Air Compressor reserve tanks

[crazy steve]

Wiring a compressor

First, don't worry about whether it's a two stage or single stage; it's all about CFM at a high enough pressure to do whatever your trying to do. But sandblasters DO require high CFM. Anything you can easily get in your garage will only blast for about 10-15 minutes before you'll want to let the compressor 'catch up'. But you almost can't have a too-big unit...

As far as electrical power, a standard 40 amp dryer circuit will supply 32 continuous amps (you are REQUIRED to de-rate by 20%). But when hooking up a motor load, you also have to take into consideration current inrush; they can draw up to 500% of nameplate amps until the motor is up to speed. So in your case, try to find out a 'minimum circuit breaker' or 'ampacity' number in amps for the unit you're looking at. If it's under 40 amps, you're good to go. If you can't locate that, then look at the motor nameplate. It should have a FLA (full load amps) number on it, and don't exceed 15 amps or you'll have nuisance tripping and eventually burn up the breaker. Wire size of #10 should be fine for a cord. You do have to be careful as some of these 'consumer' motors are 'specials' and have a higher inrush than a 'standard' one. A typical standard 3 HP 1-ph 220v motor will need a 35 amp breaker and draw 17 amps under full load. If you're completely confused, send a PM and I'll try to help you.

Thirty + years in the electrical industry...

'78 E original owner

[crazy steve]

Wiring a compressor

I'll also note that I didn't read all the previous posts, and some of the advice you were given will result in a illegal installation....

'78 E original owner

[planedick]

Notice

The ground and neutral is the same in the breaker panel. It's a code thing. Look at it closely and you'll see what I mean. Dryer plugs have three wires as do the electric stoves. The two opposite wires are 110 VAC each and the center is the neutral/ground. Been doin' electrical all my life, my business, and a good cord such as a 10/3 SO type with a plug and receptical should work just fine. #12 wire isn't the best as the distance would reduce power and heat the cord.

[79XS11F]

Thanks Planedick and I also got the same input from an Electrician I spoke to this evening and gathered up everything i need for the job. So if any one else comes across a set up that calls for 15 AMP, 220 Volt you will need the stuff in the photo as well as the correct wiring to get from the panel box to the device box.



Rob

[planedick]

Actually...

I don't believe that is what I would use. I doubt that setup would serve as use for a motor that size. The proper plug and and recepticle as found on the electric range and use #10 wire plus you should use a proper 30 A breaker.

[79XS11F]

I don't believe that is what I would use. I doubt that setup would serve as use for a motor that size. The proper plug and and recepticle as found on the electric range and use #10 wire plus you should use a proper 30 A breaker.

Well ... there's no sense in debating this with you if your an electrician.
What I have here is ... a 2 pole 2 X 15 amp breaker, The handles are bridged, same as AC units. The plug and receptacle are both rated for 15 amp / 250 volt and the wire for the plug cord is Oil resistant / 14 gage which is one size larger in DIA then what is required to meet the code. The wiring from the box to the device box will be what I already have except i will not use the red wire. It is dryer sized stuff.
Do keep in mind that this compressor will not be running 8 hours a day like in a working garage.
Why would I want a "true" 30 AMP breaker for a 15 amp device? From what I have been told if there is an issue on ether line both will open because the handles are bridged?
Rob

[79XS11F]

OK here we go again ....

I have received a few messages from folks on the board who are telling me that the way I intend to hook this compressor up is not right and or is a fire hazard. here are some photos of the electoral info plate and horse power spec. The plate on the side of the motor is the same as the one on the front of th compressor ... it'd just smaller and notes that the motor is non reversible. As can be seen in the pic the wiring from the switch to the motor is the same size as the wire I got for the plug.
here's the pics.





Rob

[79XS11F]

OH ...and the wire I have to go from the panel box to the plug box is 10/3
Rob

[Rasputin]

strange

I find it strange that the electric motor does not have a FLA rating on it as well. Every electrical motor of any size I have seen does have this on it. Maybe a Canadian thing. I am not an electrician so I dont know how to hook it up. I just want to be sure you are safe and happy once you are all hooked up. The motor you have may have a couple capacitors on it and under that cover may have additional amperage stickers. The FLA is full load amps and that is what it needs to start the motor under load. JAT

[DGXSER]

Rob,

I will preface my repsonse with the facts that I am NOT a registered electrical engineer, or a lisenced electrician. The issue with a motor load is that there can be an "in-rush" current or amperage when the motor is first turned on that can greatly exceed the rated load. That is the only reason some may suggest that at 15A you might be pushing it.

