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Discussion Starter #1
I just bought a Craftsman 5 hp 33 gallon compressor. I ran a seperate 20 amp circuit with 12 awg wire. When the compressor first starts it blows the breaker. Flip the breaker and restart the compressor no problems. So far, after the intital breaker flip the compressor cycles off and on just fine. There is nothing else connected to this circut. Any ideas? The manual calls for at least a 15 amp. 20 amp should be more than enough. Should I just replace the 20 with a 30?

You thoughts/ideas would be appreciated.

Kevin
 

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I've heard of this with Craftsman compressors on other boards....

12ga is supposed to be fused at 20a, but, for a dedicated motor circuit, it is okay to go as high as 30. That would be for THHN, Romex would be lower.

I'd try a 25a breaker and see if that doesn't trip, but the smart thing to do might be to bump it up to 10ga and then you can go to a 30a breaker.
 

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If it's a 15 amp motor, you should be using a 25 amp breaker and the correct wire to go with it.

When an electric motor starts, the amp draw skyrockets until the motor can get up to speed.

The breaker needs to be big enough to handle this "spike", but not too big.

General rule of thumb is:

Motor amp x 1.7 = Breaker size.
 

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I had something like this happening to my non craftsman compressor. I upgraded the cord to the compressor and problem went away, might be worth a try, but I'd for sure bump the breaker up too.
 

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Discussion Starter #5
Thanks for the replies.

The manual for the compressor states;

Certain air compressors can be operated on a 15 amp circuit of the following condtions are met:

1.) Voltage supply to the circuit must comply with the National Electrical Code.
2.) Circuit is not used to supply any other electrical needs.
3.) Extension cords comply with specifications.
4.) Circuit is equipped with a 15 amp circuit breaker or a 15 amp time delay fuse.

If any of the above condtions cannot be met, or if operation of the compressor repeatedly causes interuption of the power, it may be necessary to operate it from a 20 amp circuit. It is not necessary to change the cord set.

Since the walls to the shop have already been closed off, it would be a challenge to run 10 gauge.

Would it be safe to run 25 amp on 12 gauge?

Do you think there is something wrong with the compressor or my wiring?
 

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My compressor tripped my breaker each time I tried to run it the first year I had it. Only in the winter though below a certain temp. The next year I changed oil in the compressor and it hasn't tripped again since.
 

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Discussion Starter #7
That really sounds like what is happening here. When it is cold it trips the breaker. However, this unit is oil-free.
 

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12 ga might be a little small depending on the length allso the breaker . running it for any length of time will shorten motor life
 

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The cold for whatever reason even seems to also affect the oil free compressors.

If the motor is not a capacitor start type, that could also be the reason for the large amperage draw.
 

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Oil free compressors ussually have grease packed, sealed bearings on the connectinmg rods. They are just as hard as a lubricated compressor to get running on a cold morning.
 

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What is the total length of the #12 wire? Max length is 45.4' inorder to keep voltage drop below 3% per the N.E.C. Also as a 5HP induction type motor operating at 230VAC has a F.L.C of 15.2A also per the N.E.C. So if you multiply 15.2 by 125% you get 19A which would be the rating of the branch circuit protection, the circuit breaker. You should be fine with 20A and #12 unless you have a length greater than 45', a bad connection which is producing heat, bad CB, or some type of problem with the motor or compressor itself.

Regards,
Jaime
 

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I use a small 4 Gal twin stack for work and for the shop. When it is cold out I have learned to pull the defeat plug until compreser gets to temp may be 10 secs and then it works all day long work or shop.
 

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Check your line voltage. The amp draw of the breaker is rated at 115 or 120 volts depending on the breaker. If the line voltage is lower this increases your amp draw. 12 guage wire will handle a 25 amp breaker. You MUST upgrade to 10 guage if want to go to a 30 amp breaker. I don't believe you'll trip the 25 amp breaker unless your line voltage is less than 108 volts. The voltage needs to be checked at the compressor. Hope this helps.

Thanks for the replies.

The manual for the compressor states;

Certain air compressors can be operated on a 15 amp circuit of the following condtions are met:

1.) Voltage supply to the circuit must comply with the National Electrical Code.
2.) Circuit is not used to supply any other electrical needs.
3.) Extension cords comply with specifications.
4.) Circuit is equipped with a 15 amp circuit breaker or a 15 amp time delay fuse.

If any of the above condtions cannot be met, or if operation of the compressor repeatedly causes interuption of the power, it may be necessary to operate it from a 20 amp circuit. It is not necessary to change the cord set.

