Air Compressor Magnetic Motor Starters

[N_Jay]

Help.
I need a lesson on these.
I have a 1PH 220V 5HP compressor.
Right now I am using the pressure switch to directly engage the motor. (25A 5HP rated switch)
Some say I need a Magnetic Motor Starter or I will be burning up switches.
How bad of a problem is this?
The starters I have seen just look like high current "contactors" (relays) to take the load off the switch. Most also have some type of overcurrent protection.
On Zoro they seem to start about $150, but on Amazon and ebay they seem to be in the $50 to $75 range.
Is there really much more to these than just a high current contactor and a overload device?

Why not just put a $20 contactor in a small NEMA box and let the panel breaker work about overcurrent? Ii is not as if my garage compressor is running unattended in a back room.

 

[manwithtools]

They are indeed simple contactors with thermal overLOAD protection built in. The overCURRENT protection is supplied by the breaker in your load center.

Overload protection is different than overcurrent. It protects the motor from thermal damage that can occur long before a breaker would trip from overcurrent.


Zoro is simply Grainger's online store and they are typically over priced on electrical control items by quite a bit.

Get a name brand one - Square-D, Siemens, Allen Bradley, Eaton, etc sized appropriately for your compressor motor and they should last a long time.

 

[N_Jay]

Zoro did not seem bad once you get to the main-line US brands, especially when you get a coupon.
Amazon and Ebay have a good selection fo imported units with decent reviews.
It is hard to justify a $150 starter on a $100 compressor.

 

[American Locomotive]

Magnetic starters typically contain a contactor/relay and an "overload" or "heater" protection device. As mentioned, overloads protect the motor while circuit breakers protect the wiring.

You can get mag starters pretty cheap if you shop around - especially if you look for used ones on e-bay or similar. It's important that you make sure whatever magnetic starter you get is configured for whatever your motor's full-load amperage is.

 

[N_Jay]

I guess one is on my list.

 

[manwithtools]

As AmericanLocomotive mentioned and I want to reinforce - when shopping for the contactor make sure that the overload section is the right size for your motors FLA. They have relatively arrow ranges of coverage and you need the right one to avoid nuisance trips or false protection.

Some versions are adjustable and some use replaceable "heater elements". Also, you may stumble onto three phase starters that are priced reasonably. You can use them in single phase installation, but sometimes you need to wire them a bit differently (basically two phases will get wired in series) so the phase loss detection is not activated.

 

[N_Jay]

Thanks
The electrical wiring part is not my issue.
It just seems that machinery systems don't always follow normal electrical engineering logic.
For example, why are they called "Magnetic Starters"?

The issue with 3 phase units is you have top go up a couple of "HP" ratings to get the right current rating.

I can see why a large motor that runs fully unattended needs a overcurrent cut off.

 

[Movin/on]

So is this mag starter a 3 phase wired for single? Each side has a jumper from the bottom lug to the middle. This is the pressure switch that doesn't seem to cutout properly, sometimes it does and sometimes not.

Movin/on

 

[manwithtools]

Thanks
The electrical wiring part is not my issue.
It just seems that machinery systems don't always follow normal electrical engineering logic.
For example, why are they called "Magnetic Starters"?

The issue with 3 phase units is you have top go up a couple of "HP" ratings to get the right current rating.

I can see why a large motor that runs fully unattended needs a overcurrent cut off.

It's called a "Magnetic Starter" because that's the way a relay or contactor works - it uses electrical current flowing thru a coil to create a magnetic field that "energizes" the starter by a solenoid action that closes the contacts - thus allowing current to flow to the motor. It opens the contacts in the opposite manner.

This is opposed to a "Manual Starter" that utilizes a mechanical mechanism operated by a person to close / open the contacts.

Important distinction its the magnetic starter can be remotely controlled with lower voltage control circuits from far away if necessary.

Machine control follows very common engineering logic, it's just that it's not widely understood in it's application.

Again this is not for over current protection, it's for over load protection. Semantics, I know but important none the less to get the terminology correct.

 

[manwithtools]

So is this mag switch a 3 phase wired for single? Each side has a jumper from the bottom lug to the middle. This is the pressure switch that doesn't seem to cutout properly, sometimes it does and sometimes not.

