Will it trip the breaker?

[K8MHZ]

..

 

[don_resqcapt19]

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.

It might never open the circuit...the listing standard permits both breakers and fuses to carry 134% of their rating forever. They are both required to open the circuit in 60 minutes or less with a current of 135% of their rating.

 

[Gary11734]

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.

I will try one more time.

Consider this a FIXED resistor. You guys are inserting too much information in this example.

The math has been done. The breaker would trip.

That is not what the problem was to solve. It's when electricians start thinking when the voltage goes up, current goes down. You will see this if you have a dual rated irrigation pump motor. A guy will hook up an irrigation motor from 120 to 240. He sees the voltage has risen but the current has dropped. It gets in his head without thinking he changed the straps before he doubles the voltage, hence, changing the resistance. This is a fixed resistor for this example. Also, forget about the heat and change in the value of this resistor.......... It's 14.4 ohms, period at 120 volts.

No math guy would EVER get this wrong. It's the guy in the field that has been an electrician all his life. They are the first to say, the current will drop in half and the breaker will not trip.

As I said in my first post, most seasoned electricians will get this wrong. The math guys, never.


Try it on a guy that's been in the field for a long time, you will see, he will get it wrong most of the time until he thinks about it and then does the math.

I have actually changed this resistor to an incandescent light bulb. They still get it wrong! Now that is amazing to see that. We use the toaster as stealth. The light bulb should be obvious.

Thanks for the comments. This is how we think and reason and continue to learn...

 

[al hildenbrand]

It might never open the circuit...the listing standard permits both breakers and fuses to carry 134% of their rating forever. They are both required to open the circuit in 60 minutes or less with a current of 135% of their rating.

What a succinct, pithy statement. It is worthy of the stature achieved by Zen koans.

15 Amp X 1.34 = 20.1 Amp

 

[480sparky]

Mebbe I'll stop by the local thrift store and drop a couple bucks on a used toaster and push 240v through it.

 

[Gary11734]

Mebbe I'll stop by the local thrift store and drop a couple bucks on a used toaster and push 240v through it.

LOL. Maybe Emments fix it shop has one!

 

[K8MHZ]

I will try one more time.

Consider this a FIXED resistor. You guys are inserting too much information in this example.

The math has been done. The breaker would trip.

That is not what the problem was to solve. It's when electricians start thinking when the voltage goes up, current goes down. You will see this if you have a dual rated irrigation pump motor. A guy will hook up an irrigation motor from 120 to 240. He sees the voltage has risen but the current has dropped. It gets in his head without thinking he changed the straps before he doubles the voltage, hence, changing the resistance. This is a fixed resistor for this example. Also, forget about the heat and change in the value of this resistor.......... It's 14.4 ohms, period at 120 volts.

No math guy would EVER get this wrong. It's the guy in the field that has been an electrician all his life. They are the first to say, the current will drop in half and the breaker will not trip.

As I said in my first post, most seasoned electricians will get this wrong. The math guys, never.


Try it on a guy that's been in the field for a long time, you will see, he will get it wrong most of the time until he thinks about it and then does the math.

I have actually changed this resistor to an incandescent light bulb. They still get it wrong! Now that is amazing to see that. We use the toaster as stealth. The light bulb should be obvious.

Thanks for the comments. This is how we think and reason and continue to learn...

I am a math guy and here is the problem.

If a perfect device was used, the trip curve would allow 18 amps to flow through a 15 amp breaker for 60 seconds. So one answer would be 'eventually'.

If a device was used that was on the limits of tolerance, 15 x 1.34 = 20.1, so in that case the answer would be 'no, the device would not trip'.

If you are insinuating that the fuse or breaker would open as soon as the 18 amp load is connected, I will have to argue that and bet it wouldn't happen.

So, the thing to do is to actually connect a toaster line to line and see what happens.

 

[Gary11734]

I am a math guy and here is the problem.

If a perfect device was used, the trip curve would allow 18 amps to flow through a 15 amp breaker for 60 seconds. So one answer would be 'eventually'.

If a device was used that was on the limits of tolerance, 15 x 1.34 = 20.1, so in that case the answer would be 'no, the device would not trip'.

If you are insinuating that the fuse or breaker would open as soon as the 18 amp load is connected, I will have to argue that and bet it wouldn't happen.

So, the thing to do is to actually connect a toaster line to line and see what happens.

