ROOM AIR CONDITIONING mystery solved, kinda

[REFLEXX]

Here's a wierd one.

I have a milling machine (aka knee mill, Bridgeport, etc..)with a 3ph Variable Frequency Drive (VFD) motor in my shop. It's wired 220v single phase on a dedicated line. Works fine, no issues with power.

Bought three LG room air conditioners (for three rooms). Finally got the A/C that is in the same room as the mill into the hole in the wall. It was getting hot in these parts. Plugged it into it's own 115v dedicated circuit. Works great, quite, blows nice and cold. The plug has a AFCI built into it. It's the size of a ******* bar and has the typical TEST/RESET buttons.

The next day I go to use my mill and turn on the spindle (the VFD motor) and the AFCI plug pops instantly. DAMN IT! I instantly assumed that I wire something wrong. Tried it again, same result: reset AFCI, turn on machine, AFCI pops. It's on a separate circuit!

So I'm thinking that I'm a *****. Maybe my mother-in-law was right (imagine a New Yorker accent) "certain things you should leave to professionals"

A HA! I've got another A/C unit (same make) on a rolling cart. So I wheel it over to another (isolated circuit) outlet. POP! same result. Another outlet, POP again.
Now I know it's not my wiring, but I'm lost

I get on line and dig up what an AFCI is:
AFCI = arc fault, circuit interrupt. if there's an arc in you old, chafed, crappy wiring, this will keep it from throwing big sparks and starting a fire.

BUT! every time a switch is turned on, you generate a tiny arc! On this cord, I've got an "ARC SHIELD" AFCI plug made by Texas Insturments. I learn that this "patented" gizmo "can tell" the difference between a switch arc and an arc fault. I also learned that a few years ago, the government (to protect us from ourselves) made it a rule that all room A/Cs have one of these AFCIs. My guess is that too many old mobile homes got burned up when a "high amp draw" A/C cooked the wiring. But that doesn't help me. I've got oversized wiring, all 20amp for this A/C that plugs into a 15 amp receptacle.

I called LG service and they don't answer the phones. I called TI (now called Sensata or something) and no answers.

Right on the plug it says, do not remove and do not cut off. So I cut it off.

I installed a 20amp GFCI recptacle, wired on a heavy duty (20amp, 3 prong) plug and plugged it in. Turned it on, no problems, blows nice and cool. Then I truned on my machine. VIOLA! No effect on the A/C unit. No dip in voltage, no dive in the A/C fans, no big sparks. Seems to be running just fine. I've turned my machine on and off a hundred times today with no ill effects (so far).

Why did I post this? Because I want your opinions and to give you my theory and to see if others have had the same experience. I think this AFCI is too sensitive to exist in a "shop/garage" environment. All our tools, machines, and motors have switches on them that make "arcs" that this gizmo is fooled into thinking that it's a bad.

So I'm the guinea pig. I'm thinking that the GFCI will protect me and the A/C unit, just like any other electrical device. Am I wrong?

 

[bmwpower]

Weird. Never heard of an AFCI in a garage environment yet. You're theory sound correct, but I don't understand why it would trip something on another circuit.

 

[DynoDave]

Thanks for sharing this. It could come in handy.

I don't understand the whole AFCI principle, since anything in your house with an electrical motor/brushes has a small spark/arc inside it. And the bigger the equipment/motor, the bigger that spark by the brushes can be.

 

[Bradley Miller]

That's odd, when I was doing my AC I noticed the wiring though . . . the wire is encased in what looks to be a grounding sheath. I luckily didn't have to deal with splicing the cord on my new boat hatch air system. (See elsewhere DIY Portable)

 

[Dave Carney]

I think you're right, the arc fault interrupters really don't belong in a shop environment. In fact the NEC and the manufacturers rules for use are sometimes in conflict on these devices. They are on the window unit type a/c because of the likelihood of being in a bedroom.

 

[pirate]

I do not have a miling machine in my shop but have had a similar experience. I purchased a 10,000 BTU air conditioner that runs on 220 volt with a 20 amp plug on its own dedicated curcuit. The unit was protected by the AFCI plug with test and reset buttons which I understand is by required by law. After installing the unit I would notice that there were times when I would try and start the A/C and the reset button would be tripped or the unit would be running and all of a sudden trip the reset. I called the factory and was told the problem was in the wiring. I was skeptical because I had just wired the circuit for the A/C but did check it out with the help of a friend just to see if maybe i had done something wrong. The problem continued. Finally the factory sent out a local contractor who changed the plug and cord and the problem went away. He said that he had changed out several defective plugs. I had thought about just cutting off the AFCI plug and putting on a regular plug but was reluctant because the A/C was rated at 20 amp and the curcuit breaker was 30 amp. I am a bit disappointed in the A/C performance although maybe I am expecting to much. I thought 10,000 BTU's would be more than enough to cool my 20' x 20' but the unit struggles to reducethe inside temperature by 15 degrees from outside temperature. the garage is not insulated but does have a 10' pylwood ceiling.

 

[APEowner]

Hmm. I was right along with you thinking that you were on track and that you had figured out that problem when I realized that I've never had the AFCI trip on either of the air conditioners in my shop. They've been exposed to the RPC on my milling machine, MIG and TIG welding and an instrument that tests spark plugs for high voltage breakdown. Now I'm wondering if you've got an issue with the safety ground on the outlets in question or somewhere in the VFD circuit that messes up the ground reference that the AFCI is using.

