Electrical Question... Air Compressor Trouble

[Docwheelhorse 2,651]

Hello Fellow Redsqure members,

so..... this is chapter two of my air compressor saga. I decided to post this here as maybe somebody else can learn from my experiences. First lets start with the basic specs of my wiring..... I have a 20 amp breaker in my service panel with approximately a 100' run of 12 awg solid which then I connected to a 30' run of 10 awg stranded. These numbers are a bit long I believe but I figured to the long side for calculation purposes.. Now.... taking the distance into consideration I came up with a voltage drop for a 20 amp load of 115 vac single phase of 7%---this means at 20 amps I will see 108 volts on a 115 volt circuit. I figured this as 130' run, 12 gauge solid for the ENTIRE length, an open no conduit run and a conductor temperature of 86 degrees F.

At a 15 amp load with everything else being equal the voltage drop is 5%---(110 vac with full load)

Well---the compressor I bought used abought 6 weeks ago has a 14 AWG stranded household type cord and it was happy as a clam running on the above circuit with a 15 amp fuse inline to protect it UNTIL SATURDAY AFTERNOON. At that point the 15 amp breaker blew upon a re-start to build the pressure back up. I shrugged my shoulders and screwed in a 20 (all I had) that blew and I screwed in a 25 (back of mind the 20 amp breaker was at the begining of the run) and that blew.... I went oh man what the heck and at that point screwed in a 30 to see if the thing would re-start (remember--the 20 amp breaker is still at the begining of the run so I wasn't overly concerned about overload) at this point the compressor was running slow like it couldn't start and it blew the 20 amp breaker.

I gave up and went in the house...........

Today I went into the garage and hit the switch and the compressor started and ran fine.... so I hooked up my digital voltmeter and found the following--- 122 vac starting at rest voltage, voltage drops to 76 vac for an instant then comes up to 110 vac and stays at that voltage until the compressor finishes rebuilding pressure.

I dragged the compressor outside to the outside outlet by my front door---- unknown length of circuit but it is 14 awg solid with a 20 amp breaker---I switched the breaker years ago because nothing would "start" on the 15 amp breaker---yah I know its above what it should be but I'm careful on what I plug in. Anyways--the results where similar to the new wiring--with 121 vac at rest, a drop to 80 vac on startup and a running voltage of 111.

I finally dragged the compressor into my garage and plugged it into the wall outlet that was installed when I built the house---it is 12 awg solid with again an unknown run length and a 20 amp breaker. The voltages where 122 at rest, 80 at startup and 110/112 running.

After all this testing I brought it back into my new shop AND IT STARTED BLOWING FUSES AGAIN.... Sparky came over and did a running amperage load test and came up with 15.5--17 amps running. and a starting amperage of 55-60..... so I am perplexed---do I have inadequate wiring or did one of the components in the compressor start to fail? The compressor ran fine on a 15 amp fuse for weeks.... now it will start and eventually start blowing fuses (heat???) nothing seems warm---I don't get it and any advice would be appreciated. Anybody here know there way around compressors? It is an Ingersol Rand witha 2 hp motor---data plate says 20 amps for 115.

Sorry for being long winded and I am grateful I have somewhere to bounce these type of problems off of.

Tony

[multihobbyguy 35]

I am no expert but I would check the start capacitor on the motor.

[squonk 40,913]

I'm thinking you have a compressor unloader problem. I had a small compressor that smoked the belts once. I replaced them. 3 weeks later it smoked them again. Turned out the unloader was sticking. Had the same problem at work. A motor would occasionally not start on a climate control compressor. The unloader was gummed up. You may have the unloader on the line that goes into the tank from the pump or it's mounted on the pressure switch. It relieves the head pressure when the pump shuts off.

[Sparky-(Admin) 21,254]

I am no expert but I would check the start capacitor on the motor.

I agree. I also think that the voltage drop is to much when its running and over time (although not a long time) it has done damage to a component such as the start capacitor. After the compressor is back in shape the service to it needs to be "upped" the whole way from breaker to compressor. At least a #10 guage wire, maybe more.

Mike..........

[squonk 40,913]

Does your compressor hiss after it shuts off? It should. I've seen lots of motors hum when the capacitor is bad and not blow the breaker instantly where a stuck unloader can basically lock the motor right up.

