Ohm's Law & Circuit Breaker Trips: Why?

[Edweird]

If ohm's law is: current = volts/resistance, then why does a circuit breaker trip when you plug in too many appliances. It seems like every time you hook a load up to a circuit you are increasing the resistance of the circuit, and so current should be reduced cooling the circuit down, not overheating it.

 

[phinds]

If ohm's law is: current = volts/resistance, then why does a circuit breaker trip when you plug in too many appliances. It seems like every time you hook a load up to a circuit you are increasing the resistance of the circuit, and so current should be reduced cooling the circuit down, not overheating it.

Do you understand the difference between series and parallel loads?

 

[tech99]

If ohm's law is: current = volts/resistance, then why does a circuit breaker trip when you plug in too many appliances. It seems like every time you hook a load up to a circuit you are increasing the resistance of the circuit, and so current should be reduced cooling the circuit down, not overheating it.

When you add another appliance to your house wiring, it is connected in parallel, not series. This has the effect of allowing more current to flow, and the resistance is reduced not increased.

 

[phinds]

When you add another appliance to your house wiring, it is connected in parallel, not series. This has the effect of allowing more current to flow, and the resistance is reduced not increased.

Yes, I was trying to get him to figure that out for himself.

 

[Edweird]

Do you understand the difference between series and parallel loads?

Yes, I was kind of thinking that was the case. So does that mean if the circuit were in series electron flow would just stop rather than tripping the breaker?

 

[phinds]

Yes, I was kind of thinking that was the case. So does that mean if the circuit were in series electron flow would just stop rather than tripping the breaker?

Why do you think it would stop instead of just decreasing? Tech99 specifically TOLD you it would just decrease. Do you have some reason to think he's wrong?

 

[tech99]

Yes, I was trying to get him to figure that out for himself.

Sorry, our replies clashed in time and I did not see your reply.

 

[Edweird]

Why do you think it would stop instead of just decreasing? Tech99 specifically TOLD you it would just decrease. Do you have some reason to think he's wrong?

I guess I should have said slow down, then eventually stop if load continued to increase. Although, then why does a breaker trip when you're using a saw and the blade gets stuck? It's not like you are adding another parallel circuit!

 

[Windadct]

Hello EdWierd - Welcome to PF...I'll take a guess and assume you are relatively new to electricity.

So... a Circuit breaker is rated at 20 A ( amps) - that is how we measure current.

If you plug in one appliance that needs 12 A - no problem, right?

But if you then plug in another appliance needing 12A - when we talk about current in a household circuit, these two currents ADD together - and the Circuit Breaker has 24A flowing through it... and it trips.

These appliances are being fed in parallel - so the 24 A in the breaker 1/2 goes to Appliance 1 and the other half goes to Appliance 2.

I hope that helps clear this up a little... this can be drawn in a circuit concept to show the parallel paths of current as was mentioned above, but I wanted to simplify the situation as best I could.

Edit -- sorry I started this reply a while ago and did not see the new replies.
--- As for the Saw question - very good, but when you turn on a Saw (relatively large motor) the blade is stopped and it takes a larger pulse of current to accelerate the motor to full speed (from stopped), the Limit for this is typically called Locked Rotor Amps ( LRA) and - actually - one of the challenges of making circuit breakers is to have them be able to know the difference between starting - and a real Locked Rotor condition where the motor (saw) draws more current than the siring of the house can safely supply full time ( continuously).

 

[phinds]

Sorry, our replies clashed in time and I did not see your reply.

Sure, understood. Still, it's always better to try to get a poster to think rather than just spoon feed them answers.

 

[Edweird]

Hello EdWierd - Welcome to PF...I'll take a guess and assume you are relatively new to electricity.

So... a Circuit breaker is rated at 20 A ( amps) - that is how we measure current.

If you plug in one appliance that needs 12 A - no problem, right?

But if you then plug in another appliance needing 12A - when we talk about current in a household circuit, these two currents ADD together - and the Circuit Breaker has 24A flowing through it... and it trips.

These appliances are being fed in parallel - so the 24 A in the breaker 1/2 goes to Appliance 1 and the other half goes to Appliance 2.

I hope that helps clear this up a little... this can be drawn in a circuit concept to show the parallel paths of current as was mentioned above, but I wanted to simplify the situation as best I could.

So why does a breaker trip when a saw blade gets stuck?

 

[phinds]

So why does a breaker trip when a saw blade gets stuck?

