Microwave wiring

[FinallyRetired]

Update.
Electrician just left. My 1000 watt MW was really an 1800 watt MW - guess I need new glasses. No wonder it was blowing the 15 amp breaker. Electrician underbid the job at 1.5 hours, turned out to be 3 hours because of firewall wood behind the stove, having to remove the MW to get behind it, problems with the oven door, etc. But he charged me what he said he was going to charge me and, after watching him do the job, I'm glad I hired it out. Thanks for all the advice.

[REWahoo]

Thanks for the update. Sounds like you got it done right - and at a bargain.

[Nords]

Quote:

Originally Posted by SoonToRetire My 1000 watt MW was really an 1800 watt MW - guess I need new glasses.

Yowza-- do you have to register that transmitter with the FCC and the FAA?!?

I'd be a little scared to stand within ten feet when it's radiating...

[FinallyRetired]

Quote:

Originally Posted by Nords Yowza-- do you have to register that transmitter with the FCC and the FAA?!? I'd be a little scared to stand within ten feet when it's radiating...

Well, that bad boy cooks pretty fast. Maybe I can also run it as an early warning radar.

[HFWR]

Two words: lead jockstrap...

[FinallyRetired]

Update on my never-ending MW story.

The bad boy is now tripping the new 20 amp dedicated circuit 2-3 times a week, as well as interfering with my 2.4GHz phones. Called the MW repairman. He said it's 1800 watt input, 1000 output. Hooked up an ammeter and found a max draw of 12 amps, but the tripping is intermittent, and it didn't trip when he was here.

He did find a weak magneto (weak??) that he is going to replace, but he doesn't think that would trip the CB. He said what he really found strange is that the MW has an internal fast blow 20 amp fuse, which should have blown before the slower tripping house CB. Yet the internal fuse had not blown. He suspects a bad CB. Called the electrician back, he is going to change out the CB in the chance that it's bad, even though it's a new one.

Stay tuned ...

[Nords]

Quote:

Originally Posted by SoonToRetire Update on my never-ending MW story. The bad boy is now tripping the new 20 amp dedicated circuit 2-3 times a week, as well as interfering with my 2.4GHz phones. Called the MW repairman. He said it's 1800 watt input, 1000 output. Hooked up an ammeter and found a max draw of 12 amps, but the tripping is intermittent, and it didn't trip when he was here. He suspects a bad CB. Called the electrician back, he is going to change out the CB in the chance that it's bad, even though it's a new one.

Just how attached are you to that jammer? You've probably spent more than the cost of a new microwave on keeping the old one running. Admittedly it's been for a good cause, but still...

We only found one solution to the 2.4 GHz freq problem: a 5.8 GHz phone.
http://www.early-retirement.org/foru...tml#post493469

[ERD50]

curious-er and curious-er...

20 amp dedicated circuit should do it. magneto? Maybe 'magnetron'? That is the u-Wave generating tube in these ovens.

The internal 20 Amp going un-blown sure is a sign that things are OK.

So maybe that new breaker is overly sensitive, it does make some sense. I have no idea how common it is to get an under-rated breaker, but no doubt it can happen.

I'd say get the current measured, or (light bulb emoticon needed - literally) - I just though of something:

Plug in a known 2000 watt load, like 20 100 watt light bulbs, or a 1500 watt toaster plus 5 100W bulbs and see what happens. Maybe start @ 1500 W , give it some time and add 100 W each step. See 'whar she blows'.

That might help confirm the diagnosis and save you another service call, or at least load the electrician with a little more background, or satisfy your own (and mine) curiosity.

-ERD50

[FinallyRetired]

Quote:

Originally Posted by ERD50 Plug in a known 2000 watt load, like 20 100 watt light bulbs, ...

DW would love that!

BTW, you're right, they're replacing the magnetron, not the magneto. Electrician's coming by tomorrow to replace the 20 amp CB first.

[free4now]

Strange problem. Looks like you are moving toward getting it resolved. If it were me I'd try to narrow down whether the microwave itself is the issue by running the microwave for a while plugged into another outlet that has a dedicated 20A circuit. If you try this avoid extension cords (or at least make them as short and fat gauge as possible) to avoid having the extension cord lose power to heat and trip the breaker.

[segfault]

Is this a breaker that trips quickly when the rated current is exceeded, or one that trips more slowly? I'm guessing a microwave draws a lot of current when the magnetron first turns on (sort of like an air conditioner), but won't draw more than its rated wattage (1800) continuously.

[FinallyRetired]

Quote:

Originally Posted by segfault Is this a breaker that trips quickly when the rated current is exceeded, or one that trips more slowly? I'm guessing a microwave draws a lot of current when the magnetron first turns on (sort of like an air conditioner), but won't draw more than its rated wattage (1800) continuously.

I don't know, it's a standard Square D 20 amp circuit breaker. A new one now, since the electrician replaced it this morning. The MW guy ordered a new magnetron that will be in this week.

It's either the CB or the MW. The CB has been replaced, so if it blows again it has to be the MW. The strange thing is that the MW has an internal fast blow 20 amp fuse that has never blown, yet the CB has tripped. So it's logical that the electrician installed a CB that happened to be bad, even if the magnetron is also bad.

I'll let you know if this cures the problem.

[free4now]

Note that fuses and breakers aren't as predictable as you might expect. A 20A device won't stay on for ever for all currents under 20A and then trip right when you exceed 20A. It's possible that the breaker would trip from a quick >20A impulse, while the fuse could take longer to blow and therefore stay good.

Usually the fuses inside devices like microwaves are there to protect against shorts and seriously dangerous current draw; they aren't generally intended to protect against the possibility of tripping breakers.

[segfault]

Strange stuff... I also have a Square D breaker panel. I don't have a separate circuit for the microwave, so I guess it wasn't code in 1994 when my house was built. I just have a single 20-amp circuit, so I'm pretty sure I can't run the microwave and the toaster oven at the same time.

To vent frustration, I should add that the wiring in my house appears to have been done to the minimum standard that code requires--you won't find any thoughtful touches. For example, the ceiling light is on the same circuit as the room outlets in each of the bedrooms (and the master bedroom, bath, and guest bath lights and outlets share a single 15-amp circuit--good luck running the vacuum while someone is drying their hair). If you plug in a high-current device, the lights in that room dim significantly. The lights in other rooms (on separate circuits) are unaffected. I think the code allows a separate circuit, spanning multiple rooms, for lights, so that they could have installed a "bedroom lights" circuit and "bathroom lights" circuit to avoid the light dimming issue.

[FinallyRetired]

For those who gave me such useful advice and wanted an update. After replacing the 20 amp "new" fuse with another new 20 amp, and replacing the microwave's magnetron, the problem appears solved (knock on wood). The internal 20 amp never blew, so it appears the problem was the initial 15 amp that kept blowing. That weakened the magnetron and caused the 15 amp to blow even more frequently. The first 20 amp on a separate circuit appears to have been bad by coincidence, making the problem very confusing. But the new 20 amp and magnetron are good so far, and thanks to everyone again.

[TromboneAl]

It's those coincidences that can make life interesting.