Sharp microwave arcs *through* front door

Are the door seals clean? Does the door close firmly and evenly?

The door seals were passable, but not immaculate. The door itself seems to close perfectly normally. It is relatively new and lightly used, and there aren't any glaring issues like that. We did do some work on our house a while back and stirred up a lot of dust in the process, so contamination is a possibility. Supposing something like that was the cause of the arc, shouldn't it have still have followed some other path?

That isn't a suitable load for a microwave is it ? You need some water in there.

No surprise it arced.

Graham

The cause of the arc was the absense of anything in the oven that could absorb the microwave energy effectively.

Graham

I thought about that, but then I've done it a hundred times with no problem, and the micro wave has a build in 'melt butter' function, which seems to run it on low power for short bursts. That's what we were using at the time, so I dont think the load was the issue. Again though, even if that were the problem, shouldn't the arc have been contained?

-Chris

Yes, and you may want to check the outlet's ground wire just in case. But the sink may have been a lower impedance ground?

Myself, I'm not sure I'd *want* to try to fix it!

Yes, check the door gasket?

Even an empty microwave should never arc to the outside, I've never, ever seen that before, and I too have used microwaves to melt butter hundreds of times over the decades.

I don't think that's correct. Butter contains water and fat, both of which absorb microwaves. I've melted butter without problems.

Arcing usually occurs at a sharp metal edge. I once put a plastic jar of Adams peanut butter in my microwave to soften it up, and got serious arcing on the teensy bits of aluminum foil that had been left behind when I peeled off the inner seal.

¿Quien sabe?

I would thoroughly clean everything, inside and out. Also check to see that there are no bits of foil, or anything metallic, in the oven, on or around the seals, etc.

I've had that happen recently. Same product (different brand)--some surprisingly SERIOUS fireworks immediately as I hit the button. If the lights had been off, it would have lit the entire kitchen from really minuscule bits of foil.

I'm with the other poster, in that I'm not sure I'd ever trust that unit again.

jak

Yeah, I'll double check. Also noticed a second burn mark closer to the hinges, but same vertical position. Just to clarify my description of the problem, I'm not talking about an arc like you'd see from a little metal in the microwave. I'm talking about a beefy pink arc about the diameter of a pencil.

I agree it shouldn't have arced to the *outside*.

Ok. I have heard of other stories where people have done things with their microwave ovens the makers don't recommend and been puzzled why it broke after say the hundredth time though.

Graham

Maybe the quantity wasn't enough ?

Graham

Nah, it was a half a stick, well within the pre-programmed range, so that's not it. In any case, some bit of foil of just the right size or shape can lead to gradients high enough to get sparks, but this was not like this. This was some large fraction of the entire current output of the transformer, like the fireworks you see on youtube when people have pulled the guts out of the microwave and using it just to make an arc.

which

I'm not sure. The "received knowledge" on such things is that if there's nothing in the oven to absorb the microwaves, the magnetron will eventually overheat (from the reflected unabsorbed energy). The lower the power setting, the less likely this is to happen.

But overheating isn't arcing. Arcing requires a sharp metallic edge for the electric field to build to a point where the air breaks down.

If a thorough cleaning and inspection doesn't resolve the issue, I'd get a new unit. The potential for damage or injury seems too great.

This whole thing doesn't sound right. Regardless of whether the microwave oven is attached to Earth ground, the return path for the high voltage IS the chassis of the microwave oven. It would be almost impossible for that to be disrupted as the magnetron and HV transformer are bonded to the chassis. So, it's highly unlikely that the HV current (not the microwave energy) would want to jump from the oven to an external ground. Looking at the typical schematic, it's hard to come up with any sort of failure mode where such a potential difference would appear between the chassis and ground.

I'm not saying something very peculiar didn't happen. Just that an explanation relating to the HV power doesn't make sense. I'd quicker go with some combination of load (butter), dirt, and other factors affecting the microwave distribution.

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It could be possible that some part of the door, possibly one of the hinges has lost it`s bonding to chassis earth and a potential is building up there then striking to the nearest earthed metal. it`s unlikely tho in my experience.

There was a model of Phillips oven that could build up a charge on the thin aluminium cover over the lamp leading to quite spectacular arcing around the rivet which held it in place and acted as a swivel. A poor connection there was indicated by quite strong leakage of microwave radiation through the plastic menu strip on top of the oven.

Ron(UK)

Mains wont jump 2 inches !!!!!!