Microwave outlet not working

[ggunn]

I was dismayed to find the microwave not working this morning. It's the outlet that's dead and it appears that it's the only one that's dead. The microwave works fine on an extension cord to another outlet and it doesn't trip that breaker or heat up the cord. No breakers appear to be tripped; none are in the middle or have any slack in the switch, and the one that feeds the microwave isn't marked. The GFI circuit is not tripped.

Any suggestions as to how I should proceed?

 

[Besoeker3]

I was dismayed to find the microwave not working this morning. It's the outlet that's dead and it appears that it's the only one that's dead. The microwave works fine on an extension cord to another outlet and it doesn't trip that breaker or heat up the cord. No breakers appear to be tripped; none are in the middle or have any slack in the switch, and the one that feeds the microwave isn't marked. The GFI circuit is not tripped.

Any suggestions as to how I should proceed?

Loose connection in the outlet?

 

[K8MHZ]

What is your level of expertise? What tools and meters, etc. do you have?

You are asking a tough question as where I think you should start is probably different than where I would start.

 

[K8MHZ]

Loose connection in the outlet?

That's not where he should start. That is a possibility of a failure. We can make a big list of what could have failed. He may have to start by purchasing some test gear.

 

[kwired]

I was dismayed to find the microwave not working this morning. It's the outlet that's dead and it appears that it's the only one that's dead. The microwave works fine on an extension cord to another outlet and it doesn't trip that breaker or heat up the cord. No breakers appear to be tripped; none are in the middle or have any slack in the switch, and the one that feeds the microwave isn't marked. The GFI circuit is not tripped.

Any suggestions as to how I should proceed?

You have open circuit anywhere from breaker to bus connection to final termination on the receptacle in question.

Start with voltage readings, find out if you are missing hot or neutral, check for voltage output on all breakers (since you don't know which one it is)

If you have lost both hot and neutral chances of a GFCI being a issue is higher even if there isn't any that seem to be tripped.

If there are other outlets, or junctions on the circuit you may have lost a connection at one of those.

 

[gar]

190825-1124 EDT

ggunn:

With nothing connected to the outlet measure the voltage with a high impedance meter between hot and neutral. What does it read?

Get a 3 conductor extension cord, and plug in to a known good outlet with no other load on that circuit. This cord provides 3 test leads essentially back to the main panel. The extension cord should read very low voltage between neutral and EGC. Mine reads 1 mV at the moment.

Use the extension cord EGC as your common reference.

Any completely open circuit will probably read some random voltage from capacitive coupling.

Use the extension EGC as the measuring reference to measure voltage to each of the three problem receptacle slots. This is with nothing plugged into the receptacle. What you read will determine the next step.

Assume the hot line is the problem. If voltage is not as expected, then connect a 25 W 120 V incandescent from that hot to the extension neutral. What happens?

.

 

[ggunn]

I am an electrical engineer (PV system designer), and I have only basic test gear - a circuit tester block and DVM. The circuit tester shows H/G reverse. DVM readings are H-N 2.9VAC, H-G 120VAC, N-G 120VAC. Apparently it's only the one outlet that is affected, but I do not know if it's the only outlet on the circuit. The house is 32 years old and has only the one GFI outlet in a bathroom that controls outlets outside the exterior doors, in the bathrooms, and in the garage. Those outlets are all live.

The outlet in question worked fine until this morning and there was no event that I know of that would have affected it. It has been undisturbed since we put in the microwave 5 years or so ago.

 

[ggunn]

190825-1124 EDT

ggunn:

With nothing connected to the outlet measure the voltage with a high impedance meter between hot and neutral. What does it read?

Get a 3 conductor extension cord, and plug in to a known good outlet with no other load on that circuit. This cord provides 3 test leads essentially back to the main panel. The extension cord should read very low voltage between neutral and EGC. Mine reads 1 mV at the moment.

Use the extension cord EGC as your common reference.

Any completely open circuit will probably read some random voltage from capacitive coupling.

Use the extension EGC as the measuring reference to measure voltage to each of the three problem receptacle slots. This is with nothing plugged into the receptacle. What you read will determine the next step.

Assume the hot line is the problem. If voltage is not as expected, then connect a 25 W 120 V incandescent from that hot to the extension neutral. What happens?

.

Thanks. I'll do that and get back to the forum when I'm done.

 

[K8MHZ]

I am an electrical engineer (PV system designer), and I have only basic test gear - a circuit tester block and DVM. The circuit tester shows H/G reverse. DVM readings are H-N 2.9VAC, H-G 120VAC, N-G 120VAC. Apparently it's only the one outlet that is affected, but I do not know if it's the only outlet on the circuit. The house is 32 years old and has only the one GFI outlet in a bathroom that controls outlets outside the exterior doors, in the bathrooms, and in the garage. Those outlets are all live.

