Proper wiring for the new air compressor
FrankTate
| Posted in General Discussion on
Well, I finally got the addition finished. The lower level is the garage/workshop. Got a good deal on a 6hp 2 stage compressor and I need to run the electric to it now. I have plenty of room in the panel and it needs 240v. It is about a 50 ft run and I have #10 wire. Is that sufficient? Do I need to run the wire in conduit, or can I simply fasten it to the ceiling?
Also, I put radiant heat in the floor, so I can’t fasten the compressor to the floor. The compressor is a vertical 80 gal. type and is currently bolted to a wooden skid. Any ideas on how I should secure the compressor? Leave it on the skid for sound insulation and run a strap around it and fasten it to the block wall?
Thanks for any help!
Frank
Replies
" 6hp 2 stage compressor"
MANY COMPRESSOR HP RATINGS ARE MEANINGLESS. There is now a push on it get real horspe power ratings.
I need to check the MOTOR naneplate data.
What does it give for HP. And what for current.
You can't operate a true 6 HP motor on #10.
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Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
If your floor is'nt sealed yet, you can wet it so its damp, turn on the heat and pick up the impressions or ghosts of where your pipes are burried in the slab. Or glue down the pallet with a good const. adhesive. Need more info on amps. to gauge wire and breaker size. Need to run wire in conduit to be leagal or maybe run armor cable.
The plate I could see didn't give HP. Says PH1 and 182/4Y along with 240 V and 23.00 A and 60 HZ.
So, I know it is 240 volt, single phase and 23 amp draw. It doesn't show anything else. It is a Delta compressor.Frank
I am kind of guessing that it is a high eff 5 hp motor. Might be 4 plus.But without the HP numbers can't go with the code motor charts.But based on 23 amps, 50 ft then the #10 is fine.And you might want to put a 50 amp breaker on it. Actually you can go to 60, but 50 should be OK.NOTE-BEFORE PEOPLE START COMPLAINING. This is a dedicated motor circuit so the load is know. The breaker is not designed to protect the motor. It is suppose to have it's own overload protection. The breaker is designed to protect the wiring against a fault (short).And using a larger breaker means you won't have false trips when it tries to start under load.Yes, The NEC allows you run romex exposed tight against the building surface (ie, walls and ceiling). But where subject to damamge (upto the AHJ) it has to be protected by sleaving or guard strips.But some local codes don't allow it. Running conduit with a short section of flex from the wall to the compressor would be much neater looking..
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Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
#10 at 50 or 60 amps????
Absolutely.Did you read the remainder of the message?Have you looked at the NEC on MOTORS. Have you looked at the label on an airconditioner where it list wiring size and breaker size?.
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Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
So if I short a #10 wire on a 60 amp breaker it will not heat up and burn?
If you short a #10 wire on the load side of a 60 amp breaker, the breaker will trip as the instantaneous fault current will exceed 60 amps. In fact it will be more like 10,000 amps. It would be the same fault current if the breaker was sized for 15 amps. Fault current is more determined by the transformer construction and service entrance cable than anything after the branch circuit breaker. FWIW, most home breakers are rated at 65,000 amps fault current.The NEC allows this over fusing of wire because the motor should have its own protection for overcurrent (like a motor starter or thermal overload device), so the branch breaker should only see normal current or short circuit current, no overload due to plugging in a toaster....Frank DuVal You can never make something foolproof because fools are so ingenious.
The NEC allows this over fusing of wire because the motor should have its own protection for overcurrent (like a motor starter or thermal overload device), so the branch breaker should only see normal current or short circuit current, no overload due to plugging in a toaster....
True as long as you install a single, 30A receptacle. Nothing else on that circuit. That way nobody can come after the fact and plug in the 50A toaster...
dgbldr,Very true, but you bring up a good point:If the over fused conductors feed a receptacle, then the motor could be unplugged and the 50 amp toaster plugged in, melting the wires...I have only used the over fused motor wiring with hard wired motors, not plug connected. My opinion is if there is a receptacle, then branch circuit wiring methods should be employed, not dedicated motor circuit wiring methods. Hence no over fusing allowed on receptacles.Frank DuVal You can never make something foolproof because fools are so ingenious.
