Short Circuit Test on 14 gauge wire

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I have lots of questions about trying to make a high current test setup for testing 5000 amps on 14 gauge wire for .03 seconds.

I have tried to use high current current sources but are unable to push enough current through such a small piece of wire using the low voltage of the machine.

SO what I am thinkin about doing is just simulating a short circuit with the wire.

SO the basic question is if I have 100 V and .02 ohm resistance in the wire, is there any way that I can get 5000 amps on the wire for .03 seconds before the breaker trips?

I am going to stop with that question until someone can give me hope that I can do it. I am no expert in electrial laws, being that my major is mechanical engineering, so any advice from anyone who can help will be greatly appreciated.

It would be nice to make this homemade setup instead of spending 100,000 grand to buy something.

Saying thanks in advance
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
What you are describing is something that should only be attempted in a controlled laboratory environment by persons familiar with the related test equipment and safety precautions. I don't know if that describes yourself or your intended experiment. But I am concerned not only for your safety, but for any liability that might arise if some Forum member gives you advice that leads to you (or someone working with you) getting hurt.

Speaking now as the Chief Moderator of this Forum, before I can allow anyone to give you such advice, I am going to have to ask you to share the reason for your question, and to give us some confidence that you are experienced in the types of experimentation you seem to have in mind.
 
We are needing to do a test on the wire to make sure that it does not burn into. We have to do this for 5000 amps and 2400 amps. I know that there will be a lot of trouble in measuring the time and in measuring the current, but I think I can figure that out if I know that it is possible.

I have read about short circuit current loads and interrupting capabilities of breakers. Of course I don't want to blow anything up.

So, we are basically testing the wire to make sure that it does not burn into before the breaker trips.

Does that make any sense?

Thanks
 
Replying to Mr. Beck,

I cannot say that I am very experienced, because I am just starting my career. I am just trying to brainstorm and think of ideas to figur this out. Iapologize if this forum is not for that, being that it deals with code work (it seems).

I was just wanting a litlle insight on some basic principles to see if this was even possible

We are in the most very early stages of trying to figure out how to do this.


I can guarantee that before the test takes place, it will be reviewed by the senior level engineers for safety and applicablity.
 

haskindm

Senior Member
Location
Maryland
That makes sense, but WHY are you trying to do this? What steps have you taken to protect yourself and the area from molten copper when the wire does burn? This does not sound like something that should be attempted in other than a controlled testing laboratory with the proper safeguards in place, by people that have been trained to do such a test properly and safely. This is not a good subject for a "science experiment".
I believe this thread should be closed as any information would make the poster liable.
 
Replying to Haskindm

We have a controlled laboratory with certified technicians doing all of the work. We do various high current testing on different types of parts.

As I said we have already tried using high current current sources.

We have only been able to get about 3000 amps on the wire with them.

We simulate high pressure steam line breaks and various other types of tests.

This would be no "science experiment". Before it would take place, it would be a controlled test setup.

All that said, I understand your concerns about safety and reliabilty.

If you can help, it would be greatly appreciated. If not, I understand fully
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
To directly answer what I think is your question, I do not know of a method by which you can impose a current of 5000 amps and compel that current to continue to flow for a period of 0.03 seconds. Perhaps some other member can address that question better than I.

But I would imagine that you are already aware that every model of breaker has its own tripping characteristics, that each breaker's time-current characteristic curves give the range (in units of time) during which period a breaker will trip (as a function of the amount of current), and that the breaker could trip at any point in time within that range. From your description, I see that you are also aware that a small wire carrying a high current will, in time, act as a fuse (burn in two, as you say).

But do you not understand that there is no way to guarantee that one will happen before the other? There are too many variables. Your test might give you the results you want under the set of conditions you impose, but an actual fault event might have different results.

I have no way of knowing whether the "senior engineers" you mentioned are any more experienced than yourself, when it comes to testing wires to the point of their failure. But I can say that when a wire is overheated to the point of failure, it melts, and sends molten copper around the room at high speeds. It can seriously injure, even kill, anyone in the area.

And by the way, your test results might not give you the results you are hoping to get. If the wire "fuses," before the breaker trips, what does that do to your plans?

Just out of curiosity, does the term "EQ" mean anything to you, and does it come into play here?
 
Mr. Beck,

"EQ" is exactly what we are doing. I assume that you know that is always trying to simulate worst case scenarios.

We have been discussing this back and forth the last couple of days.

We would do this test in a safe environment for the workers of course, and there would have to be all kinds of safety precautions (as always).

