Can a 3way switch short?

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Jadnashua

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The simplistic answer is that a switch in a completed circuit IS a short - just like a piece of wire. If you look at it in the context of an ohmmeter, a closed switch looks exactly like a short between two terminals. Now, if it is 'shorted' to a place you didn't intend it, then you have problems. Bantering about context and common usage doesn't necessarily help with the underlying understanding. If you have a good grasp of that, this bickering is kind of funny.
 

JWelectric

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Yes I too find it funny that on a DIY web site we will have folks from different walks of life that knows more about electrical theory than someone who has paper hanging on the wall from different colleges, licenses, certificates, and is even hired by a college to instruct electrical theory.

I also find it sad that these fine folks are too dense to learn.
short′ cir′cuit
n.
an abnormal condition of relatively low resistance between two points of differing potential in a circuit, resulting in a flow of excess current.

With a circuit of a 120 volt source, a 100 watt light bulb, and a switch, if the circuit is not shorted the light will never come on.
Now let’s take a moment and think a little. Let’s take a piece of wire and connect it to the two terminals of the light bulb. With the switch in the off (open) position does anything happen? Turn on (close) the switch and describe the circuit.
If you say the circuit is shorted then the closing of the switch is what caused the short plain and simple.
 

Murphy625

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this bickering is kind of funny.

I would hesitate to call this bickering.. at least not from my perspective. I rather enjoy nit picking out the finer details of conversations like these as it is entertaining and frequently educational. The trick is not to hold a difference of opinion against anyone and/or let it get personal in any way. If one can master that, the debates are a very good thing in almost all respects.
 

Murphy625

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Yes I too find it funny that on a DIY web site we will have folks from different walks of life that knows more about electrical theory than someone who has paper hanging on the wall from different colleges, licenses, certificates, and is even hired by a college to instruct electrical theory.

That's impressive! Congrats on all your dedication and hard work. It takes real focus to achieve a career with that prestige.
I don't have all that paper.. I'm just a lowly engineer from Northern Michigan University Electrical Engineering program who spends most of his time designing specialized processing machinery for the automotive industry rather than any real engineering.


I also find it sad that these fine folks are too dense to learn.
short′ cir′cuit
n.
an abnormal condition of relatively low resistance between two points of differing potential in a circuit, resulting in a flow of excess current.

With a circuit of a 120 volt source, a 100 watt light bulb, and a switch, if the circuit is not shorted the light will never come on.
Now let’s take a moment and think a little. Let’s take a piece of wire and connect it to the two terminals of the light bulb. With the switch in the off (open) position does anything happen? Turn on (close) the switch and describe the circuit.
If you say the circuit is shorted then the closing of the switch is what caused the short plain and simple.

The dictionary definition you provided and the example you provided contradict each other. The key word is ABNORMAL.
Throwing a switch is not an abnormal function.

In your example, the switch doesn't create the short, the abnormal wire connecting the two terminals of the light bulb is what created the short. Closing the switch just energized the already shorted circuit.

Just because a circuit is not currently energized does not mean its not yet shorted via an abnormal condition.

Also, as the dictionary definition you provided is mostly correct, consider the following:
If two different conductors from two different circuit breakers originating from the same phase leg come into contact with each other (lets say via a break in the insulation of both wires running next to each other), what condition would you call that? In such a situation, that condition may go unnoticed for a very long time until special circumstances occurred between the two circuits.
 

DonL

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If two different conductors from two different circuit breakers originating from the same phase leg come into contact with each other (lets say via a break in the insulation of both wires running next to each other)what condition would you call that? In such a situation, that condition may go unnoticed for a very long time until special circumstances occurred between the two circuits.


I would call that cheap ass wire.
 

JWelectric

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That's impressive! I'm just a lowly engineer from Northern Michigan University Electrical Engineering program .
This is good as we both know what a simple circuit is, a source, a path, and a load. We both now understand that in this simple circuit the load is a short of the source or if you would rather the difference of potential.

What we have come accustom to calling any circuit that doesn’t work a shorted circuit when in fact a shorted circuit is what is needed in order for current to flow. We have become accustom to calling a faulted circuit a short circuit when the fact is the circuit is faulted.

In the scenario you posted it would be a parallel circuit that is protected by one or the other overcurrent device. There would be no danger except the fact it would take both devices to turn off either circuit.

When teaching the NEC the word “fault” is used to define both a fault to ground and a fault between two opposing legs of a system.
 

DonL

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It seems that Many People think that if anything using electricity does not work, "It must have a Short".

Most of the time it is because it has a Long.
 

Murphy625

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This is good as we both know what a simple circuit is, a source, a path, and a load. We both now understand that in this simple circuit the load is a short of the source or if you would rather the difference of potential.
Did you just call the load an abnormal condition per the definition you posted?


In the scenario you posted it would be a parallel circuit that is protected by one or the other overcurrent device. There would be no danger except the fact it would take both devices to turn off either circuit.
Two circuit breakers feeding a single conductor will create a situation that could involve the fire department, the insurance company, the hospital, and possibly the morgue.
 

JWelectric

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Did you just call the load an abnormal condition per the definition you posted?
Yes it could be abnormal should it start to fail and if it burned into a low resistance load it would still be the load none the less.
Should the source be shorted with nothing but a conductor then the conductor becomes the load one of the three fundamentals of a simple circuit, source, load, and a complete path.