That being said, the double pole 15A breaker you are planning to use should be fine IMHO. #10 is a good wire to pull in my opinion. If the outlet you are using is rated up to 30A use, then I would not hesitate to put it in. A range type outlet is usually rated at 50-60 amps and would be overkill in my opinion. Not wrong, just overkill.

As to the wire from the outlet to the compressor, again, I would make sure the plug end connector you use is rated for up to 30 amps. I would probably also use #10 wires in the plug wires to the compressors Jbox. Basically, this gives you the ability to upsize the breaker only in case the in-rush current is more than the 15A can take without redoing the entire circuit. Again all of this is JMHO.

FLA is the in-rush current mentioned. What I tend to see is MCA = Maximum Circuit Ampacity and MOCP= Maximum Over Current Protection. The MOCP is the size breaker typically used.

[79XS11F]

I find it strange that the electric motor does not have a FLA rating on it as well. Every electrical motor of any size I have seen does have this on it. Maybe a Canadian thing. I am not an electrician so I dont know how to hook it up. I just want to be sure you are safe and happy once you are all hooked up. The motor you have may have a couple capacitors on it and under that cover may have additional amperage stickers. The FLA is full load amps and that is what it needs to start the motor under load. JAT

Just checked it and thee is no FLA rating on it. What we did see is rather low amperage draw when the motor starts up with the higher draws being when it starts working to increase the tank pressure but it did not throw the breaker even once. She's hooked up and good to go as soon as I fasten it to the floor :-)
Rob

[DGXSER]

Awesome Rob, Happy compressing

[crazy steve]

Wiring a compressor

To avoid a super-long post, I'll just point out several things...

1. ANY inverse-time circuit breaker HAS TO BE DE-RATED to 80% of it's indicated size ALWAYS! Attempting to run one at 100% of it's rating will result in tripping, fast breaker failure, and fire hazard. THIS DE-RATING IS A CODE REQUIREMENT!! So, a 15 amp breaker is really a 12 amp, a 20 = 16, a 30 = 24, etc. The 'time-delay' breaker you made mention of is a specialty 'motor' type and would likely cost you 5-6 times as much if you can even find one to fit your residential panel (which I doubt).

2. The '6 1/2 Peak HP' is a advertising/selling number and has no basis in fact. This MAY be a semi-accurate indication of how many amps the motor draws when starting though. It takes 746 watts to produce 1 HP unless they've changed physics when I wasn't looking, assuming 100% efficiency. So your '6 1/2 HP' will require 4849 watts and at 220 volts, that's 22 amps MINIMUM. This is still a too-low number in the real world; the code requirement for sizing a inverse-time breaker serving a motor is it should be AT LEAST 300% of the 'Full Load Current' which is the number shown on the tags, in this case, 15 amps.

If there's any interest, I could post a full-blown tutorial on connecting garage equipment that will put you very close, but you still may have to check local codes for any oddball requirements. I'm recently retired, but I was a fully-licensed electrician for 30+years.

'78E original owner

[79XS11F]

Thank you for the input Steve and if that breaker even pops once I will indeed replace it with a larger size unit.

On a different note now that this puppy is leveled, on blocks with rubber dampers and anchored to the floor it does in deed vibrate the entire floor when it is running. It was no where near as noticeable when it was just standing on the concrete floor. Perhaps I should bolt it to a flat dolly that has lockable wheels?
Rob

[fredintoon]

Doing a Brough

Hi Rob,
your compressor saga has inspired me to (finally) install a drainage boss & valve on the (formerly propane) air tank of my homebuilt compressor.
Without that inspiration I would most likely never gotten around to doing it.
Which brings us to George Brough and the way that Brough Superiors were always completely assembled "in the white" and when every little part was seen to fit & function properly then and only then was it completely dismantled for painting & plating before reassembly and road test.
Having to remove the tank to weld a half-coupling on it's belly I then decided to "do a Brough" and completely tear the thing down to do a paint job.
So right now the various parts are scattered all over the garage painted John Deere green instead of the previous natural iron oxide and until the compressor is reassembled the Buick has to shiver outside in -16ºC.
I truly did not realize how handy the compressor was until I couldn't use it.
With no air supply I had to dismantle and will have to reassemble without using the air ratchet and I had to paint it at appalling cost with rattle cans instead of using the paint gun.