusible disconnect.

 

[rlitman]

...A surprising number of mini splits require fuses, so it's probably best to install one. A lot have manuals that are wrong, they say X amps OCP, but the name plate says 'max fuse'. Nameplate is controlling, so until you have the machine you can't be sure you don't need a fusible disconnect.

Kind of. I've seen this argument passed around a lot, but in general when someone brings this up with the manufacturer, the response is that a breaker is acceptable. My guess is that most of where this happens is with someone doing a poor job translating the nameplate from Chinese into English, and the NRTL stamp will be questionable.

That's also because the nameplate doesn't override the instructions, which typically says fuse or HACR breaker.

So I'm yet to see an actual need for a fused disconnect for a mini-split, but I'm also not willing to say the need doesn't exist. I will say that exterior fuses are a point of failure to be avoided at all costs.

 

[mm08822]

If you install a fusible disconnect, it can be fed from a 30a breaker, and fuses fitted to suit the machine. A surprising number of mini splits require fuses, so it's probably best to install one. A lot have manuals that are wrong, they say X amps OCP, but the name plate says 'max fuse'. Nameplate is controlling, so until you have the machine you can't be sure you don't need a fusible disconnect.

If you don't have the unit yet, even using a 30a cb on the 10s could be trouble. What if a 30 tripped on startup and was below the MOC? So best to wait. Unterminated wires will be just fine in the panel.

 

[dscheidt]

Kind of. I've seen this argument passed around a lot, but in general when someone brings this up with the manufacturer, the response is that a breaker is acceptable. My guess is that most of where this happens is with someone doing a poor job translating the nameplate from Chinese into English, and the NRTL stamp will be questionable.

That's also because the nameplate doesn't override the instructions, which typically says fuse or HACR breaker.

So I'm yet to see an actual need for a fused disconnect for a mini-split, but I'm also not willing to say the need doesn't exist. I will say that exterior fuses are a point of failure to be avoided at all costs.

No, the nameplate is controlling. Equipment changes faster than manuals get updated. It's very common to find nameplates that don't agree with the manual, even by generally reputable manufacturers in the USA, because they changed something based on availability, customer requirement, or an engineering change. This is why stuff has nameplates.

I don't disagree that most of these machines are probably suitable for being protected by a breaker, but the manufacturer needs to put the right data on the nameplate. If customer service ells you you can use a breaker, make them send a corrected nameplate. If they can't do that, then how do you know the customer service person isn't telling you something based on what they think you want to hear? Or they're just reading from the manual, which was written by someone not familiar with the US requirements.

I have two splits, both the same model. When I got the first one, the manual it came with didn't even list that model. The second one came with a revised manual, that does have the new models in it.

 

[wyliesdiesels]

That's also because the nameplate doesn't override the instructions, which typically says fuse or HACR breaker.

not true. The nameplate is the final authority. you really think an AHJ is gonna pull out a manual when theyre doing an inspection? plus manuals change and are poorly written... never go by the manual...

 

[Codyboy]

Kind of. I've seen this argument passed around a lot, but in general when someone brings this up with the manufacturer, the response is that a breaker is acceptable. My guess is that most of where this happens is with someone doing a poor job translating the nameplate from Chinese into English, and the NRTL stamp will be questionable.

That's also because the nameplate doesn't override the instructions, which typically says fuse or HACR breaker.

So I'm yet to see an actual need for a fused disconnect for a mini-split, but I'm also not willing to say the need doesn't exist. I will say that exterior fuses are a point of failure to be avoided at all costs.

Lol
The nameplate trumps all.
It is permanently affixed to the device.
Printed manuals are mostly discarded with the lunch trash that day or its the wrong manual supplied. It's just a piece of paper.
But even if not discarded the nameplate rules.

Quick, not so quick story.
Worker goes to POCO yard to pick up a transformer to install. He knows he needs a 120/240.
There is a handmade Manila tag on the primary bushing that reads 34.5 Y/ 19.9, 120/240.
Ok cool. Here it is boys, loader up. Let's get this thing changed out so I can get to my son's BB game! Hurry up hurry up!

Transformer replaced. Woohoo. Heat'r up let's go!
Transformer energized.
Holy ****, open it up, open it up. Wtf?
So now house are smoking, people are running out saying wth is going on? My house is full of smoke!

Well , a 120/240 transformer looks the exact same externally as a 240/480 transformer,
Except for the NAMEPLATE.
Turns out the warehouseman mismarked it when doing inventory.

Lesson.
Always check the NAMEPLATE when you load it up.
Always check the NAMEPLATE when you hang it on the pole.
Always check the NAMEPLATE before you energize it.
Always and NEVER trust a written or printed document when there is a NAMEPLATE affixed to the device.
If the NAMEPLATE is wrong then that is not on you.