This problem is to see if an electrician would think the current would drop. I give up on this one but it was fun. I was looking for pics on my GR2000 Heathkit TV, K8MHZ. Do you have any pics building Heathkits? Let's post a couple.

 

[K8MHZ]

This problem is to see if an electrician would think the current would drop. I give up on this one but it was fun. I was looking for pics on my GR2000 Heathkit TV, K8MHZ. Do you have any pics building Heathkits? Let's post a couple.

Then the question should have been, 'will the current go up, or down?' Adding the toaster and fuses and breakers to the problem makes it a poor one and people like me will tear it apart. What if someone told you they actually connected a 1000 watt toaster line to line and the fuse (or breaker) did NOT trip. How would you then say the correct answer would be that it would trip???

I did this same thing to my instructors in my apprenticeship for 5 years (extra year for motor control) and actually had test questions changed.

I finished #1 in my class of 40.

I never got into Grief Kits. I own a PS a buddy of mine (now SK) made and it's a tank. My home brew is mostly antennas.

 

[texie]

This conversation reminds me of a similar question to ask of an electrician. Will a dual voltage motor use more power at the low or the high voltage? Sadly, many "electricians" respond along the lines of "of course the lower voltage, just look, the current is double. It will cost twice as much to run"

 

[LarryFine]

No math guy would EVER get this wrong. It's the guy in the field that has been an electrician all his life. They are the first to say, the current will drop in half and the breaker will not trip.

As I said in my first post, most seasoned electricians will get this wrong. The math guys, never.

Try it on a guy that's been in the field for a long time, you will see, he will get it wrong most of the time until he thinks about it and then does the math.

As what you call a seasoned electrician (45 years plus), I believe your generalization is incorrect, unless you have quizzed a good-sized sampling and documented their responses. I could see rookie helpers getting this wrong, but not someone who has had a decent variety of electrical work experience over the years.

I believe that most electricians do understand the difference between adapting, adjusting, or modifying a piece of equipment to receive a different voltage and merely applying a different voltage without making any changes to it. Dual-voltage transformers, for example, require field wiring to match the supply.

We consider motors to be the main exception. A resistive load is a constant-impedance load whose current varies with the voltage, but a motor is a constant-power load whose current varies inversely with the voltage - within a designed range, of course. We know whether we selected a voltage during installation.


Now, as to your specific question, you asked whether the fuse would blow when the applied voltage was doubled, hoping for a simple yes or no answer. As you see, it's not that simple a question. We strove to answer your question, as it was asked, accurately. I believe you should have phrased it differently.

What you should have asked, now that we know where you were headed, was simply whether the current would increase or decrease, or double or halve. In my opinion, at least in this forum, you would have received a great number of correct answers; the answers you did receive should show you that.

 

[al hildenbrand]

This conversation reminds me of a similar question to ask of an electrician. Will a dual voltage motor use more power at the low or the high voltage? Sadly, many "electricians" respond along the lines of "of course the lower voltage, just look, the current is double. It will cost twice as much to run"

Yeah, exactly. Or the 208Y / 120 Volt four-wire feeder situation. Put an ammeter on the neutral to see the neutral current. With moderately unbalanced resistive load connected and running, what happens to the neutral current when only one feeder hot leg is shut off? Does the neutral current go up, or down?

 

[Strathead]

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.

Well, as a second year apprenticeship instructor I will say that few "electricians" would get this wrong. At least if you asked, Will the current go up or will it go down? As you can see from the 3 pages of responses that the answer to your question as asked is far more complex than the thought you were trying to induce. Until I read this post, I misinterpreted your question. The thought that the current would go down didn't even cross my mind. And I don't accept that any person I would respect enough to use the term electrician, would get it wrong, at least on 8 hours of sleep.

What electrician would think a 120 volt light bulb with 240 volts across it would use less electricity?

 

[Adamjamma]

The toaster will probably be just fine, but even on lowest setting your pop tarts might be black

 

[Gary11734]

As what you call a seasoned electrician (45 years plus), I believe your generalization is incorrect, unless you have quizzed a good-sized sampling and documented their responses. I could see rookie helpers getting this wrong, but not someone who has had a decent variety of electrical work experience over the years.

I believe that most electricians do understand the difference between adapting, adjusting, or modifying a piece of equipment to receive a different voltage and merely applying a different voltage without making any changes to it. Dual-voltage transformers, for example, require field wiring to match the supply.