Since the walls to the shop have already been closed off, it would be a challenge to run 10 gauge.

Would it be safe to run 25 amp on 12 gauge?

Do you think there is something wrong with the compressor or my wiring?
 

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All of the above have some good ideas. The first thing that I would do if all else checks out is to replace the 20 amp breaker with a NEW 20 amp breaker.
Most people don't know it, but breakers can "wear out", especially if thy are constantly tripping.
If the breaker was an old one, it could be tripping at a lower treshold than it is designed for. Additionally make sure that ALL the connections are bright and tight.
Signs of discoloration/heat is notification that all is not well.
I would be careful of running #12 wire with that starting load. A fire & the loss of your shop would be a tall price to pay for an inadequate electric service. :eek:

Britt
 

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Discussion Starter #15
navion, thanks for the info. Here is what I have read. I can get the links if it helps. All of the websites I have read state that a 2hp motor requires 30 amp breaker and 14 wire when 1/2 of the circuit distance is 25' I'm not sure about the circuit distance if that calculates round trip or not but one way I'm at about 30'

I will check to make sure the outlet the compressor is hooked to is nice and tight and showing no signs of heat discloration. Over the weekend I replaced the 20 amp with a 30. I couldn't find a 25. It is not tripping anymore. My rational here is that once the motor was up and running, the 20 amp breaker never tripped. Long story short, it seems as if the motor on startup was pulling more then 20 amps but 12AWG should be able to handle this brief surge... shouldn't it?

Thoughts?
 

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navion, thanks for the info. Here is what I have read. I can get the links if it helps. All of the websites I have read state that a 2hp motor requires 30 amp breaker and 14 wire when 1/2 of the circuit distance is 25' I'm not sure about the circuit distance if that calculates round trip or not but one way I'm at about 30'

I will check to make sure the outlet the compressor is hooked to is nice and tight and showing no signs of heat discloration. Over the weekend I replaced the 20 amp with a 30. I couldn't find a 25. It is not tripping anymore. My rational here is that once the motor was up and running, the 20 amp breaker never tripped. Long story short, it seems as if the motor on startup was pulling more then 20 amps but 12AWG should be able to handle this brief surge... shouldn't it?

Thoughts?

12 gauge wire (romex or thhn) will handle a 25 amp breaker max. You are taking a big chance running a 30 amp breaker on 12 or 14 gauge wire. You are correct that there is a surge at start-up on the motor. But there are other conditions that will also increase amp load such as bearings, clogged filter in compressor intake, etc. It's just not worth the risk. IMHO
 

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Discussion Starter #17
This is the website I used to calculate the wire size.

http://www.csgnetwork.com/wiresizecalc.html

Wire type - Copper
Circuit Phase - Single
Circuit Voltage - 120
One half circuit length - 30
Total circuit amperage - 30
=
Required minimum wire size #12

Am I missing something?
 

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This is the website I used to calculate the wire size.

http://www.csgnetwork.com/wiresizecalc.html

Wire type - Copper
Circuit Phase - Single
Circuit Voltage - 120
One half circuit length - 30
Total circuit amperage - 30
=
Required minimum wire size #12

Am I missing something?
I'm only saying that I wouldn't go with the minimum wire size. If you want to run a 30 amp service for your compressor, that's fine, just use 10 gauge wire for piece of mind. I am an Electrical Engineer and I know for a fact that a length of 12 gauge wire carrying 30 amp continuous service will get hot. I just don't want your shop to catch fire over a light piece of wire. Only trying to help.
 

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Discussion Starter #19
Southern Bred:

I do appreciate your help and advice. Do you think that the motor is pulling 30 amps continously? I don't think so since after the intial load, the 20 amp breaker was not tripping. Thoughts?
 

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kkirt1, you keep asking good questions. It seems to me you are over-thinking the situation, or trying to convince yourself you don't need to buy thirty feet of 10 gauge wire.
Quit trying to save a few bucks and buy the wire everyone advises, or swap out the breaker to a 25 amp.
It isn't that your compressor is pulling a 30 amp load continuously, because you know it is not. But, the fact is that it COULD, since you have a 30 amp breaker. So in that case, the WIRE becomes the weak link, so to speak, not the breaker, and the wire will get hot and possibly fail, without tripping the 30 amp breaker.
You always want the breaker (or fuse) to be the limiting factor in the event of a short or overloaded circuit, not the wire.
Your sig says you've got a nice truck with some nice mods, so I'm guessing you can swing for the 30 ft hunk of 10 gauge wire, so ... :grd:
Good luck.
 
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