 

[porschedude996TT]

Never heard of them. Sounds like a PITA.

Link below is from Square D.

http://www.ae-service-maintenance-co.net/downloads/square_d/afci_facts.pdf

 

[tdkkart]

I'm guessing it has something to do with your VFD. VFD's are well known for sometimes causing electrical noise issues that create havoc with some electronic devices.
Yes, the VFD is on a dedicated 220v line, but back at the breaker panel one leg of that 220v is the same leg that your A/C is hooked to.
The AFCI is seeing the VFD noise as an arc. You might try swapping the A/C line to the other phase in your breaker panel.

 

[sneezer41]

What TDkart said. The VFD is sending out noise on the ground or the AC legs. They also have to absorb current on startup and stopping and if it gets too high it ends up on the AC bus.

If you are starting it with the VFD try starting it with the motor switch. If you are starting it with the motor switch, try starting it with the VFD. You can usually also play with accel and deccel ramps

If you found an isolation transformer cheap it might pay to keep it on the VFD, although I have never had an issue.....although all mine have been on machines with transformers on them.

 

[Charles (in GA)]

The AFCI is seeing the VFD noise as an arc. You might try swapping the A/C line to the other phase in your breaker panel.

Wouldn't do any good. The VFD is 240 and fed from both legs of the panel. The 120 v A/C units AFI would simply see the same noise on the flip side of the buss.

Charles

 

[Falcon67]

I tear all the DO NOT REMOVE stickers off the pillows and blankets, would not hesitate to chop off the end of the cord and rewire. I imagine the VFD noise was causing the rukus. Nice heads up in case I upgrade the 12K unit in the garage.

I am a bit disappointed in the A/C performance although maybe I am expecting to much. I thought 10,000 BTU's would be more than enough to cool my 20' x 20' but the unit struggles to reducethe inside temperature by 15 degrees from outside temperature. the garage is not insulated but does have a 10' pylwood ceiling.

Yes - without insulation, you are expecting too much from that bitty 10K unit. I'm surprised it does the 15F.

 

[bjcouche]

It doesn't surprise me that an AFCI is being tripped when you use your mill. The key here is that your mill is using a VFD. My previous job was at Rockwell Automation as a VFD Drives service engineer, just to give you my background. VFD's produce a _lot_ of harmonics and RFI back into the power source. Some AFCI's and GFCI's trip during these conditions. Myself, I would have done just as you did with removing the AFCI plug, although this may be a NEC violation. I have operated a VFD off of 240V single phase to run a 3 phase motor myself on residential "garage" power. I have also seen the large amount of noise that they generate on the power lines. When I tried this test, both UPS's in my house went crazy and switched to battery backup. What helped my situation was to add an RFI filter between the 240V power and the drive. This greatly reduced the trash the drive was generating from going into the rest of the house. The UPS's are now happy when the vfd is operating. RFI filters aren't too common here for industrial drives in the states, but are almost always used in Europe due to tighter power grid quality requirements. I recently built a 5hp air compressor using a 3 phase motor with VFD and it's been running fine in my garage with the RFI filter in place.
Remember that these VFD's are _industrial_ drives and designed for industrial power. In an industry, the power supply for the VFD's in the plant are on separate distribution transformers than 120V and 240v single phase devices.
Some more background. The latest 2008 NEC 210.12 requires all 120V 15 and 20A branch circuits supplying outlets in the home to be protected by a AFCI breaker. So far your garage is excluded if I read correctly. This basically makes you buy $35.00 breakers instead of $5.00 breakers for all the breakers in your house. I can't say I agree with this since I haven't heard any blind studies confirming these devices prevent fires. I have heard of breaker manufacturer funded studies proving this fact though... I'll give into the fact that they trip faster under short circuit conditions, but a fast blow class CC fuse would trip even faster. When AFCI breakers first came out, I heard a lot of rumors of certain models of vacuum cleaners tripping them. The devices aren't perfect and can sometimes nuisance trip, some brands are more prone than others, and some types of loads trip them more than others. You found a circumstance that nuisance trips one every time.
Then there's GFCI protection, The 2008 NEC 210.8 requires all 120V 15 and 20A outlets to be GFCI protected, in certain locations including garages. I have seen certain devices cause GFCI's to nuisance trip as well. I fully understand this requirement though as GFCI's do save lives, but wish NEC allowed exception for fixed critical appliances like freezers, refrigerators, or sump pumps. Refrigerators and freezers if not in a basement or garage would be allowed to be supplied without gfci protection. Imagine how ticked you would be if a GFCI nuisance trips to your sump pump and your basement floods...
Finally there's the 2008 NEC at 406.11 that requires all 120V 15 and 20A outlets to be of the tamper resistant type. I'll get off my soapbox now before I start ranting on why tamper proof outlets are required for the garage door opener outlet mounted to the ceiling. I guess in the off chance that your 2 year old climbs up an 8ft ladder to stick a paper clip in the outlet....

Brian

 

[Falcon67]

My previous job was at Rockwell Automation as a VFD Drives service engineer,

Ah-ha! The Turbo/retro Encabulator people! I imagine that my VFD is not pestering anything in the house because the garage is feed off the meter. Maybe - the noise should travel back into the house anyway. But I've not noted (knock on synthetic wood) any issues with line noise.