Thanks Bill! The electrician ran some #12 tight to the ceiling when the inspector pointed out he forgot a GFI in the new bath above the garage.
Since I am going to run it tight to the ceiling along the side of the steel beam that has been framed and drywalled, I should not have a problem.
As usual, you guys come thru! Thanks!Frank
Trying out the posting of a pic of the garage.Frank
Looks like an early Thunderbird.Frank DuVal You can never make something foolproof because fools are so ingenious.
Yup, a 55 for my wife.Frank
I hope he does have dedicated motor protection. Would the "klixon" thermal switch in the motor be sufficient?
http://jhausch.blogspot.comAdventures in Home BuildingAn online journal covering the preparation and construction of our new home.
Yes.The motor needs either internal motor protection (klixon) or a starter with with overload protection. In any case circuit breakers don't come sized with fine enough granularity for motor protection..
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Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
There is a reason that electric work ( as well as others) is considered a SKILLED trade. It's not something that can be learned from reading a book, or memorizing a few 'rules of thumb.' The electrician is forced to make a number of 'judgement calls,' based upon the information available, technical knowledge, trade practices, and experience. The NEC, being a "consensus" code, has to take this expertise into account when the rules are written. As for wire sizing, while there is a 'general rule,' there are ten exceptions specifically noted. These special conditions -compressor motors are but one- take into account reality, and make a reasonable allowance. ("Reasonable" being defined as several thousand informed parties voting on it every three years). For example, it is recognized that a motor -especially a motor starting against a load, as in a compressor- has a 'starting current' many times higher than the running current. This high current lasts but a fraction of a second; not long enough to heat up the wires, but high enough to blow a fuse or trip a breaker. Therefore, practice (and code) allow a larger than usual breaker to be used. Can that circuit later be used for some other purpose, and result in a hazardous condition? Sure it can. Anything can be abused. It seems that as soon as you make something 'idiot proof,' they come out with a better idiot. In short, if you change the question, you change the answer. I am sure that every trade can cite examples of when they've been able to set the rulebook aside, and have everything turn out OK. The danger is that Joe Six-Pack will see this, assume too much, toss the book away, and hillbilly-engineer a disaster. "But it worked last time" is a pretty lame explanation! A little knowledge IS a dangerous thing.
In my previous post I used the wrong words. I said short when I should have said overload.
It looks to me the safe way for "Joe six pack" would be to size the wire to the breaker and put in a 30 amp receptacle if the wire will fit the lugs.That way any future accidental (or not) changes and loads would be covered.
The best thing would be to hire a licensed Sparky.
Thanks and Merry Christmas
FrankTate,
My similar sized compressor stands on it's original pallet and has for the past decades (2) it's hammered away for hours on end without risk of tipping and when I get ambitous I move it to clean underneath it.. (happens ever 5 years or so). Plus it makes draing the tank so much easier!
More important than the way you mount the compressor is how you deal with the hoses.. I eventually got tired of tripping over mine and screwed a hose real into the ceiling. I can't tell you how much nicer life is with a retractable hose that will reach the roof of my three story house . (100 feet minimum length and I bought 150 simply because I knew that sooner or later I'd need to shorten it because of cuts .. (last weekend I made it six feet shorter and got rid of two splices.)
Thanks Frenchy. You are right, it does look to make draining the tank a whole lot easier! I am planning on running the piping along the ceiling and then branching off. I already have a retractable reel waiting to install.Frank
The local code will determine how you need to run the wiring. In many places, if it's a vertical run (like down to a box), you can staple it to the studs. If it's horizontal and it's below the bottom of the joists, it needs to be in pipe. If it's a horizontal run in a wall, it needs to be covered or in pipe so somebody won't hang things from it.
The gauge will be determined by what the manual for the compressor says it actually draws. I just had my garage wiring checked/brought up to code since the effin' dirtbag contractor is a big steaming POS and he wanted to make sure the wire was the right gauge so he needed the current draw specs. The guy I had come in is someone I have worked along side and he does mostly industrial electrical. I trust him and he knows how to do things in a way that they won't cause trouble later.
As people have said, the HP ratings on most motors and compressors is just marketing. It's like the old audio power output specs- 120W JBF(Just Before Fire) or 200W WLS(When Lightning Strikes).