Magnetic Contactor

[Cruzan80]

I am sure there is an easy solution to this, but having trouble getting the search to cooperate. Recently picked up a static phase converter, and it had this thrown in. The phase converter itself will be easy enough to wire (2 hots in, 3 out).


Wanting to figure out a way to add the contactor in, so I can use the static converter with a spare motor to convert to a rotary version. The static is sized appropriately for the motor, and the idler motor is big enough to cover all downstream motors.


I get that the plugs on the side (hard to see in the picture are incoming/outgoing current, and when the coil on the bottom is energized, it "pulls down" the contacts. What I am having trouble with is the DIY version, building from scratch (previous wiring has always been able to follow a wiring guide for theachine with a mag contactor), and the fact that it is a 24v coil. Each side of the coil has two silver prongs pointed up, which I know will connect to a NO and NC switch, for start/stop. Does anyone know of a basic "off the shelf" On/Off switch that I can buy, that can step down from the 120V incoming to the 24V the coil needs? Would be open to the idea of getting two individual buttons, but would need to figure out a safe housing for them to be held/wired.
Or would it be easier to simply buy an entirely new mag contactor, rated for the power I need, with On/Off already part of it?

 

[jhelrey]

RIB relay?

 

[Cruzan80]

Not familiar with those. Quick look shows it may be a way to get the 24V I need for the coil, but it would still need a NO/NC contacts?

 

[dogdog]

Not sure about the whole problem you have... but the contactor you shown are just any ordinary 24Vac contactor found in HVAC systems specifically the ones on the compressor units outside. Cheap $10 to $30 Item I think. I got a bulk load for $50 on ebay, new pull from system because some one didn't like the COO...

anyways it's just a 2Pole single throw contactor with normally Open contacts. the 2 silver prong on each sides are for the control coil taking 24vac as input... supposedly work with DC also but never tried.... Not even sure if NC(normally Closed) contactors are common in these.

 

[Cruzan80]

I am wanting to use this to start/stop the motor for a rotary phase converter. What I am looking for help with is how to wire to control coil, and options for buttons to do so.

Or if it isn't worth it to mess with this particular option for it.

 

[wyliesdiesels]

wait. backup. you want to use THAT contactor to switch the incoming power to the idler motor in a rotary phase converter? guaranteed that contactor is way small and its not HP rated but just for shits & giggles, what is the HP rating on the idler motor?

 

[Cruzan80]

Phase converter says it pulls a max of 22A for 1ph. I understand that code says to use HP, not FLA, but in this case I am using the limiting factor of the phase converter. 5HP idler motor, will be powering no more than a 2HP motor under load (both 3ph).

 

[dave*99]

That is a 2 pole contactor. A Start/Stop latching circuit uses 1 pole of a contactor as part of the control circuit. So a 3 phase contactor will have 4 poles on the contactor. If your intent it to have a start/stop latching circuit using a 2 pole contactor, there will only be 1 pole available for the motor circuit.

Am I missing something?

 

[Cruzan80]

The sides where power comes in/out each have two spade terminals per line. So I can pull power from one and still have it control the switch/coil.

I am planning on using this BEFORE the static converter, so incoming 240V 1ph.

 

[Cruzan80]

And before this goes off the rails, I did ask in the OP if this would be appropriate, or if it was easier to simply buy a new mag starter AIO. This came with the converter, so someone somewhere thought they could make it work.

 

[dave*99]

And before this goes off the rails, I did ask in the OP if this would be appropriate, or if it was easier to simply buy a new mag starter AIO. This came with the converter, so someone somewhere thought they could make it work.

If you want a latching start stop circuit and to control 2 legs of a 240V circuit, you will need a contactor with 3 poles.
So yes a mag starter for a 5 HP motor is in order.

 

[Cruzan80]

Not latching, but momentary for the start stop. 5HP is 30A, so not wire why this @ 25A is so bad. The idler will never be under load itself, and the others are going to be 2-3HP max (one at a time).

I know it is not code (not HP rated), but current plan will have a 6-30 to the wall, and a 14-20 out the other side to tap into. This is so it can be moved as needed.

 

[dave*99]

Maybe I don't know what you mean by momentary.

A start/stop latching control circuit uses 2 momentary push buttons. Start button is normally open and stop button is normally closed. As shown in the schematic in post 8. It's called a latching circuit because when you push the start button it latches on and will remain latched until you push the stop button and break the latching current to the coil.

The reason the for HP ratings is motors are inductive loads. They are not purely resistive - where current is the only item of concern.

