Originally Posted by AllanJ
After connecting the neutral and ground wires of that branch circuit to the respective bars in the panel and before connecting the hot wire to the breaker, clip one lead of the test lamp to the circuit hot wire and the other lead of the test lamp to the breaker screw.
Now when you turn on the breaker, if there is a short, the short current will be limited to what the lamp draws and the lamp will light up.
Things plugged into the branch circuit while you are doing this test may also cause the test lamp to light up depending on what those things draw in terms of current.
this is what I said. yoyo said no.
If you connect the light to an open breaker, there is nothing that will ever make it light. There can be no current flow because there is no place for it to flow, just the same as my ability to a touch a 25kV line and not get shocked as long as I do not provide a current path to any point with a difference of potential.
When you turn the breaker on, (this is presuming there are no loads on the circuit), if there is a hot to neut or hot to ground connection, the light will light because there is a current flow. If it is a low resistance short, the light will light near to what it would normally since near to 120 volts would be dropping across the lamp. If the short is a high resistance connection, the lamp will not light brightly since the resistance in the short will cause more voltage to be dropped across that load than the lamp and that will result in a dimmer glow of the lamp.
this happens because the lamp and the short are loads in series so the voltage dropped across each load is relative to the ratio of the resistances of either load to the total load and due to that, the current flow through the lamp varies due to the varied voltage available at the lamp.
if the breaker is never closed, there will never be any voltage drop across the lamp because the connection to the breaker is isolated from both the hot or ground/neut sides of the power. It is simply there.
I'm just not seeing what you have going here yoyo. You cannot have a lamp light unless there is current flow and you cannot have current flow unless there is a diff of potential between each side of the filament. Due to the fact the open breaker is isolated from all electrical equipment, there will be no diff of potential, regardless what shorts you may have. Fruit of the Looms have been known to cause a difference of gender affiliation but not a difference of potential. (that's a joke. get it, shorts, fruit of the looms?)
School me if I am wrong but I don't believe I am concerning this.
btw: if a breaker is tripped on a short circtuit, most, if not all breaker manuf, recommend the breaker be replaced. The warranty is now void due to the short circuit trip.
I know we all do this, right?