We consider motors to be the main exception. A resistive load is a constant-impedance load whose current varies with the voltage, but a motor is a constant-power load whose current varies inversely with the voltage - within a designed range, of course. We know whether we selected a voltage during installation.


Now, as to your specific question, you asked whether the fuse would blow when the applied voltage was doubled, hoping for a simple yes or no answer. As you see, it's not that simple a question. We strove to answer your question, as it was asked, accurately. I believe you should have phrased it differently.

What you should have asked, now that we know where you were headed, was simply whether the current would increase or decrease, or double or halve. In my opinion, at least in this forum, you would have received a great number of correct answers; the answers you did receive should show you that.

Yes, generalizations. Ask a couple and see for yourself. No matter how you word a problem to an electrician, he will always go off on a tangent. That makes us human... This thread is a prime example of that. We are all in our reality world. Everyone has a bias as they see through their lens of life. This thread shows that at its finest.

This problem came from first-year apprentice class. I didn't make it up... But, could you imagine the teacher seeing all the answers above? He would have the doggy head cock... He just wanted to know if we could come up with the answer above 15 amps if we could do the math problem. What was so hard about that? And, some said that the current would drop in half if you raised the voltage. That is what the problem was to see.

 

[Strathead]

As what you call a seasoned electrician (45 years plus), I believe your generalization is incorrect, unless you have quizzed a good-sized sampling and documented their responses. I could see rookie helpers getting this wrong, but not someone who has had a decent variety of electrical work experience over the years.

I believe that most electricians do understand the difference between adapting, adjusting, or modifying a piece of equipment to receive a different voltage and merely applying a different voltage without making any changes to it. Dual-voltage transformers, for example, require field wiring to match the supply.

We consider motors to be the main exception. A resistive load is a constant-impedance load whose current varies with the voltage, but a motor is a constant-power load whose current varies inversely with the voltage - within a designed range, of course. We know whether we selected a voltage during installation.


Now, as to your specific question, you asked whether the fuse would blow when the applied voltage was doubled, hoping for a simple yes or no answer. As you see, it's not that simple a question. We strove to answer your question, as it was asked, accurately. I believe you should have phrased it differently.

What you should have asked, now that we know where you were headed, was simply whether the current would increase or decrease, or double or halve. In my opinion, at least in this forum, you would have received a great number of correct answers; the answers you did receive should show you that.

:thumbsup: You must have been typing while I was. You said it better.

 

[K8MHZ]

Yes, generalizations. Ask a couple and see for yourself. No matter how you word a problem to an electrician, he will always go off on a tangent. That makes us human... This thread is a prime example of that. We are all in our own reality world. Everyone has a bias as they see through their lens of life. This thread shows that at its finest.

This problem came from first-year apprentice class. I didn't make it up... But, could you imagine the teacher seeing all the answers above? He would have the doggy head cock...

A good teacher would then realize that this is a bad question and would fix it. Either by change or omission.

 

[Gary11734]

A good teacher would then realize that this is a bad question and would fix it. Either by change or omission.

So, the teacher had a bad question? Well, it won't be the first or last!

The apprentices didn't have an issue with it. We solved the problem and learned something about resistance when it's a fixed value.

 

[jaggedben]

My first thought was yes, it will trip the breaker. Quick review of Ohms law in my head to confirm it will draw roughly twice the current.

What muddies the question is the somewhat arbitrary choice of 1000w for the toaster. And thus the resulting borderline calculation on the trip curve of a 15A breaker. It might take long enough (5 minutes?) for a particular 15A breaker to trip that the answer to the question might as well be 'no', because by that time something has gone up in flames.

Why not make it a 1500W toaster oven? Then the answer is a pretty clear 'yes' and you can separate the seasoned electricians from the not so seasoned.

 

[K8MHZ]

I have actually changed this resistor to an incandescent light bulb. They still get it wrong! Now that is amazing to see that. We use the toaster as stealth. The light bulb should be obvious.

I can pretty much assure you that light bulb will go poof before the fuse blows or breaker trips.

What is the purpose of adding the variables to the question? Why not just ask what happens to the current if that is what you are looking for? I saw 120 volt bulbs hit with 240 before I entered my apprenticeship, I worked in factory maintenance. They get real bright and then went poof. No OCPD trippped, as the entire event takes 2-3 seconds.