[squonk 40,913]

I have a 75 ft run on 12 ga. wire and run a 6 HP compressor on a 20 A breaker. I would think your set up should run a 2 HP unit

[Docwheelhorse 2,651]

Motor hisses when it shuts off like it should...... I dunno, I thought all looked within a respectable tolerance on paper and with my luck its just not good enough...

Tony

[multihobbyguy 35]

Capacitors can start leaking or ground themselves out when they go south. They are fairly easy to diagnose with a ohm meter or sometimes you can just see that they are swollen and leaking. They are also DANGEROUS when not handled appropriately. They help with the initial load when a motor starts or restarts.

[squonk 40,913]

If the unloader is working and the motor does not even try to start (humms) when the breaker/fuse trips I'd be looking at another motor. I work in a fairly large hospital with hundreds of motors. I've seen 3 bad caps in 8 yrs. but dozens of bad motors

[Docwheelhorse 2,651]

Thanks everybody....

Squonk---the motor isn't humming, it does turn over but only at abut 50 rpms and like its trying to get going..... this goes on for 10 seconds or so and POP.... Sparky tested this while it was happening and found that the voltage was ~75 vac and never raised above this like the motor was stuck in startup mode. This makes me wonder if the wiring is on the edge of not being able to feed enough initial voltage/amperage.

Like I said----looked good on paper and I'm just dissipointed in the whole thing.

Tony

[wh500special 2,156]

I’m no electrician, so take this with a grain of salt…

Unless I’m interpreting your saga incorrectly, it sounds like you’re only having trouble with the compressor on one circuit…your shop’s. I’m going to bet that you have a marginal connection somewhere inside a junction box, at the outlet, or in the breaker box that’s screwing things up. My next step would be to retrace and check all connections, wire nuts, and even the receptacle for something amiss. If you do it closely following the tripped breaker event, you might even find a hot spot somewhere.

Steve

[squonk 40,913]

What bugs me is the fact the compressor did work for a while. Get that capacitor out and have it checked. At least that will be a cheap repair if it's bad. A bad cap can do strange things. I had a window A/C brought to me once that was running in reverse because of a bad cap. It could be a connection loosened up. I'm leaning towards a bad run winding in the motor or maybe a bad centrifugal switch in the motor if it has one. You say it ran for weeks on a 15a breaker and it hisses so the unloader is working. Unless the wiring to the new shop is shoddy, I'm thinking it's the cap or motor itself.

[Docwheelhorse 2,651]

Siggghhhh "shoddy" is such a cruel word.... Yes I did all the electrical myself... yes I did some research and ran the numbers and figured out the voltage drop.... I knew it was below optimum but above acceptable. I thought it out and believed 12 solid which was run into my house garage when it was built would provide enough power to attach a 10 gauge stranded wire to it and power the compressor setup in the new shop. In the end I exceeded the "code" load amount of 80% and the voltage drop has proven to be too high and it looks like it is on the edge and may start the compressor or may not. An interesting find is that when the electric oven in my house is running it almost guarantees that the compressor will experience all the trouble. I also realise that increasing the wire size as the run goes along instead of starting big and stepping down is another problem. I dunno.... I posted this to try and help others and I am not upset or offended by anything anybody has to say. I guess thats why there are electricians and code books and formulas to figure stuff out...... I just thought I could handle it and was pretty impressed with getting it done..... but it just doesn;t work. A little black cloud of dissapointment has settled over me..... oh well I will get over it and figure it out.,

Tony

[squonk 40,913]

Is the line buried?How hard would it be to undo it. Or how about running a new sub feed from your main house panel to your garage with say #8 stranded and the #10 out to your shop. If you have a basement it shouldn't be to hard to do.

[SousaKerry 501]

You could also try wireing the compressor for 220 if it is rated as such your amprage should drop in half then, Of coarse this means you need 220 out to the shop and who knows maybe someday you'll get a welder and you'll already be set up

I would take the motor into a motor shop and have it tested at least, most will test it for free and the repair may be cheaper then you think.

[dobeleo 7]

I had borrowed my brother in law's compressor a year ago and over the winter it started blowing the circuit breaker over the winter. I knew my wiring was good, short runs, 12 ga wire. I checked the oil in the pump and it was filthy. I changed the oil and it has worked fine since. I got lucky.

