Compressor disconnect box

[smalltown]

I heard a couple of instances of fires starting from compressors not shutting off after closing up a garage. So I wanted to add a manual shut off without opening the garage sub panel each time.

I bought a small mini 2 ckt load center http://www.homedepot.com/p/Square-D-QO-30-Amp-2-Space-2-Circuit-Indoor-Main-Lug-Load-Center-QO2L30SCP/100157760. I installed a double pole QO breaker of which I had a few laying around. I would have preferred a shut off with a "knife switch" type on/off, but the only ones I found used cartridge fuses.

That said is it ok to feed the mini load center from my garage sub panel, and then bring the wiring back into a different knockout in the sub panel to route the wires up through the top of the sub panel?

 

[MTW]

404.3 B
(B) Used as a Raceway. Enclosures shall not be used as
junction boxes, auxiliary gutters, or raceways for conductors
feeding through or tapping off to other switches or overcurrent
devices, unless the enclosure complies with 312.8.

312.8
312.8 Switch and Overcurrent Device Enclosures with
Splices, Taps, and Feed-Through Conductors. The wiring
space of enclosures for switches or overcurrent devices
shall be permitted for conductors feeding through, spliced,
or tapping off to other enclosures, switches, or overcurrent
devices where all of the following conditions are met:
(1) The total of all conductors installed at any cross section
of the wiring space does not exceed 40 percent of the
cross-sectional area of that space.
(2) The total area of all conductors, splices, and taps installed
at any cross section of the wiring space does not
exceed 75 percent of the cross-sectional area of that
space.
(3) A warning label is applied to the enclosure that identifies
the closest disconnecting means for any feedthrough
conductors.

MTW Ω

 

[MTW]

Another option for a 2 pole motor rated disconnect installable in a wall box.

2HP rated
http://www.homedepot.com/p/Leviton-30-Amp-Industrial-Double-Pole-Switch-White-R62-03032-2WS/100356941

Cut Sheet:
http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=3032-2I&section=41455&minisite=10251


5HP 2pole 240V rated:
http://www.ebay.com/itm/Leviton-MS302-DS-30-Amp-Double-Pole-Motor-Switch-Black-1Ph-2-15HP-/181881066538?hash=item2a58f4d42a:g:4J4AAOSwv0tVO5ut

Cut Sheet:
http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=MS302-DS&section=40132&minisite=10251

MTW Ω

 

[wyliesdiesels]

I would have used an AC disconnect.

 

[motofool33]

you could use a magnetic starter with a start stop button on the compressor

 

[sberry]

An even better solution is to use a ball valve on the comp, shut it in, the comp doesn't leak and doesn't turn on. As long as its charged one can even use the breaker without switching under load. There are probably as many issues with additional wiring and a crappy AC switch as are saved from adding it.

 

[Norcal]

I would have used an AC disconnect.

Can't beat the price for them. I prefer a safety switch but the OP did not want a fusible model, non-fusible would have to be sourced at a supply house, but pullout A/C discos are as economical and simple as you can get.

 

[sberry]

You have to open this box instead of that box, add another device in to the middle of a perfectly good wire to switch a switch next to each other which essentially has to have some special rules all to do something the code intends to discourage and doesn't require.
This is typical more than I realize I guess, a how to question gets good or legal technical answers but misses the most basic point of whether this is a good idea. A bit like how do I wire a used 240 fan draws an amp as a temp use in my workshop.

 

[sberry]

I heard a couple of instances of fires starting from compressors not shutting off after closing up a garage.

Were these internet instances or real life hearings?

 

[Norcal]

The mag starter that used to be on my compressor had the habit of welding contacts, always knew when it happened as the safety valve would open due to overpressure & could hear it from quite a distance.

Replaced the contacts on the starter, still continued to have the same issue, problem solved by replacing the starter with another brand, for those who may have been curious.

 

[lakeroadster]

I would have preferred a shut off with a "knife switch" type on/off, but the only ones I found used cartridge fuses.

What's your concern with cartridge fuses?

I have a Square D knife switch panel, that utilizes screw in fuses, that I have used on my compressor since 1985... have yet to have a fuse blow.

Even if the fuse does blow, just screw in another one.

 

[sberry]

One of the primary reasons to go to th trouble of running a sub in to a garage in the same room as the appliances is it simplifies the electric. How many masters would really rig this booger on a spec home or sell this to someone. Went to all the trouble to bring disconnect means and then put a booger on it,,, ha

 

[sberry]

The mag starter that used to be on my compressor had the habit of welding contacts, always knew when it happened as the safety valve would open due to overpressure & could hear it from quite a distance.

Replaced the contacts on the starter, still continued to have the same issue, problem solved by replacing the starter with another brand, for those who may have been curious.

Mine has been on for 40 yrs, maybe more. All this runs together so I cant remember exactly what service I have done but I recently blew a cap and tripped the breaker. I cant remember if I flipped the contacts but its went a long time without service.
A guy that serviced equipment would see more but not sure how adding another switch would help. Its a little like a car too, if one is using it often the issues get serviced before failure or the failure will fault a breaker if the belts are adjusted. I have always considered air as one of the utilities, worked around it all my life and really cant think of a single incident extra equipment would have helped prevent.
Some of it was the outright cause of every problem with it they ever had after that. Now one is swamped with good ideas from everywhere and its really eaiser than ever to get away from good fundamentals.
I guess that the fact it is loud is some safety but sticking with the breaker to the wire to the machine to start with and see how it goes

 

[sberry]

I brought a sub in so I was done having to add local switches, simple as that. If I was to run a separate branch circuit from the basement then we would need disconnect and might even make sense to switch it at that point.

