Questions about adding 220v circuits

[VoodooCLD]

I have a shop that was built during 2020 by the previous owner. It has a 15 amp breaker running a mini split heat/ac system for the upstairs apartment. I want to add a second identical minisplit for the downstairs garage portion. I'm on vacation right now so I can't take any pictures or measue wiring, but if the wire running to the original mini split is 10 gauge, can I just replace the breaker with a 30 amp and then run some conduit from the existing mini split junction box over to where I'm going to mount the new mini split?

I'm asking this because I only have 2 slots left in my electrical panel. They're not next to each other, but I'm guessing I can move around some 120v circuits to get 2 slots available for another 220v branch. I need to use those 2 available slots for a 30 amp 220v circuit with 3 outlets to run a small mill, lathe, and eventually a welder (not at the same time).

My final question is, if I don't have 10 gauge wire running to my current mini split and I have to run 2 separate 220v circuits for the new mini split as well as the machine tools how do I know if I can run tandem breakers for some of the 110v light circuits? I'm thinking I can combine 4 of the single spot 120v circuits into 2 tandems and free up 2 more spaces for the second 220v circuit. Are the tandem breaker allowances determined by the panel itself? Is it as simple as seeing if the panel allows them and then rearranging as needed to make it all fit? I'm interested in doing this to code as it's all new and built to code currently. Located in Oklahoma.

I'll try and get some pics if needed when I'm back home.

 

[u2slow]

You most likely need to keep 15A ocp for the existing mini-split. Check the unit for its requirement.

 

[VoodooCLD]

You most likely need to keep 15A ocp for the existing mini-split. Check the unit for its requirement.

Oh ya, wasn't thinking about that for some reason. There is a junction box right above the mini split mounted on the exterior wall. Do they allow you to put 2 breakers in a box like that? Where I could replace the breaker in the main panel to 30 amp and then have 2 separate 15 breakers for each mini split?

 

[Terry D]

Its not likely someone ran a #10 for a 15 amp circuit. The junction box you are seeing outside is most likely a disconnect for the minisplit, so cant add breakers. Post some pictures of your panel and label inside the door to see if tandems can be added. Your best bet is to run a new circuit from your panel. You possibly could run a sub panel off the panel you have now or replace it with a larger panel. But to give the best advice, we would need to see pictures.

 

[VoodooCLD]

Its not likely someone ran a #10 for a 15 amp circuit. The junction box you are seeing outside is most likely a disconnect for the minisplit, so cant add breakers. Post some pictures of your panel and label inside the door to see if tandems can be added. Your best bet is to run a new circuit from your panel. You possibly could run a sub panel off the panel you have now or replace it with a larger panel. But to give the best advice, we would need to see pictures.

Ok, thanks for the info. I'm gonna have my dad grab a picture of the box when he's over there later today.

 

[u2slow]

If the unit has a local disconnect, it could probably be changed to a fused disconnect, or a small 2-space breaker box. It probaby has to be at a certain accessible height.

It's possible the circuit was pre-wired with #10 before the unit was chosen.

 

[Terry D]

If the unit has a local disconnect, it could probably be changed to a fused disconnect, or a small 2-space breaker box. It probaby has to be at a certain accessible height.

It's possible the circuit was pre-wired with #10 before the unit was chosen.

How would you get (2) 240 volt circuits out of a fused disconnect, with a 2 space panel, it would have to accept a quad breaker or would have to be a 4 space panel

 

[Terry D]

Ok, thanks for the info. I'm gonna have my dad grab a picture of the box when he's over there later today.

Try to get a picture with the cover off so we can see the size or the wire installed to the existing minisplit

 

[u2slow]

How would you get (2) 240 volt circuits out of a fused disconnect, with a 2 space panel, it would have to accept a quad breaker or would have to be a 4 space panel

The quad or 4-space would work too.

I was envisioning a 15A fused/breaker disconnect at each mini-split, off the 30A/#10 circuit at the panel.

 

[dcg9381]

Its not likely someone ran a #10 for a 15 amp circuit. The junction box you are seeing outside is most likely a disconnect for the minisplit, so cant add breakers. Post some pictures of your panel and label inside the door to see if tandems can be added. Your best bet is to run a new circuit from your panel. You possibly could run a sub panel off the panel you have now or replace it with a larger panel. But to give the best advice, we would need to see pictures.

When I wired for a mini-split, I ran 10/3. Turns out I didn't need it. So it's possible.

OP, another way I see to do this is to run the 10 gauge wire down to a outdoor sub-panel and split it into two 15A circuits. If you are nearby the AC units, I believe the sub-panel can replace the function of disconnects EXCEPT in the case of units that require fuses... Someone will slap me if I'm wrong.

