tripping breaker when testing switch and circuit

[gs8212]

I installed a switch on a new circuit. After installing and before closing it up, I test the switch and receptacle on the circuit with a multimeter to make sure the metal boxes are grounded properly. I do this by seeing how much voltage registers between a hot screw and the metal box itself. I also use one of those plug in testers on the receptacles to test for reversed polarity and several other things.

My question is why am I tripping the breaker when I touched the hot screw with the metal lead on the multimeter while also inadvertently allowing the same lead to touch the edge of the metal switch box. The switch is still screwed into the box so I was sort of reaching into the box with the lead to do this test. However, of course, when I cleanly touch the hot screw with one lead and say the same metal box with the other lead, I don't get a flash/bang and the multimeter registers about 124 volts without incident.

Thanks.................Greg

 

[Rookie2]

Dahh

 

[Mustang51js]

Is this a serous question, you just said your shorting out the circuit and wondering why you have a flash, well that's what happens when you short out a circuit lol

 

[gs8212]

Okay, so this is shorting out a circuit. Thanks. I didn't know what to call it or search for. Trying to educate myself.

 

[pattenp]

When you touch one lead of the tester to hot and the other to ground or neutral the meter provides a resistance and reads the voltage across the two conductors and the breaker does not trip because it's not sensing a short circuit. When you touch the meter probe to the hot and also happen to touch the metal box, which is grounded, with the same probe there is no resistance at all and the current flow is at full potential which the breaker senses as a short circuit, so the breaker trips. It's the same as if you took the 2 wires (hot and neutral) and touched them together.

 

[Milton Shaw]

If the breaker is a GCFI, some testers have enough resistance to trip if you connect from the hot to ground with the meter leads. Connecting hot to neutral would not trip the GCFI breaker.

 

[wyliesdiesels]

Is this a serous question, you just said your shorting out the circuit and wondering why you have a flash, well that's what happens when you short out a circuit lol

dude, back off!

We all have to start somewhere.

Hes just trying to understand the basics!!

 

[Mustang51js]

dude, back off!

We all have to start somewhere.

Hes just trying to understand the basics!!

Yeah I know,reads worse than what I meant,no harm meant

 

[Mr. T]

Okay, so this is shorting out a circuit.

More of a ground fault but same general idea.

 

[gs8212]

It's all good mustang51js. You've been very helpful on a lot of questions for me and others. I'm learning that I've been a little cavalier about the electricity which is just stupid, so a little biach slap was probably in order!

 

[Rookie2]

It's all good mustang51js. You've been very helpful on a lot of questions for me and others. I'm learning that I've been a little cavalier about the electricity which is just stupid, so a little biach slap was probably in order!

In school I was constantly told that 1 (one) milliamp can Kill you if it passes thru your Heart via your arms. Now that may have been revised since the 70's but when it grabs you the first time you'll say WTF !!!!!!!!!

 

[justsam]

If the breaker is a GCFI, some testers have enough resistance to trip if you connect from the hot to ground with the meter leads. Connecting hot to neutral would not trip the GCFI breaker.

A hot to neutral short WILL trip a GFCI BREAKER. Not because of a ground fault but because the BREAKER is acting as any other ordinary breaker and will trip from over current.

A hot to neutral short WILL NOT trip a GFCI RECEPTACLE, since current on hot and neutral are equal, and no ground fault is detected.