Movin/on

Hard to tell from the picture, but possibly is a three phase pressure switch. I don't think that that is your problem. But if you have a single phase motor, you could change to single phase pressure switch when you replace it. Again, if it's three phase or not, should not effect it's functionality.

 

[N_Jay]

So is this mag starter a 3 phase wired for single? Each side has a jumper from the bottom lug to the middle. This is the pressure switch that doesn't seem to cutout properly, sometimes it does and sometimes not.

Movin/on

That looks like just a contactor. (wired for single phase)


EDIT:" Looking closer probably a pressure switch. They both seem to use similar style contact arraignments.

 

[N_Jay]

It's called a "Magnetic Starter" because that's the way a relay or contactor works - it uses electrical current flowing thru a coil to create a magnetic field that "energizes" the starter by a solenoid action that closes the contacts - thus allowing current to flow to the motor. It opens the contacts in the opposite manner.

This is opposed to a "Manual Starter" that utilizes a mechanical mechanism operated by a person to close / open the contacts.

Important distinction its the magnetic starter can be remotely controlled with lower voltage control circuits from far away if necessary.

Machine control follows very common engineering logic, it's just that it's not widely understood in it's application.

Again this is not for over current protection, it's for over load protection. Semantics, I know but important none the less to get the terminology correct.

I certainly understand what relays are, and contactors are just high current relays.

I have even built "starters" for running three phase motors (at reduced capacity) from single phase lines.


As for overload vs. over current. Both measure current over time. Just seems that local one is set closer to the machine threshold and the breaker is set to the circuit threshold.

 

[md21722]

Something like this for 5 HP

https://www.ebay.com/itm/SQUARE-D-MAGNETIC-STARTER-5HP-SINGLE-PHASE-208-240-VOLT/281738313386

 

[Citation]

Help.
I need a lesson on these.
I have a 1PH 220V 5HP compressor.
Right now I am using the pressure switch to directly engage the motor. (25A 5HP rated switch)
Some say I need a Magnetic Motor Starter or I will be burning up switches.
How bad of a problem is this?
The starters I have seen just look like high current "contactors" (relays) to take the load off the switch. Most also have some type of overcurrent protection.
On Zoro they seem to start about $150, but on Amazon and ebay they seem to be in the $50 to $75 range.
Is there really much more to these than just a high current contactor and a overload device?

Why not just put a $20 contactor in a small NEMA box and let the panel breaker work about overcurrent? Ii is not as if my garage compressor is running unattended in a back room.

How many amp is the motor? I'm asking because for a while the hp numbers were way over spec'ed. It's not unusual to find one of the "5" hp compressors has a 15A 230v motor. From what I've seen and read 5hp is the limit for traditional pressure switches. So you will see low end 80 gallon compressors with motors near but typically under 20 amps switching with a pressure switch. I have seen some 22-23A motors directly controlled by the pressure switch but most in that range use a mag starter.

If your motor has a breaker built it (typically a red button on the motor) then you only need the starter to physically switch the current. You don't need it for motor protection. In higher power setups the mag starter has some over current and over temp protection for the motor. This is why you will hear people say the starter has to be sized for your motor.

Based on what you have said I'm guessing your compressor came from the factory with the motor directly switched. If so and if you haven't had any trouble don't need with it.

 

[N_Jay]

Based on what you have said I'm guessing your compressor came from the factory with the motor directly switched. If so and if you haven't had any trouble don't need with it.

I'ved got no idea what came from the factory other than 60 gallon vertical tank and (probably) a Chinook/Rol-Air 18 CFM (K28) pump.

I replaced the pressure switch when I got it as the old one looked bad.
The pump will build pressure at a full 18CFM without the motor sounding over loaded so I am fairly sure it is a "real" 5HP electric motor. I did not get any current measurements, but that is on my list.
I had to replace a belt sheave and decided to slow it to about 15CFM. (And the sheave I needed was at full price and the next size down was on ebay cheap).

I did not notice a reset button on the motor. My guess is it had a starter that never made it to the last owner.