 

[PCustoms]

Lol
The nameplate trumps all.
It is permanently affixed to the device.
Printed manuals are mostly discarded with the lunch trash that day or its the wrong manual supplied. It's just a piece of paper.
But even if not discarded the nameplate rules.

Quick, not so quick story.
Worker goes to POCO yard to pick up a transformer to install. He knows he needs a 120/240.
There is a handmade Manila tag on the primary bushing that reads 34.5 Y/ 19.9, 120/240.
Ok cool. Here it is boys, loader up. Let's get this thing changed out so I can get to my son's BB game! Hurry up hurry up!

Transformer replaced. Woohoo. Heat'r up let's go!
Transformer energized.
Holy ****, open it up, open it up. Wtf?
So now house are smoking, people are running out saying wth is going on? My house is full of smoke!

Well , a 120/240 transformer looks the exact same externally as a 240/480 transformer,
Except for the NAMEPLATE.
Turns out the warehouseman mismarked it when doing inventory.

Lesson.
Always check the NAMEPLATE when you load it up.
Always check the NAMEPLATE when you hang it on the pole.
Always check the NAMEPLATE before you energize it.
Always and NEVER trust a written or printed document when there is a NAMEPLATE affixed to the device.
If the NAMEPLATE is wrong then that is not on you.

Seems like a dumb example.

You guys don't verify secondary voltage after hooking everything up?

 

[Codyboy]

Seems like a dumb example.

You guys don't verify secondary voltage after hooking everything up?

Actually yes we do verify voltage and load.

Hard to verify secondary voltage when not energized .

The point was the nameplate .

But you already knew that.

 

[Skyman]

Thanks for the additional replies and advice, all. I was planning to leave those 10ga wires unterminated in the panel until time to connect.

 

[wyliesdiesels]

Lol
The nameplate trumps all.
It is permanently affixed to the device.
Printed manuals are mostly discarded with the lunch trash that day or its the wrong manual supplied. It's just a piece of paper.
But even if not discarded the nameplate rules.

Quick, not so quick story.
Worker goes to POCO yard to pick up a transformer to install. He knows he needs a 120/240.
There is a handmade Manila tag on the primary bushing that reads 34.5 Y/ 19.9, 120/240.
Ok cool. Here it is boys, loader up. Let's get this thing changed out so I can get to my son's BB game! Hurry up hurry up!

Transformer replaced. Woohoo. Heat'r up let's go!
Transformer energized.
Holy ****, open it up, open it up. Wtf?
So now house are smoking, people are running out saying wth is going on? My house is full of smoke!

Well , a 120/240 transformer looks the exact same externally as a 240/480 transformer,
Except for the NAMEPLATE.
Turns out the warehouseman mismarked it when doing inventory.

Lesson.
Always check the NAMEPLATE when you load it up.
Always check the NAMEPLATE when you hang it on the pole.
Always check the NAMEPLATE before you energize it.
Always and NEVER trust a written or printed document when there is a NAMEPLATE affixed to the device.
If the NAMEPLATE is wrong then that is not on you.

ouch i bet that was an expensive mistake... hope they made the homeowner whole

 

[wyliesdiesels]

Seems like a dumb example.

You guys don't verify secondary voltage after hooking everything up?

how do you do so without energizing the can?

 

[Codyboy]

ouch i bet that was an expensive mistake... hope they made the homeowner whole

Oh I'm sure the claims dept phone was ringing off the wall.
No doubt the customers were made whole.
Hell they probably took advantage of it.

Hey mee maw, got claims from POCO on the phone, what else burned up?
Well uh , there's that old VCR that hasn't worked in 5 years , and the vent hood over the stove hasn't worked since 10 Thanksgivings ago when it clogged up with the turkey I burned up.
Oh yeah and the automatic dishwasher stopped working too.
Uh mee maw. We don't have a DW.
Bill they don't know that.

Lol

 

[PCustoms]

how do you do so without energizing the can?

Granted I wasn't there when they finally reconnected, but I assumed they checked before reconnecting my overhead to the transformer. There was also a couple sets of footprints at the meter, maybe they pulled that?

 

[Codyboy]

how do you do so without energizing the can?

Actually it can be done and we actually used to do it long ago in the 90s.
Hang it , wire everything up except the secondaries, energize it and check voltage.
It was a pia for easement stuff with no truck access.
It meant the apprentice had to climb the pole twice. Lol.
I think at the time we'd do that was because a lot of our transformers were rebuilt in house by our shops dept.
Sometimes they wouldn't be "right" if ya know what I mean.
They more or less stopped rebuilding them and bought new ones from the manufacturer.
There were some special ones that would get rebuilt that were no longer available new or was cost prohibitive.
We had 13.2 kv (primary) rated transformers
13.2 - 277/480.
Those would always get checked before connecting the secondaries.
New ones not so much.

