Will it trip the breaker?

[jaggedben]

The crux of the biscuit here is whether one assumes the toaster to be a constant power device, which it isn't. That's what the question is testing, not what the time constant of the breaker is. It's a question for apprentices; it has to be kept simple. I think that if "seasoned electricians" often get it wrong, it's more likely because they are thinking about all the complicating details, not because they don't know how electricity works.

But the complicating details could have easily been adjusted so that the more knowledgeable don't get the answer 'wrong.' That's what makes it a poor question.

 

[Gary11734]

So..... if you're an apprentice the answer is 'yes', and if you're experienced the answer is 'no'?

I gave this problem to my Ex-wife, which was a CPA. She took the Electrical Unlimited Florida test and passed it the first time. ZERO field worker. She knew NOTHING about electricity, but was good at math and can take a test.

She did the math and said, yes Gary, it will trip the breaker. It wasn't a complicated problem at all. And, knowing she knows absolutely nothing about the field, she would give this answer.

The "Seasoned Electrician" got a lot of dander up on this one. It wasn't meant to.

You have to answer the question; Why did some think immediately that the current would drop in half as the voltage doubling? I haven't seen anybody here answer that question. I've tried to explain that to no avail.

The apprentices that got this wrong, ALL, had been in the field for years before taking the class. Not all got it wrong, but some... There is a reason why...

 

[roger]

I gave this problem to my Ex-wife, which was a CPA. She took the Electrical Unlimited Florida test and passed it the first time. ZERO field worker. She knew NOTHING about electricity, but was good at math and can take a test.

Help me out here, how did she qualify to take the test with out the required experience?

Roger

 

[480sparky]

Help me out here, how did she qualify to take the test with out the required experience?

Roger

In some places, all that's needed to take the test is paying for it. Getting the license is a different story.

 

[jaggedben]

...

You have to answer the question; Why did some think immediately that the current would drop in half as the voltage doubling? I haven't seen anybody here answer that question. I've tried to explain that to no avail.

Because they don't know Ohms law and thus don't realize that the nameplate wattage is dependent on the nominal voltage input. It is simply lack of education on the relevant theory. And, I would add, not generally a reflection on their intelligence.

(Neither the length of this thread nor the criticism of your formulation of the question are due to anyone's failure to understand that on this forum. And it's not a coincidence that people who participate here and are interested in your thread are more knowledgeable than the apprentices you're catching unawares. )

 

[LarryFine]

The "Seasoned Electrician" got a lot of dander up on this one. It wasn't meant to.

I didn't resent being called seasoned; only being told that being seasoned means getting it wrong.

You have to answer the question; Why did some think immediately that the current would drop in half as the voltage doubling? I haven't seen anybody here answer that question. I've tried to explain that to no avail.

Because it's common to forget that equipment designed for one voltage has to be changed for another; that the rated wattage presumes being fed with the rated voltage.

 

[winnie]

Agree 100%


What has to be remembered, this was a first-year apprentice class. What does a first-year student know? But, what are we doing in class this first year? Learning math. The teacher is saying, do the math.

This was to understand a FIXED resistance, and how to solve for it, period. But, what we found was that persons that had been in the field were claiming pretty quick that the current would drop in half immediately without doing the math. That to me was a surprise.

So in the context of the class, it would have been reasonable to expect the students to say 'the current will double'.

In the context of this forum, I think that you got very good answers. The _fact_ is that the resistance of the heating element will increase as it heats up, and that the breakers will have a trip curve, and in this forum where we do a fantastic job of picking little nits, I think you got lots of interesting and useful information.

But I absolutely agree that it is a surprise that people would expect the current to fall.

-Jon

 

[Gary11734]

Help me out here, how did she qualify to take the test with out the required experience?

Roger

They give you credit for the CPA degree. Plus, she got the rest of the qualifications working at the company. I made her a project managers position. It was the only electrical test she ever took. And, we did reciprocate her license, too.

She was the accounting side of the business, too. Getting a PL/balance sheet, and job costing on a monthly basis was a big plus that most didn't have.

She missed one question on pneumatics. She was all upset.

It was weird coming home hearing Mike Holt as she was watching his DVD's.

And, it was good to have two masters in the shop in case something happened to one of us.

 

[kwired]

Because they don't know Ohms law and thus don't realize that the nameplate wattage is dependent on the nominal voltage input. It is simply lack of education on the relevant theory. And, I would add, not generally a reflection on their intelligence.

Exactly.

A common misconception in this area comes from knowing that a motor that draws 10 amps @ 480 volts will draw 20 amps @ 240 volts - but they forget you have to reconfigure the motor for it to work properly. Each individual winding still sees same voltage and current with either supply there is just a series vs parallel difference in configuration. Or another example is transformer primary vs secondary current gets one thinking higher volts means less amps - true but Ohm's law means resistance will be different to get same power out of it.

They give you credit for the CPA degree. Plus, she got the rest of the qualifications working at the company. I made her a project managers position. It was the only electrical test she ever took. And, we did reciprocate her license, too.

She was the accounting side of the business, too. Getting a PL/balance sheet, and job costing on a monthly basis was a big plus that most didn't have.

She missed one question on pneumatics. She was all upset.

It was weird coming home hearing Mike Holt as she was watching his DVD's.

And, it was good to have two masters in the shop in case something happened to one of us.

How does one successfully take an electrical license exam, even if they are a math wizard, if they don't know the theory to know what values to plug into formulas or have any experience with code book?

