Air compressor contactor/wiring problem. Need help please!

[CITIZEN F16]

I didn't thoroughly read all of the prior posts, mainly the pictures to produce the sketch.

By code the wild leg is required to be identified with orange wire or tape. Since he has undersized wire connected that should be corrected when he wires it permanently. He will likely have more issues once he installs the belts and puts a load on it. Were just discussing how to get the controls working at this point.

Also the code requires that the wild leg be place on L2 in all cases, except for utility meter cans. This is why the factory starter control connections are tapped from L1 and L3, even provides an extra lug hole, only there for the purpose. Its standard procedure.

The fuse is also required for any control conductors that leave the control enclosure, such as the pressure switch and the low oil switch. The supply circuit should be on the order of a #6 or #8 wire, the breaker to provide the circuit protection, is too large to protect #14 control wiring circuits, once they leave the enclosure.

The starter is wired correctly from the factory to comply with code, its the field wiring that leaves something to be desired.

Is this NEC code or local. Is it new? Is this something specific to compressors? I don't ever recall seeing a fuse in a control circuit and I have hand my grubby hands inside quite a few motor controls.

 

[SAF]

In post #34 I gave some snippets of NEC code that applies for reference. Those sections have been on the books for more than 30 years from recollection. The fusing applies to control circuits fed from larger motor circuits starting around the NEMA size 2 starter range. The section numbers are there in the post if you would like to study it further.

The orange conductor rule is really for your own good, and is one of the few color rules in the NEC. It helps you prevent from burning up 120V accessories and devices, that are not designed to see higher than 120V. A bit of orange tape could have saved many posts in this thread, with the fussing over which wire was the wild leg. The original poster only corrected it in the final post due to a rotation issue, an did not recognize the importance of this issue. If he gets it wrong in his final connections he will be back to his original problem, contactor chattering. Tape is not that expensive, to save a bunch of grief and mistakes.

If your interested NFPA now allows free reading access of the NEC code online if you sign up for a free account.

 

[rons]

Sanding and polishing the points is not good. Should just brush them clean and/or soak to remove the black soot.

How do you know the pressure switch is adjusted? I got fed up with the mechanical pressure switch. Use this instead. SMC pressure switch.

 

[CITIZEN F16]

In post #34 I gave some snippets of NEC code that applies for reference. Those sections have been on the books for more than 30 years from recollection. The fusing applies to control circuits fed from larger motor circuits starting around the NEMA size 2 starter range. The section numbers are there in the post if you would like to study it further.

The orange conductor rule is really for your own good, and is one of the few color rules in the NEC. It helps you prevent from burning up 120V accessories and devices, that are not designed to see higher than 120V. A bit of orange tape could have saved many posts in this thread, with the fussing over which wire was the wild leg. The original poster only corrected it in the final post due to a rotation issue, an did not recognize the importance of this issue. If he gets it wrong in his final connections he will be back to his original problem, contactor chattering. Tape is not that expensive, to save a bunch of grief and mistakes.

If your interested NFPA now allows free reading access of the NEC code online if you sign up for a free account.

Thanks for the info, I just always check the wires to ground or neutral before hooking them up, I also can't recall running across a machine that had more than a 120 v control circuit. As for the fusing of the control circuit I will just plead elderly. I actually worked in an electric supply house in my early 20's and now I am in my early 60's. I actually designed control panels and built mag starters and the like. Furnas was one of our product lines. We just stocked the basic contactors and assembled the add ons or changes ourself, coil changes, interlocks, overloads, etc. So since that was the early 80's and I bought a bunch of NOS Furnas contactors off
E-bay., the fusing requirement post dates any starter I have ever seen. The OP's picture was the first time I have ever seen a fused control circuit. I think Furnas ceased to exist about 30 years ago. Nowhere have I worked including large places ages ago permitted work after the service entrance.

You would not believe what exists out in the sticks where I live, looks like my only violation is a missing fuse in a mag starter. As long as you're off the beaten path you will never get a building inspector or fire department walk through in these parts.

 

[Ltk]

Well one problem taken care of, another one happens..

My phase converter is a 20HP American Rotary, it’s fed from a 60 amp breaker. Upon first starting the compressor with no other equipment running the breaker kicked after about 5 seconds. The motor was barely turning the pump over.. I guess I don’t have a big enough rotary converter to start something like this?

 

[dalmatiangirl61]

What does AR recommend for breaker size? PAM recommends 125A breaker for maximum power on the 20hp rpc.

 

[Bob-J-H]

My paperwork for that size converter says 100 amp breaker and #3 wire

 

[Ltk]

What does AR recommend for breaker size? PAM recommends 125A breaker for maximum power on the 20hp rpc.

The chart in my operators manual says minimum breaker size 60amp, does this mean I can safely up that to a 125 amp? I'm not familiar with PAM, forgive me I'm very new to all of this!

My paperwork for that size converter says 100 amp breaker and #3 wire

The chart in my operators manual says minimum breaker size 60amp but does not list a maximum breaker size for adequate protection and operation.

 

[dalmatiangirl61]

The chart in my operators manual says minimum breaker size 60amp, does this mean I can safely up that to a 125 amp? I'm not familiar with PAM, forgive me I'm very new to all of this!

Odd that they would give a minimum, but not a maximum, but then PAM only gives a maximum, not a minimum. Compressors are considered "hard starting" in the rpc world, and I have heard of cases where people had to go 3x the hp for an rpc, ie a 10hp compressor needing a 30hp rpc. I would call AR and get their recommendation for maximum breaker size. PAM = Phase A Matic, a different mfr of rpc's.

 

[Ltk]

Odd that they would give a minimum, but not a maximum, but then PAM only gives a maximum, not a minimum. Compressors are considered "hard starting" in the rpc world, and I have heard of cases where people had to go 3x the hp for an rpc, ie a 10hp compressor needing a 30hp rpc. I would call AR and get their recommendation for maximum breaker size. PAM = Phase A Matic, a different mfr of rpc's.

Okay, I will give them a call and see what they recommend, I’m sure there’s some wiggle room since I’m at the minimum. The fact that it started at least gives me some hope that I won’t have to upgrade RPC’s.

I might end up with a 40 HP vfd from automation direct if all else fails. Their customer support steered me to the right one, albeit a little pricey!

Would any of you recommend giving a soft starter a try to ease the strain?

They told me which one to get and it’s reasonably priced I’m just unsure because I’ve never heard of one until I spoke with them.

 

[dalmatiangirl61]

Okay, I will give them a call and see what they recommend, I’m sure there’s some wiggle room since I’m at the minimum. The fact that it started at least gives me some hope that I won’t have to upgrade RPC’s.

I might end up with a 40 HP vfd from automation direct if all else fails. Their customer support steered me to the right one, albeit a little pricey!

Would any of you recommend giving a soft starter a try to ease the strain?

They told me which one to get and it’s reasonably priced I’m just unsure because I’ve never heard of one until I spoke with them.

Before trying a soft starter you should make sure the unloader is working correctly, or add one if you don't have one. Another member, I forget who, advises putting a time delay on the unloader to make sure the motor gets up to speed before the unloader disengages. Starting with no pressure in the tank should be doable, the hard part is when there is 100psi in the tank, that is where the unloader is really needed.

Edit: The unloader dumps the compressed air leaving the compressor to atmosphere, you should hear it when its dumping, it should dump whenever the motor is started.

 

[SAF]

What I would recommend is checking what size utility transformer you have supplying you and neighbors. Then what size wire feeds your house panel and its service panel. Lastly what is the feeder size to the shop.

Putting a 120A breaker on a subfed shop panel, fed from a shared 15KVA utility transformer isn’t going to make a big difference.

If the neighbors lights blink out every time the pump tries to kick on, you could become very unpopular.

 

[Ltk]

Before trying a soft starter you should make sure the unloader is working correctly, or add one if you don't have one. Another member, I forget who, advises putting a time delay on the unloader to make sure the motor gets up to speed before the unloader disengages. Starting with no pressure in the tank should be doable, the hard part is when there is 100psi in the tank, that is where the unloader is really needed.

Edit: The unloader dumps the compressed air leaving the compressor to atmosphere, you should hear it when its dumping, it should dump whenever the motor is started.

I do have an unloader valve, but not a time delay. I think the problem is definitely the breaker size supplying the rotary converter. I called American Rotary and they told me not to go higher than an 80 amp on the AD20 model converter. This conflicts with what I have read and been told in this thread (100-125 amp max).

What I would recommend is checking what size utility transformer you have supplying you and neighbors. Then what size wire feeds your house panel and its service panel. Lastly what is the feeder size to the shop.

