Ohm's Law & Circuit Breaker Trips: Why?

  • Thread starter Edweird
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In summary, when you plug in multiple appliances to a circuit, the current in the circuit increases, causing the resistance to decrease and potentially overheating the circuit. This is because the appliances are connected in parallel, allowing more current to flow. However, if the circuit were in series, the current would decrease and eventually stop. Additionally, a circuit breaker is designed to trip when the total current exceeds its rating, which can happen when multiple appliances are connected in parallel. In the case of a saw, the motor draws a larger pulse of current when starting up, which can exceed the circuit breaker's rating and cause it to trip. It is important to understand the basics of electronics in order to fully grasp these concepts.
  • #1
Edweird
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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.
 
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  • #2
Edweird said:
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?
 
  • #3
Edweird said:
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.
 
  • #4
tech99 said:
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.
 
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  • #5
phinds said:
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?
 
  • #6
Edweird said:
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?
 
  • #7
phinds said:
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.
 
  • #8
phinds said:
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!
 
  • #9
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).
 
  • #10
tech99 said:
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.
 
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  • #11
Windadct said:
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?
 
  • #12
Edweird said:
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.
 
  • #13
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 -
 
  • #14
Edweird said:
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.
 
  • #15
phinds said:
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.
 
  • #16
Edweird said:
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.
 
  • #17
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.
 
  • #18
Edweird said:
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.
 
  • #19
russ_watters said:
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.
 
  • #20
Edweird said:
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.
 
  • #21
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.
 
  • #22
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.
 
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1. Why does Ohm's Law matter in electrical circuits?

Ohm's Law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points, is a fundamental principle in electrical engineering. It helps us understand how voltage, current, and resistance are related in a circuit, and allows us to calculate values such as current flow and power dissipation.

2. How does Ohm's Law affect circuit breaker trips?

According to Ohm's Law, when the resistance in a circuit is low, the current will be high. This high current can cause the circuit breaker to trip, as it is designed to protect the circuit from dangerous levels of current. So, understanding Ohm's Law can help us prevent circuit breaker trips by properly sizing and designing circuits.

3. What are the consequences of ignoring Ohm's Law in circuit design?

If Ohm's Law is ignored in circuit design, it can lead to overloading and overheating of the circuit, leading to potential fire hazards. It can also result in damage to electrical equipment and appliances, as well as frequent circuit breaker trips.

4. Can Ohm's Law be applied to all types of circuits?

Yes, Ohm's Law is a universal law that applies to all types of circuits, whether they are simple or complex, AC or DC. However, it is important to note that the values of voltage, current, and resistance may vary depending on the type of circuit and the components used.

5. How can I use Ohm's Law to troubleshoot circuit breaker trips?

If a circuit breaker is tripping frequently, you can use Ohm's Law to calculate the current flowing through the circuit and determine if it is within safe limits. If the current is too high, it may indicate an issue with the circuit, such as a short circuit or an overload. By using Ohm's Law, you can identify and fix the problem, preventing future circuit breaker trips.

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