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  • Circuit Overload Device

    A friend of mine has a self-made circuit tripper. It is an extension cord connected to a light switch. You plug it into a recepticle and when you turn on the switch it shorts the circuit. Another electrician told me that this is dangerous because it can melt the house's wires. What do you guys think? Is this save to use to find circuits for common repairs, or is the risk of melting a wire too great? Thank you for your thoughts!

  • #2
    Re: Circuit Overload Device

    This is extremely dangerous. If there is anything wrong with the wiring, he is asking to start a fire. There are much better ways to trace out the circuit.

    Comment


    • #3
      Re: Circuit Overload Device

      While I can see the danger part of this I cannot help think that any 'normal' overload has the same potential to cause problems. Though:

      - to melt copper a very high temperature is needed - much higher than the self ignition temp of paper and plastic surrounding the wire, a fire would result first
      - the breaker would have to be compromised and fail to trip
      - isnt this the exact same operation that store bought circuit testers use?
      ~~

      ... it was plumbed by Ray Charles and his helper Stevie Wonder

      Comment


      • #4
        Re: Circuit Overload Device

        A normal overload is drawing 20 amps on a 15 amp circuit causing the breaker to operate. The method the poster is describing is a dead short circuit which can be hundreds or thousands of amps. What if the breaker fails to operate? The breaker does not instantaneously stop the amperage flow and it takes a short period of time for the breaker to react to the over current.

        Also this type of tripping can cause the breaker itself to fail.

        Comment


        • #5
          Re: Circuit Overload Device

          What school are you attending?
          What classes are you taking?


          Cactus Man

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          • #6
            Re: Circuit Overload Device

            Originally posted by rjniles View Post
            A normal overload is drawing 20 amps on a 15 amp circuit causing the breaker to operate.
            Says who? Anything that has a capability to fail can cause a dead short. Thinking that any overload is just 5 amps over the breaker rating is foolhardy at best.
            ~~

            ... it was plumbed by Ray Charles and his helper Stevie Wonder

            Comment


            • #7
              Re: Circuit Overload Device

              Originally posted by Plumber Punky View Post
              Says who? Anything that has a capability to fail can cause a dead short. Thinking that any overload is just 5 amps over the breaker rating is foolhardy at best.
              I said that amperage (I used 5 as an example) over the rated current will cause a trip. Something that fails and causes a dead short with very high amperage fault current is not the normal occurence. Certainly a working breaker will protect and trip but it has the danger of destroying the breaker.

              Comment


              • #8
                Re: Circuit Overload Device

                The normal load rating of a breaker and its interrupting current rating are two very different values.
                Intentionally overloading a breaker is not something you want to do if you can help it.

                As was said how domy0u know it will trip at 125% or whatever its trip point is. The only way to know is to test it. Places I have worked we test ALL breakers, no matter what size, from 1Amp up to the big 4kv, 400Amp breakers, before they are installed. The failure rate, that is those that DO NOT trip within their specified tolerance is about 20 %, or 1 out of 5. Most do trip, but some are at two or three times their load rating. Some MCCBs can be adjusted, some not so. MCCBs (molded case circuit breakers) after installation don't get tested as often as the more critcal, large breakers do, but still they're tested on some schedule like every 18 or 36 months, and sometimes longer periods depending on what the application is. Those that can be are adjusted to trip at the required current and they are timed also. Those data points are calculated by the electrical engineers and are unique to each circuit/application.

                The current required to create an arc flash is not as much as you might think. Intentionally creating a dead short, even inside the switch across its contacts is not wise.

                My point is you can't trust them, and fuses are no better as far as accuracy.
                Last edited by Bob D.; 09-21-2013, 07:58 PM.
                ---------------
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                • #9
                  Re: Circuit Overload Device

                  Cactusman, I am still working on my general eduation. I have some family members that are teaching me about electrical work. I want to thank everyone for sharing their considerable experience and knowledge with me.

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                  • #10
                    Re: Circuit Overload Device

                    Originally posted by rjniles View Post
                    Something that fails and causes a dead short with very high amperage fault current is not the normal occurence.
                    In the 13 years that I've been in the Plumbing/HVAC fields I can reliably say that a good 95% of electrical shorts I've encountered are dead shorts that trip the breaker. The rest are 'regular' overloads as would be caused from motors drawing too much and other similar occurrences.
                    ~~

                    ... it was plumbed by Ray Charles and his helper Stevie Wonder

                    Comment


                    • #11
                      Re: Circuit Overload Device

                      Rjniles (and others) are exactly right. Fault current is considerably higher (thousands of amps) and to purposely introduce a short circuit is just plain stupid. (My words not his)

                      Yes, you may have seen the breaker trip 95% of the time, but you don't realize that the electrical devices and conductors are getting slightly stressed with each fault. An example could be the back stab contacts in a receptacle which is often a weak spot in a circuit. You thought the breaker tripped and all is well, but actually the backstabs are now slightly looser causing high resistance, which causes a smoldering fire.

                      Evidence of insulation degradation can be seen with a megger, while that same circuit appears to be functioning fine it can be on the verge of failure.

                      I know an electrician who used to be lazy and instead of tracing down which breaker he needed turned off, he used to just short out the circuit with a jumper wire and then the breaker in question would pop.

                      Then one fateful day, shorting a 120v outlet caused the buss inside the panel to fail causing a short across the main, which caused the panel to blow up (flew 40 feet or so in a huge ark flash) Luckily no one was killed that time.

                      Comment


                      • #12
                        Re: Circuit Overload Device

                        Must have been one of those fancy Federal Pacific panels.
                        ~~

                        ... it was plumbed by Ray Charles and his helper Stevie Wonder

                        Comment


                        • #13
                          Re: Circuit Overload Device

                          It was Square D equipment.

                          The moral of the story; Any part of the circuit can fail.

                          Shorting something out intentionally reliant on the breaker is like running your car into a telephone pole... because you have air bags.
                          Last edited by johncameron; 09-22-2013, 10:02 PM.

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                          • #14
                            Re: Circuit Overload Device

                            Originally posted by johncameron View Post

                            Shorting something out intentionally reliant on the breaker is like running your car into a telephone pole... because you have air bags.

                            Actually it would be 'running your car into the pole to test the air bags.'
                            ~~

                            ... it was plumbed by Ray Charles and his helper Stevie Wonder

                            Comment


                            • #15
                              Re: Circuit Overload Device

                              when a person can put a light bulb or a tester in the receptacle to see if you have shut off the correct breaker, If there is a distance one can use an AC plug in radio, you can hear when it goes off,

                              It just seems kind of unprofessional to directly short the circuit potentially wreaking or damaging the breaker. (yes I know it is designed to shut down under over load) but it does not mean that it does not shorten it life.

                              when you have a heavy load and break the circuit there is arcing that pits and removes metal from the contact points in the breaker, and any where else it arcs, (try cutting a hot wire with a pair of side cutters if you do not believe me),
                              Push sticks/blocks Save Fingers
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