Putting a 120A breaker on a subfed shop panel, fed from a shared 15KVA utility transformer isn’t going to make a big difference.

If the neighbors lights blink out every time the pump tries to kick on, you could become very unpopular.

I live out in a very remote area, my power pole is about 900 feet away from my house, I have underground power to a 25kVA transformer that is only used by my property. I'm only pulling 200 amp service off of that transformer, do you know by chance if I'd be able to pull say 400 amps total off of this? (of course I'd upgrade my shop panel to a seperate 200amp service and leave the house with 200amps also)

In the meantime as that will probably be costly and a few months down the road, I think I will upgrade my 60 amp breaker to a 100 amp for the phase converter and see if this helps, American Rotary was pretty confident that I could start a 10hp compressor on this model of phase converter.

 

[DaveKamp]

So... Before you jump to any conclusions, it is best that one has a solid understanding of just how an unloader is supposed to operate, and why.

An improperly operating, or dysfunctional unloader, can make a perfectly good compressor and/or motor look bad. It can burn out contactors, trip breakers, and send your teenage daughter home with an embarrasing social disease.

there's several different types of unloaders, before assuming an operation scheme, it's important to determine what type of unloader. It's also important to recognize where the unloader discharges from, and to, and where the check valves are that backstop air to protect the unloaded volume.

There's unloaders that operate in cyclic duty... meaning, when target pressure is reached, they shut off the motor, and vent the compressor's outlet volume... then there's continous-duty, which do the same, but keep the motor running.

The former is the most common you'll see in a typical home or commercial shop environment... the latter is frequently found in industrial or prime-mover applications. The former is obvious, the latter is most often used when either stopping the driving source is either impossible, impractical, or subjects the motor to excessive starting and stoppling under high load. A diesel-electric locomotive or a tugboat is an excellent example where continuous running makes most sense, but it is also used in high-demand electrically-driven units where the electric motor would be subjected to a higher number of starts-per-hour that the manufacturer rated the motor. (Starting causes high inrush currents, thus considerable heat... so excessive starting cycles can overheat a motor, whereas, simply unloading the motor and allowing it to spin free helps cool it between loading cycles).

There are unloading systems that can do BOTH, the only difference being some componentry that makes the decision whether it is appropriate to shut down the prime mover.

So WHAT does an 'unloader' really do?

Every PROPER compressor has unloading, and the purpose of unloading is threefold:

First, to prevent the compressor from having to start up under full head pressure... i.e., with high pressure air already against the piston (or scrolls). This stalls the compressor, and leaks past the seals, blowing them (and oil) out into places oil is not supposed to be.

Second, to prevent the compressor valves from being captivated as a result of head pressure. Some inexpensive compressors use the cylinder's outlet valve as the ONLY check valve between pump and tank. This means the tank's full pressure bears against the outlet valve immediately amidst the first rotation. IF the valve is held down tight, the very first compression stroke will stall the compressor, if not by simple pressure, it will hydraulically lock from condensation (occupying compression volume) and an outlet valve that has been rather firmly seated by full tank pressure downstream.

Finally, it allows a series of rotations for the motor to get up to speed BEFORE the pump builds any significant workload. The pressurized flow leaves the compressor's last outlet valve, travels THROUGH a tube which is frequently covered with fins (aftercooler), which then feeds through the tank check-valve, and into the tank. This volume gets discharged on unloader actions, so that once the unit has been engaged in a restart, it will take several rotations BEFORE the compressor's last stage has brought up that volume up to high enough pressure to constitute a working load.

Aside from conveying compressed air from the last compressor stage into the tank, this volume also cools the compressed air. Combined gas law says that all the thermal energy in a given volume of air, will be packed into a smaller space when that air is compressed, and the end result of more thermal energy in a smaller area, is heat. That air coming out WILL be hot. Running it through that tube, especially if it has cooling fins integrated into it's exterior, will COOL that compressed air, allowing it to stabilize in density. It ALSO means that moisture in that air will condense and precipitate out, which is necessary evil in obtaining 'dry air'. That condensate will USUALLY depart into the main reservoir, where a drain valve at the bottom will discharge moisture at regular intervals (we hope, right?) Why would that matter? Well, if you've got an aftercooler tube that's three-fourths full of water, that means only a fourth of it's volume is available for AIR.

