Finally decided to upgrade my compressor so I can run a paint gun but I need to wire it into the garage.  Knowledgeable electricians please chime in.

The compressor I am looking at is a Kobalt (VT6362) 3.7hp, 60 gallon which runs 13.4cfm @40psi.  It is a 230v/1 and is listed at 15amps (does not state if this is max or running).

Now for the wiring.  Below is a picture of my breaker panel.  There are two slots at the bottom which should accept a double pole breaker.



Should I use a 20amp breaker or 30amp breaker?

The wiring run is roughly 75 feet if I run it through the attic and looks to be a pita snaking it down the wall but I need to get in the attic to check.  I could possible run it underground from the panel to the garage which would shorten the length but I would have to figure out how to get it under the front sidewalk.

For the wire, should I run 10-2 or 8-2 UF?  If it is sheathed, does it need to be in conduit (either in the attic or buried)?

When it reaches the garage I plan on wiring it to a Siemens 30amp fusible disconnect switch and then hardwired in conduit to the compressor.  What is the difference in fusible and non-fusible disconnects? It seems the non-fusible are in the 60 amp range.

For the actual hook-up I plan on getting my neighbor who has electrical experience.  But i would like to get everything ran myself.  Thanks.

Tag.

Just looked at the breaker panel again ( mounted outside in AZ for some reason) and where the large pvc holding the main providing wire going into the ground below the panel has enough room next to it to run a conduit pipe into the wall up to the box. I'll probably try this route as opposed to the attic run. That should cut the entire length down by 20 feet. Snaking under the sidewalk should be easy enough with some pvc connected to a garden hose. And up into the garage is a piece of cake.

Really need an opinion on my specs above so I can get started tomorrow

Disclaimer....I'm not an electrician....just a homeowner who understands most things electrical.  And, I read a lot.

I have a similar compressor and it's on a 20 amp breaker.  Works fine.  

I built a shop building (not being used at the moment...future house site) and wired it up.  I planned out where my compressor will be and installed a 240 volt outlet.  I put in a 30 amp breaker for the circuit....even though 20 would work.  I installed a 30 amp just in case I buy an 80 gallon compressor in the future (probably won't but better to install the heavier wire now than to wish I did later).

I would use 10 ga wire for the circuit.  12 ga wire can handle up to 20 amps but if you're going to be putting in a compressor, I'd go with a 20 or 30 amp breaker and 30 amp capable wire (which is 10 ga).  You could use 8 ga but it would be overkill.  Not that overkill is bad........

You won't be pulling anything close to 30 amps for that compressor.  

Make sure you size the breaker for the wiring you will be installing (not your compressor).   The breakers job is to protect your wiring and prevent a fire in the case of overload.  Electric motors (like compressors) will pull extra current at startup and it's a good idea to use wiring/breaker sized at 80% of the load ( 15/.8 =18.75 amps).  Therefore, you will need to use a 20 amp breaker and you will need 12 ga wiring.

UPDATE:  I have it ran.  Took all day and still need to backfill but no one died and nothing is on fire.  Digging was a pain as the ground resembles dried mortar but I figured out to soak the ground with water and let it soak in.  Much easier.  Also, had to repair the stupid underground watering lines as I nicked it twice when digging.  Going under the sidewalk was a piece of cake.  Used 3/4" pvc with a hose connector and an angle cut on the digging end.  Really cut through the ground.

I went with 10-2 and a 30amp breaker, all enclosed in waterproof conduit (sidenote: I realize why the term "pull some wire" is not "push some wire". Getting 45' of it through the single piece conduit was very sporty).  The disconnect box went in very easy (2 screws) but fishing the conduit up was wall sucked.  Ended up cutting a bigger hole than I would have liked so I could get my meat hook into the wall to find the wire.  No compressor yet so I will have to wait to hardwire it and then hit the juice.

Conduit and wire:

Trench in my front yard:

Here is where service comes into the house and this is where the wire was ran:

Tunnel cutting tool:



And through:

Finished breaker box:

Finished (almost) disconnect:

See Article 440.
Hermetic compressors have their own set of conductor rules.
It is NOT the same as general; purpose circuits.

The breaker only protects the wires from short circuits.
The equipment protects itself.

Wires are sized to 120% of full load running current, breakers can be larger if required for reliable starting.

Just a novice, but don't you want your two hot leads running to the side of the disconnect box and then looping over the top to connect?  If the hot leads short out to the connections below them it will completely defeat the purpose of the disconnect.

