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Old 08-15-2009, 10:46 PM   #31
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Yeah they are just giving you the maximum breaker and calling it good. If it don't start on that then it ain't gonna start.... it also keeps you from playing with breaker sizes to see what the lowest breaker you can get by with would be. I can't imagine that compressor not starting on a 50 amp breaker and frankly I think it will start fine on a 40. Not much cost difference though so I'd just follow the manual instructions if you want.

Circuit breakers are tested under UL489 (I think it's 489) for multiple inrush currents. A typical residential 30 amp inverse time breaker will hold 6 times its current rating from 2 to 6 seconds. The torque rest to start inrush back to running amps on your motor will be less than a second. Locked rotor or start current will be 6 times 21.5 or pretty close...so call it 130 amps motor inrush current at start up. To play it safe lets just say that inrush is 6 x 30 = 180 amps. That breaker will hold that somewhere between 2 and 6 seconds before tripping. If it is less it will hold longer lets say starting inrush is 130 amps which would be 6 times the nameplate fla. A 30 amp inverse time breaker will hold that from 4 to 20 seconds depending on what the circumstances are and design type of motor your starting. Just very basically explaining just to give you an idea whats going on with the breaker and start currents. The thing to remember is the maximum inrush current (much higher than locked rotor) or the current needed to establish the magnetic field is only seen briefy by the motor before it rapidly starts falling towards running amps as the motor comes up to speed. That high inrush current will actually diminish due to the cycling of the motor on the air compressor retaining residual magnatism in the motors steel core needing less current to establesh the magnetic field. The chief obstacle in getting a motor started is the locked rotor current which generally is 6 times the FLA of the motor. It is possible your existing 30 amp breaker will start that motor on the compressor. So it's worth a try IMO.

Sorry for the long wind it really is going too far technically but thought you might be interested.
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Old 08-15-2009, 11:28 PM   #32
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Thanks for breaking it down. I'll see what it does on the 30 Amp that's in there. If it trips, I have spare 40 and a 50 Amp breakers on hand, but I went ahead and picked up a 60 at the big orange box while I was there for a whip and some concrete anchors.

For what it's worth, the manual vaguely suggests that during heavy cycling, anything short of a 60 Amp breaker may trip under some circumstances, but doesn't get in to why that is. Anybody want to tackle that one? We seem to be making one very informative thread, so we may as well keep at it.

I'm gonna go make some sparks, now. What better way can a guy spend a quiet Friday night?
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Old 08-16-2009, 01:09 AM   #33
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Being more specific your nameplate shows the code letter "L". This equates to a value of 9.0 to 9.9 kva per horsepower at locked rotor. Using the mean of 9.5 KVA the calculation becomes 9.5 x 5 hp x 1000/ 230 volts which is a locked rotor current of 207 amps. Probably a big reason they want it on a 50 or 60 amp breaker. This is all revolving around NEC 430.7 and table 430.7(B).

In contrast if the motor used a Design letter we could use table 430.251(A) and the locked rotor current becomes 6 x the table 430.248 FLA of 28 amps which would be 168 amps.

Essentially what this means is that the motor rotors (for lack of a better word) are made out of steel that requires them to use a code letter for locked rotor instead of a design letter like A or B. It takes more current to establish the rotating magnetic field and consequently the LRC goes up considerably. It ends up code L is on the high end for locked rotor current for your type motor.
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Old 08-16-2009, 11:26 AM   #34
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As usual a very good discussion. What is the "Starter Kit"? The one that extends the warranty. Not the one that starts the motor.
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Old 08-16-2009, 11:32 AM   #35
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Quote:
Originally Posted by J. V. View Post
As usual a very good discussion. What is the "Starter Kit"? The one that extends the warranty. Not the one that starts the motor.
If I remember it right some compressor brands do have starter kit which it will have syentic oil plus diffrent air filter to extend the warranty on the compressor but not the magatic starter I think that what happend we may end up on wrong track with the discussion.

However that how some compressor do that.

Mine compressor do not have syentic oil at all due two reason one the size is very large { 15 HP two stage } and run very slow speed driect drive { no belt on this one } and I do change oil twice a year reguards of running hours that how I keep the crankcase very clean.
And the intake port is piped to outside to keep the chuffing noise down it is loud BTW.

Merci,Marc
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Old 08-16-2009, 12:17 PM   #36
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The 'starter kit' mentioned in this thread is synthetic oil and super duper air filters. They will extend the warranty if you buy it from them....
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Old 08-17-2009, 03:50 PM   #37
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And... It works!

I had a chance to run the compressor extensively yesterday. (I love how I can media blast now, and it actually catches up and shuts off. I used to wait in the compressor, but now the compressor waits on me. I'm loving this!)

It seems to have no problem running on the 30 Amp breaker. I had it cycling on and off for two straight hours yesterday, and not an issue to be seen. Everytime it kicks on, it's up and running at full speed within two seconds.

Slogarage, from my experience, you're identical compressor should have no problem on your #8 AWG and 30 Amp breaker. You should be good to go. Now we just need to plumb some proper hard lines for air. I don't know what you were using before, but you're gonna love your compressor.
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Old 08-18-2009, 12:57 PM   #38
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Good job.
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Old 08-20-2009, 03:57 PM   #39
 
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congrats KAdams on your install. Good to hear the 30amp breaker works for you. I still have to get it wired up, I was actually waiting to see how yours turned out.

On a side note, i know that you are using yours in a commercial application, but, how loud is it?? I've read that you can talk to someone standing next to it without shouting. Can you give some feedback??

And to answer your question about what I was using before, nothing. This is my first, and I hope last, compressor.
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Old 09-07-2009, 04:13 AM   #40
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Quote:
Originally Posted by slogarage View Post
congrats KAdams on your install. Good to hear the 30amp breaker works for you. I still have to get it wired up, I was actually waiting to see how yours turned out.

On a side note, i know that you are using yours in a commercial application, but, how loud is it?? I've read that you can talk to someone standing next to it without shouting. Can you give some feedback??

And to answer your question about what I was using before, nothing. This is my first, and I hope last, compressor.
Somehow my post in response to your question about how loud the compressor is fell off the map, and I didn't want to just not respond, even if it has been a while. Anyway, I'm sure you've heard yours by now, but in case you haven't, it's not terribly loud at all. It beats the heck out of standing next to one of those direct-drive oil-less compressors.

I think having a conversation next to it is possible, but will still requires raising your voice. I'm still using the stock air intake on mine, but experimented one day by holding a bucket over it, and it muffled the noise quite a bit. At some point in the future, I'll upgrade the intake and filter to one of the fancy muffled versions. It should be pretty good after that.

And to keep my response at least a little on the electrical topic, I've been running the heck out of the compressor, and the ol' 30 amp breaker hasn't given me any trouble at all.
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