Using air compressor in the garage


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Old 03-27-17, 08:47 AM
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Using air compressor in the garage

PROBLEM: I got an air compressor. 120V 15A motor trips 15A circuit breaker. The motor can be wired for 240V. Main panel is full. The circuit dedicated to garage has 14-2. All house wires are 14-2 by the way. House is stick frame.
LOCATION: Both the main panel and air compressor are located in the garage.

What is the easiest way to fix this problem? Pull out 14-2 and install 12-2 in its place and use 20A circuit breaker? I am not an electrician, but can do electrical work with your help. I have 2007 NEC code book. Actually, took the training. If I do the work, will it be code violation? Thanks.
 
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Old 03-27-17, 10:16 AM
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You have a few options:

1) New run of 12/2 cable from a new 20A breaker to a new 20A (5-20R) receptacle.

2) New run of 14/2 cable from a new double-pole 15A breaker to a new (6-15R) receptacle.

3) Repurpose your existing 14/2 cable from a 120v to 240v operation with a new breaker and relabeling the white wire as black. This is assuming there aren't other devices on this circuit. You don't want to take your only power to the garage!


What does the nameplate on the compressor motor say? There should be a MAX OCPD rating on it.
 
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Old 03-27-17, 10:34 AM
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Air compressors use the most juice when they first start up, especially if the tank already has air in it. I'd opt for upgrading to a dedicated 20 amp circuit.
 
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Old 03-27-17, 02:52 PM
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Thank you for the suggestions. I will abandon existing 14-2 and lay a new 12-2 w/20A circuit breaker. But the best seems to be adding a subpanel right next to existing main. This will give me both 120V and 240V in the garage and room for addition. If I do this, I will have to remove 2 single pole circuit breakers from the main and move the wires over to the sub. Can I use twist nuts to extend existing wires? I don't have to run a conduit between main and sub, if the wires are behind the gypsum board, correct?

I don't see MAX OCPD on the motor. The label has only current rating 15A/7.5A. I bought a used compresser.
Thank you.
 
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Old 03-27-17, 03:06 PM
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Since this is a compressor load you can possibly install a 30 amp breaker on the #12 to allow the compressor to start without tripping the breaker.
 
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Old 03-27-17, 09:07 PM
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I decided to add a subpanel since the main panel is full. Please help me with subpanel selection. Local Lowes has Square D 12-Circuit 6-Space 100-Amp Main Lug Load for $20 and Square D 12-Circuit 6-Space 100-Amp Main Breaker Load for $36. Which should I buy? Difference? My goal is to replace 2 single pole circuit breakers with 1 double pole 40A circuit breaker in the main, and populate subpanel with 2 single pole 20A circuit breakers.

The main panel has no marking for half size circuit breakers. Thank you.
 
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Old 03-27-17, 11:34 PM
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If this is in the same building as the service panel there is no need for a disconnect like the built in main breaker. You can use the main breaker if you wish.
 
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Old 03-28-17, 12:30 PM
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Since this is a compressor load you can possibly install a 30 amp breaker on the #12 to allow the compressor to start without tripping the breaker.

pcboss
This option is only allowed if compressor is hardwired on a dedicated circuit. A plug and outlet can not be used.
 
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Old 03-28-17, 12:50 PM
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You should also check if your main panel allows tandem (skinny) style breakers. You may be able to gain some space easily by swapping full height for half height breakers. Not all panels are compatible. Check the panel label for approved breaker types, number of spaces and maximum allowed circuits.
 
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Old 03-28-17, 05:10 PM
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1/2 size is not shown on the label. If not shown on the label, not allowed. So I was told. Square D QOC30U. I don't see a rectangle divided into 2 thin rectangles on the label.

Owner-builder has to sign permit application at the city hall. I am waiting for an off day. A few questions I still have are:

1. Since the main is full, I need to move 2 circuits over to the sub. Are twist nuts acceptable to extend the wires (14-2)?

2. Conduit and sub will be surface mounted. What about receptacles and conduits to the receptacles? Can they be surface mounted, too?

3. I am going to use 2 gauge aluminum wire. I see 2-2-4 cable (3 conductors twisted together) and 2-2-2-4 SER cable with an extra jacket. 2-2-4 will need an extra grounding condctor. Can I remove 2-2-2-4 jacket? Are they different conductors/insulation?

Thank you.
 
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Old 03-28-17, 05:40 PM
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Are twist nuts acceptable to extend the wires (14-2)?
Yes.
Conduit and sub will be surface mounted. What about receptacles and conduits to the receptacles? Can they be surface mounted, too?
Yes.
Can I remove 2-2-2-4 jacket?
The individual wires are not labeled for use outside the sheath.
I am going to use 2 gauge aluminum wire. I see 2-2-4 cable (3 conductors twisted together)
Do you mean to run to the garage? If so wrong cable. Use four wire cable, 2-2-2-4-6. Example: http://www.homedepot.com/p/Southwire...3099/205001794
 
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Old 03-28-17, 08:05 PM
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Based on what you have stated the feeder to the sub could be smaller, especially if you move 4 smaller circuits out and leave the compressor and subpanel feed in the main panel.
 
