My New House & Workshop

[Curious Hound]

Any microwave that puts out more than 900 watts will trip a regular 15A breaker occasionally as the load is too great for 15A. The 15A breaker may be tripping on load, not ground fault.

Your math is off. 900watts is only 7.5 amps. Appliances are rated for their max power or current usage at full load. If a 900watt microwave is tripping a 15amp breaker, that microwave is malfunctioning.

 

[Curious Hound]

The microwave worked fine on another outlet but the breaker would kick when the fridge kicked on. I realized there was an outlet by the sink for a microwave in the corner. There's one other GFCI outlet that runs off of it on the other side of the sink, but nothing is plugged in to it.

It makes sense for the refrigerator compressor and microwave running at the same time to trip the breaker. The fridge is supposed to be on it's own dedicated circuit.

Have you made sure all the connections are tight on the other outlet on this circuit?

What is the power or current rating on the microwave?

 

[Jim Oaks]

I didn't think to check the other outlet since there isn't anything plugged in.

Power feeds from this outlet to the GFCI on the other side of the sink. I think I read where you only need one GFCI in the circuit. I'm wondering if I could put a normal outlet here and leave the GFCI on the other side of the sink and be legal since there's a GFCI in the circuit.

Is it possible that the GFCI could be contributing to the breaker kicking?

I'll have to check the power output of the microwave. I'm not home right now.

 

[Jazzer]

Eric says: "Your math is off. 900watts is only 7.5 amps. Appliances are rated for their max power or current usage at full load. If a 900watt microwave is tripping a 15amp breaker, that microwave is malfunctioning."

Your math is entirely correct, sir. I said the above because I had a client who wanted to replace a range hood with an over the stove microwave. The cable was 14gauge and the breaker 15A. The data from all microwaves I looked at, 1000 watts operating load, specified a dedicated 20A circuit. I could only provide them with a 900 watt micro that the manufacturer approved for a 15A circuit. While the disparity in the math puzzled me, I put it down to inrush current for the fan and magnetron.

-Jazzer

 

[franklin2]

I didn't think to check the other outlet since there isn't anything plugged in.

Power feeds from this outlet to the GFCI on the other side of the sink. I think I read where you only need one GFCI in the circuit. I'm wondering if I could put a normal outlet here and leave the GFCI on the other side of the sink and be legal since there's a GFCI in the circuit.

Is it possible that the GFCI could be contributing to the breaker kicking?

I'll have to check the power output of the microwave. I'm not home right now.

Depends on how the wires are hooked up on these GFCI recepts. You have the power coming in from the breaker, most people call that the "home run" back to the panel. That will enter a recept box. If that box is in the kitchen, it needs to be GFCI. If you have more recepts down the line on the same breaker, you have two choices;

1. Feed them all from the other special set of terminals from the first GFCI recept. That will make the whole line from then on protected by that first GFCI recept and all other recepts down the line can be regular recepts. Any problems down the line is going to make the first GFCI trip and kill ALL the recepts down the line from the first GFCI recept.

2. Feed them all from the same top terminals where the home run wires hooked in. This means the recepts down the line will not be protected from the first GFCI. So the next recept down the line, if its still in the kitchen, will need another GFCI recept in it. And after that, you have a choice again. Either feed the rest of the kitchen recepts on that line from the special terminals on the 2nd GFCI recept, and that 2nd GFCI recept will protect all the others down the line, or feed the remaining recepts down the line from the top of the 2nd GFCI, so then you will need to add a 3rd GFCI recept, and so on.

However you want to do it, just so every recept in the kitchen is GFCI protected. There are rules about it being so many feet away from the sink or something like that, but I can't remember what the actual rules are for GFCI required recepts.

 

[Curious Hound]

Eric says: "Your math is off. 900watts is only 7.5 amps. Appliances are rated for their max power or current usage at full load. If a 900watt microwave is tripping a 15amp breaker, that microwave is malfunctioning."

