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John Dirks Jr

circuit for microwave

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I'll be putting an over range microwave oven where a simple fan hood used to be. The 15 amp circuit that served the fan is also serving it's fair share of lighting circuits. This new microwave is also a convection oven so it's rated at 1750w. I dont trust the existing 15 amp circuit for the new oven.

My house has 60 amp service but I get away with it due to gas heat, cooking and water heater. Still, over the years stuff has gotten added and I'm looking for a place to add the microwave feed. I've managed to keep things balanced and we don't have problems with blowing fuses, either circuits or mains. The main fuses are still 60 amps so they protect the SEC from overload as they should.

The microwave needs 120v. I want to tap into one leg of a 20amp 240 circuit that is currently only serving a small air compressor that rarely gets used. I thought this over and I think it's safe but I wanted to make sure before I go forward.

My plan is to run a separate cable of 12/2 from the microwave receptacle to the main panel. In the panel I want to pigtail into one of the legs of 240v compressor circuit. By the microwave having its own 12/2 cable it will have its own neutral. This should work and be safe right?

The pictures show the fuse type and the location I plan to tap. The hot for the microwave will be pigtailed into the black lead at the compressor fuse pullout and the microwave neutral will go the the neutral bar in the panel.

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At 120v, and 1750 watt, you should be pulling 14.5 amp. Have you tried the microwave just to see if it does blow a fuse? I'm with you are far as having a 20 amp line, just saying you may not have to.

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Your sure that service is only 60 amps? That type of fuse box might have separate lugs at the bottom to tap into into and install a subpanel box.

The lugs are already tapped and they're at the top directly of the main lugs. The sub is a 240 for drier and AC. I prefer to stay out of that subpanel since its not covered by the main.

I rate it at 60amp since that is the size of the main pullout fuses and it has a #4 AL service entrance cable. Trust me, it's 60amp service.

Were ditching a 1500 watt microwave in the addition of the new one so the total load should be fine for our family use as thats pretty much what is has been anyway.

The reason for wanting to pigtail like I suggested is to keep things balanced better relative to various circuits on each pole.

Ben,

The existing 15amp for the hood has enough other lighting on it that connecting to new microwave oven to is will likely cause fuse blowing issues.

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John, how much tonnage has the AC in your house? Will there be any other 240V loads besides the new microwave, AC and air compressor when you're done?

Sourcing the single pole microwave circuit at 2 pole breaker is not a safe way to do that.

Marc

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John, how much tonnage has the AC in your house? Will there be any other 240V loads besides the new microwave, AC and air compressor when you're done?

Sourcing the single pole microwave circuit at 2 pole breaker is not a safe way to do that.

Marc

The AC is a small unit that draws less than 10amps. The drier pulls about 25amps when all cranked up. No other 240's will be added.

Since the new microwave circuit will have its own neutral, why is it unsafe?

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Because 2 pole breakers (240 Volt) are listed only for 2 pole service.

Install a new 20A, 120V breaker in your main panel if you have an empty slot available. If not, maybe a duplex breaker (2-120V breakers in one slot), or even upgrade the feeder to the sub to 4 wires and use that for the micro.

Another option is to install an additional sub.

Marc

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John, it sounds like you're remodeling this place backwards. Quit working around obstacles and gut that place already. A new service and a rewire will be real easy then.

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Because 2 pole breakers (240 Volt) are listed only for 2 pole service.

Install a new 20A, 120V breaker in your main panel if you have an empty slot available. If not, maybe a duplex breaker (2-120V breakers in one slot), or even upgrade the feeder to the sub to 4 wires and use that for the micro.

Another option is to install an additional sub.

Marc

He's got an antique fuse panel there. Not likely there's any space to add a breaker of any kind.

He does not want to go from the sub, because it is installed wrong, double tapped off the service conductor connections. I think that's the feeder to the sub leaving the panel on the left ? and if so, it is already 4 wire.

John, I'm with Tom, replace the service with a larger rated panel (200 A). Install a 60 amp main breaker in it for now. When cash flow allows, have the service increased to 200 Amp.

You can repair the feed to the subpanel, which I assume is a breaker panel, modern-like?

If you have #8 or #6 installed to the sub, then you can remove the double taps and connect that feeder to the fuse pull where you have the 20's for the compressor now. Replace the 20's with 40 or 60 amp cartridge fuses.

Then you can run the new micro circuit and the compressor and other circuits from the sub with new breakers. You'll be that much closer to an upgraded system.