[Jim_M 178]

Pulling 50 to 60 amps on start up with a 2 hp motor is a problem, that's way too much inrush current. If the motor data plate says 20 amps, they mean full load amps and you should never see over 22 amps on start up.

If it's a belt drive compressor pull the belt off and check the start up amperage of the motor by itself. If it's 20 amps or less, I suspect the unloader. If it's still high buy a new motor, they're cheap enough these days that it's not even worth changing the capacitor, especially after that motor has overloaded that bad, the windings had to get pretty hot.

[can whlvr 993]

im not an electrician but am famiular with house hold wiring,as you know its better to go bigger when long runs are used,ive seen breakers get finniky from heating up with loads thats go near the limit for periods of time,sure sounds like the compressor is acting up,but you are near the limit if not a bit over,you said you are hooking up a 10 gauge from the comp to a 12 gauge,wouldnt it be the other way round,shouldnt you be feeding with 10 and 12 gauge from the load? not being a wise guy just asking and putting some input,

[Docwheelhorse 2,651]

Hi---can't change the 12... its the 12 solid they wired my garage with 16 years ago..... I stepped up to 10 figuring it may help with voltage drop etc.... and there is a fuse I installed with a rating below the circuit breakers rating. I will not overtax the 12.... I just thought larger wire would help...

Tony

[Jim_M 178]

The wiring wouldn't cause a 60 amp draw at the motor. The problem is at the compressor, either the unloading valve or the motor is bad. A 60 amp load on the wiring will cause you problems with the wiring, possibly even a fire.

[coldone 35]

More than likely you have a motor problem and not wiring. A bearing maybe dragging, start windings maybe toasted, start cap maybe shot. From the descripsion of it "lugging for 10 seconds and then poping the fuse", Plus the high start current, that is usually an indicator any of the above. I would pull the motor and check it out before I started looking at the wiring. Can you take a pic of the motor and post it?

[GlenPettit 1,716]

I would suspect the compressor/motor may be a problem. The start-up draw should not exceed 2-3 times the running draw; dirty oil, scratched insides or even a too-tight belt could contribute to this.

When wiring, a kink in the hard wire can cause a break in the wire which may only show up when the wire gets warm & expands, and 12 gauge will warm up in a heavy sustained draw.

A 6 or 7 hp motor should be on 10 gauge wire and 220v, but your 2 hp should be no problem with 12 gauge 100v wiring.

In wiring, every connection is an interruption in the wire, and a lot of in-out duplex connections in route will reduce the quality of electricity at the end, especially outside where corrosion builds up on the individual connections.

Good Luck - really enjoyed this discussion thread,

Michigan Glen

[Docwheelhorse 2,651]

Well Folks..... I did the easy part and dug an 18" trench and installed conduit. Sparky then came over with some 2/0 (I think???) alluminum wire and ran it and installed a 100 amp sub panel in the new shop. I helped as much as I could but he made it look easy. We ran 10 solid to the compressor and installed a couple other circuits--a 15 amp lighting and a 20 amp outlets. Tommorow we need to splice the 2/0 in my first garage and then install it in my 200 amp main panel. Then we flip the switch and see what happens.... maybe the compressor was being starved all this time and I totaled it or it was being starved when the electric load in the house crept up---electric oven, dryer, TV all on etc...

I willl post the results and my hats off to Sparky......

Tony

[squonk 40,913]

2/0! That will certainly"Git er Done!" Lots of fun working with that. Not as much fun as 400 or 600 mcm though! If that compressor doesn't work now make a boat anchor out of it and get a new one. You should have enough juice for a nice 5 or 6 vertical :)

[Docwheelhorse 2,651]

I dunno if its 2/0 or not..... all I know is the entire cable was about 1" in diameter and the two feeds where about 1/4" and he said it was rated for 100 amps max.....maybe its a different gauge----I dunno this electrical stuff and I guess I proved it this week....

I'm just really appreciative he did it... hes been telling me too run a sub panel to my first garage for years and I never did....

I was having trouble running cable into the new conduit yesterday and asked for his help and the next thing I know he says why don;t we just get this done----and he starts pulling parts and wire and "stuff" out of his electrical stash.. He even had a new in the box 100 amp sub panel with 5 breakers.... the alluminum wire he had coiled up too,,,, All in all it cost me $100 in misc. items to get it done.

Tony