when is a magnetic starter needed for building big air compressor

[hondacivic247]

So I currently have a older 1988 Rolair k25 pump with a 60 gallon vertical tank that has a century 5hp 3450rpm motor driving it. This compressor doesn't use a magnetic starter box I has a 30/50 amp plug that plugs into the receptacle. Anyways over the coming NY winter I want to build a bigger and badder air compressor that makes between 20-30cfm as my k-25 pump is making around 16cfm at 130psi.

So here's my question If I pick up a older quincy, t30, champion, Kellogg pump or one of the older pumps and hook up a 184 frame 5hp Baldor single phase motor, will I need a magnetic starter box. I don't want to get in over my head with wiring as I know the basic's I just wired up 10g 10-2romex from my panel with a double 30amp breaker to a 30/50amp receptacle for the Rolair 60 gallon I got right now. I don't have a disconnect box or anything installed as I'm only 10ft from the panel in my home garage.

I'm wondering how hard it will be to wire in this magnetic starter to the pressure switch and if it needed.

 

[AndeiH]

I have a 5hp 80 gallon quincy that draws around 22 amps and it doesn't have a magnetic starter. I don't use it constantly so this works great for me. What ends up happening is the switch gets "worn" out and needs to be replaced. A magnetic starter is more robust and handles the amperage better. If I had my compressor in a shop or used it constantly I would have opted for the magnetic starter.

 

[scw1991]

most industrial rated compressors have at least a 5HP motor with dedicated motor mag starter. However, if you don't have a mag starter, then all the current must pass through the pressure switch to stop/start the motor. There are pressure switches commercially available to handle this current but I think as far as reliability is concerned, the life expectancy of the pressure switch contacts would be far less than the contacts on a mag starter.

In addition, the mag starter also incorporates use of thermal heaters for the motor in case of overload. If the motor you are planning on using does not have a thermal overload reset button, you'll need to use a dedicated motor mag starter.

The Square D 8911 dedicated motor mag starter is one example.

http://www.ebay.com/itm/NEW-Square-...166?pt=LH_DefaultDomain_0&hash=item2c6538fb36

 

[G_P]

If the motor has no built in thermal protection then you need a mag starter. But If it was me, I would use one on anything 5hp or more. Just to save the wear on the pressure switch contacts.

 

[404]

To protect the pressure switch you might use a relay similar to this one...

http://www.digikey.com/product-detail/en/7-1611004-4/PB1646-ND/2053669

Surplus ones would be even less expensive.

Regards,
404

 

[EOC_Jason]

Anything larger than 5HP you *really* need one... For a 5HP motor it would be preferred but not always necessary.

 

[C96]

The motor you speak of: 184 frame 5hp Baldor single phase motor will not have thermal protection. Therefore, you must use a mag starter. A mag starter is always the best way to go period!

All good quality compressors will have them. It’s the cheaper lower end units that use the internal thermal protection (red button) motors without a mag starter.

 

[hondacivic247]

Yeah my current 5hp has the red button and 4 capacitors with no mag switch it runs off the pressure switch like you guys are saying.
I know the baldor 5hp motor doesn't have one built in so I'll have to look into the cost of one of those I don't want to go over 1000 bucks I've seen some baldor 5hp 184 frame motors going for 400 I figure I could find a old quincy or champion pump on Craigslist for 400-500 and I already have the 60 gallon vertical tank.

Even tho the baldor motor is a different frame it's still pulling around the same amps as my current 5hp so I wouldn't need to rewire from my panel I got 10g 10/2 romex currently or would I need to go to a lower gage wire? Also how hard is it to wire a mag starter?
I

 

[Pumpman1968]

If the motor has no built in thermal protection then you need a mag starter. But If it was me, I would use one on anything 5hp or more. Just to save the wear on the pressure switch contacts.

Great rule of thumb right there.