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Old 08-29-2007, 10:22 AM   #1
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magnetic starters for compressors


Hi, can someone tell me the purpose for a magnetic switch or starter for a compressor? Doe's it help in reducing wear on the motor? is it really needed? I plan on getting a 220v 1 ph. 2 stage and want it to last longer then me. Thanks Jim

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Old 08-29-2007, 10:31 AM   #2
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magnetic starters for compressors


Hi,
It is basically a "safety" feature. It is much easier for a protective device on your compressor, ie.. pressure switch, possible temp switch, etc, to allow the MAGNETIC aspect of the contactor cease providing power to that system, thus reducing the possibility of malfunction and injury.
You definitely want a magnetic contactor on a compressor.

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Old 08-29-2007, 10:40 AM   #3
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magnetic starters for compressors


Thanks J, now where does the switch go? between pressure switch and power ? or between the motor and pressure switch? can you configure a magnetic switch to operate more then 1 appliance? and what type of switch do I need for these applications single ph or 3 ph? Thanks Jim
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Old 08-29-2007, 11:24 AM   #4
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magnetic starters for compressors


The pressure switch is located on the tank.
The magnetic starter is AFTER the power disconnect switch. The pressure switch is a device which is connected to auxiliary contacts to control the contactor (open/close).
That starter is for the compressor only ... not multiple devices.
That contactor and pressure switch should already be on the compressor skid. Did you get this at some flea circus .... that someone stripped down .... I'd be really careful with these pressure vessels .... many a good ole boy has blown them up ....
You need a SINGLE Phase, 2 POLE Contactor....
Size .... you have to know the specs of your motor ..... there are tons of them out there ....

Be really careful ......
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Old 08-29-2007, 12:22 PM   #5
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magnetic starters for compressors


Thanks , no have not gone to any flea circus's yet . Lowes has the compressor . in many cases they just sell the compressor without any of the other items. Switches power, power cord and filter separator sold extra. Thanks For info. Jim
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Old 08-29-2007, 01:38 PM   #6
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magnetic starters for compressors


That doesn't sound right.
Those components are an integral part of a compressor system.

Well, atleast it's Lowes....not Dog Fighter Depot ..... like the owner Arthur Blank ( HD & Falcons) didn't know about that stuff for 7 years ..... wanna buy a bridge ....

Those guys would sell their own sisters into a brothel to make a buck ....
I'm starting to think drug dealers have more scruples than some of those professional sports team owners, and we don't to pay for their stadiums.

I hope he doesn't get a dime back from Vick ... he was stupid enough to give him 130 mil ..... he deserves to lose every penny of it ..... maybe he'll think twice about pushin him around in a chair and smiling ....

GO LOWES.....!!!!

Last edited by JGarth; 08-29-2007 at 01:49 PM.
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Old 08-29-2007, 10:49 PM   #7
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magnetic starters for compressors


A pressure switch is unable to switch larger motors (There should be a chart w/ the rating on or under the cover.) so a magnetic starter is used to switch the motor and provide overload protection.
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Old 08-30-2007, 12:09 PM   #8
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magnetic starters for compressors


Listen to Norcal, magnetic starters are used for switching heavy loads. Unless your compressor is some industrial unit with a large hp motor, the pressure is more than enough. I'm sure the unit went through UL testing first and if it needed a mag contactor, they would have stated that.
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Old 08-30-2007, 06:05 PM   #9
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magnetic starters for compressors


most resdentail or light duty pressure switch are genrally rated for 15 amp some are marked for 20 amp but majorty of them useally marked for hp rated switches

for 15 amp pressure switches the rating for motor useally 1-2 hp @120 v
for 240 volt useage typicaly 2-3 hp range

for 20 amp the 120 v will be the same as above but 240 volt hp rating go up to 5 hp max if i recall it right


Anything more than 5 hp i stronly recomed that have a mangatic switch work together with the pressure switch for twofold reason

1] will provided overload protection [ most med to larger motor useally dont have thermal protection on this ]

2] the mangatic concates is far beefier and can handle the starting and shutting off load espcally with higher HP motor

{ this for anyone use 3 motors must use the magatic switch per code }

most 5 HP motors on 240 volts useally draw about 28 amp range so you can see why need a magantic switch will be nessecary

