Testing an Installation: Accidental Grounds and Continuity

Yoyizit

I wouldn't even turn on the breaker if the lamp glows at full intensity or the voltage across the bulb measures 120v, unless you want to test the CB for proper response to a short (cover your eyes). Breaker lifetime is probably designed for a limited number of trips.

Bocolo

Why does the light bulb comes on? It probably sounds like a dumb question but I am trying to figure this out. I mean I know you said because there is a short but I would like to know the specifics. Always good to learn stuff like this. Thanks for your time.

PirateKatz

I've been trying to figure out the same thing. I think the light would come on because there is a short somewhere down circuit, where a hot wire is somewhere connected to either the neutral or ground by mistake. This would create a return path and as a result light the bulb

The light wouldn't come on if there is no short because there is no return path.

Am I on the right path here?

nap

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?

Bocolo

Keep it coming I think I am getting this. Fun stuff.

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.

Why they just don't make fuses then instead of breakers?

nap

From my understanding, it is a matter of liability more than one of true need. In todays litigious society, everybody sues for anything and anytime a company can limit their liability by doing something like this, it is simply a money preservation move on their part.

I suspect some of the manuf's have figured out that a hard short causes some problems in the breaker so, rather than accepting the liability, they state that the breaker should be replaced.

such is an ass saving action.

Bocolo

I see where you coming from. Makes sense.

AllanJ

When you connect up the lamp (between the breaker screw and the branch circuit hot wire that is loose for the moment), you must turn on the breaker to begin the test.

If the lamp stays off, the test is done and you have no shorts. Turn off the breaker, disconnect the lamp, and connect the branch circuit hot wire to the breaker.

If the lamp comes on (this really does not happen often), you may need to troubleshoot for shorts. But first double check around the house, unplugging anything that might still be plugged in to that branch circuit and also turning off bathroom fans, baseboard heaters, etc. that might be connected to that branch circuit. No harm has been done since the maximum possible current flowing is what the lamp draws.

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Bocolo

Now it starting to make more sense to me. Thanks.

Yoyizit

Schematics are unambiguous; who wants to post one first?