1 2
thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/7/22 3:08 p.m.

Hi all. I have a microwave on my counter that I'd like to move. It's currently plugged into a 20a outlet. I'd like to move it to a regular 15a outlet, but I think that's underrated? The outlet I'd move it to is protected by a 20a breaker and fed by 14 ga wires. Would using that outlet for just the microwave cause any problems (like burning my house down)?

thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/7/22 3:11 p.m.

I should mention the microwave's manual says it should be plugged into a 20a circuit. 

The wiring is undersized for the microwave.  You will be drawing more current than the 14 gauge wires are rated for.     The 20A breaker won't protect the #14s.  It is for #12 and larger gauge wires.


I will leave the rest of the math up to you. 

thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/7/22 3:42 p.m.

In reply to Russian Warship, Go Berkeley Yourself :

Gotcha, thanks. The bigger breaker kinda threw me. 

Also, as a sanity check: I used my wire strippers as a test for the wire gauge. That make sense right? The wire cleanly fit in the 14 ga hole and was loose in the 12 ga one. 

Are the strippers for solid of stranded wire?   Same question for the wire itself.


The insulating jacket on the wire should be marked with the gauge of the wire.  If you can access enough length.

Datsun310Guy
Datsun310Guy MegaDork
8/7/22 5:50 p.m.

Years ago my job sold a medical film processor requiring a 20amp cord so everyone installing one was pissed off and bent the prong to fit into the receptacle.  

Smart ass salesman running the company had us include a 20 amp receptacle so they could change it out.

Electrical engineer that designed the processor told him he was an idiot and threw his hands up in defeat.  

Never heard of any fires.....

1988RedT2
1988RedT2 MegaDork
8/7/22 6:57 p.m.

thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/7/22 10:30 p.m.
Russian Warship, Go Berkeley Yourself said:

Are the strippers for solid of stranded wire?   Same question for the wire itself.


The insulating jacket on the wire should be marked with the gauge of the wire.  If you can access enough length.

I couldn't get enough of the wire out to see the insulation label, thus leading to the half-assery. 

Wire in the wall is solid, and the Klein Katapult strippers I use can do both apparently. 

In reply to Datsun310Guy :

Today I learned...

11GTCS
11GTCS Dork
8/8/22 9:03 a.m.

In reply to thatsnowinnebago :

Also, please replace that 20 A breaker with a 15 A!  

dean1484
dean1484 GRM+ Memberand MegaDork
8/8/22 12:51 p.m.

How many watts is your microwave?  Do the math and it will tell you the working amps it draws.  Go from there. 

dean1484
dean1484 GRM+ Memberand MegaDork
8/8/22 12:54 p.m.

Oh and for easy math and a margin of safety I use 100 volts not 110 or 120. 

dculberson
dculberson MegaDork
8/8/22 1:42 p.m.

Does the microwave have a 20a plug? (like above, with the sideways pin.) I'd be shocked if a residential microwave had that. It may be that they're saying it needs a 20a circuit due to the possibility of sharing the circuit with other devices. If it has a regular 15a plug you'll be fine as long as you're not operating any other high draw devices on that circuit at the same time.

thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/8/22 1:52 p.m.
dculberson said:

Does the microwave have a 20a plug? (like above, with the sideways pin.) I'd be shocked if a residential microwave had that. It may be that they're saying it needs a 20a circuit due to the possibility of sharing the circuit with other devices. If it has a regular 15a plug you'll be fine as long as you're not operating any other high draw devices on that circuit at the same time.

Nope, it's got a normal plug. 

thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/8/22 1:56 p.m.
dean1484 said:

How many watts is your microwave?  Do the math and it will tell you the working amps it draws.  Go from there. 

1000W. Which means it only draws like 8.3 amp, according to the calculator I found online. Is that right?

dean1484
dean1484 GRM+ Memberand MegaDork
8/8/22 4:18 p.m.