The outlet in question worked fine until this morning and there was no event that I know of that would have affected it. It has been undisturbed since we put in the microwave 5 years or so ago.

When you say 'outlet', do you mean receptacle, or have you removed the receptacle and tested the conductors feeding the receptacle?

 

[K8MHZ]

If the receptacle has not been pulled yet, I'll bet once it is, the answer will be easy to find.

 

[Little Bill]

With what test/meter equipment you have, turn the breakers off until you find the one that feeds the recep for the MW by making sure your test equip now shows no voltage. After confirming that it is dead, remove the receptacle and check the connections and/or wiring. If nothing seems wrong there, check any receptacles near it that also are dead from turning the breaker off for the MW. Chances are, it is the last working receptacle before the dead one. Sounds like you lost the neutral either at the MW receptacle or the receptacle that feeds it.
Another way, since you seem to have a plug/receptacle tester, plug a lamp in where the MW is, then take your plug tester and go to the next receptacle and plug it in. Wiggle/move it around and watch the lamp to see if it flickers or comes on. If it does, there is a loose connection in that receptacle that is feeding the dead one.

 

[gar]

190825-1223 EDT

ggunn:

Some broad scope information.

The circuit has at least two wires to it, in modren times three wires. Any one or more of these wires can be open or a high resistance.

If at least one of the wires is good (normal low resistance), then by passing an AC current thru it it is possible to trace the circuit in the wall with an AC magnetic field sensor.

If you know the path of the circuit, and one lead is completely open, then you can backfeed that open wire with a detectable signal, and trace to where you loose the the signal. For a high resistance point in the circuit, like 100 ohms, I would have to experiment with techniques to pinpoint its location. TDM might work.

.

 

[K8MHZ]

With what test/meter equipment you have, turn the breakers off until you find the one that feeds the recep for the MW by making sure your test equip now shows no voltage. After confirming that it is dead, remove the receptacle and check the connections and/or wiring. If nothing seems wrong there, check any receptacles near it that also are dead from turning the breaker off for the MW. Chances are, it is the last working receptacle before the dead one. Sounds like you lost the neutral either at the MW receptacle or the receptacle that feeds it.
Another way, since you seem to have a plug/receptacle tester, plug a lamp in where the MW is, then take your plug tester and go to the next receptacle and plug it in. Wiggle/move it around and watch the lamp to see if it flickers or comes on. If it does, there is a loose connection in that receptacle that is feeding the dead one.

I second the above motion.

 

[K8MHZ]

To add to the above, depending on how much work it it is to get the panel cover off, I would probably start there just to be sure there isn't a loose screw. I have found those rascals on occasion and with my back the way it is, pulling a panel cover is easier than pulling receptacles. If it was more than a 2 minute job I would pass on that for the time being.

 

[Dennis Alwon]

You either have a bad connection, bad circuit breaker or a hidden gfci

 

[MAC702]

You have a bad connection, probably a backstab. Probably a neutral. Probably in a receptacle feeding the one that isn't working.

 

[synchro]

I am an electrical engineer (PV system designer), and I have only basic test gear - a circuit tester block and DVM. The circuit tester shows H/G reverse. DVM readings are H-N 2.9VAC, H-G 120VAC, N-G 120VAC. .

Your measurements are consistent with having a bad or open connection on the neutral side of the circuit. There may be another load on the circuit that is pulling the neutral voltage close to the "hot" wire voltage. I suggest identifying which breaker controls the hot, and then tracing that hot wire to where it exits the panel to help identify the corresponding neutral wire of the circuit going to a cable or conduit. Once identified, check that neutral for good connections on each end (panel and receptacle). If connectons are good then check the neutral wire continuity to each end. If you disconnect any neutral wire make sure the breakers on that circuit are shut off (including all that feed a MWBC using that neutral, if there is a MWBC).

 

[ggunn]

The thing is, I don't know which outlets (receptacles) are on the same circuit with the problematic one, or even if there are any. The only GFI I know of is the one I described earlier, which is not tripped; there are no GFI breakers in my MDP and no other outlets have test buttons.

 

[K8MHZ]

The thing is, I don't know which outlets (receptacles) are on the same circuit with the problematic one, or even if there are any. The only GFI I know of is the one I described earlier, which is not tripped; there are no GFI breakers in my MDP and no other outlets have test buttons.

When you locate the breaker you need to turn off that shuts down the power to the MW outlet, others on that circuit will also go dead.

 

[Besoeker3]

That's not where he should start.

Really??

The op has ascertained that the microwave is functioning.
And that other outlets are functioning.

So what's left other than that one particular outlet?