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Hampton

Hampton

Air Defense Dept
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Nov 26, 2006
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Panama City, Fl
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I am relatively competent in home electrical systems, however, I'm not sure what would cause this: I plan to start with the ground wire, though. When we run the microwave, the gfci immediately trips on a completely unrelated circuit. After the gfci trips, the microwave continues to operate normally. I have replaced the gfci outlet twice. It is not the issue.

By the way, the microwave is 220. The gfci is not.

Ideas? ? ?
 
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Disconnect anything on the same circuit as the GFI, verify the GFI & microwave don't share a hot and also don't share a neutral. Sounds like maybe someone jury rigged the microwave circuit to get the 220? If they are sharing a neutral, you may be getting some harmonics issues.
 
I'm thinking the same thing as Humph. The GFCI could be tapped off one hot leg and the neutral from the micro.
If the GFCI is down stream of the micro then the GFCI would trip but wouldn't affect the breaker.
I'd start by opening the box where the micro is connected and see what I had in there.
If it is tapped off of the micro I hate to say it but your best bet is to run a new circuit from the GFCI to the panel.
 
Kill the circuit in your breaker panel and see if the GFI goes dead as well as the microwave, that will confirm what the others are saying. Then find that electrician and string him up!
 
I think Ken is right on with his theroy. I just troubleshot some similiar issues (although 120V) and found one of my lights was at the end of a circuit that had mostly outlets on it. That light was wired as a 3 way switch. In the same switch box was 2 other light switches that were fed from different circuits however the Common (WHITE) wires were all tied together causing a shared common situation and the GFCI was seeing that and would not reset. The bad news was this was at the end of a circuit so I did not find this until I disassembled ever other outlet on the circuit trying to pinpoint the problem.

My house was built in the early 1980s and I was later told this is more common in older homes that were not subject to the same standards used today. Luckily though the upside is I have 12 gauge wire which is not common today.
 
John,

Our house is on Front Beach Road right across from the Gulf so we've had our share of electrical gremlins to hunt down. All of the problem are eventually traced to corrosion related causes. Since your microwave is 240V, I'd bet you a Diet Coke(!) that you have a bad contact on one side of the other on the microwave breaker and the bad contact is on the same leg in the panel as the GFI breaker. The GFI is sensing it and is tripping. If you feel the breaker after the microwave has been on a while it will probably be hot......you might also flip the microwave breaker an see if it "feels" right. If you can pull it out of the panel box, look at the lugs on the back for signs of arching or heat.

The truth of the matter is that a new 20A 2 pole breaker costs less than the gas to get you to Lowes and back, so I'd just change it and see what happens.


Good Luck with it................
 
I went through a similar thing in my apt, ended up being corroded connections.
 
The installer of the 220V range in my house forgot to remove the neutral to ground bridge at the range cable connections for a four wire plug (the bridge is only used for three wire 220). So it ended up running juice onto the ground wire and onto the chassis of the range (that's how I found out about it - got shocked). You may have something like that going on.
 
fwebster said:
John has been in that house for as long as I've know him.......he or rather his wife has not lived with the problem for 15 years.
Click to expand...

Very astute. That is the piece of info I left out. Nothing has changed in 15 years in the wiring set up other than replacing the GFCI a couple of times due to another, unrelated issue. On another note, this GFCI feeds two items outdoors - a pool light which has not been turned on for a couple of years (need new light) and an outdoor outlet below the pool light switch. I'll check for corrosion at all of these points.
 
I just spent 2 hours chasing electrical wires. I reset the ground screw on every wire in the cb box. I chased the microwave wires inside the box behind the oven. They all look good. I reset every connection. I changed the 220 cb. I changed the GFCI cb. No change.

FINDING: I have a new, digital box on the outside of the house (don't know when I got that). There is an electrical short sound behind the cb panel in the wall when I run the microwave. This can also be heard in the new electrical box on the outside of the house. I suspect I have a loose ground out there. The electric company is on the way to see if there is an issue on their end (this visit is free - I will be responsible if there is something on my end).
 
Gremlins, that is what it must be!
 
It was. Electrical Co guy came out and did not find an issue outside. He told me an electrician would trace the issue from outlet to outlet. He was very nice and had some great advice. I took the microwave apart. I couldn't believe this was an outlet issue. I found a burnt red wire connection. I cut off the affected end and re-attached it. The buzz in the CB Panel went away, but the GFI kept tripping.

I disconnected the subordinate (slave?) outlets from the GFI - no trip. I reconnected one - no trip. I reconnected the other - trip. (Only with microwave on in all cases.)
I disconnected the Master Bath outlets - trip. I disconnected the exterior outlet, pool light, and pool light switch - no trip.
So, I reconnected all of the outlets except I by-passed the exterior outlet by the pool. All is well. I put the house back together (Had even pulled out the wall oven to check the 220 connections behind it.) The microwave had about 10 wire bundle connectors and 25 screws. All is well. Need to replace the outdoor outlet and the pool light (already knew that).

I'd like to thank all who replied here. I learned a lot.
 
After re-reading all of the above, the microwave gets its power from a double CB in the CB box and a huge wire for 220 running to it. Still don't know how/why it affected the GFI, except, the electrical co guy mentioned that all of the systems share a common ground. There may have been a trickle of electrons through the ground of the microwave due to a completely corroded exterior outlet and flooded pool light (on the same wire). It wasn't enough to trip the 20 amp breaker, but enough to tell the GFI that something wasn't right somewhere and cause it to trip.
 
OUCH!!!!!!!!!!! WFT? Now, the microwave heats up the coffee in 1/2 the time! I asked my wife if she had noticed. She said she had, but didn't say anything because she thought I'd tell her that she was crazy!

The burnt, red wire in the microwave needed a better connection - no doubt.
 
Good deal John! People would be surprised on how many loose connections they have in their house. An easy thing to do is when you go to paint a room, turn off the power and replace all outlets and switches. While doing this you inspect the splices behind the devices to see if there is any discoloration. It is cheap to do, makes the room look better and gives you peace of mind that your wiring is in good shape. The 220v connection behind the microwave is a different story but when replacing appliances, check the wiring at the same time. Many, many houses use aluminum wire for the loads 30 amp and larger so those require maintenance over the years. Power off, remove the outlet and add some deoxidizer and tighten back to the outlet. If everyone did this, not only would Home Depot appreciate it, fewer homes would burn down.
 
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