 

[VoodooCLD]

When I wired for a mini-split, I ran 10/3. Turns out I didn't need it. So it's possible.

OP, another way I see to do this is to run the 10 gauge wire down to a outdoor sub-panel and split it into two 15A circuits. If you are nearby the AC units, I believe the sub-panel can replace the function of disconnects EXCEPT in the case of units that require fuses... Someone will slap me if I'm wrong.

If I have to run a new line I'll just run a dedicated 15 amp 220v circuit for the new mini split. I'm hoping to run both mini splits off of the existing wiring so that I can use my last 2 spots in my panel to run a circuit for the machine tools. That will keep me from having to buy tandem breakers and rearrange my whole box.

 

[Terry D]

The quad or 4-space would work too.

I was envisioning a 15A fused/breaker disconnect at each mini-split, off the 30A/#10 circuit at the panel.

Makes sense

 

[Terry D]

If I have to run a new line I'll just run a dedicated 15 amp 220v circuit for the new mini split. I'm hoping to run both mini splits off of the existing wiring so that I can use my last 2 spots in my panel to run a circuit for the machine tools. That will keep me from having to buy tandem breakers and rearrange my whole box.

Like I said, until we have pictures, we cant give you the best advice. If it is #10 to the disconnect, then yes you could put a small outdoor sub panel and feed both minisplits. This would be easy, especially if the condensers were going side by side. If it isn't #10, you have to look at how hard it would be to replace it verses running a separate circuit for the new one. But if you only have 2 spaces left in your panel now, I guarantee down the road you will want to add something and have to deal with then, by adding tandems ( if the panel accepts them ) or replacing the panel with a larger space one or adding a sub panel. Do you know what size the service is to the shop

 

[VoodooCLD]

Here's some pics of the panel and the current outside disconnect. Unfortunately didn't get a photo inside of the disconnect to see what the wire size is, but I'll check when I'm back in town. How do you tell if tandem breakers are allowed?

This is a 100 amp panel in the shop feeding from a 200 amp panel in the house. I think if I can get the second mini split and one more circuit for machine tools I should be good. It's pretty well wired already. The 30 amp dryer circuit is going to be used for my 220v dust collector and a 5hp air compressor. Just need a second one for the machine tools.

 

[alfredeneuman]

How do you tell if tandem breakers are allowed?

According to the diagram in the first image you posted here tandems are not allowed

 

[VoodooCLD]

Ya, I just read that it only allows 20 circuits. Any of you have any good (cost effective) ideas how to go about adding a 220v 30 amp machine circuit, and another 220v 15 amp circuit for a mini split?

 

[Terry D]

Your panel will not accept tandems. You are looking at a panel replacement. Siemens makes a 30 space 100 amp, so you could reuse your breakers and still have 10 more spaces after adding a minisplit, or adding a sub off that panel. It looks like you have a sub already off that panel, is there room in that panel? Also that 15 amp 2-pole breaker for your existing minisplit is a Square D Homeline, it is not listed for that panel and should be changed to a Siemens

Siemens PN Series 100 Amp 30-Space 30-Circuit Main Breaker Plug-On Neutral Load Center Indoor with Copper Bus PN3030B1100C - The Home Depot

Save expensive cable and time in your home with Siemens PN Series Main Breaker PlugOn Neutral Load Center Indoor with Copper Bus.

www.homedepot.com

 

[VoodooCLD]

Your panel will not accept tandems. You are looking at a panel replacement. Siemens makes a 30 space 100 amp, so you could reuse your breakers and still have 10 more spaces after adding a minisplit, or adding a sub off that panel. It looks like you have a sub already off that panel, is there room in that panel?

Siemens PN Series 100 Amp 30-Space 30-Circuit Main Breaker Plug-On Neutral Load Center Indoor with Copper Bus PN3030B1100C - The Home Depot

Save expensive cable and time in your home with Siemens PN Series Main Breaker PlugOn Neutral Load Center Indoor with Copper Bus.

www.homedepot.com

Not sure I'm ready for a full panel swap. Is there any issue with wiring in 3 outlets to my current 30 amp 220v circuit? I could move the mill near those outlets but would like to have them all plugged in permanently. The mill and dust collector only pull 9 amps full load a piece. I will eventually add an air compressor in there, but would only ever have 2 of the units running at once.

 

[Terry D]

Not sure I'm ready for a full panel swap. Is there any issue with wiring in 3 outlets to my current 30 amp 220v circuit? I could move the mill near those outlets but would like to have them all plugged in permanently. The mill and dust collector only pull 9 amps full load a piece. I will eventually add an air compressor in there, but would only ever have 2 of the units running at once.