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I figured it out. I was wrong when I earlier stated that the sub panel wan not covered by the main. After a quick study of the schematic on the main panel (shoulda done that first), the sub feeder lugs are after the 60amp main fuses so the main fuses protect the SEC from everything the house can dish out. Furthermore, every circuit has the correct size breaker or fuse for the conductors they feed.

Now I'm not afraid to go into the sub to find a place for the new microwave. There's a position in the sub that serves hard wired smoke alarms that I put in not too long ago. I'll move the smoke alarm feed into the main panel and pigtail it wherever since it draws next to nothing. Then, I'll install a BR 20amp breaker in that position in the sub for the microwave.

I know it's best to get an upgrade and that is on the list. For now, I don't believe I'm doing things backwards. I'm making extra effort to make sure things are balanced and safe for the equipment I currently have.

The time spent making things work with an older system has given me a new understanding of how electrical systems work and why it's important to keep things balanced.

My panel is crowded. However, it's balanced and properly fused. It's working fine.

main panel label

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That plan gets my approval. I was picturing a mess worse than that.

Now that we know what you've got, including a picture of Kristen, could you move those wires? [:)] maybe Jim can tell us if you can go back to plan A and use one of the 20 amp fuses, provided you disconnected the compressor?

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I'm slammed this evening. All I've got time for this minute is to say that you have a 100-amp service with copper SECs.

- Jim Katen, Oregon, back to work.

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That plan gets my approval. I was picturing a mess worse than that.

Now that we know what you've got, including a picture of Kristen, could you move those wires? [:)] maybe Jim can tell us if you can go back to plan A and use one of the 20 amp fuses, provided you disconnected the compressor?

Kristen...The Baltimore Ravens Cheerleader who used to work out in the same gym we belonged to years ago. Seems like I remember putting in extra effort workouts whenever she was there.

http://www.baltimoreravens.com/People/C ... ten_D.aspx

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I'm slammed this evening. All I've got time for this minute is to say that you have a 100-amp service with copper SECs.

- Jim Katen, Oregon, back to work.

I'm seeing aluminum SEC all the way in person here.

You can just barely make out 4 AL - 3

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A very careful scratch of the conductor at the lug shows soft aluminum.

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John, looking at the size of the Service cable entering at the top right of the panel, it looks like a 100 amp service to me. You don't see too many 60 amp service cables that aren't 50+ years old and cloth jacketed. And they're usaully tin clad copper.

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You need a #2 aluminum or copper clad aluminum to get a 100 amp service as per Table E3503.1, 06' IRC.

In either case, I'd say that John doesn't have to worry about his service being too small for right now, even with the new micro.

Marc

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John, looking at the size of the Service cable entering at the top right of the panel, it looks like a 100 amp service to me. You don't see too many 60 amp service cables that aren't 50+ years old and cloth jacketed. And they're usually tin clad copper.

Those are odd-looking conductors, but that stranded grounding conductor looks like Al. At least from here.

John, if you have trouble or expense finding a breaker, you could replace that whole subpanel with a nice new breaker panel. We're not worried about the fuses, but those breakers are antiques.

You could temporarily feed the new panel with the 60 amps from your main panel. Then you'd have plenty of space for new kitchen circuits when you do the rest of the kitchen upgrade.

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John, looking at the size of the Service cable entering at the top right of the panel, it looks like a 100 amp service to me. You don't see too many 60 amp service cables that aren't 50+ years old and cloth jacketed. And they're usually tin clad copper.

Those are odd-looking conductors, but that stranded grounding conductor looks like Al. At least from here.

John, if you have trouble or expense finding a breaker, you could replace that whole subpanel with a nice new breaker panel. We're not worried about the fuses, but those breakers are antiques.

You could temporarily feed the new panel with the 60 amps from your main panel. Then you'd have plenty of space for new kitchen circuits when you do the rest of the kitchen upgrade.

That sounds like a good idea and I might do it eventually. For now I'll just pigtail the smoke alarms to the other side 15amp breaker which currently only serves a few receptacles in the basement. I already picked up a 20 amp breaker for the micro and I'll install it where the 15 amp smoke alarm breaker was.

This old Sears sub was installed in the early 70's. It accepts Cutler Hammer BR type breakers so getting replacements is not a problem.

I have a question about time delay cartridge fuses. My mains are 60 amp and currently not time delay. Even though I have things well balanced and have not had trouble blowing mains, if I switched to time delay mains, how many extra amps do they let slip by and for what period of time before they blow?

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