 

[soj]

I just put a heavy duty toggle switch in a handy box, wired in series with the pressure switch. No wear and tear on the circuit breaker, no having to open the pull out box, just flip a switch.

For now it is mounted on the compressor. When I move the compressor out of the shop to it's own little shed (to cut down on noise), I will relocate that switch next to the man door to make it convenient to turn off when I leave for the day.
jp

 

[sberry]

You don't need to do anything else but hook it to the breaker in the panel. It doesn't get any better than that. If the compressors was remote it would need a means of disconnect there.

 

[smalltown]

Tough crowd today . I appreciate all the comments. Even if I don't agree it makes me look at things from other angles. Yes they are real world happenings. Just wanted something very simple (yes without opening another cabinet) to shut off the compressor when I left the garage, and locked up.

lakeroadster your comments about your knife switch disconnect has me taking a second look at http://www.homedepot.com/p/Square-D-30-Amp-240-Volt-Two-Pole-Indoor-Light-Duty-Safety-Switch-with-Neutral-L221N/100190295?MERC

It wasn't available in store, but can be ordered. It would fit the bill, and no extra cabinet to open just push the handle down.

P.S. If I have't already posted so I want to say I really do appreciate all of you, and how you help me.

 

[lakeroadster]

That is very similar to the Square D unit that has served me well over the years. I turn it on when I enter the shop... and turn it off when I leave for the day.

Happy Trails...

 

[sberry]

The best insurance is a ball valve. The only reason for this comp to start once its reached pressure is a leak. It wont jump on in the middle of the night if there is no air used. Shut it in with the breaker for extended vacations I spose but mine aint used the breaker from a dead stop but for a dozen times in 40 yrs.
If its pumped when you leave and shut breaker it will prolly be the same next time, turn breaker on and when you use air it will run as normal but if you are a daily user like me and most shop rats the air is just on.
I disconnect tools from the hoses when I am done and wind up. I pick up cords as soon as I am done with them too. 10x as effective a safety as an extra disconnect. Same for limiting quick connects. Many home/hobby types and as many pros set them up wrong and have 2x as many as needed.

 

[smalltown]

Just for clarification before I need to reverse something. According to the NEC 312.8 as mentioned above by MTW (thanks MTW), and reading Mike Holt's interpretation. I want to be sure you agree that I am ok ( well maybe not that I am ok, but my wiring diagram is ).

If I read the code correctly it is ok for me to add a small conduit stub off of my sub panel within which to wire the feed from the circuit breaker to the switch, and then return from the switch back into the sub panel, and exit via conduit at the top.
Provided that I do not exceed 40 % of the cross-sectional area of the (sub panel) space.

 

[Cmreschke]

That is correct. Fmi what's the current draw on the cokpressor?

 

[zmaxmotorsports]

I would have used an AC disconnect.

 

[smalltown]

CMreschke can't tell you at the moment as I just shifted all my garage contents to one side to allow me to run some conduit. One I can get things back in order I'll check the plate on the compressor. Off hand it's just a single stage 60 gallon compressor from Home Depot that was on sale at the time.

 

[finn]

The mag starter / switch on the old Champion compressor I bought wouldn't always shut off (as disclosed by the seller) so it does happen.

A few minutes with a file and some contact cleaner fixed it, but I'd be uncomfortable without a convenient way to cut all power to a compressor when not in use.

I installed an A/C disconnect on the (rarely used) electric oven I use for powder coating. Again, it provides a positive power disconnect within reach of the device in case something goes wrong, like a fire.

 

[Cmreschke]

If less than 20 amps put it on a toggle switch. No opening boxes to get to the shut off. Can get a 2 pole switch if 240 volt.

 

[smalltown]

Yes it's 240, and I am getting a two pole switch. I like the idea of simply pulling the handle down when I leave the garage. I wanted to be sure I was ok with my proposed wiring as depicted in my drawing.

 

[wyliesdiesels]

U only need to switch one side of the coil. The other side should be running through the overload relay.

 

[smalltown]

Was able to take a few photos off of the information plate on the compressor, and tank decal.

The instruction manual specifies 240 Volt single phase 13.5 Amps.
Also states a 20 Amp minimum requirement, fuse type time delay. So far haven't located any time delay circuit breakers (Square D QO). maybe this is for the older screw in fuses?

Furthermore although the manual says 3.7 HP the sticker on the tank indicates 3.2 HP

I was hoping to wire with 12 Ga THHN wire, solid conductor. I will be placing a conduit box close to the compressor to wire from there to the compressor. In my searching I see mention of flexible conduit: it appears you buy that and insert whatever gauge your circuit needs? If flexible conduit is what I need, how much slack do I allow?

Also on the motor decal on the bottom what are they referring to?
" Line to ungrounded side of supply when grounded supply is available"


Lastly since I will in the same time frame be adding power to a new hanging propane heater can I assume that any information about a wiring method is applicable to both the compressor and heater?

 

[wyliesdiesels]

Is that a portable (ie wheeled) compressor?

If so then i would use #12 cordage and a 6-20r and p for the hookup.

 

[smalltown]

Wiley no it's not a portable compressor.