Seems the guy I got it from bought it (or was given it) from where he worked when they upgraded, and he never got it hooked up and running.

 

[Citation]

I'ved got no idea what came from the factory other than 60 gallon vertical tank and (probably) a Chinook/Rol-Air 18 CFM (K28) pump.

I replaced the pressure switch when I got it as the old one looked bad.
The pump will build pressure at a full 18CFM without the motor sounding over loaded so I am fairly sure it is a "real" 5HP electric motor. I did not get any current measurements, but that is on my list.
I had to replace a belt sheave and decided to slow it to about 15CFM. (And the sheave I needed was at full price and the next size down was on ebay cheap).

I did not notice a reset button on the motor. My guess is it had a starter that never made it to the last owner.

I would check the motor plate to be certain but it sounds like this is a motor that should have one.

 

[John Timmins]

Very helpful. I am shopping for a magnetic contactor myself. I will post a picture of my motor nameplate. I have seen USA made magnetic contactors on ebay for $130 or so.

 

[N_Jay]

https://www.amazon.com/dp/B00Y4X7J44/?tag=atomicindus08-20

 

[Bert_]

https://www.amazon.com/dp/B00Y4X7J44/?tag=atomicindus08-20

Those WEG starters actually aren't bad. Even for IEC gear they are CHEAP. It isn't built like a NEMA but then neither is the price. Will last a long time in a home shop.

 

[N_Jay]

Also looking at some of the NEMA style import stuff.
The reviews seem OK for hobby use.
Heck, once I get the box, I can always replace a contactor for about $15 to $20.

 

[Bert_]

Also looking at some of the NEMA style import stuff.
The reviews seem OK for hobby use.
Heck, once I get the box, I can always replace a contactor for about $15 to $20.

Not sure what you mean by "nema import suff".

The cheap euopean plastic starters are called IEC. The weg pictured above is this style.

NEMA starters are built with quality 1st. Many times they outlast the equipment they are running even in industrial environments. These are not cheap new, a size 2 which would run a 5hp 1 phase motor is going to be around $500 new. Not practical to buy a new one for home use, I would not be afraid to buy a used one though.

 

[N_Jay]

I was looking at the metal box enclosure imported starters, like these;
https://www.amazon.com/dp/B00Y1OZTFM/?tag=atomicindus08-20

They are probably not actually NEMA type boxes, but are more like it than IEC or DIN style.

 

[Bert_]

I was looking at the metal box enclosure imported starters, like these;
https://www.amazon.com/dp/B00Y1OZTFM/?tag=atomicindus08-20

They are probably not actually NEMA type boxes, but are more like it than IEC or DIN style.

That's an IEC starter, I'd be more inclined to go with the WEG starter linked above since they have a pretty good reputation.

FYI in this case NEMA and IEC refers to the starter itself not the box. Enclosures also have nema ratings for the environments they are rated for. For example you can get an IEC starter in a N1 (nema 1) box. Or a nema starter with no enclosure.

Clear as mud?

 

[N_Jay]

I didn't realize that NEMA specified starters and contactors. I am (way too) familiar with their enclosure specifications. I assumed that in general NEMA and IEC were being used to describe the mounting.

Seems to me, that unless you are getting a used part at a substantial discount, or plan on replacing contacts and coils. rater than a whole contactor, buying an IEC starter properly sized in more economical.

 

[Bert_]

For home use an IEC starter is by far the more economical choice. If it was powering something that gets used hard in an industrial environment then the NEMA stuff starts to make sense. It will handle multiple starts an hour everyday and still last 30+years, plus they can be rebuilt. The IEC stuff won't do that and when it wears out you have to throw it away, but it is also a lot cheaper to replace. The IEC stuff might last 20 years with occasional use.

 

[American Locomotive]

All of our European equipment at work uses IEC contactors. They're used on 5-7.5 HP screw pumps that typically see 2-3 starts per minute. Many of them have over a million cycles on them. I think Siemens rates them for something like 25-30 million cycles.

The trick we found with IEC contactors is that they have very little wiggle room in their ratings. They're typically rated based on full-load current and in-rush current. If your motor is within the full-load current, but has an in-rush just 10-15% higher than the contactor's rating - it will fail. As long as you stay within their ratings, we rarely see them have problems.

