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Air Compressor power question

bbaley

Plastic
Joined
Jan 21, 2018
Location
SW Washington, in the sticks sorta
Hi,
I am installing a new air compressor in my shop, and started out connecting it to an existing 240v 30A circuit.
But when it starts I get a bit of momentary light dimming from the startup power surge. not good.

So, I am guessing maybe some or all of the following may need to be addressed:
1. It is currently a 30A breaker
2. currently 10/2 wire (romex)
3. perhaps a hard start capacitor kit might help as well ?

The compressor is an IR SS5L. The specs show 22.5A max running load, 100A startup and recommended 60A breaker.

The shop subpanel is only 100A
IR recommends a 60A breaker

So aside from upgrading the breaker to a 60A, and the wire to 8/2 or 6/2, I am wondering if there is a hard start capacitor option that may help due to the potential startup INRUSH current being nearly what the subpanel is ??

Thanks for any input/knowledge you may have!
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
You aren't going to do much to help your issue. Is it that bad you can't live with it?

If you were really going all-out, you'd use a VFD to start the compressor motor. There would be essentially no inrush then. But the controls and cost would be 'real'.
 

Strostkovy

Stainless
Joined
Oct 29, 2017
Best you can do is a timed unloading valve to keep the motor unloaded while it starts, but I doubt that will help all that much.
 

scsmith42

Aluminum
Joined
Jul 28, 2020
Location
New Hill, NC
Upsizing the wire and breaker (but mainly the wire) will help reduce the current inrush. Air compressors are notorious for their high startup current requirements.
 

Strostkovy

Stainless
Joined
Oct 29, 2017
Also I think a hard start capacitor kit wouldn't help you. The motor would attempt to draw more amps to make more startup torque, dropping your voltage even more.
 

CITIZEN F16

Titanium
Joined
May 2, 2021
That is typical of an air compressor that starts and stops. Just leave it on it's own dedicated circuit off the main panel.
 

eKretz

Diamond
Joined
Mar 27, 2005
Location
Northwest Indiana
That's a 5 HP single phase motor. I have a similar IR compressor in my garage rated about the same, also running on single phase. I run the compressor on 10AWG and it's on a 30A breaker. Been that way for about 20 years now with no issues. The garage subpanel (60A) has 4AWG run to it from the main panel. I'd leave it alone if it's not gonna mess up your lights.
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
The motor inrush is fixed...wire size won't help. Using a larger wire will minimize the effect of the inrush, but it won't change the inrush. and it will minimize it only to a small degree....especially when it's a short run.
 

bhigdog

Stainless
Joined
Jul 20, 2005
Location
Eastern PA
Associated question. Shop has a 100 amp panel. 5HP single phase compressor motor on it's own breaker. When it runs the over head lighting flickers just enough to be noticeable. Did it with high output flourescents and still does it after I converted to LED's. Any thoughts? Sorry if this is a hijack...Bob
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
Since he says Romex, it's 10/2. If it were rubber jacketed SJ, it would be 10/3. Go figure.

But then...surely there is not Romex running to the air compressor directly....I bet it has a rubber jacketed cord of some sort.
 

kineticmx

Aluminum
Joined
Mar 10, 2014
Location
United States, CT
Associated question. Shop has a 100 amp panel. 5HP single phase compressor motor on it's own breaker. When it runs the over head lighting flickers just enough to be noticeable. Did it with high output flourescents and still does it after I converted to LED's. Any thoughts? Sorry if this is a hijack...Bob

Pretty typical, fluorescents and led are both going to be sensitive to voltage fluctuation which you will get running a big compressor. Potentially an indicator of the motor run caps failing


Sent from my iPhone using Tapatalk
 

ratbldr427

Stainless
Joined
Mar 21, 2006
Location
jacksonville,fl.
I have a 5hp 2stage off a 100amp panel,single phase, in my home shop. Never noticed my shitty lights dimming. Use a knife switch(50amp breaker) to feed the compressor.Starts runs and cycles with no flicker?

Seems to be exactly as the poster has.Whats the difference?
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
A 100 amp panel is plenty....if you are 50 feet from the 134kv step down transformer that is 50 feet away from the 1.1GW nuclear generating plant that does nothing but feed your shop.

A 100 amp panel is not enough...if you are 2 miles from a 600v step down transformer being fed by a 134kv transformer that is 4 miles away that is 190 miles from the 25MW hyrdo plant that also feeds a small town.
 

Tony Quiring

Titanium
Joined
Nov 5, 2008
Location
Madera county california usa
You have a voltage drop.

Simple ohms law.

Current through a resistance causes a drop in voltage across the resistance.

Digital voltmeter is too slow.

Your lights however, AR working fine for this.

Do lights dim in house?

No?

Lights on sub panel dim so voltage drop between main panel and shop panel.

If yes, then drop between supply and main panel.

Often the main breaker can get oxidized where it connects to buss.

Depending on your panel, you may have access to the wire on the meter side of main breaker.

Carefully attach a test light to this connection and ground other side.

When you fid the spot that does not dim as much then inspect it.

You can use your light, one side to each side of breaker, any light indicates problem.

We have 7.5 hp single phase with proper unloader, lights indicate compressor starting but just tiny amount.

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