Electricians: Explain This!

[Jinx]

My microwave and Keurig plug into the same outlet, and they cannot be operated together without blowing the circuit breaker. I understand that, but why this?: Often, at the end of a day, I like a cup of coffee. The microwave probably has been used earlier that day as has the Keurig. BUT! Usually at the end of the day, the Keurig forgets how to turn on when I press the button! I actually have to unplug it from the outlet AND replug it back in!

Given this info, why would the Keurig forget how to turn on???

[beowulff]

I’d guess that the Keurig is getting “browned out” by the microwave. The embedded controller in it is poorly designed, and doesn’t know that it is locked up.
A properly designed controller would have a “watchdog timer” which would force a reset if it got into a “wedged” situation.

[Jinx]

@beowulff

I’d guess that the Keurig is getting “browned out” by the microwave. The embedded controller in it is poorly designed, and doesn’t know that it is locked up.
A properly designed controller would have a “watchdog timer” which would force a reset if it got into a “wedged” situation.

“Brwoned Out” makes sense. I guess, ideally, we should relocate the Keurig.

[HeiLo]

But a brownout doesn’t make sense to me. The microwave shouldn’t be able to cause a massive voltage drop on the mains. If it does, the microwave might have a defect, or the wiring to the outlet simply isn’t meant to carry as much current as the microwave wants.
From googling around, there is also a thing called “lost neutral” which apparently is quite dangerous.

You can move the Keurig, but I think you might be ignoring a serious problem.

[snfaulkner]

Might be that if it EVER detects a voltage sag, it goes into a safety mode type thing.

[engineer_comp_geek]

While a brownout/voltage sag could possibly cause something like this, I think it’s more likely that it’s just simple electrical noise from the microwave that is scrambling the Keurig’s brains. Microcontrollers in general tend to be fairly robust, but the ones that they put into consumer items like a Keurig are the el-cheapo crap controllers, and I doubt that the designers would add much circuitry (if any) to protect the microcontroller from noise spikes.

Either way, relocating the Keurig to a different circuit should eliminate the problem.

@HeiLo

From googling around, there is also a thing called “lost neutral” which apparently is quite dangerous.

It is pretty dangerous. The way that most homes in the U.S. are wired is that they are fed from what is called a “split phase” transformer, or a single transformer with a center tap. You have 240 volts AC from one end of the transformer to the other (line to line, in electrical terms), and 120 volts from either end to the center tap. The center tap is the neutral, which gets grounded at the service entrance to your home.

If the neutral connection develops a problem, then the neutral wires inside the house tend to “float”. You still have 240 volts from line to line, but the neutral is no longer at the zero point between them. It becomes a voltage divider, and the voltage depends on the load connected to the two lines. Basically, roughly half of your house should be connected to one line and the other half of your house should be connected to the other line, with all of your 240 volt appliances (oven, dryer, etc) connected from one line to the other. The loads on each line won’t be perfectly balanced though, so as one half gets dragged down, the other goes up, so that the total still equals 240. In other words, if one line to neutral gets dragged down to 100 volts, then the other line to neutral will measure 140 volts, so that the total is 240 volts. The neutral is “floating” between the two line voltages.

When the voltage goes low on one line and high on the other, this can damage electronic devices and, especially on the high side, it can cause excessive currents which can start fires. In other words, this is the type of problem that can burn your house down and kill everyone inside. So yes, it is indeed quite dangerous.

It’s possible that something like that is happening here, but you would notice it in other parts of the house, namely that some lights will dim and others will get brighter as things like the microwave or vacuum cleaner are turned on and off.

[Sparky812]

Relocating the Kuerig is the simplest answer.

However… you should not ignore why the breaker was tripping. What is the amperage of that breaker? What else is on that circuit? Is it a dedicated kitchen circuit? Does it have a GFCI breaker and/or outlet. How many times has it been tripped?

FTR, around here each kitchen outlet should be on a dedicated circuit with minimum 12 gauge wire and a 20A GFCI breaker. A GFCI outlet is required if within 36" of a water source.

If you’re using a regular outlet in a house, office, classroom, etc… it could have multiple outlets on the circuit and a 15A breaker would not be able to handle the load.
ETA after some googling it appears the Kuerig could peak at 1000-1500W which is about 9-13A while a typical 1100W microwave peaks at 10A.

[Chefguy]

@Sparky812

Relocating the Kuerig is the simplest answer.

However… you should not ignore why the breaker was tripping. What is the amperage of that breaker? What else is on that circuit? Is it a dedicated kitchen circuit? Does it have a GFCI breaker and/or outlet. How many times has it been tripped?