In a motor circuit the contactor needs to make and break the current from the motor. There is a greater chance of arcing etc. with an inductive load. The contacts must be rated appropriately. At start up, that 5 HP motor has all the inductance of a 5 HP motor......

 

[Cruzan80]

Gotcha. I was thinking you meant latching as "latched on", even with loss of power. We are talking the same thing. The motor is a 5HP 3ph, but the static converter reads 22A 1ph for FLA, which is how I was sizing things (25A for contactor, 30A breaker).

For arcing, etc you are meaning with regards to contactors, not plugs, correct? I understand the logic behind plugs and arcing, but am ok with the risk (single man shop, will not be unplugging while on).

 

[dave*99]

I mean arcing in the contactor. It's the same effect.
You may be able to control someone pulling the plug but the contactor contact points see that inductive kick every turn on and turn off.
This erodes and pits the contacts, they eventually make poor contact and can overheat/burn.

 

[wyliesdiesels]

the problem with using an improperly rated contactor is the contacts in the contactor will start to become pitted from the arcing and will eventually cause a bad high resistant connection causing your motor to intermittently work and/or chattering of the contactor.

why not just buy the properly rated contactor and be done with it?

 

[RPH]

I mean arcing in the contactor. It's the same effect.
You may be able to control someone pulling the plug but the contactor contact points see that inductive kick every turn on and turn off.
This erodes and pits the contacts, they eventually make poor contact and can overheat/burn.

the problem with using an improperly rated contactor is the contacts in the contactor will start to become pitted from the arcing and will eventually cause a bad high resistant connection causing your motor to intermittently work and/or chattering of the contactor.

why not just buy the properly rated contactor and be done with it?

Both of these guys are correct on the arcing and point failure. Worst case scenario is they weld closed. Now, you have to have the alternative disconnect. Pulling a plug due to the inductive kick will cause arcing at the next point of disconnect.
Rather that be a disconnect box then a plug on the wall.
Get the correct parts, do right and keep it a one man shop. Instead of there was a man’s shop here.

 

[Cruzan80]

Let me start by saying I am not trying to argue with you guys.

However, I am not sure how to rate the contactor. The phase converter and the motor both show amps under 25A. Would the contactor say 5HP on it, or should it be a specific level of amps (1ph version or 3ph version?). Not trying to cheapen out on this, just trying to figure out the correct way to do this. As I said, this contactor came with the phase converter (used purchase), hence why I thought it may be acceptable. I have seen pitted contacts before, and am familiar with the effects.

Both of these guys are correct on the arcing and point failure. Worst case scenario is they weld closed. Now, you have to have the alternative disconnect. Pulling a plug due to the inductive kick will cause arcing at the next point of disconnect.
Rather that be a disconnect box then a plug on the wall.
Get the correct parts, do right and keep it a one man shop. Instead of there was a man’s shop here.

I feel like this is a bit of a straw-man/overkill. The circuit will be on a 30A breaker, inside the shop. So even if worst case (welded shut), the motor will be spinning (with no load). Hard to understand how it would pull over 30A for an unloaded motor. If I pull the plug, the next point of disconnect would be the breaker (once). Or I flip it off at the breaker (disconnect box in a wall). Either way, not going to destroy the shop ("There was a man's shop here."). Or do you not understand why I may want it to be mobile hence why it is not a disconnect box on the wall?

 

[RPH]

I’ve had contactors weld up and burn cabinets. Always was an interesting call to go on. I did work with industrial systems but seen enough damage to respect it. Plus the education to go with the work.
Your shop, your choice but arcs are common especially when the counter emf from the windings collapse.

 

[Cruzan80]

I guess what I am saying is that I am going to be standing right near to the cabinet, with multiple disconnect options (within 20ft), on under 30A 240V 1ph. If the cabinet burns before the breaker, something is wrong (5A difference between contactor and breaker). And if I use this converter more than 5x a month, it would be rare.

Industrial strength is a different beast altogether.

 

[onetonbb74]

That contact is a general purpose and not rated for a continuous load or a induction motor. There is no exposed contacts to cool off like on motor starters and lighting contactors. The coil is the wrong voltage so why use it, now you need a control transformer. Seems like a lot of work for the wrong stuff and you will be back in there again.

 

[Cruzan80]

Thanks for letting me know. I wasn't sure what portion meant it was unsuitable (sounds like exposed contacts are needed). Would it say "Rated for continuous load" on a correct one?

 

[dave*99]

Forget about amps. It’s a motor . 5HP. That’s the rating.

 

[Cruzan80]

Gotcha. So a motor rated one will list a specific HP, not an amp number, correct? Again, trying to make sure I know what I am looking at (besides throwing the pictured one away...).