I added in my prior post that your existing minisplit breaker needs to changed to a Siemens brand. If your air compressor is a true 5hp, you will not be able to use that 30 amp circuit if it is wired with NM-b (romex) There are a lot of threads on here how to wire a 5 hp compressor. It should be on its own circuit. Plus the plug and receptacle rated for 5 hp are crazy expensive, so hard wiring is the way to go. If your area falls under the IRBC, then you cant wire multiple 240 volt receptacles on the same circuit

If it was my shop, I would want all the 240 volt equipment on dedicated circuits anyway.

 

[VoodooCLD]

I don't have an air compressor yet so I can look at my options when I get there. Its been a while since I've looked at air compressors but I remember a lot being rated at 5hp, but weren't actually 5hp.

Should I look at using my last 2 slots to run a 50 amp sub panel? Or would that cost as much as swapping the main panel? Trying to find the most efficient way to do this. Considering I don't have a 220v air compressor yet, nor a welder. I'm wondering if I should just make do with my one current 220v plug. I can rewire my lathe as 120v since it's only a 1 hp motor, but I hate having to switch out plugs since the outlet is at the back of a closet that is always packed. What is IRBC and how do I know if I'm allowed to have multiple recepticles? Can I use plug in splitter? I've seen those for sale, but they're pricey.

 

[Terry D]

The IRBC is the International Residential Building Code. It overrides the NEC on certain things. I would think you could go to their website and look it up. You don't have your location listed in your profile. Is this just a one man shop? Main thing is that you don't overload that 100 amp service. You can add a sub off your panel, as far as which one is cheaper, I don't know. If your hiring this out, then the bids will tell you.

 

[VoodooCLD]

The IRBC is the International Residential Building Code. It overrides the NEC on certain things. I would think you could go to their website and look it up. Is this just a one man shop? Main thing is that you don't overload that 100 amp service. You can add a sub off your panel, as far as which one is cheaper, I don't know. If your hiring this out, then the bids will tell you.

Yes, this is just a personal hobby shop right next to my house. I'm the only one ever working in there so most that will run are 2 machines. Dust collector and a machine, or air compressor and a machine. I was sort of surprised to see they only put in 100 amp service when the on demand water heater is on an 80 amp circuit itself.

 

[Terry D]

Yes, this is just a personal hobby shop right next to my house. I'm the only one ever working in there so most that will run are 2 machines. Dust collector and a machine, or air compressor and a machine. I was sort of surprised to see they only put in 100 amp service when the on demand water heater is on an 80 amp circuit itself.

What is the actual amp draw on that water heater, I just saw a sub panel, didn't realize it was for that. You might be pushing it by adding anything to this panel.

 

[VoodooCLD]

What is the actual amp draw on that water heater, I just saw a sub panel, didn't realize it was for that. You might be pushing it by adding anything to this panel.

I'll have to check when I get home. The water is all upstairs in the apartment. I couldn't possibly run it while running a machine so I'm not worried about it. The apartment is just more workspace for me, no one is living in it.

 

[dcg9381]

If I have to run a new line I'll just run a dedicated 15 amp 220v circuit for the new mini split. I'm hoping to run both mini splits off of the existing wiring so that I can use my last 2 spots in my panel to run a circuit for the machine tools. That will keep me from having to buy tandem breakers and rearrange my whole box.

I'm not suggesting you run new wire. I'm suggesting you use the existing wire and feed a sub-panel with it. The sub-panel splits to feed both mini-split compressors and the breakers replace the required disconnects. I am assuming that both compressors are at around the same spot.

 

[VoodooCLD]

I'm not suggesting you run new wire. I'm suggesting you use the existing wire and feed a sub-panel with it. The sub-panel splits to feed both mini-split compressors and the breakers replace the required disconnects. I am assuming that both compressors are at around the same spot.

That's my goal, but I won't know if I can do that until I know what size wire was run to the original mini split. All the other talk is about a back up plan if the wiring is only sized for 15 amps.

 

[pattenp]

The IRBC limits 240V 30A and greater to one receptacle per circuit. 240V 15A and 20A can be multiple receptacles per circuit.

 

[Terry D]

The IRBC limits 240V 30A and greater to one receptacle per circuit. 240V 15A and 20A can be multiple receptacles per circuit.

Wasn't sure how it read, thanks for clarifying

 

[alfredeneuman]

He stated the building is in Oklahoma in his 1st post.
Oklahoma recognizes the NEC, not the IRBC

 

[VoodooCLD]

He stated the building is in Oklahoma in his 1st post.
Oklahoma recognizes the NEC, not the IRBC

That's interesting information. Is the NEC a national code? Is there also Oklahoma code? I'd like to read into if I can add more outlets on my current 30 amp circuit. That would simplify things a lot.

