Issues with GFCI circuits and induction motors

[RKA]

I have an issue with my air compressor tripping the GFCI.  I thought since the motor isn't all that different from a tablesaw motor and many of you have tablesaws in your garage where GFCI outlets are installed, maybe you've run into a similar situation? 

I have a small 4 year old Ingersoll 110v 15A 20 gallon air compressor.  It's been connected downstream of a GFCI outlet (both within 10 feet of my panel) and plugged directly into the wall for 4 years and has operated flawlessly (until now).  The unit has no more than 50 hours of run time on it.  The motor and pump are made in asia to Ingersoll's specs.  Last weekend the compressor tripped the GFCI outlet for the first time.  After a little testing I have determined that it will no longer run on a GFCI outlet at all.  It trips upon start up.  I have two separate GFCI circuits in the garage and it failed to run on either of them.  I've also tested it on a regular circuit and it runs fine and brought the tank up to normal pressure within 5 mins (which is normal). 

Based on my searching, it appears the motor can develop small leaks as they age, which can trip the GFCI.  Also, the start capacitors can create some fluctuations in the amperage on the hot and neutral lines tripping the GFCI.  Given that it happens immediately on start up, I'm guessing it's the later?  Since it's worked fine until now, I'm assuming it's age related.  I can try putting a clamp on the hot and neutral lines, but I doubt my meter would have sufficient resolution for me to see a 30mA differential.  The question is, am I on the right track here?  Are better quality start capacitors a possible solution?  Easy to replace on a motor?  (I haven't pulled the covers off the motor yet to see)

Ideally I'd like to make this air compressor work on this GFCI circuit.  The single non-GFCI circuit is already spoken for.  I don't want to remove the GFCI on the air compressor's circuit because I use my electric pressure washer on it from time to time.  The panel is relatively full and walls are finished, so adding a dedicated circuit for the compressor that sees very little use is not preferable.  Any suggestions on how I can make this work again?

 

[tjbnwi]

To start with, blow the dust out of the motor and pressure switch.

If you're going to pull the cap , make sure you discharge it before you contact the terminals. Do so by bridging the terminal with a screwdriver. You can test the cap with an analog ohm meter, connected to the terminals the needle will sweep.

I assume I don't need to tell you to make sure the compressor is unplugged while servicing the unit. But....for safety sake, makes sure the compressors unplugged.

Tom

 

[wow]

What is the age on your GFCI's and what brand are they?

I have seen some bad/weak/cheap GFCI's that have acted the way you described. I believe those in my kitchen were compromised by a nearby lighting strike and resulting surge. They worked fine for years, then wouldn't stay on with the same microwave plugged into them that had been plugged into them for many years.

Replacing them solved the problem. Cheap fix.

 

[Rick Christopherson]

What you are experiencing is a nuisance trip, and does not automatically mean anything is wrong with the compressor. In very simple layman's terms, motors and capacitors store energy for a short period of time before releasing it. This can cause the circuitry in the GFI to falsely detect a trip condition. Newer or higher quality GFCIs can discriminate this condition better than older ones. So if keeping the GFI is required, consider replacing it with a better one.

There are other solutions such as having this receptacle be non-GFI but other downstream receptacles be GFI. However, I don't know enough about your situation to specifically advise on how to set this up just yet.

 

[RKA]

Thanks guys!  I wasn't able to find anything quantitative that would distinguish better from not so good.  I ordered heavy duty commercial hubbell receptacles from grainger (USA made).  Should be here next week.  Let's see if that works.

 

[buckmaidt]

Is it possible that you have an afci (arc fault circuit interuptor)?  Theses are code in my area for any occupied areas with no water. I.e. Bedrooms and living rooms. Any motor that makes a spark will trip them.

 

[TelcoRandy]

I have a sump pump I use on my pool every spring/fall and it always trips my GFCI. I'm guessing it's just a cheap junky one because it's only 3 years old. I just live with it by running an extension cord into my basement window and run the pump that way (through a regular outlet).

 

[RKA]

No, they should be GFCI's.  These were required in circuits placed in garages, bathrooms, kitchens and outdoor locations when the house was built 18 years ago.  I don't know the brand yet, but they were most likely installed by the builder.  The covers have paint all around the edges, done by the first owner of the house, so it's pretty safe to say they haven't been touched since they were installed.  When the new outlets arrive, I'll replace one of the accessible outlets and test.  The one used by the compressor is unfortunately buried between a very large (and heavy) tool chest and some wall cabinets.  That will be an afternoon project to clear the area so I can swap it.  But first let's see if the compressor will work in the other location with the new outlet.

