Will it trip the breaker?

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Gary11734

Senior Member
Location
Florida
I know this is an easy one for most, but it can hang up even the most seasoned electrician that has a bias in his thinking. When you see the problem, what's the first answer that comes to mind?

Ok, we have a 110-volt toaster, 1000 watt, on a 15 amp circuit.

The new apprentice (JW would never do this) lol, takes off the neutral and wires it to 220 volts. Still, 15 amp circuits.

Will it blow the fuse?
 

Little Bill

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Location
Tennessee NEC:2017
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Semi-Retired Electrician
Probably right after it melts/burns/blows the heating element. The element probably will end up shorting to the case after it burns clear. Of course, it won't trip on a short to ground if there is no EGC, but may trip on overload.
 

Gary11734

Senior Member
Location
Florida
Probably right after it melts/burns/blows the heating element. The element probably will end up shorting to the case after it burns clear. Of course, it won't trip on a short to ground if there is no EGC, but may trip on overload.

This problem can trip up a lot of electricians. When I did this problem on the road as a Tramp in the seventies, more than half got it wrong. And, they were good electricians...
 

480sparky

Senior Member
Location
Iowegia
Short-to-ground fault notwithstanding, I'd say no, even though it would be drawing just over 18 amps. The trip curve of a typical household 15a fuse probably wouldn't open in the time it takes to burn up the heating element.
 

Gary11734

Senior Member
Location
Florida
Short-to-ground fault notwithstanding, I'd say no, even though it would be drawing just over 18 amps. The trip curve of a typical household 15a fuse probably wouldn't open in the time it takes to burn up the heating element.

For the sake of the problem, assume the fuse is the weakest link in the circuit.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
I'm not sure where you're getting 110 and 220 volts from ... Japan?

Anyway, a 110-volt, 1000-watt toaster will draw 9.1 amps. The element will have a resistance of about 12Ω and a temperature of about 800°C.
When connected to 220 volts, the temperature of the element will increase, and as the temperature increases, so will the resistance. It won't draw 18 amps; but somewhat less.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
For the sake of the problem, assume the fuse is the weakest link in the circuit.
He did, using real-world behavior of a typical fuse. If you want to speak strictly theory, and/or specify that "the fuse is the weakest link," then you're answering your own question, that in theory, the fuse will blow.

We can give you the math, which says the current will double and, as 480 said, be slightly above 18a. The wattage will quadruple, however, so how long do you want to speculate the heating elements will last?

To answer your question accurately, you have to compare the time the elements take to melt to the time the fuse takes to blow at the 18+a. Well, there should be two fuses, so the weakest link will still prevail.

The point is that time is a definite factor in the operation of over-current devices, and we're very theory-oriented when we answer questions. That's why you often see more questions than answers here.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I'm not sure where you're getting 110 and 220 volts from ... Japan?
I believe we collectively chose to skip that point; I almost used 120 and 240 to show the current would be even higher.

When connected to 220 volts, the temperature of the element will increase, and as the temperature increases, so will the resistance. It won't draw 18 amps; but somewhat less.
For how long, though?
 

Gary11734

Senior Member
Location
Florida
I believe we collectively chose to skip that point; I almost used 120 and 240 to show the current would be even higher.


For how long, though?


It's a math problem.

But, it also is a way of looking at the circuit. When do electricians get this wrong without thinking? They think, if the voltage goes up, the current goes down. They are thinking about transformers or pool pump motors that they are switching from 120 to 240. That is why an electrician will get this wrong. Then, simple math will tell them if the current is higher than the breaker or not.

Don't try to work the problem past simple math. Do the math, period. Whatever the math says, that will determine if the breaker will trip or not. Electricians don't do the math on the spot, they think first and work the problem later. It is what gets them in trouble.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
I'm not sure where you're getting 110 and 220 volts from ... Japan?
When connected to 220 volts, the temperature of the element will increase, and as the temperature increases, so will the resistance. It won't draw 18 amps; but somewhat less.
For how long, though?
Not very long. Only until the element reaches the temperature where it loses strength, sags and opens.
I'd need to solve simultaneous equations to be more specific, and I'm not going to make that effort for a purely-hypothetical question about an obvious wiring error.
 

Gary11734

Senior Member
Location
Florida
Until the thermal controller turns it off, which should happen before the fuse blows.

Is that the reason a toaster was used for a load?

The toaster was used because it has a fixed resistor.

Is anybody going to do the math here and see if you get OVER 15 amps? lol

If it does, then the breaker would trip. If it doesn't, the breaker will not trip. You guys are reading too much into this problem. I love you guys!!!! I am the worst at that!

I said in an earlier post that assume the fuse the weakest link in the circuit...

K8MHZ. I assume you are a ham? I'm N4KTF.... As they say, 73's and 88's
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
The toaster was used because it has a fixed resistor.

Is anybody going to do the math here and see if you get OVER 15 amps? lol

If it does, then the breaker would trip. If it doesn't, the breaker will not trip. You guys are reading too much into this problem. I love you guys!!!! I am the worst at that!

I said in an earlier post that assume the fuse the weakest link in the circuit...

K8MHZ. I assume you are a ham? I'm N4KTF.... As they say, 73's and 88's

I did the math and got 18.1818181 amps.

Also, the element in the toaster is NOT a fixed resistor but I figured it as such. It changes resistance as it heats up.

This July I will have been a ham for 25 years.

73 de K8MHZ
 

Gary11734

Senior Member
Location
Florida
I did the math and got 18.1818181 amps.

Also, the element in the toaster is NOT a fixed resistor. It changes resistance as it heats up.

This July I will have been a ham for 25 years.

73 de K8MHZ



Fantastic! My Kenwood gear is in storage. And a bunch of Heahkits. When I was dating my second wife to be, I had her solder a practice code oscillator kit together from Heathkit. Darn thing worked so I married her!

I've been a ham since '76. Somehow when I got the general, they were giving out N numbers...

73's to you too..

Gary
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
The toaster was used because it has a fixed resistor.

Is anybody going to do the math here and see if you get OVER 15 amps? lol

If it does, then the breaker would trip. If it doesn't, the breaker will not trip. You guys are reading too much into this problem.

Trust me, a 15 amp breaker will not trip for quite some time with 18 amps going through it. Remember we have trip curves to deal with.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Is anybody going to do the math here and see if you get OVER 15 amps? If it does, then the breaker would trip. If it doesn't, the breaker will not trip.
It is not as simple as that. Any breaker may be able to sustain a constant current above its rating without ever tripping. The higher the current, the faster the trip. The closer the overload gets to the breaker's rating, the longer it takes to trip. How much of an overload a breaker can handle without tripping depends on the breaker's physical characteristics.

 
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