 

[Terry D]

He stated the building is in Oklahoma in his 1st post.
Oklahoma recognizes the NEC, not the IRBC

Did not even notice that. OP, sorry to confuse things, Disregard everything about the IRBC. You can have multiple 240 volt receptacles on a single circuit. Amperage doesn't matter.

 

[Theruse]

When you say "most efficient way" to do it, I think you are really saying the cheapest way. Not always the same. I would suggest rather than replacing the main panel, just add a sub panel devoted to the two items you note. Not really that expensive.

 

[VoodooCLD]

When you say "most efficient way" to do it, I think you are really saying the cheapest way. Not always the same. I would suggest rather than replacing the main panel, just add a sub panel devoted to the two items you note. Not really that expensive.

No, I'm not looking at the cheapest way as I want it to be to code, and also usable. It seems like there's a few ways to skin this cat and I want to find the way that doesn't cut any corners, but also doesn't involve just ripping out the whole panel and replacing with a new one and then running two new circuits. I'm trying to find the least invasive way (and yes, hopefully this will result in it being cheaper although that's not my ultimate goal) to get the circuits I need using what I have. I'll be getting home tomorrow and am gonna look at my options.

1. See if the current mini split has 10 gauge wiring, if so then Ill add 2- 15 amp breakers on that circuit for both mini splits and use my last 2 spots for a 220v circuit to run 3 outlets for my machine tools.

2. If its not 10 gauge I'll probably just use my last 2 spots for a 15 amp circuit to run the 2nd mini split. I'll then have to get fancy with some conduit on my existing 30 amp circuit, run it out of one closet, through the water heater closet, and then across the garage back wall to add 2 more outlets for my mill and lathe.

3. Another option I'm thinking of is using the last 2 spots to put in say a 50 amp circuit. Running that across the ceiling to the other wall (where the machine outlets are needed as well as where the new mini split will be) where I'll add a sub panel. That would allow me to run the 15 amp circuit for the mini split as well as a 30 amp circuit for the machine tools.

Does anyone see any issue with running a 50 amp breaker feeding a sub panel from my shop panel? The shop panel is already a sub panel from my main house panel, and I'm hoping I could just use the 50 amp breaker in my shops panel as the main breaker for a small 4 slot box with a 30 amp circuit and 15 amp circuit.

 

[TRWham]

That's interesting information. Is the NEC a national code? Is there also Oklahoma code? I'd like to read into if I can add more outlets on my current 30 amp circuit. That would simplify things a lot.

The NEC (aka NFPA 70) is the National Electric Code as written by the National Fire Protection Association (NFPA). While it is nominally a national code covering the entire US, there are many exceptions by state, county or city across the country. You need to determine what applies in your area.

The International Residential Code (IRC) covers all aspects of home construction and, in my experience, is widely cited for everything except electrical.

 

[VoodooCLD]

Looks like I do indeed have 10 gauge wire running to my current mini split!

My plan is now to remove the current disconnect box and install it further down the wall to the left where the new mini split will go. Replace the current disconnect box with a 4 slot breaker panel with 2 - 220v breakers, and then replace the 15 amp breaker in my electrical panel with a 30 amp breaker. I would then run metal conduit from the new 4 panel breaker along the exterior brick wall to the disconnect box, where I'll wire up the new mini split.

Does this sound like a good plan? Would I be violating any codes?

 

[Terry D]

Awesome. Make sure the sub panel is outside rated, and use compression fittings for your conduit. Since the breaker will be insight of the new mini split, the disconnect would not be needed, but since you already have it, it wont hurt installing it. Another way of telling it is #10 is by the orange jacket

 

[VoodooCLD]

Awesome. Make sure the sub panel is outside rated, and use compression fittings for your conduit. Since the breaker will be insight of the new mini split, the disconnect would not be needed, but since you already have it, it wont hurt installing it. Another way of telling it is #10 is by the orange jacket

Good to know! Should I use romex, THHN, or THWN wire for running to the new mini split? Can I use EMT conduit as long as I use waterproof compression fittings? I'd like to avoid have to thread pipe if possible.

Thanks for the help everyone. While I'm pretty familiar with electricity in general, I've not done much with household wiring.

 

[Terry D]

EMT with compression fittings is fine . No reason to run heavy wall and have to deal with threading. Use THWN inside the conduit. When conduit is installed outside, the interior is considered a wet location. Indoor romex can not be installed in outside conduit.

 

[wyliesdiesels]

NM-b and THHN are not permitted in conduit that is outside.

Most THHN however is dual rated THWN though...

Do you have an outlet nearby for servicing?

 

[VoodooCLD]

NM-b and THHN are not permitted in conduit that is outside.

Most THHN however is dual rated THWN though...

Do you have an outlet nearby for servicing?

I do not. What do you mean by servicing?