Merci, Marc
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Old 09-01-2007, 12:50 PM   #10
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magnetic starters for compressors


The 1 HP motor at 240 volts will pull approximately 3.8 amps while running. However, the starting (inrush) current will be appoximately 30 amps. A pressure switch would not last long if it started the motor.
Let the pressure switch control the starter and the starter control the motor.
If the motor does not have built in overload protection, you can add one to the starter.
Another option is a manually operated starter. Push button type.
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Old 09-01-2007, 04:02 PM   #11
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magnetic starters for compressors


If it is a magnetic starter it has a overload relay, no O/L relay then it is a contactor, a magnetic starter is contactor combined with a overload relay.
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Old 09-10-2007, 09:23 AM   #12
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magnetic starters for compressors


Further to the already posted comments, when sizing the contactor you must use its 'AC3' rating (in this case). Eg your compressor motor is rated at 10 Amps (FLA). If you look on the contactor, it will show you its AC1, AC2, AC3 & AC4 current ratings. Ensure that the AC3 rating is minimum of 10 Amps.
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Old 09-10-2007, 11:19 PM   #13
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magnetic starters for compressors


Quote:
Originally Posted by elkangorito View Post
Further to the already posted comments, when sizing the contactor you must use its 'AC3' rating (in this case). Eg your compressor motor is rated at 10 Amps (FLA). If you look on the contactor, it will show you its AC1, AC2, AC3 & AC4 current ratings. Ensure that the AC3 rating is minimum of 10 Amps.
Those rating are for IEC type starters/contactors, a NEMA type is more reliable ,and rugged and easier to specify.
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Old 09-11-2007, 11:36 AM   #14
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magnetic starters for compressors


Norcal,
IEC magnetic starters and contactors do not come standard with the OLR installed, unless it is a manual type. Usually you purchase the starter and overload seperately. With NEMA you do get the OLR if you request it, but you don't get the heaters.

By the way. In this business starters and contactors are the same thing. Magnetic or Manual.

Quote:
Originally Posted by Norcal View Post
Those rating are for IEC type starters/contactors, a NEMA type is more reliable ,and rugged and easier to specify.
Norcal,
While you may be correct that NEMA builds a heavier duty control, do not dismiss the advantages to IEC contactors/starters.

1) Smaller (takes up less than half the space)
2) Cheaper (Can cost 1/10th the price of NEMA)
3) Adjustable overload relay (NEMA you must change the heaters)
4) Reliability in regards to price.
5) Ability to add several aux contacts to the side and front of the control.
6) Much easier to specify. By Current. NEMA you have to know current then chose NEMA size control.

Note: Control, Contactor and Starter for this writer means the same thing...

Last edited by J. V.; 09-11-2007 at 11:40 AM.
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Old 09-11-2007, 07:41 PM   #15
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magnetic starters for compressors


Quote:
Originally Posted by J. V. View Post
Norcal,
IEC magnetic starters and contactors do not come standard with the OLR installed, unless it is a manual type. Usually you purchase the starter and overload seperately. With NEMA you do get the OLR if you request it, but you don't get the heaters.

By the way. In this business starters and contactors are the same thing. Magnetic or Manual.



Norcal,
While you may be correct that NEMA builds a heavier duty control, do not dismiss the advantages to IEC contactors/starters.

1) Smaller (takes up less than half the space)
2) Cheaper (Can cost 1/10th the price of NEMA)
3) Adjustable overload relay (NEMA you must change the heaters)
4) Reliability in regards to price.
5) Ability to add several aux contacts to the side and front of the control.
6) Much easier to specify. By Current. NEMA you have to know current then chose NEMA size control.

Note: Control, Contactor and Starter for this writer means the same thing...
IEC controls are just more to fill our landfills, throwaway junk. NEMA is a lot easier to specify, all you need is to know the voltage, HP, # of phases. BTW most NEMA starters come w/ adjustable O/L relays with the exception of Cutler-Hammer "Freedom Series" starters and their "heater packs". Siemens/Furnas ESP 100 and SQ D Motor Logic are a couple of examples.

Good results are useally not possible when somebody tries to put 10 Lbs. of manure in a 5 lb. bag.

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