Electrical Safety

[apostolakisl]

Touch the probes to the + and common wires - if the light comes on then there is power. If it stays off, then the power is off. Simple as that.

I am not so sure thats correct. Here at my house (an older home) I use AC. The AC stands for alternating Current. Which means the + and - aren't like the DC (Direct Current) examples we we had in grade school. So if my old wiring uses a switch to break the (+) black wire.... I might still get a nice jolt off the white (-) wire... if I happen to be grounded.

A very common cause of shock at home is messing with a light when the switch is switched OFF.

The AC in a house is driven by one side of the wire set (the hot wire) in a 110 circuit. You can think of it as pushing and pulling electrons 60 times per second. When the hot wire is not part of a closed circuit, the pushing and pulling goes nowhere. The electrons can only move back and forth if provided with a "bucket" at the other end which can let those electrons at the end of the line move out of the wire for 1/60th of a second and then back in. This is what the white wire is for (usually called a common sometimes neutral) The white wire connects to earth via a rod buried next to your house. The earth acts as that bucket letting electrons in and out. The uninsulated wire also goes to this rod. When you power on a device, the white wire is used to complete the circuit from the hot side to earth. So, if the device is not on, then the white wire should not have any connection to electrical current. Be advised that I have used the word "should" because your house may not be wired properly.

It is possible to get shocked by a white wire if you turn the device on, then cut the white wire or otherwise separate it from earth. Now the electrons are pushing and pulling from the black wire, through the switch to the device, through the device, into the white wire, and are looking for the easiest path to earth. Your body would only be the easiest path if the white wire were no longer connected to the grounding pole buried in your yard.

If you want to be sure the power is off, use your little 99cent deal from home depot. Touch one lead to your ground (the bare wire) then the other lead to each of the other wires in question one at a time. This will work almost 100%. The only time it would fail is if the ground wire isn't hooked up. If you want to test your ground wire, turn the circuit breaker on, then touch one lead of the 99cent deal to the ground and the other end to other wires (one at a time). If the 99 cent thing ever lights up, the ground is good.

 

[tmbrown97]

My garage outlets share a GFCI with the kids' bathroom outlets, upstairs on the 2nd floor, and with an outlet at the front door.

Yup - had that too a few days after I bought the house and started tampering with wiring... the GFCI that was behind some boards in the garage took out every outlet in the garage, kids bathroom, and a few in the livingroom where there was once a bar (now inside my entertainment center). For about 2 hours I thought I'd really screwed something up...

 

[drozwood90]

That's one thing I still need to correct in my house. I have the powder room's GFCI outlet chaining the other two bathrooms. What I'd like to do, since I bought 12 GFCI for the last house, and never got to installing them, is take those and distribute them about this house...so each bathroom has it's OWN GFCI...

Might as well since I own them...

Same with the "one" in the basement that feeds the two outside plugs...

This way if I knock one out, it doesn't take out other rooms in the house.

--Dan

 

[BraveSirRobbin]

I believe there was some discussion on this here before (old age getting to me), but can you have two GFCI's on the same circuit (i.e. one installed "downstream" from another?)

 

[apostolakisl]

I believe there was some discussion on this here before (old age getting to me), but can you have two GFCI's on the same circuit (i.e. one installed "downstream" from another?)

You can install as many gfi's on the same breaker as you want. Each one needs to have a clear shot back to the breaker box though, you shouldn't daisy chain gfi's together. The daisy chaining is if you want to use one gfi to portect a bunch of plugs where you just have regular plug installed downstream. They do this to save a couple of bucks since a gfi costs like $7 instead of $1 for a regular plug.

If your electrician originally daisy chained several regular plugs onto one gfi and you want to change out those regular plugs for independent gfi's you need to go back to where the primary gfi is installed and connect the wires such that the wire from that box to the next one is spliced directly to the leads from the breaker box. Now you will have hot wires at the next box that aren't under the control of the gfi at the previous box.

To figure this out you need to pop the gfi and then locate all of the plugs that are under its control (they will all shut down). Now turn off the circuit breaker to the affected items. Open up all of those boxes and then ohm things out figuring how the wires travel from one box to the next. This is easiest done with two people. Disconnect all of the outlets at each location and leave the wires all unspliced. Then go to the first box where the gfi was and put an ohm meter on the hot and common that were outputted from the gfi plug. Go to each of the other boxes and touch the common/hot together and see if the ohm meter bounces. If so you have found the wire that goes from the gfi box to the next box. From there you can do the same thing and track the wire to the next box etc etc. Once you know how the wires hop around from box to box, you can design your gfi system.

If you want to just put an independent gfi at each location, then it really doesn't matter what order the wires hop arond. Just connect the hot to hot and common to common at each box and all of the boxes will have a direct line to the circuit breaker. Then you can attach a gfi at each location by connecting the hot and common to the hot/common spot on each gfi and not using the load output spot on each gfi.

Also an fyi. Gfi's protect people and circuit breakers protect your house. A circuit breaker pops when more electricity goes through it than the rated number. A gfi pops when the electricity on the hot side doesn't equall the electricity on the common side. Or, in other words, the electricy has found an alternate path to ground besides the white wire. For example, the electricity is going through you and into the plumbing of your house (which is usually grounded). A gfi will pop even if a tiny bit of electricity has leaked out of the circuit. You could electicute yourself and not pop a regular breaker since 20 amps is way more than is technically necessary to electricute a person.

 

[cornutt]

I believe there was some discussion on this here before (old age getting to me), but can you have two GFCI's on the same circuit (i.e. one installed "downstream" from another?)

Don't wire up a circuit where a GFI is protecting another GFI. They'll "fight" each other and you'll get lots of nuisance trips.

 

[blue_8019]

You should purchase a cheap multi-meter for around $5 and use that. They are handy to have around the house and better than the neon indicators.

 

[drozwood90]

Sorry if my post was misleading...I thought it was obvious...but I guess not...

I'm going to change the wiring, so, instead of each GFCI being downstream...they will all be in parallel...otherwise there would be not point in doing this, as a GFCI upstream will STILL kill a GFCI (or plug) downstream.

--Dan