We have some very old machines with 30 year old Allen-Bradley IEC contactors still truckin' along.

 

[manwithtools]

IEC contactors are perfectly fine for any home or industrial application. You simply need to read the fine print on their application. If you have high duty cycles, it's always better to up-size to the next available size.

I've had IEC contactors go over 300,000 cycles with no issue. They were always one or two amperage ratings above what was obvious.

NEMA specifications - starters and Intrusion Protection is so out of date, it's almost not relevant anymore.

 

[John Timmins]

I'm thinking of this for my 3 HP single phase 240V air compressor :
https://www.ebay.com/itm/Elimia-ACM...ressor-Motor-Starter-Nema-4X-NEW/372312260748

So is the circuit breaker in my electric panel box enough protection ? I also have a knife switch with 2 fuses.

 

[Citation]

I'm thinking of this for my 3 HP single phase 240V air compressor :
https://www.ebay.com/itm/Elimia-ACM...ressor-Motor-Starter-Nema-4X-NEW/372312260748

So is the circuit breaker in my electric panel box enough protection ? I also have a knife switch with 2 fuses.

Why not just use a pressure switch?

 

[6PTsocket]

They are indeed simple contactors with thermal overLOAD protection built in. The overCURRENT protection is supplied by the breaker in your load center.

Overload protection is different than overcurrent. It protects the motor from thermal damage that can occur long before a breaker would trip from overcurrent.


Zoro is simply Grainger's online store and they are typically over priced on electrical control items by quite a bit.

Get a name brand one - Square-D, Siemens, Allen Bradley, Eaton, etc sized appropriately for your compressor motor and they should last a long time.

That Zoro is part of Grainger is very interesting. On many items they are far cheaper, though Grainger customer prices vary with their buying volume. I just priced TB Woods v belt pulley at Zoro for 8 and change that was around 15 at Grainger. Funny that Grainger discourages non business sales while Zoro advertises on ebay and Walmart.com for lower than the undiscounted Grainger prices.

Sent from my SM-G900V using Tapatalk

 

[farooq12]

you can easily find magnetic contactors on ecommerce sites..

 

[N_Jay]

That Zoro is part of Grainger is very interesting. On many items they are far cheaper, though Grainger customer prices vary with their buying volume. I just priced TB Woods v belt pulley at Zoro for 8 and change that was around 15 at Grainger. Funny that Grainger discourages non business sales while Zoro advertises on ebay and Walmart.com for lower than the undiscounted Grainger prices.

I think Zoro was started separately and then picked up by Grainger. (I could be wrong).
I understand it runs separately other than using Grainger as its "warehouse".

Not a whole lot different than a car dealer that also sells parts at a discount on the Internet.

 

[manwithtools]

That Zoro is part of Grainger is very interesting. On many items they are far cheaper, though Grainger customer prices vary with their buying volume. I just priced TB Woods v belt pulley at Zoro for 8 and change that was around 15 at Grainger. Funny that Grainger discourages non business sales while Zoro advertises on ebay and Walmart.com for lower than the undiscounted Grainger prices.

Sent from my SM-G900V using Tapatalk

Yeah, the pricing doesn't make any sense whatsoever. I think they discovered to sell direct to the consumer, they needed a lower sales price. They didn't want to dilute their overall pricing structure at Grainger, so they spun off Zoro so they could keep pricing to their commercial accounts higher.

It's an interesting strategy, Sometimes with the 20% off sales, Zoro can get competitive. There is generally shipping and tax to factor in, so there can be less expensive alternatives at the end of the game.

From a bit of research, it seems Zoro has helped Grainger increase their bottom line. Zoro was started by Grainger, not acquired from what I can recall.

 

[N_Jay]

Apparently Zoro works hard to keep the "Start Up" mentality of the company.

It is not that hard to see how they can run a different pricing structure. They are probably a lot leaner on customer support than Grainger, and all that has a cost.

I have a friend who started the Internet sales department for a car dealership's parts department back in the late 90's.

We spent a lot of time talking about how the business runs and how the costs structure was developed.