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Old 03-28-17, 08:07 PM
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Thank you for answering all my questions. Both main and sub are in the garage. Yes, 2-2-4-6 will be the short run between main and sub less than 5 feet. Please glance over my parts list.

100A 6 space panel, Square D QO612L100DS, Square D QO 100 Amp 6-Space 12-Circuit Indoor Flush Mount Main Lug Load Center with Cover and Door-QO612L100DF - The Home Depot

QO circuit breaker, Square D QO120CP 20A single pole, 2 ea (for subpanel), Square D QO 20 Amp Single-Pole Circuit Breaker-QO120CP - The Home Depot

QO circuit breaker, QO260CP 60A double pole, 1 ea (for main panel), Square D QO 60 Amp Two-Pole Circuit Breaker-QO260CP - The Home Depot

7 terminal ground bar kit, PK7GTACP, can take #4 aluminum, Square D 7 Terminal Ground Bar Kit-PK7GTACP - The Home Depot

1-1/2" pvc conduit, elbow, and lock nut

4"x4"x2" PVC junction box, 4 in. x 4 in. x 2 in. PVC Junction Box-E989NNJ-CAR - The Home Depot

Twist nuts for 14-2

2-2-4-6 aluminum wire, Southwire (By-the-Foot) 2-2-4-6 Gray Stranded Al MHF Cable-30163099 - The Home Depot

1 gang electrical box, surface mount, 1-Gang 12 cu. in. Electrical Handy Box-B112HBR - The Home Depot

20A duplex outlet, Leviton 20 Amp Commercial Duplex Power Outlet, White-R62-CBR20-00W - The Home Depot

1/2" pvc, sleeve, lock nut for receptables.

12-2 copper cable

Thank you.

PS: One more question. Can I put 2-2-4-6 and 14-2's in the same conduit? This is between main and sub.
 
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Old 03-28-17, 09:37 PM
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Both main and sub are in the garage.
Then why the 2-2-4-6 cable? You put the sub next to the main and use a metal nipple. You use individual THHN/THWN conductors. With a metal nipple ground wire is optional but often recommended. What am I missing?
 
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Old 03-29-17, 06:47 AM
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You don't want to use MHF between the panels. That is a direct bury style cable. Use individual pieces of THHN/THWN or SER cable such as ... Southwire (By-the-Foot) 2-2-2-4 Gray Stranded Al SER Cable-13102999 - The Home Depot If the SER is in the wall cavity and protected, conduit isn't needed between panels if panels are flush mounted.
 
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Old 03-29-17, 09:55 AM
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Do not use a 12 cubic inch handy box. They are too small for anything .
 
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Old 03-29-17, 09:56 AM
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What is the 4x4 PVC junction box for?
 
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Old 03-29-17, 10:18 AM
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Thank you for the corrections. I didn't know the difference between cable for burial and cable for above ground.

The whole project was based on a youtube video. All parts were listed. The subpanel was also approved by inspector. He showed the seal on the panel. So I decided to copy his.

This person had his main flush with drywall. He didn't want to cut dry wall for subpanel. So he put a plywood on the dry wall and mounted subpanel on it. He used PVC conduit, also surface mounted. The 4x4 box covered the hole where wires entered the wall, where the conduit ended.

It was suggested to install the subpanel flush with the drywall and run a short metal pipe between the two. Can I drill a hole on the stud? An inch at least I suppose. Should I nail an extra 2x4 for strengthening before drilling a hole? How large a hole can I drill on load-bearing studs? I prefer receptacles embedded in the wall space to surface mounted. I just don't know how to yet.
Thank you.
 
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Old 03-29-17, 10:23 AM
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I like the look of a flush mounted panel much better when it's possible. Drilling through the stud isn't that big of a deal, just use a bit that can cut flat like a forstner or a hole saw with the arbor retracted so you don't plow through the existing panel. You can drill up to 40% the width of a bearing stud through the center without adding any structural reinforcement.
 
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Old 03-29-17, 10:44 AM
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NEC calls for bored holes through framing members to be at least 1.25 inches from the nailing surface. Otherwise a nailing protective plate is needed.
 
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Old 03-29-17, 01:31 PM
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The whole project was based on a youtube video.
That was your first mistake. A lot of idiots posting on the internet.

If power to the main panel comes from the top I'd drill the hole in the stud below the panel rather than into the side just easier to me though the nipple between the boxes is more usual and maybe simpler. (If the power comes from the bottom reverse these instructions.) Make temporary hole below the main panel. You can then just drill your hole(s) run short lengths of NM-b from the main panel and into the cutout for the new panel. Slide the NM-b into the sub panel before you insert it. Patch the hole under the main panel or install a removable cover.

