Compressor hook up .

[sphelps]

I took this that he had a 60 amp sub-panel in his shop or garage fed from the house.

That's what I have ...

 

[bigdee]

Correct...I understand that part about 10 gauge up to the outlet from the compressor.

So now from the breaker side...So it's ok to have 10 gauge from a 30A breaker to a 60A outlet? Is the outlet required to have a label saying 30A max?

I haven't looked at the NEC code you just quoted...going to look at that now

Nec states that breaker size shall be limited by the amperage capacity of the conductors in a branch circuit. Receptacles and disconnects can be rated above but not less than breaker capacity. Now Article 430 throws a spin on that rule if motor has thermal overload protection. The thermal O.L in the motor or motor starter IS the over current protection for the conductors going to motor. The breaker becomes short circuit or locked rotor protection. Therefore on a motor circuit the conductors CAN be derated to less than breaker capacity. Motor conductors are sized at motor full load amps plus 25%......a 60 amp breaker is fine in his application. The branch circuit short circuit and ground fault protection device using an inverse time breaker is sized at 60A, according to 430.52
Circuit protection = 22A ? 2.50 = 55A, next size up 60A [240.6(A)]

 

[sphelps]

For some reason it doesn't seem smart to run a 10 ga wire to a 60 amp breaker /plug . Unless as you say the thermal overload on the motor will keep the wire from melting and catch my garage on fire before the 60 amp breaker trips ... What if the overload switch malfunctions ?

 

[bigdee]

For some reason it doesn't seem smart to run a 10 ga wire to a 60 amp breaker /plug . Unless as you say the thermal overload on the motor will keep the wire from melting and catch my garage on fire before the 60 amp breaker trips ... What if the overload switch malfunctions ?

Thats what the nec is for..... your protection. It doesn't makes sense to plug in a chinese lamp with a 18 guage wire into a 20 amp outlet either,does it? I have installed and authorized hundreds of motor circuits using the NEC as my bible. That 60 amp breaker will trip instantly if motor shorts out. I have never seen a thermal overload fail except in a fail safe mode.

 

[dolluper]

Is that a pup panel you have in the garage powered from the house .underground? or above either case 10 is to small not safe

 

[bruceb58]

No outlet if your talking about the electrical hook up ... It's wired strait into a sub panel box ..

OK..that's what I didn't understand.

 

[bigdee]

No outlet if your talking about the electrical hook up ... It's wired strait into a sub panel box ..

OK that clears things up. Question; are you doubling up on breaker that also feeds welder outlet? Does sub-panel have space to add another breaker? If you no longer have a need for a welder your ok but you can not double up circuits on a single breaker. Also you should not wire directly to panel without having a disconnect switch or receptacle close to the compressor. 10/3 NM (romex) cable is correct size.....max allowed breaker size is 60. If you no longer need welder you can reduce breaker size if it makes you feel better. Most 5hp compressors recommend at least 40 amps to handle starting current. If panel does not have room for an additional circuit and you still need the welder your only legal choice is to use the welder outlet for either one....but not both at same time.

 

[sphelps]

Wire from house to sub panel 4 ga aluminum
60 amp breaker at main panel .
6 space sub panel with 50 amp breaker for welder and the 25 amp for the compressor ..
I had thought about a disconnect or switch for the compressor but did not add one thinking I could just flip the breaker off when not use int .
I could add one if you think it's nessessary ..

 

[bigdee]

Wire from house to sub panel 4 ga aluminum
60 amp breaker at main panel .
6 space sub panel with 50 amp breaker for welder and the 25 amp for the compressor ..
I had thought about a disconnect or switch for the compressor but did not add one thinking I could just flip the breaker off when not use int .
I could add one if you think it's nessessary ..

Your good. Breaker used for disconnect ok if within sight of compressor and labeled. If you have nuisance trips you can increase breaker size.....25 amps is marginal, I would have used a 40.

 

[HT32BSX115]

Your good. Breaker used for disconnect ok if within sight of compressor and labeled. If you have nuisance trips you can increase breaker size.....25 amps is marginal, I would have used a 40.

Just went out and measured mine using a Fluke 373 Clamp-Meter. . Starting current momentarily spiked to 110A and and then settled at 20.6A, and then eventually 21.0A when the pressure got to 135 PSI and it shut off.

Momentary spikes are nearly impossible to read accurately with either a digital or analog meter. The most accurate way would be with a shunt and a scope.

Either way, momentary spikes will not trip regular circuit breakers.

I used a 30A breaker. Your 25 is marginal but you're still 5A above what the motor will be drawing. If it doesn't trip (and it doesn't get hot) I probably wouldn't change it unless it starts tripping.

 

[bigdee]

Just went out and measured mine using a Fluke 373 Clamp-Meter. . Starting current momentarily spiked to 110A and and then settled at 20.6A, and then eventually 21.0A when the pressure got to 135 PSI and it shut off.

Momentary spikes are nearly impossible to read accurately with either a digital or analog meter. The most accurate way would be with a shunt and a scope.

Either way, momentary spikes will not trip regular circuit breakers.