The difference between a gas, and a liquid... is that liquids aren't compressible... gases are.
Pneumatic systems that are full of water, are called "Hydraulic systems". Hydraulic systems that are full of gasses are called "Pneumatic". Best to keep Hydraulics and Pneumatics well-separated, as once circumstance results in fast moving objects coming to a very immediate and traumatic stop, while the other results in devices becoming diesel engines.

In an intermittant system, when the pressure switch's upper temperature is met, three things happen:
1) Motor power is cut off
2) A valve is opened which discharges all pressure between the TANK check valve, and the compressor's last outlet check valvej
3) Any MOISTURE in that volume, gets evacuated.

Compressors have a line between the last stage's outlet valve, and the tank.... and it is THIS volume that is discharged upon shutdown. It seats the tank check valve, and relieves pressure against the last stage outlet, and in doing so, any prior stages are also relieved. This means that, when that motor stops, you'll hear a puff-hiss (which is the aftercooler line being evacuated.

When it's time to restart, the contacts of the switch snap shut, and at the same time, the unloader valve pin is released (sealing off the aftercooler volume's discharge), and the pump starts spinning. It takes three-four turns of the pump before that aftercooler volume reaches any significant pressure, and by THEN, the AC motor has gotten up to a high-enough operating speed (let's say, to within 10% of it's rated speed) to be 1) Well below it's start surge current, and 2) capable of developing a useable torque for the compressor's need.

Make certain that the unloader is set up right. If it's a simple unloader, the pressure switch that controls the system will also have a little valve of some sort... frequently it'll look like a schraeder valve, and a lever arm coming off the switch operator will depress the center pin when in an unloaded state. If that isn't operating, OR someone has crimped, disconnected and blocked off, etc., the line, or replaced the original tank check valve (because the tank check valve is often an integral component to the unloader's operation), then there's a very high likelyhood that your compressor will just not operate right... and an equally, if not higher likelyhood that you'll replace darned-near-everything-else thinkin' that they're all bad, when it's just part of the unloader that isn't operating properly.

 

[SomeoneSomewhere]

^this

However, if it isn't starting even with an empty tank, it's unlikely to be an unloader issue.

25kVA at 240V is a shade over 100A. Note that that's probably the continuous rating, and short-term overload periods (cyclic loading) tend to be much longer for a transformer than the cables your breakers are sized to protect. Big tank of oil, copper, and steel etc.

It may be an issue for volt drop, though. I would want to see how much current it's drawing at start and what the voltage dips to at the motor terminals.

 

[DaveKamp]

^this

However, if it isn't starting even with an empty tank, it's unlikely to be an unloader issue.

This is absolutely right...
The odd circumstance that COULD be in that 'unlikely' case... is if somehow, the unloader setup got either put together wrong, or blocked, such that it is somehow holding the tank check valve CLOSED...

And that isn't likely, but I've seen it happen... it was on a Quincy compressor, in an EMD locomotive... but the only difference was, the prime mover wasn't an electric motor... it was the diesel prime mover, and the motor didn't stall... the area around the compressor got extremely uninhabitable right quick.

Something is certainly awry here.

 

[Ltk]

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A little update on this issue to show that I haven't disappeared. Just got the shop powered back up yesterday after upgrading my service and panel to 200 amps, now currently running the phase converter on a 100 amp breaker fed with 3AWG conductors. I took a video upon starting the compressor, I will upload it from my phone in the post below this one for any further ideas..

The compressor is now temporarily wired with 6AWG and a 60 amp breaker.
**(I do not want to put the compressor in place until I see that it will work, hence the temporary wiring.)

No breakers are tripping, no wires are getting hot, the tank is building pressure but the motor is not turning at full speed and the contacts sound bad, whether started manually or with the switch.

Thanks guys for your continued help.

 

[Ltk]

 

[CITIZEN F16]

I thought this one was solved? How many volts at the motor? Will the motor run ok, unloaded?

 

[Ltk]

I thought this one was solved? How many volts at the motor? Will the motor run ok, unloaded?

Nope still unsolved.. I'm getting the proper 240 volts at the motor, verified again that the motor is wired for low voltage, all connections are ran as per the wiring diagram on the motor starter circuit.

It's spinning really slow, not dimming my lights or anything, not tripping the breaker. The motor is getting hot to the touch, tank is building a tiny bit of pressure. Only thing I can guess now is that my RPC is just not heavy duty enough at 20hp to start this thing properly?