A simple battery with nothing attached does not conduct current. Short the positive to negative and current will flow. The amount of resistance in this short will determine how much current flows, Ohm’s Law hard at work.

The path cannot be shorted but maybe shortened, the load cannot be shorted, but maybe lowered, but alas the source can be shorted as it is the only place the energy comes from.



Two circuit breakers feeding a single conductor will create a situation that could involve the fire department, the insurance company, the hospital, and possibly the morgue.
If both breakers are the same size and the conductor is properly sized then the only problem is there are two breakers to trip instead on one but they both open under the same load.

No fire department needed nor is there any need to get in touch with the morgue or the insurance or even the hospital.

Are you thinking that somehow the two breakers would add up to a higher current or something like that?

The term as used improperly does not constitute something else.
 

Murphy625

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Are you thinking that somehow the two breakers would add up to a higher current or something like that?

You think that two breakers feeding one line wouldn't???

15 amp breaker + 15 amp breaker feeding 14ga wire = big trouble... (think toaster element)

Think parallel circuit.
 

DonL

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You think that two breakers feeding one line wouldn't???

15 amp breaker + 15 amp breaker feeding 14ga wire = big trouble... (think toaster element)

Think parallel circuit.


If that could EVER happen, then the electrician that installed it should lose his or her job.

Stuff like that can not happen if installed properly.

And Your "Short" would have to be in the breaker box, or the current for each breaker will not be divided by half, It will depend on the resistance of the wire on the Other "Short".

Is everyone confused yet ?

We all need to stay on the same page.
 
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JWelectric

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You think that two breakers feeding one line wouldn't???

15 amp breaker + 15 amp breaker feeding 14ga wire = big trouble... (think toaster element)

Think parallel circuit.
two 15 amp breakers feeding one 14 gauge wire that would mean that they would be on the same leg in the panel would equal 15 amps protecting one 14 gauge wire
 

Murphy625

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If that could EVER happen, then the electrician that installed it should lose his or her job.
Stuff like that can not happen if installed properly.

You would be surprised at the stuff that happens inside industrial factories. I've seen conduits crushed by high-low forks, boxes damaged when someone drops a 200lb bearing housing, wires melted by someone welding too close, etc etc. No one wants to take responsibility and things go unreported.
Residential wiring is so simple I would generally agree with you, however, even then, I've seen mice chew through insulation and people put nails through wires.

And Your "Short" would have to be in the breaker box, or the current for each breaker will not be divided by half, It will depend on the resistance of the wire on the Other "Short".
Yup.. that is correct. That said, the difference in the lengths of the wires would have to be significant to create enough of a resistance to have any real world effect.
 

DonL

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You would be surprised at the stuff that happens inside industrial factories. I've seen conduits crushed by high-low forks, boxes damaged when someone drops a 200lb bearing housing, wires melted by someone welding too close, etc etc. No one wants to take responsibility and things go unreported.
Residential wiring is so simple I would generally agree with you, however, even then, I've seen mice chew through insulation and people put nails through wires.


Yup.. that is correct. That said, the difference in the lengths of the wires would have to be significant to create enough of a resistance to have any real world effect.


I have worked in industrial factories.

I do not recall any 14 Gauge wire used in them.

You are mixing apples with oranges. I like them both.

I thought we were talking residential, not 3 phase stuff.


My Bad.
 

Wet_Boots

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Did you just call the load an abnormal condition per the definition you posted?



Two circuit breakers feeding a single conductor will create a situation that could involve the fire department, the insurance company, the hospital, and possibly the morgue.
I lived in a house that had a wiring fault that was unresolved for years, involving the entire second floor being on a single 15 amp breaker. This was due to a mistaken connection somewhere in the second floor wiring that joined two separate 15 amp circuits together. The two breakers were positioned in the box so as to provide a dead short in the event that they were both on, and being good breakers, that never happened.
 

Murphy625

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Wouldn’t your two wires also add up?

I'm not sure what you're asking with that question... But, the fact is that two 15 amp breakers feeding a single conductor would theoretically be capable of delivering 30 amps. IE: 15 x 2 = 30. The 14ga wire would eventually melt and catch fire if that happened.
 

Murphy625

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I have worked in industrial factories.
I do not recall any 14 Gauge wire used in them.
You are mixing apples with oranges. I like them both.
I thought we were talking residential, not 3 phase stuff.
My Bad.

I've done my share of single phase stuff too... Every 3 phase factory has at least one step-down transformer to feed single phase to the offices and sometimes the lighting.

Ohms law and all the other stuff doesn't care how many phases there are or where its located... :D
 

Murphy625

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I lived in a house that had a wiring fault that was unresolved for years, involving the entire second floor being on a single 15 amp breaker. This was due to a mistaken connection somewhere in the second floor wiring that joined two separate 15 amp circuits together. The two breakers were positioned in the box so as to provide a dead short in the event that they were both on, and being good breakers, that never happened.

It sounds like the two breakers were on opposite phases.. You got lucky because your crossed wires showed their ugly head.. had those breakers been on the same phase, you would have never known until you drew 20 amps on a 15 amp conductor...
 
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