For the electricians out there…

[fuzeman]

We have a stairway and hall with a pair of lights and on/off switches, which control both lights. One switch at the bottom of the stairs and another in the hall.

Bottom switch broke so I replaced it with a new heavy duty 3 way toggle switch. It’s an older house and the switch had three wires going to it. The safety ground is attached to the metal box and not the switch. The switch is old enough to not even have the green safety ground. I decided not to pigtail the box to safety ground on switch. Wasn’t needed before so don’t add it.

Tested after I put it together and new switch works well. Just to check everything I test hall switch. After the test I call that switch ‘Sparky’ and add it to the list. That one doesn’t get used often so it can wait a day. So it gets replaced and I test it and I swear I see a spark when I toggle the switch. Toggle, toggle, toggle and no more toggle as the breaker was tripped.

Wiring seemed fine before and only two switches replaced and wiring transferred over correctly ( pictures before to compare ).

 Bad switch?  I didn’t yank the wires at all and only reformed the ends a bit to get them n new switch.  Where to start troubleshooting besides the switch.

[Shuffler]

This should help.....

[Eagler]

Please use an ohm meter to confirm your hot and ground...I wouldn't take it for granted that it was installed properly before

Eagler

[fuzeman]

The Sparky channel, appropriate.

I thought as long as I was careful and only touched one wire at a time I could switch the switches without even turning the power off.

I have to say working on electrical stuff is more fun with someone within hearing distance.
That way you can do the ‘Of course the power is turned <SCREAM>’ joke.

[fuzeman]

Please use an ohm meter to confirm your hot and ground...I wouldn't take it for granted that it was installed properly before

Eagler

Even if Dad wired it I guess I should double check his work.
He made mistakes! I’m proof of that. 

[AKIron]

The Sparky channel, appropriate.

I thought as long as I was careful and only touched one wire at a time I could switch the switches without even turning the power off.

I have to say working on electrical stuff is more fun with someone within hearing distance.
That way you can do the ‘Of course the power is turned <SCREAM>’ joke.

I worked for a year as an electrician's helper back in '72-'73, between high school and the USAF. A couple of the electricians scoffed at turning off the breaker to replace a switch or outlet.

[AKIron]

I've been bit more than a few times and am more cautious. Especially after working around high voltage in radar sets for many years. The ASR-9 had a klystron at 75KV. It was shielded to protect us from radiation.

[The Fugitive]

You didnt say if you were getting the "spark" while the switch was mounted or hanging out of the box. This is a picture on how it should be connected.

https://www.hometips.com/wp-content/uploads/2012/07/3-way-switch-wiring-diagram-1.png

Even if you dont use a pigtail on the ground, with the switch mounted the ground is good enough. With the switch hanging out you can test the circuit by flipping the switches to see if it sparks or pops a breaker.

First be sure that it is wired correctly.

Second, even if you dont think you could have damaged the wires coming into the box by switching the switch check them. Loosen the clamp that holds the cable and give them a tug to see if there is some slack and you can pull a bit more into the box. Inspect the cable, tape off any iffy spots and tighten down the clamp.

When "reforming the ends" be sure to only have enough wire exposed to wrap around the screw. Any more could leave enough to get a ground connection when mounted. Once Im sure I have the plug/switch wired right I'll wrap a bit of tape around the unit to cover the screws to be sure it cant short to the box if jostled.

Next test the switches while they are hanging out of the box. If no sparks, mount one and test again. If you have sparks, unmount that one, mount the other one and test again. If sparks again, your wired wrong or your grounded some place else.

And yes, if you are only touching one wire at a time and NOT grounding yourself it is easy to do this with out shutting off the power. However everyone slips and a good zap keeps the resect strong in all of us