I used a 30A breaker. Your 25 is marginal but you're still 5A above what the motor will be drawing. If it doesn't trip (and it doesn't get hot) I probably wouldn't change it unless it starts tripping.

You just demonstrated why a 25A breaker is too small. That large inrush current is beating the h*!! out of that breaker.
Life is so simple if we follow rules and recommendations.

NEC rule= #10 conductors with breaker no larger than 60 amps
recommendation by 5hp compressor manufacturer = # 10 conductors with 40 amp breaker

 

[HT32BSX115]

You just demonstrated why a 25A breaker is too small. That large inrush current is beating the h*!! out of that breaker.
Life is so simple if we follow rules and recommendations.

NEC rule= #10 conductors with breaker no larger than 60 amps
recommendation by 5hp compressor manufacturer = # 10 conductors with 40 amp breaker

Actually I didn't. since didn't measure it. As I indicated above, It's not possible to measure inrush with my Fluke 373 ....... but they do have other models that will They're probably as accurate as a scope and shunt.

Fluke has a pretty good description on AC motor inrush and how an inrush current can be several (4-10) times higher than the steady state running current but still not open a circuit breaker.

I would not ever suggest under-size conductors under any circumstances. But if I only had a 25A breaker laying around unused, I probably would run it too. (until it started tripping And it might in the summer time since they should be derated in hot ambient temps)

I've had the 30A on mine for a couple of years now and my compressor runs several times per day. If it ever fails, I'll replace it with whatever I have in the junk box.

 

[bigdee]

Actually I didn't. since didn't measure it. As I indicated above, It's not possible to measure inrush with my Fluke 373 ....... but they do have other models that will They're probably as accurate as a scope and shunt.

Fluke has a[url]http://en-us.fluke.com/trainin.../clamp-meters/why-inrush-current-matters.html pretty good description on AC motor inrush[/URL] and how an inrush current can be several (4-10) times higher than the steady state running current but still not open a circuit breaker.

I would not ever suggest under-size conductors under any circumstances. But if I only had a 25A breaker laying around unused, I probably would run it too. (until it started tripping And it might in the summer time since they should be derated in hot ambient temps)

I've had the 30A on mine for a couple of years now and my compressor runs several times per day. If it ever fails, I'll replace it with whatever I have in the junk box.

Like I said...the answer is in the NEC article 430. 125% of his full load amps is 27.5 amps that makes it wrong right there. Secondly, breakers are oversized to handle the start current....tripping has nothing to do with it. The physical components of the breaker are only rated to carry a safe current level. Besides nuisance trips a undersized breakers contacts can become welded closed which is a big safety issue. I would never authorize that installation.

 

[HT32BSX115]

Like I said...the answer is in the NEC article 430. 125% of his full load amps is 27.5 amps that makes it wrong right there. Secondly, breakers are oversized to handle the start current....tripping has nothing to do with it. The physical components of the breaker are only rated to carry a safe current level. Besides nuisance trips a undersized breakers contacts can become welded closed which is a big safety issue. I would never authorize that installation.

Just referred to that publication. You are absolutely right. The circuit protection suggested for a single phase 220 motor drawing 20-21A full load would be a 40.

I wouldn't run a 25 either, nuisance trip or no...... :thumb:

 

[sphelps]

Well I can certainly change it out ... I may have a 40 laying around my garage ... I might pick up a filter on my way home tomorrow .
https://www.harborfreight.com/38-in-desiccant-dryer-with-oil-removal-filter-69923.html Probably work ok for now ...

 

[Leardriver]

I just wired up a Dewalt 60 gallon single phase, and used a Square D 30 A and yellow 12 gauge wire.

 

[HT32BSX115]

I just wired up a Dewalt 60 gallon single phase, and used a Square D 30 A and yellow 12 gauge wire.

According to Home Depot, it draws around 17A when running. so a 30 is probably A-OK.! Is a leardriver similar to an impact driver?

 

[MTboatguy]

Well I can certainly change it out ... I may have a 40 laying around my garage ... I might pick up a filter on my way home tomorrow .
https://www.harborfreight.com/38-in-...ter-69923.html Probably work ok for now ...

I have the same one and it works fine, never had a problem with it at all.

Pick up one of their cheap auto drain valves as well, they work good, I have one on mine and only had to replace the rubber disc in it once.

https://www.harborfreight.com/automatic-compressor-drain-kit-68244.html

 

[bruceb58]

I used to have a HF water separator. Started leaking after awhile and bought a much better quality one.

 

[sphelps]

I got this one to try .. https://www.harborfreight.com/industrial-air-filter-regulator-68247.html
Ok lets say hypothetically this guy wasn't thinking at the time and wired his compressor with #10 solid wire .. Hind sight would have been to get braided wire ..
And lets say that while he was moving the compressor around to re- position it the wire sheathing was compromised by the wire clamp going into the sub panel box .. Other than just waking him up the 25 amp breaker did exactly what it was supposed to do . Trip .. Now lets say he had a 40 amp breaker and the same thing happened .. Would the bigger breaker have tripped ?