This^^^

Best practice is to loop those wires around the side, up to the top, and then connect from the top down into the terminals. As shown, flipping the disconnect can pinch or rub the insulation on the wires and cause a short or failure to disconnect...

And the point you are trying to make is..............?????

It's correct. The box is setup for bottom entry and exit only and the plastic box around the contacts only has a recess on the bottom (no way to wire it from the top.) Depth perception on the pic is bad. The 2 hot leads on top jut out, as the load leads on bottom are recessed. The hot wires are not close to the load contacts.

Breaker rating and conductor size do NOT follow general purpose rules.
He has a regular motor load so see Article 430.
Look at Figure 430.1 for starters.
Table 430.248 determines full load currents based on marked HP, no mater what the motor nameplate claims.
The conductor size is 120% of the motors full load running rating.
The breaker size for a conventional inverse-time breaker (thermal magnetic) cab be up to 250% of the motor full load current to allow reliable starting.
That means you could have a breaker far larger than the wire size based on general use branch circuits.


I have a 3 HP motor (17 FLA) on #10 wires with a 45 A breaker to allow repeated starting.
The larger wires are for the starting surge based on 430.7(B) Locked-Rotor Indicating Code Letters.
The surge is over 100 amps (and I measured it after hooking up).
A clamp pm ammeter with peak hold is not hard to find any more.
Keeping the voltage up allows for faster and cooler starting (less sag on start-up).

Ahh...glad you cleared that up for everyone.

Maybe someone with a current code book will chime in and answer this question. Is it not against code to run Romex in conduit?

It can be run for short distances for physical protection.  The fill factors do not apply.

If you want to run it in a conduit system the fill factors eat you alive.
There is arguably a prohibition since the conduit articles have not been updated since the NM articles so they are not 'in sync.'

just out of curiosity, did you read the NEC on pertinent items such as,
1) wire burial depth?
2) 3 wire vs 4 wire 240Vac circuits?
3) cable in conduit derating?

ar-jedi

From what I read, 18" deep for non metallic casing.

Not sure I understand #2. I know three wire is used for dryers and large appliances where there are 2 hot, one neutral and a ground and have the 4 prong plug. 2 wire is what I used (2 hot and a ground) and hardwired to the compressor. What is 4 wire?

I ran into derating and it was confusing. I have 2 wires in a 3/4" conduit, 10-2 w/ 30amp breaker but I am not sure the derating value. It has to do with number of wires, casement size and heat correct? If you could explain please.

I did look into running UF rated wire in conduit (which is what I used) and it seems to go both ways. The wire is rated "for underground use, or direct burial." I only ran it in conduit for protection and so I didn't have to dig deeper.

If you see something that isn't correct or have other questions please ask. I want it to be correct and safe. Thanks.

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A straight 240 V load only requires 3 wires (hot-hot-ground).
A typical air compressor has no 120 V portion.
The motor is a straight 240 V load.

A mixed 120/240 V load requires 4-wires (hot-hot-neutral-ground).
There are older exceptions allowing mixed loads on electric dryers and ranges to use 3-wire.
While you can replace the appliance and use the exception, you cannot otherwise "alter" the circuit.

Your local AHJ decides what 'alteration' voids the old exception.  Some are more of a PITA than others.

Not an electrician by any means but with the addition of that breaker do you now have a completely full panel?

Usually when you only have two spots left and you need to add breakers it is either time for a sub-panel or replace some of the 110 breakers with the slimline ones that fit two breakers in the space of one so you always leave two empty spots.  A full panel will be a red flag to any home inspector if you ever decide to sell.

A red flag for what? The saying making a mountain out of a mole hill comes to mind with this post

Too late now but it would have been cheaper and easier to use individual wires when you are running conduit. 2 #12 THWN hots & 1 #12 THWN for the ground would have went in the conduit much easier than that oversized #10 UF cable. And a 20A circuit would be sufficient for your 15A compressor.

Breakers on loads that already protect themselves (like motors) are for short circuit protection of the feed wiring.
They are sized to allow starting of the equipment and have a far more liberal rating than just wire size.

A standard 'inverse time' (AKA 'thermal-magnetic) breaker can be many times the wire size rating for full load running amps.

Wires are 120% of motor full load running amps (and NOT from the motor nameplate current).
The NEC has its OWN table of horsepower to full load running current.

The breaker can then be increased to allow motor starting.
350% of full load.
Straight magnetic breakers (AKA 'instantaneous trip') are 700%.

Absolutely correct. Conduit was an afterthought because of burial depth and I already had the burial rated shiethed wire. For the size, it should be ample if I go with a larger compressor in the future.

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