But our primary voltage was 12470Y/7200.
They would work phase to phase on 12470 wired delta ,but would have to adjust the voltage with the taps setting.
So they rebuilt those for a while but then as some of that older stuff from the 60s and 70s ran its course we'd just end up replacing g the whole bank with 7200-277/480 transformers instead of just the one that was burned up in the bank.

 

[Codyboy]

Granted I wasn't there when they finally reconnected, but I assumed they checked before reconnecting my overhead to the transformer. There was also a couple sets of footprints at the meter, maybe they pulled that?

Yes easy to do for a single customer. Pull the meter or turn off the breaker if accessible.
Check voltage before applying load.

A little different when there are 10 customers on the transformer in Houston and 6 of them have pitbulls in the yard and no access.

 

[wyliesdiesels]

Actually it can be done and we actually used to do it long ago in the 90s.
Hang it , wire everything up except the secondaries, energize it and check voltage.
It was a pia for easement stuff with no truck access.
It meant the apprentice had to climb the pole twice. Lol.
I think at the time we'd do that was because a lot of our transformers were rebuilt in house by our shops dept.
Sometimes they wouldn't be "right" if ya know what I mean.
They more or less stopped rebuilding them and bought new ones from the manufacturer.
There were some special ones that would get rebuilt that were no longer available new or was cost prohibitive.
We had 13.2 kv (primary) rated transformers
13.2 - 277/480.
Those would always get checked before connecting the secondaries.
New ones not so much.

But our primary voltage was 12470Y/7200.
They would work phase to phase on 12470 wired delta ,but would have to adjust the voltage with the taps setting.
So they rebuilt those for a while but then as some of that older stuff from the 60s and 70s ran its course we'd just end up replacing g the whole bank with 7200-277/480 transformers instead of just the one that was burned up in the bank.

so you were running them wye/wye? instead of delta/wye?

 

[Codyboy]

so you were running them wye/wye? instead of delta/wye?

Our system is a wye system .
12470Y/7200.

The 13200 were the only ones ever connected delta (2 phases per transformer) on the primary.
So they were delta on the primary side and wye on the secondary side . No idea why it was ever a thing as it happened way before I hired on in 85.
I presume the company could not get 7200-277/480 so they bought 13200 and made it work.

There are still some in the system here and there but most have been converted to wye/wye, 7200-277/480.

 

[wyliesdiesels]

from all my reading of HV systems and pole pig hookups I seem to recall that wye/wye hookups can be problematic.... our PoCo is almost all delta/delta and delta/wye. few old locations have wye/delta and wye/wye but those are really large cans on H frames from the old days and theyre working on replacing them. Last one they replaced had 3 100kVa cans and changed it to 3x 50s along with getting rid of the wye hookup on the HV side. The H frame was cut down too

 

[Codyboy]

from all my reading of HV systems and pole pig hookups I seem to recall that wye/wye hookups can be problematic.... our PoCo is almost all delta/delta and delta/wye. few old locations have wye/delta and wye/wye but those are really large cans on H frames from the old days and theyre working on replacing them. Last one they replaced had 3 100kVa cans and changed it to 3x 50s along with getting rid of the wye hookup on the HV side. The H frame was cut down too

So is the distribution system out of the sub wye or delta?
I know some places have a delta distribution system (no neutral)
and have to run at least two phases everywhere.

Ive never had to really deal with a delta system except maybe on some storm restoration trips to a different POCO.

My SIL works for the POCO in Norcal and a lot of what they have runs through the mountains . They have a wye system but run a lot of delta because when they have a downed neutral or miles of spans don't have a neutral they have to wire it delta.
One issue they do have is single phase URD.

They have to build what he calls an Iso bank to create a neutral to run with the URD primary.
He tried explaining it and I somewhat get it but was just batting my eyes in amazement to have to do that.
I asked him why they dont repair their system and just pull in a neutral where they are missing ?
He said the company doesn't want to spend the money so they just keep limping along.

As far of which would cause more issues, idk. A wye system to me is less complicated. Basically a hot and a neutral.

And on that 100kva to 50s changeout, I would just assume the demand for the 100s was no longer needed for that customer.

 

[wyliesdiesels]

They have both wye and delta (or maybe its all wye just no neutral ran in some spots)

I have never seen a bank connected via 2 phases and neutral with the PoCo i have

The banks that are wired wye on the high side only have 3 phases over head that drop down to 4 wires and the 4th wire is just connected between the cans.

Profit Gouge and execute on the other hand does have banks (single and 3 phase) that are connected wye on the high side via 1 or 2 phases (3 phase) and neutral. The way i can tell is the high side neutral has a jumper that goes down to the secondary bushing for the neutral on the service