Because the motor is trying to draw more current than the breaker allows. A motor is not a passive resistance, it is an active impedance. There is a big different.

Really, you would do well to do more reading in the basics of electronics. This asking questions on an internet forum before you understand the basics really isn't the best way to learn. Take one basic concept at a time and learn it and when you get to the point where taking more than one of them at a time gets confusing, then that's the time to ask questions. Your questions here suggest that you have not yet done enough reading on the basics.

 

[Windadct]

Another point you may be missing(have not learned yet), as current flows in the wiring of the house, it creates heat - and if you double the current you get four times the amount of heat - so you can easily get in trouble. The Circuit Breakers (CB) job is mostly to prevent the wiring from overheating and starting a fire. So when you have too much current - the CB trips and shuts off the circuit that is using too much current.

Edit - also look at the edit of my post above about the Saw Blade -

 

[phinds]

don't judge what I know by the questions I ask.

Hm. I don't follow your logic on that. If you ask a question that implies lack of knowledge of the basics, why is it wrong to infer that you lack knowledge of the basics? I'm not trying to give you a hard time here, I'm trying to get you to think about what you said.

 

[Edweird]

Hm. I don't follow your logic on that. If you ask a question that implies lack of knowledge of the basics, why is it wrong to infer that you lack knowledge of the basics? I'm not trying to give you a hard time here, I'm trying to get you to think about what you said.

Maybe I don't want to pay for scholarly articles, nor drive a half hour to a library. Anyways, thanks for the help.

 

[phinds]

Maybe I don't want to pay for scholarly articles, nor drive a half hour to a library. Anyways, thanks for the help.

Well, certainly if those were your only options, I would understand but I'm sure there are good free tutorials online for basic electronics. Probably easy to find one with a simple search.

 

[Edweird]

when it comes to this stuff 95% of the info on the net is ineffective due to poor writing/describing by the producer plus the info isn't presented with appropriately organized prerequisite information. The net is basically a bunch of recombinant garbage, not solid info. I need a textbook and time to double major really if I was trying to master the material, however I'm simply trying to fill in a few gaps.

 

[russ_watters]

Maybe I don't want to pay for scholarly articles, nor drive a half hour to a library. Anyways, thanks for the help.

You are on the Internet. There are loads of free resources. Wikipedia would be a fine place to start, or you could Google for introductory texts or courses. Internet forums are not a very good place to go for a detailed course in a subject . That isn't a very efficient use of your time or ours. And you aren't anywhere close to ready for scholarly articles.

 

[Edweird]

You are on the Internet. There are loads of free resources. Wikipedia would be a fine place to start, or you could Google for introductory texts or courses. Internet forums are not a very good place to go for a detailed course in a subject . That isn't a very efficient use of your time or ours. And you aren't anywhere close to ready for scholarly articles.

it was actually an incredibly simple question, not detailed course I was asking for. I guess what you're trying to say is you don't have time to answer questions about basic material. however, the fact that you have time to start drama over the interweb tells me otherwise.

 

[Edweird]

it was actually an incredibly simple question, not detailed course I was asking for. I guess what you're trying to say is you don't have time to answer questions about basic material. however, the fact that you have time to start drama over the interweb tells me otherwise.

I must be at a physics board if within my first hour I got people questioning my intelligence lol. You guys are funny, there's more to life than who is the biggest poindexter or thinking you know everything which you don't.

 

[Windadct]

Ok EdWeird - your initial question was very basic but to me a fair or understandable question. Still I tried to provide an answer based on judging you or on the questions you asked; but this judging has many contexts. I judged you on a level of understanding, knowledge and to be honest a bit on age. There are other reasons people ask basic questions, lack of effort, lack of ability, conflict with personal belief ( frequently this conflicts with science at large) and other reasons.
This is an Electrical ENGINEERING forum, and I believe there is a a high expectation of the newcomers... If you look over my posts I have tried to temper my possibly offensive posts.

There is a major contributor here who's tagline is " the enemy of understanding is classification" - while I agree at some level - the real enemy is arrogance... we think we know more than we do - and assume we are correct.

As your first post - please step back and take a breath, and accept a little criticism without getting upset or defensive.

 

[russ_watters]

Ok, question is asked and answered, so the thread is locked. Edweird, whether you believe it or not, we're just trying to help. Please consider taking our advice. We have been doing this long enough and successfully enough to know when someone is taking a bad approach to learning.