 

[gkaiseril]

It is also a good idea to have a GCI on any circuit that supports any electrical device in, under or around water.

Before GCI's faulty underwater pool lights could put electrical currents that swimmers could feel and could have become dangerous. Mostly caused by poor waterproofing or grounding.

 

[Brice Burrell]

It is also a good idea to have a GCI on any circuit that supports any electrical device in, under or around water.

Before GCI's faulty underwater pool lights could put electrical currents that swimmers could feel and could have become dangerous. Mostly caused by poor waterproofing or grounding.

Of course in and around water, but in a garage?  The newer code requirements are going a bit far.  I know how I'd solve the problem and it wouldn't be with new GFCI receptacle(s). 

 

[leakyroof]

It is also a good idea to have a GCI on any circuit that supports any electrical device in, under or around water.

Before GCI's faulty underwater pool lights could put electrical currents that swimmers could feel and could have become dangerous. Mostly caused by poor waterproofing or grounding.

Of course in and around water, but in a garage?  The newer code requirements are going a bit far.  I know how I'd solve the problem and it wouldn't be with new GFCI receptacle(s). 

  Okayyyyy, give up your secret, what would you do?  [popcorn]

 

[gkaiseril]

It is also a good idea to have a GCI on any circuit that supports any electrical device in, under or around water.

Before GCI's faulty underwater pool lights could put electrical currents that swimmers could feel and could have become dangerous. Mostly caused by poor waterproofing or grounding.

Of course in and around water, but in a garage?  The newer code requirements are going a bit far.  I know how I'd solve the problem and it wouldn't be with new GFCI receptacle(s). 

Some garages are not always above the surrounding ground level, do not have level floors, have no floor drain, or have a floor drain that backups. I would expect that a damp garage floor is These types of situations or others can result with standing water in a garage which can provide a better chance for an electrical fault by water.

Then there is just the uses garages are used for and what is stored in them. The sharp tools, and moving vehicles could cause breaks in the wiring or extension cords across the floor.

Couple all of this with many people, you have an accident waiting to happen.

Do you know anyone that uses a lighted match to check for gas leaks or if a gas line is live?

 

[RKA]

Well, the new outlet was installed and the compressor tripped the ground fault instantly.  [sad]

 

[tbellemare]

Is your neutral bus properly grounded at the distribution panel?

Tom

 

[RKA]

I've got my neighbor coming tomorrow so we can take a look in the panel and put a clamp on the circuit to see if that will reveal any issues.  If I stick my fingers in the panel, my wife will be having a fire sale on green & black goodies the next day!

 

[CharlesWilson]

Does it rotate at all on startup, or does it just trip the GFCI without any motion?

Charles

 

[wow]

Well, the new outlet was installed and the compressor tripped the ground fault instantly.  [sad]

Thats not good.

If your tests on the panel tomorrow don't find the problem, I'd start checking wiring and caps on the compressor. Caps are fairly cheap to replace and with the age you stated they are a good likelihood to be the problem.

 

[Rick Christopherson]

There is nothing in the panel that will cause the GFI to trip, so that is just chasing ghosts. The only thing you can try is to remove all possible ground paths from the compressor, including the outlet's ground, and if the GFI still trips, then get rid of the GFI.

 

[RKA]

The motor will run, from anywhere under 1 sec to up to 4 seconds before tripping.  I did pull the covers on the caps and there isn't anything odd visually. 

So by removing the grounds that isolates the issue to a capacitance issue with the motor? 

 

[CharlesWilson]

The motor will run, from anywhere under 1 sec to up to 4 seconds before tripping.  I did pull the covers on the caps and there isn't anything odd visually. 

So by removing the grounds that isolates the issue to a capacitance issue with the motor? 

Your testing so far indicates that the motor trips regardless of which GFCI it is plugged into, so the problem most likely originates in the motor. Single phase motors have a mechanical switch that energizes the start winding at startup, and then opens when the motor is spinning up at a high enough speed.

What may be happening is that this switch arcs to ground when it opens, as it is trying to interrupt a current. If you can somehow get a look at the start winding switch, you may see the root of your problem. Access to the switch may very difficult depending upon its location and design.

When the switch opens, large voltages will appear on the start winding, which may be another place that arcing to ground can occur. Fixing the problem on a small motor like this one can be more trouble than it is worth.

Charles