Your math is entirely correct, sir. I said the above because I had a client who wanted to replace a range hood with an over the stove microwave. The cable was 14gauge and the breaker 15A. The data from all microwaves I looked at, 1000 watts operating load, specified a dedicated 20A circuit. I could only provide them with a 900 watt micro that the manufacturer approved for a 15A circuit. While the disparity in the math puzzled me, I put it down to inrush current for the fan and magnetron.

-Jazzer

That was just the microwave mfrs covering their butts. Inrush current shouldn't be much more than 125% of full load current and should only exist for a few milliseconds at that level, if at all.

A circuit should be designed so that it's normal load is 80% or less of the overcurrent protection, ie; the breaker. Granted, we don't have ultimate control of what people will plug in to a circuit. But that's OK. That is why we have circuit breakers - to prevent overload currents from melting wires and causing fires.

So, on a 15amp circuit, 80% would be 12 amps. 12amps X 120volts = 1440watts. So, any device up to 1440 watts can be plugged into that circuit with no problem. There is room to spare. So, if inrush current of the microwave is 125% of it's 1440watt rating, we are at 15 amps and the breaker won't trip. In reality, you could operate a 1500watt microwave on that circuit. Because the inrush would be so brief that the breaker would not have time to respond.

Circuit breakers are designed to trip slower at lower currents and faster at higher currents. So, a 15amp breaker that sees 16amps may actually take 1 or 2 seconds to trip. But at 50amps, it will be much faster. At 500amps, it will seem to be instantaneous. But it is still following the designed time vs current curve.

I really think Jim's issue here is in the wiring. Perhaps at the other receptacle on the circuit.

 

[Jim Oaks]

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So....................

Remember a year ago when I was talking about cutting out this door opening and enlarging it so I could use the building as a garage?

I let life get in the way but I'm back at it.

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I can't wait to get this done and get this area cleaned up.

The alley isn't that wide and I found that pulling up to the door and swinging the truck in could be a challenge, but I found that backing in is going to make it easier to get in and out.

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I hooked up the trailer to the new Ranger and went to get some lumber. I needed some 2x8x12's, 2x4x16's, a 2x8x20 along with some 2x4's, and there was no way they were going to fit in the bed. LOL.

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I cleaned up this section of the building so I had room to work.

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Marley came in to inspect the area.

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I created a wall to brace up the ceiling so I can start cutting out the cinderblock wall. The wall is 14-feet wide. I bought (2) 2x4x16's because they didn't have any 14's, and then cut them down to 14.

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I made it a 1/2-inch taller than the floor to ceiling height. Getting this thing wedged in there by myself was not fun.

Tomorrow I cut out the wall and build and install a new header.

 

[Snoranger]

We expect a time-lapse video of the entire job.

 

[RobbieD]

Busting blocks is good therapy.

Good luck!

 

[Blmpkn]

We expect a time-lapse video of the entire job.

With Benny hill music ideally.

 

[BiggSherm1988]

What’s the problem?

View attachment 49831

i was in this crazy house in august. its pretty cool inside.

 

[franklin2]

Life getting in the way can be a good thing. Lumber is a little cheaper than it was earlier in the year.

 

[Jim Oaks]

I got the wall cut out and the header in. I glued and screwed (2) 2x8x12's together and then attached a 1x on the bottom. Painted it with oil base paint, and put it up on the blocks. I had to reset (3) of the blocks with new mortar. Then I glued and screwed (3) more 2x8x12's to them. The one on the exterior is pressure treated.

I ended up with a 8'9" rough opening. I still need to clean up the edges of the block and trim it with wood. If I do 2x's it should leave me with a 8'6" opening and 1x's will give me a 8'7.5" opening.

Now I need an apron outside of the door, and I need to cut down the sewer cleanout so it's just below the apron so I dont hit it. Also need to do something with the busted block. I was wondering if I could use them as part of the apron and then fill in on top of it with something else.

I also measured 8-inches of clearance between the lightbar of TRS-2 and the ceiling. If I set a new rafter on top of the old on and remove the old one, it should give me 13-inches of clearance to jack the truck up.

 

[Uncle Gump]

Nice...

 

[Jim Oaks]

No I need to build a barn door and get some rollers and a track. Any suggestions on building a door?