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Discussion Starter · #1 ·
Hi guys I am a newly qualified electrician and having trouble grasping a theory concept. Basically I know a short circuit is when the full amps of the transformer go through a circuit of no resistance and then get returned to the transformer right.

My question is though lets say we have the transformer connected to the input side of a circuit breaker and the circuit breaker is off. On the output side a resistance is connected from a load. As soon as I turn on the breaker how will the resistance cause less amps to be drawn from the transformer then the short circuit amps. I hope you guys get what I am saying.

Thanks guys
 

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Bilge Rat
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Higher resistance = lower amps.

A short is low resistance, hence high current. A load is high resistance, hence lower current.
 

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Short circuit current can be anywhere from 900 to 2000 amps but if you have a set "resistor" worth only so many "x" amount of amps then you do not overload your circuit. There is such a thing called " inrush current" that comes from things such as transformers and motors but we fuse these appropriately to accommodate the turning off and on of such equipment.
 

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Discussion Starter · #5 ·
Thanks guys I think I just clicked from "inrush current" so basically from the transformer you will get those high amps coming in as you switch on the power but as soon as it goes through the resistance the amps will be lowered depending on the resistance right
 

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Thanks guys I think I just clicked from "inrush current" so basically from the transformer you will get those high amps coming in as you switch on the power but as soon as it goes through the resistance the amps will be lowered depending on the resistance right
Well, yeah you have a high demand of electrons for a split second.
 

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Short circuit current can be anywhere from 900 to 2000 amps but if you have a set "resistor" worth only so many "x" amount of amps then you do not overload your circuit. There is such a thing called " inrush current" that comes from things such as transformers and motors but we fuse these appropriately to accommodate the turning off and on of such equipment.
A short circuit can be well above 2000 amps. Fault current is limited by the impedance of the source. What can the utility provide in the level of fault current, how far are you from their transformer, what type of feeders, what is your over current protections, what impedance do you have in the particular circuit that faulted, voltage level, type of fault, phase to phase or phase to ground. Is the fault a VERY RARE bolted fault or an arcing ground fault and a myriad of different faults in between the two
 

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Thanks guys I think I just clicked from "inrush current" so basically from the transformer you will get those high amps coming in as you switch on the power but as soon as it goes through the resistance the amps will be lowered depending on the resistance right
In an AC distribution system it is impedance NOT resistance
 

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Short circuit current can be anywhere from 900 to 2000 amps but if you have a set "resistor" worth only so many "x" amount of amps then you do not overload your circuit. There is such a thing called " inrush current" that comes from things such as transformers and motors but we fuse these appropriately to accommodate the turning off and on of such equipment.
I am curious how you arrived at these numbers
 

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oh my god, you one upped me, the point was made dude. ive read that and the info was probably an average.
It could be depending on all the variables I mentioned and it has nothing to do with one upping, it has to do with answering a question properly and I was curious where you got these numbers, which seems a very logical question to ask. Sorry if your ego was damaged,:thumbsup:
 

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It could be depending on all the variables I mentioned and it has nothing to do with one upping, it has to do with answering a question properly and I was curious where you got these numbers, which seems a very logical question to ask. Sorry if your ego was damaged,:thumbsup:
no it wasnt, dont worry, whered you get your info from. i just dont get the argumentative attitude, whos to say your infos right. remember, this is THEORY.
 

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no it wasnt, dont worry, whered you get your info from. i just dont get the argumentative attitude, whos to say your infos right. remember, this is THEORY.
Look I am not arguing with you; you made a statement and I was curious where you got the information.

It is not theory it has been proven over better that a century, where did I get my information from IEEE, GE and a slew of other books on the subject we are discussing, in addition I have been working in the trade 43 years.

In lieu of you and I disagreeing on the subject as you clearly feel you have the right information. I would suggest you do a little homework.
 

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Look I am not arguing with you; you made a statement and I was curious where you got the information.

It is not theory it has been proven over better that a century, where did I get my information from IEEE, GE and a slew of other books on the subject we are discussing, in addition I have been working in the trade 43 years.

In lieu of you and I disagreeing on the subject as you clearly feel you have the right information. I would suggest you do a little homework.
wow.
i dont care how long youve been doing this or what you think you know, my answer was as good as yours and yet you questioned mine. i dont disagree with your answer by the way,. i realize there might be different info out their. ive done plenty of research and homework by the way, thats why i have a broader outlook then you.
 

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wow.
i dont care how long youve been doing this or what you think you know, my answer was as good as yours and yet you questioned mine. i dont disagree with your answer by the way,. i realize there might be different info out their. ive done plenty of research and homework by the way, thats why i have a broader outlook then you.
Sorry you cannot broaden your horizons, Get some books and read.YOU ANSWER WAS WRONG.
 

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wow.
i dont care how long youve been doing this or what you think you know, my answer was as good as yours and yet you questioned mine. i dont disagree with your answer by the way,. i realize there might be different info out their. ive done plenty of research and homework by the way, thats why i have a broader outlook then you.
No, your answer wasn't as good as his because your answer was WRONG. If you have done plenty of research out there like you say, you wouldn't have made a statement like "short circuit current is between 900 and 2000 amps". That is complete fiction. Why is common interrupting ratings of circuit breakers 10KA and 22KA if we only have to be concerned with 2KA?

If you want to start researching, find a copy of the Bussmann SPD. It explains things very well.
 
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