Install a 4x4 or 6x6 box above/below the subpanel using a nipple. Add an extension ring to it so you can run surface conduit to any loads in the garage.
 

Last edited by ray2047; 03-29-17 at 02:25 PM.
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Old 03-29-17, 07:10 PM
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Thank you. Feed to the main comes from above. Please check if the picture I have is correct.

1. The main, the sub, and the box are vertically aligned, from top to bottom in this sequence.

2. All are flush with the drywall. Only the extension ring sticks above the surface.

3. The sub and the box will be screwed to the same stud as the main.

3. There will be no drilling of vertical studs. Only horizontal wood pieces (are these called runners?) will be drilled for cables if necessary.

4. 2-2-2-4 SER aluminum cable will run between 2 panels without a conduit. I also need to run 2x 14-2 NM cables between the panels. No conduit is needed for them, either.

Please check if I have the right picture. Thank you.

One final question: Do I need a permit-inspection for this project? Rephrased, is it illegal to do this without a permit?

EDIT: I re-read the post by ray2047. He said drilling the stud below the main. So the sub will be on the right, lower than the main. Can I also put the sub immediately below?
 
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Old 03-29-17, 07:40 PM
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Can I also put the sub immediately below?
Yes, and might be the simplest.
4. 2-2-2-4 SER aluminum cable will run between 2 panels without a conduit.
As stated earlier that type of cable isn't intended for this purpose. If your main breaker panel breaker to sub is 60 amps you could use 6-3 NM-b. If you put it directly below with a nipple just use #6 THHN/THWN for hots and neutral. An optional #10 can be run as ground but not required if a metal nipple is used.

Forget the mobile home cable it isn't appropriate for this situation.
 
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Old 03-29-17, 08:39 PM
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Thank you, Sir. Now I know what needs to be done. Will post a photo when completed.
 
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Old 03-30-17, 06:10 AM
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4. 2-2-2-4 SER aluminum cable will run between 2 panels without a conduit. I also need to run 2x 14-2 NM cables between the panels. No conduit is needed for them, either.
Yes. Both SER and NM can run between panels without the use of conduit as long as the wires are run where protected from possible damage, such as within the stud bay. SER install methods are the same as NM.
 
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Old 03-30-17, 06:15 AM
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4. 2-2-2-4 SER aluminum cable will run between 2 panels without a conduit.
As stated earlier that type of cable isn't intended for this purpose.
He's now asking about SER, not MHF.
 
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Old 03-30-17, 12:04 PM
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He is now putting the sub below the main connected by a nipple and using THHN/THWN. You guys are going to confuse him.
 
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Old 03-30-17, 03:44 PM
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He is now putting the sub below the main connected by a nipple and using THHN/THWN. You guys are going to confuse him.
As of post #22, paker hadn't confirmed he was using a nipple as you suggested. When he asked about SER with no conduit, you responded that type of cable isn't intended for this purpose. I just wanted to clarify that SER is okay to use as a feeder to a subpanel without conduit. If paker uses a nipple between panels, then SER is not the proper wire to use.
 
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Old 03-30-17, 05:04 PM
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I thought he was still talking about MH cable. My mistake. I'd never refer to it the way he did so I didn't catch that. Still that seems too large for what seeme to need no more than a 60 amp feed. In my defense did write "Forget the mobile home cable" not that SER was wrong.

Packer, can you tell us what you plan to do including the size breaker in the main panel.
 
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Old 03-30-17, 09:30 PM
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I was going to use 6-3 NM that you recommended with 60A circuit breaker in the main. But if 2-2-2-4 SER can also be used without conduit, I will take advantage of the aluminum cable and put 80A circuit breaker in the main. Please advise. Thank you. I don't need 80A or even 60A for now. But expansion is for the future.

In the subpanel, I will install 2x 20A circuit breakers, one for compressor and the other for general use/lighting. For now.
 
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Old 03-30-17, 09:54 PM
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If you are going to put the sub below the main and use a nipple you do not need cable, just individual wires such as THHN/THWN. How you do it though is your choice.

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Sized for 80 amp feed at 75
 

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Old 03-31-17, 06:53 AM
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Thank you, Sir. I will follow your recommendation. Will post a photo when completed and inspected.
 
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Old 03-31-17, 09:00 AM
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Just a note or two. I didn't think moving the neutrals on the two 120v circuits you are moving was needed. Your inspector may differ. Install the new panel so knockouts in both panels align. Fasten a board across the back of the space using corner irons and mount through the back of the panel. Finally remember ground bar bonded, neutral bar isolated.
 
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Old 03-31-17, 01:31 PM
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Thank you for the box mounting instruction. I was wondering how to line up the openings for the conduit. This thread is already bookmarked until the project is done.
 
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Old 04-09-17, 05:11 PM
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At the last minute, I noticed bottom 6 rows had a dotted line in the middle. I moved 2 circuits to a 1/2 size circuit breaker and was able to install a 12-3 for the compressor without a subpanel. I apologize for not having noticed it earlier.
 
 

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