FTR, around here each kitchen outlet should be on a dedicated circuit with minimum 12 gauge wire and a 20A GFCI breaker. A GFCI outlet is required if within 36" of a water source.

If you’re using a regular outlet in a house, office, classroom, etc… it could have multiple outlets on the circuit and a 15A breaker would not be able to handle the load.
ETA after some googling it appears the Kuerig could peak at 1000-1500W which is about 9-13A while a typical 1100W microwave peaks at 10A.

I don’t know where you live, but I’ve never seen a kitchen in the US that has every outlet on a dedicated circuit. Generally speaking, the refrigerator (and possibly microwave) is on its own circuit, but other outlets are not. All are protected by GFCI, however.

[friedo]

@Chefguy

I don’t know where you live, but I’ve never seen a kitchen in the US that has every outlet on a dedicated circuit. Generally speaking, the refrigerator (and possibly microwave) is on its own circuit, but other outlets are not. All are protected by GFCI, however.

Edit: nevermind, misread.

[ZonexandScout]

@Sparky812

Relocating the Kuerig is the simplest answer.

However… you should not ignore why the breaker was tripping. What is the amperage of that breaker? What else is on that circuit? Is it a dedicated kitchen circuit? Does it have a GFCI breaker and/or outlet. How many times has it been tripped?

FTR, around here each kitchen outlet should be on a dedicated circuit with minimum 12 gauge wire and a 20A GFCI breaker. A GFCI outlet is required if within 36" of a water source.

If you’re using a regular outlet in a house, office, classroom, etc… it could have multiple outlets on the circuit and a 15A breaker would not be able to handle the load.
ETA after some googling it appears the Kuerig could peak at 1000-1500W which is about 9-13A while a typical 1100W microwave peaks at 10A.

This is correct, though I have no idea how your house was wired or how old it is. Most special purpose dedicated outlets (the ones above your counter in your kitchen, for example) are 20A circuits.

According to Keurig, peak draw on their units can be as high as 1500 watts, so I’m not surprised that your microwave and Keurig combined manage to overwhelm a 15A circuit.

Ooops! Ninjaed.

[Snnipe_70E]

@engineer_comp_geek

While a brownout/voltage sag could possibly cause something like this, I think it’s more likely that it’s just simple electrical noise from the microwave that is scrambling the Keurig’s brains. Microcontrollers in general tend to be fairly robust, but the ones that they put into consumer items like a Keurig are the el-cheapo crap controllers, and I doubt that the designers would add much circuitry (if any) to protect the microcontroller from noise spikes.

Either way, relocating the Keurig to a different circuit should eliminate the problem.

It is pretty dangerous. The way that most homes in the U.S. are wired is that they are fed from what is called a “split phase” transformer, or a single transformer with a center tap. You have 240 volts AC from one end of the transformer to the other (line to line, in electrical terms), and 120 volts from either end to the center tap. The center tap is the neutral, which gets grounded at the service entrance to your home.

If the neutral connection develops a problem, then the neutral wires inside the house tend to “float”. You still have 240 volts from line to line, but the neutral is no longer at the zero point between them. It becomes a voltage divider, and the voltage depends on the load connected to the two lines. Basically, roughly half of your house should be connected to one line and the other half of your house should be connected to the other line, with all of your 240 volt appliances (oven, dryer, etc) connected from one line to the other. The loads on each line won’t be perfectly balanced though, so as one half gets dragged down, the other goes up, so that the total still equals 240. In other words, if one line to neutral gets dragged down to 100 volts, then the other line to neutral will measure 140 volts, so that the total is 240 volts. The neutral is “floating” between the two line voltages.

When the voltage goes low on one line and high on the other, this can damage electronic devices and, especially on the high side, it can cause excessive currents which can start fires. In other words, this is the type of problem that can burn your house down and kill everyone inside. So yes, it is indeed quite dangerous.

It’s possible that something like that is happening here, but you would notice it in other parts of the house, namely that some lights will dim and others will get brighter as things like the microwave or vacuum cleaner are turned on and off.

Good description of floating neutral.
I had this problem once in a high rise building. 3 phase and 208 volts high rather than 240. Strange thing were happening in one office. I tested the voltage at one outlet 190 VAC. Knew I had a neutral problem and found a burned neutral (Zinsco panels). In the office every computer that was protected by an APC power supply/ surge protector the surge protector was fried. The other computers that were protected by cheep surge protectors were fried. The management company purchased several computers and surge protectors.

[Marvin_the_Martian]

@Chefguy

I don’t know where you live, but I’ve never seen a kitchen in the US that has every outlet on a dedicated circuit. Generally speaking, the refrigerator (and possibly microwave) is on its own circuit, but other outlets are not. All are protected by GFCI, however.