Edited. Found one with this contactor inside. The pic attached shows the HP rated, so that means I should be good trusting it? Does it matter that the 3ph number is higher than the motor HP (or since it will be on the 1ph side, is that ok?)

 

[dave*99]

The 1ph 5HP rating is what you need. And this part has it.

 

[dave*99]

You can also switch the motor with a motor rated switch like this:

https://www.amazon.com/dp/B003AU724E/?tag=atomicindus08-20

Rated 5HP @ 240V

 

[dave*99]

Here is the 3 phase version

Leviton 30 Amp 600 Volt Industrial Grade Three Pole Three Phase AC Manual Motor Controller Short Toggle Switch - Black MS303-DSS - The Home Depot

Leviton's Industrial Grade AC Manual Motor Starter Switches provide safe, reliable control of a variety of motor loads. Typical applications include manual ON/OFF switching control of bottling lines, pumping machines, air compressors and other heavy manufacturing equipment. These motor...

www.homedepot.com

 

[dave*99]

An a box to mount it in:



There are many manual motor switches available - if you don't require the control circuitry.

Search 5HP motor switch.

 

[Norcal]

Gotcha. So a motor rated one will list a specific HP, not an amp number, correct? Again, trying to make sure I know what I am looking at (besides throwing the pictured one away...).

Edited. Found one with this contactor inside. The pic attached shows the HP rated, so that means I should be good trusting it? Does it matter that the 3ph number is higher than the motor HP (or since it will be on the 1ph side, is that ok?)

This contactor & the one shown in the first post are both UL recognized components not UL or other NRTL listed, they really should not be used.

 

[Cruzan80]

An a box to mount it in:



There are many manual motor switches available - if you don't require the control circuitry.

Search 5HP motor switch.

Thanks Dave. I am guessing these will fit into a "normal" sized metal outlet box (or a slightly deeper one)? The original contactor was in a box that was connected to the top of the phase converter (two KO's matched up, then a ring installed to mate them). That may be the "cleanest" installation option.

Could I simply use two legs of the 3ph switch for the same effect? Cost looks to be about half that way.

Just to make sure I am not overlooking anything, what I would give up by going this route is that if power were lost and then restored, it would come back on, whereas a magnetic contactor would stay off in a loss of power situation. Gain is ease of install, and relative size of install, correct?

 

[dave*99]

If the 3 ph unit has additional ratings specifically for 5HP in a single phase application you can use it. Check carefully.

This is a simple on off switch. If there is a power failure it does not turn itself off.

 

[Cruzan80]

If I am willing to wait, HD has the single phase version cheaper than the 3ph one. For future reference, it says 15HP on 1ph version, 20HP on 3ph version, title is the same for either (30A 600V Industrial grade).

Think for $25, this will be the best way to go.

Leviton 30 Amp 600 Volt Industrial Grade Double Pole Single Phase AC Manual Motor Controller Short Toggle Switch - Black MS302-DSS - The Home Depot

Leviton's Industrial Grade AC Manual Motor Starter Switches provide safe, reliable control of a variety of motor loads. Typical applications include manual ON/OFF switching control of bottling lines, pumping machines, air compressors and other heavy manufacturing equipment. These motor...

www.homedepot.com

 

[dave*99]

You have to look at the voltage and HP. At 240V it’s 5 HP
Those high HP ratings are at much higher voltages.

 

[Cruzan80]

You have to look at the voltage and HP. At 240V it’s 5 HP
Those high HP ratings are at much higher voltages.

Now I see. Under the brochure option under Description? I thought those numbers initially seemed extremely high.

If I were to have bought the 3ph option (MS303-DS), it says 7.5 @ 240V (but I am guessing it thinks it would be 3ph power). How would I know what 1ph rating it would have (if any)? Contacting the manufacturer, or is there a proper scale for "derating" a motor from 3ph to 1ph? Just trying to increase knowledge here.


It says it fits in a standard sized box, do I need to use the specific Leviton Motor box with it? Seems like it has a spot for a looking bar, but otherwise looks the same as what I could buy much cheaper.

Also, realized I linked to the short-throw above. Regular throw is a few dollars cheaper https://www.homedepot.com/p/Leviton...roller-Toggle-Switch-Black-MS302-DS/302119822

 

[dave*99]

A 4” square box will work well with a single gang cover or mud ring.
As for derating it’s best to match the manufacturer’s spec to the application. If it does not state 5HP single phase 240v then don’t use it.

 

[fitter30]

Ac contactor coil on dc read this

Can a DC coil of a contactor be used with AC or vice versa ?

A Website on Electrical and Electronics Engineering

www.electrotechnik.net