Or with the safety margin included with the 100 volts it is 10 amp

 

Another thing to consider is the breakers ware out.  They fail in safe mode meaning it takes less amps to trip them. If you are having an issue with one that is tripping and you know everything else in the circuit is good replace the breaker.   I would put a new 15 amp beaker in and call it good.  
 

Lastly spend a little more when replacing breakers.  It is the kind of thing you just don't go cheap on. Think of it like safety gear for your race car.   

dean1484
dean1484 GRM+ Memberand MegaDork
8/8/22 4:19 p.m.

There has to be an electrician on here that can chime in on what is a quality brand to look for 

thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/8/22 4:26 p.m.
dean1484 said:

Or with the safety margin included with the 100 volts it is 10 amp

 

Another thing to consider is the breakers ware out.  They fail in safe mode meaning it takes less amps to trip them. If you are having an issue with one that is tripping and you know everything else in the circuit is good replace the breaker.   I would put a new 15 amp beaker in and call it good.  
 

Lastly spend a little more when replacing breakers.  It is the kind of thing you just don't go cheap on. Think of it like safety gear for your race car.   

I haven't moved the microwave from the 20a outlet so nothing is tripping. There's a recent inspection sticker on the breaker panel so all the wiring was inspected before we bought the house two years ago. 

This kind of work isn't in my wheelhouse so I'm being cautious and moving slowly. I don't like getting shocked. 

dean1484
dean1484 GRM+ Memberand MegaDork
8/8/22 4:33 p.m.

Yes but how old is the house?  Are the breakers original to the house?   Did they test the circuits and the breakers as part of the home inspection?   (Not normally done so I would assume no).   Replacing a breaker is easy but yes you can definitely get zapped if you mess up.  
 

 

thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/8/22 4:48 p.m.

In reply to dean1484 :

The house is from 1928 so the breakers are not original smiley. Luckily all of the knob-and-tube wiring has been replaced at some point in the last 96 years though. 

dean1484
dean1484 GRM+ Memberand MegaDork
8/8/22 5:47 p.m.
thatsnowinnebago said:

In reply to dean1484 :

The house is from 1928 so the breakers are not original smiley. Luckily all of the knob-and-tube wiring has been replaced at some point in the last 96 years though. 

How old are they?  

dculberson
dculberson MegaDork
8/8/22 5:55 p.m.

In that case, the owners manual is definitely being overly conservative to compensate for additional load on the circuit. If you aren't sharing it with other high draw items I would not worry about running it on a 15 amp circuit.

SV reX
SV reX MegaDork
8/8/22 6:18 p.m.

A couple notes:

-No recent inspection would have been able to see the wiring unless they opened the walls. The sticker is for the panel only. 
- Typical residential modern wiring uses 12 ga wire for outlet circuits. Sometimes 14 ga for lighting circuits. 
- Microwaves typically are wired now with dedicated 20A circuits. 
- If that wire is really 14 ga, you MUST CHANGE THAT BREAKER!!

- Standard electrical calculations typically include a 20% safety margin.  That means a 15A circuit can handle 12A of load.

-Lots of 20A circuits use 15A receptacles.

- If the circuit is 14 ga wire, I would only put the microwave there if it is a dedicated circuit. 

SV reX
SV reX MegaDork
8/8/22 6:26 p.m.

One more thing...

Residential microwaves typically operate at about 40-60% efficiency. So, if the output of the microwave is actually 1000w, the load it draws could theoretically be 1600w or more. That's why they are wired with dedicated 20A circuits. 
 

 

thatsnowinnebago
thatsnowinnebago GRM+ Memberand UberDork
8/8/22 7:01 p.m.

Good to know on the sticker just being for the panel.

I'm assuming there's some kind of tool to check wire gauges? 

I'm not sure how to tell the age of the breakers, so I took a photo. 

1 2

You'll need to log in to post.

Our Preferred Partners
Wdg8CFApPn1efMLhVQL4u7Vu4hfUjj4FyswBnXnAq8rrt71KmCKLA877a5mMKOZk