I just wanted to use the wide world of internet to get some more info of this kind of setup.

Being a ME, I would say if you have 100V and .02 ohms then you would have 5000 amps (until something opens the circuit), but I do know that it can't be that easy.

I am a young guy (24), so I have lots to learn. The best way to do that is ask for expert advice and use it wisely.

Thanks for the help.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
So can you fill me in on what "EQ" means? I am still wondering why you want to do this type of test when the properties of a piece of #14 are so well known (the link Don provided, for example.)

Anyhow, the answer is no. Per Ohms law, with 100V and .02 ohms of resistance, 5000A would be the maximum possible current. However, your voltage source will have some internal resistance, and that will limit the current to something smaller.

You will probably need 150 or 200V. Getting your current to do a square wave (0 amps, then 5000A in an instant, and then back to 0 amps) will also be a challange.

Steve
 
O

oliver100

Guest
SO the basic question is if I have 100 V and .02 ohm resistance in the wire, is there any way that I can get 5000 amps on the wire for .03 seconds before the breaker trips?

Provided that you have a source with 0.0000000 ohms internal resistance/impendance AND the contact resistance of the breaker is 0.00000000 ohms. Theoretically, Ohm's law applys.
 
I apologize. The wire is #10, not # 14. So as I look at the table in the article I see we these test numbers come from.

EQ is environmentsl qualification. We test parts to their limits (basically) to make sure they do what they are supposed to.

So you say that I would have to have greater voltage to get that current.

I was reading an article about single pole interrupting capacity. This is how I found this forum. I was reading through that and wandered if the test setup would be better if you shorted out just one leg of 480 volt service. So, would I be better off trying this or is that crazy thinking?

Again, I am talking like I am about to go and try this. That is not the case at all. I am only brainstorming and trying to get a good understanding of how I could do this.

How could I calculate a short circuit current for one leg of the 480 volt service and then size the breaker to trip without blowing anything behind it.

I am not worried about the wire burnign into, if it does, O.K.. I'll have to have less juice on it next test. It will be protected in case of explosion.

I realy just want to get the amps on it, try to measure the current, try to measure the time, and not blow anything up (besides the wire)

How would I go about setting the circuit up to do so.

The voltage would be the only thing that I could regulate. Resistance would have to stay the same.

All would have to be done by testing?

Back to original question, Is it possible?
 
Just want to say:

I really like this forum. I have sort of got into a field dealing with more electrical than mechanical stuff.

I hope to be able to post more reasonable questions in the future to get help with.

Seems like their is a lot of smart people on here that help people out.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
steve66 said:
So can you fill me in on what "EQ" means?

That was a "shot in the dark," on my part. I asked the question about "EQ" because the original question started to look like it pertained to my former life in the nuclear electric generation industry. In that world, they must perform analyses and testing to demonstrate the ability of electrical components to survive the impact of a pipe rupture. I'm not talking about nuclear radiation issues, but rather the high temperature, high humidity, high pressure, and steam environment that would result from a pipe break. The utility is required to prove that each and every electrical component within the plant can withstand the environment to which it would be exposed during a design-basis pipe rupture, and that it can continue to operate within that environment at least as long as is needed for that component to complete its safety-related function. No easy task.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Flangehead said:
So, would I be better off trying this or is that crazy thinking?

That is crazy. You really need to bring in the services of an electrical engineer who has experience not only with laboratory testing, but also with the requirements of the EQ Program. I don't think you will find anyone fitting that description on this Forum. I might have been able to do this once (I've been out of the nuclear industry for six years), but I have no interest in the topic any more.
 

bphgravity

Senior Member
Location
Florida
My guess is that your company produces a piece of equipment that has been determined to have an available fault current of 5,000-amperes and you plan on protecting this equipment with a 1/2 cycle circuit breaker and are looking to determine what the minimum size conductors could safely carry the fault currents? :?

The experiment you want to perform has already been done. There are plenty of calculations that allow you to perform the experiment mathematically rather than physically. I just can't imagine what you are hoping to learn? :?:
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Posted by Charlie:



The utility is required to prove that each and every electrical component within the plant can withstand the environment to which it would be exposed during a design-basis pipe rupture, and that it can continue to operate within that environment at least as long as is needed for that component to complete its safety-related function

Too bad they don't test parts for exposure to a candle flame!! I have heard that one of the worst nuclear emergencies started with a technician using a candle to test for air leaks!
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I believe that was the fire at the Brown's Ferry plant. Another set of major rule changes arose from the ashes of that event.
 
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