For quite some time the NEC has required kitchens have two GFCI protected 20A countertop circuits. Usually half the outlets on each circuit, frequently alternating circuits as you move along the counter. It is also good practice to have the fridge and microwave on their own circuits. Frequently there is a dedicated circuit for the dishwasher and garbage disposal.

[Daylate]

Looks strange to me. I’ve had a Kuerig and a 1100 watt microwave plugged into the same outlet for years, and have never had a problem. The Kuerig and the microwave can both be run simultaneously with no difficulty.

The only time there has been an issue is if I happen to be running the entire house on a backup generator instead of line power, and decide to operate both at once. This overloads the generator which will immediately go off circuit, requiring a trip out to the generator shed to reset things. Soon learn not to do this.

BTW, my house was built in 1966, so it has 1966 wiring and power panels. Nothing excessive or fancy.

[Chefguy]

@Marvin_the_Martian

For quite some time the NEC has required kitchens have two GFCI protected 20A countertop circuits. Usually half the outlets on each circuit, frequently alternating circuits as you move along the counter. It is also good practice to have the fridge and microwave on their own circuits. Frequently there is a dedicated circuit for the dishwasher and garbage disposal.

Sure, but unless I misread Sparky’s post, he’s saying that every kitchen outlet requires a dedicated breaker. I suppose that could be local municipal code or something, but it seems extreme.

[rbroome]

This floating neutral sounds serious. How does one test for this problem?
Is there something a knowledgable homeowner can do?

[PoppaSan]

@rbroome

This floating neutral sounds serious. How does one test for this problem?
Is there something a knowledgable homeowner can do?

It is serious. Mostly it is found by empirical evidence. Turn off light in kitchen and living room lights dim. Motors seem to surge or not run at rated speed; sometimes faster sometimes slower. Motion activated LEDs stay on dim with the switch off. I’ve smoked electronics by knocking a wire nut off in a junction box. One reason not to share neutrals between circuits.
For your house, a loss at the transformer requires a call to your power utility. Your breaker panel mains would require a pro.
If you suspect one and your house is fairly recent, on a turned off line I’d check for continuity between the neutral and ground at an outlet. That would be the slot that shows zero voltage to ground normally. With everything else on the circuit unplugged, run a space heater and, on an unused outlet but same circuit, check for voltage between neutral and ground. That should still be zero. This checks that specific circuit between that point and the breaker panel mains.

Or get this for <$20.

[Snnipe_70E]

@PoppaSan

It is serious. Mostly it is found by empirical evidence. Turn off light in kitchen and living room lights dim. Motors seem to surge or not run at rated speed; sometimes faster sometimes slower. Motion activated LEDs stay on dim with the switch off. I’ve smoked electronics by knocking a wire nut off in a junction box. One reason not to share neutrals between circuits.
For your house, a loss at the transformer requires a call to your power utility. Your breaker panel mains would require a pro.
If you suspect one and your house is fairly recent, on a turned off line I’d check for continuity between the neutral and ground at an outlet. That would be the slot that shows zero voltage to ground normally. With everything else on the circuit unplugged, run a space heater and, on an unused outlet but same circuit, check for voltage between neutral and ground. That should still be zero. This checks that specific circuit between that point and the breaker panel mains.

Or get this for <$20.

Also check voltage between the hot and neutral at any outlet. It should reed between 110 and 130 VAC.

When I built my kitchen out I was required to have two 20 amp circuits, one feeding one side of the kitchen and the other the other side. With GFI protection on any outlets within 3 feet of water. A decated 20 amp circuit for the Frig and dishwasher and I believe one for the desposal.

[rbroome]

@PoppaSan

It is serious. Mostly it is found by empirical evidence. Turn off light in kitchen and living room lights dim. Motors seem to surge or not run at rated speed; sometimes faster sometimes slower. Motion activated LEDs stay on dim with the switch off. I’ve smoked electronics by knocking a wire nut off in a junction box. One reason not to share neutrals between circuits.
For your house, a loss at the transformer requires a call to your power utility. Your breaker panel mains would require a pro.
If you suspect one and your house is fairly recent, on a turned off line I’d check for continuity between the neutral and ground at an outlet. That would be the slot that shows zero voltage to ground normally. With everything else on the circuit unplugged, run a space heater and, on an unused outlet but same circuit, check for voltage between neutral and ground. That should still be zero. This checks that specific circuit between that point and the breaker panel mains.

Or get this for <$20.

Thanks! I have one and have never detected any problems in my house. Which is a good thing. Especially since the wiring was “fixed” after Katrina. The fixes after that storm that were done caused a lot of fires in the ensuing years.