 

[Gary11734]

Exactly.

A common misconception in this area comes from knowing that a motor that draws 10 amps @ 480 volts will draw 20 amps @ 240 volts - but they forget you have to reconfigure the motor for it to work properly. Each individual winding still sees same voltage and current with either supply there is just a series vs parallel difference in configuration. Or another example is transformer primary vs secondary current gets one thinking higher volts means less amps - true but Ohm's law means resistance will be different to get same power out of it.



How does one successfully take an electrical license exam, even if they are a math wizard, if they don't know the theory to know what values to plug into formulas or have any experience with code book?

You get the prize! This is exactly why guys that have been in the field get this wrong. You hit it on the head! They think so quick and say what they see on a daily basis. Transformers have this too. Voltage goes up on the primary, but the current goes down. It's not about math at this point, but how they are thinking without really thinking the problem through. I am so happy finally see's what I have been trying to articulate for four days!

She watched all of Mike Holts classes on DVD. I guess she could read n OHMS wheel just like the rest of us. I would not trust her to hook up a 3-way! Lol But, she passed it and in the nineties. That four-year degree from Florida State had some value after all! Go Miami Hurricanes!

So, when guys would come to me and say they couldn't pass their masters class, I would show them her EC Unlimited License. And say, you have no excuse but to study more and take the test. I always had a full set of Mike Holts DVDs at the shop for their use. I also use to pay for all the apprentices that went to school. But, I would tell them, if they quit, they would have to refund the money to me. A bad way to force them but it helped keep them in class.

 

[Little Bill]

You get the prize! This is exactly why guys that have been in the field get this wrong. You hit it on the head! They think so quick and say what they see on a daily basis. Transformers have this too. Voltage goes up on the primary, but the current goes down. It's not about math at this point, but how they are thinking without really thinking the problem through. I am so happy finally see's what I have been trying to articulate for four days!

She watched all of Mike Holts classes on DVD. I guess she could read n OHMS wheel just like the rest of us. I would not trust her to hook up a 3-way! Lol But, she passed it and in the nineties. That four-year degree from Florida State had some value after all! Go Miami Hurricanes!

So, when guys would come to me and say they couldn't pass their masters class, I would show them her EC Unlimited License. And say, you have no excuse but to study more and take the test. I always had a full set of Mike Holts DVDs at the shop for their use. I also use to pay for all the apprentices that went to school. But, I would tell them, if they quit, they would have to refund the money to me. A bad way to force them but it helped keep them in class.

Unless I missed one, I didn't see a single post that said they didn't understand Ohms law and why the current would go up. Most even said as much. As was said, you question (or your instructor's) was poorly worded. A better question would have been "what happens to the current if 240V was applied to a 1000W, 120V device with a fixed resistance?" Then maybe give your toaster example and ask "will it trip the 15A breaker?"
But just given your question to what you called "seasoned electricians" we of course are going to factor in all the variables to give you the answer.

 

[Gary11734]

Unless I missed one, I didn't see a single post that said they didn't understand Ohms law and why the current would go up. Most even said as much. As was said, you question (or your instructor's) was poorly worded. A better question would have been "what happens to the current if 240V was applied to a 1000W, 120V device with a fixed resistance?" Then maybe give your toaster example and ask "will it trip the 15A breaker?"
But just given your question to what you called "seasoned electricians" we of course are going to factor in all the variables to give you the answer.

Ok. I'm with ya...

It's been a good run on this thread...

Gary

 

[LarryFine]

You get the prize! This is exactly why guys that have been in the field get this wrong. You hit it on the head! They think so quick and say what they see on a daily basis. Transformers have this too. Voltage goes up on the primary, but the current goes down. It's not about math at this point, but how they are thinking without really thinking the problem through. I am so happy finally see's what I have been trying to articulate for four days!

I just started at the beginning. The very first post that mentioned the inverse voltage/current relationship was yours:

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.

Nobody's response up to that point mentioned what you basically claim is most "seasoned electricians' " default way of thinking. We may not have given you a definitive "yes," but nobody said "no because the current will decrease or halve" either.

I'm glad we disappointed you.

 

[Gary11734]

I just started at the beginning. The very first post that mentioned the inverse voltage/current relationship was yours:



Nobody's response up to that point mentioned what you basically claim is most "seasoned electricians' " default way of thinking. We may not have given you a definitive "yes," but nobody said "no because the current will decrease or halve" either.

I'm glad we disappointed you.

Me, disappointed? No, not on the contrary. Thanks for your expert responses.

It was fun to see all the fantastic responses. Thanks for participating.

Gary

 

[LarryFine]

Me, disappointed? No, not on the contrary. Thanks for your expert responses.

It was fun to see all the fantastic responses. Thanks for participating.

Well, in that case, I'm glad we didn't disappoint you.

 

[Gary11734]

Well, in that case, I'm glad we didn't disappoint you.

Why would you think I was disappointed?

You guys answered the question as you saw it.

I never sleep! It's 4:20 AM and I'm still awake!

Gary

 

[drcampbell]

How do I hide a thread here?

 

[kwired]

How do I hide a thread here?

You can unsubscribe and it won't show up when you search subscribed threads. Will still show up in general searches of all threads.

 

[ggunn]

I am so happy finally see's what I have been trying to articulate for four days!

We (most of us, anyway, I surmise) have seen this for what it is from the beginning.

 

[jaggedben]

We (most of us, anyway, I surmise) have seen this for what it is from the beginning.

^ what he said. :thumbsup: