Understand the circuit
A standard duplex receptacle functions as both a receptacle, and as a junction. It allows you to connect cord-and-plug devices to the circuit, while at the same time allowing other hardwired devices to be connected to the circuit. Ground-fault circuit interrupter (GFCI) receptacles are similar, however, they offer ground-fault protection to all connected devices. To offer this protection, GFCI receptacles have two specific sides.
Line VS. Load
The Line side of a GFCI receptacle is where the feed line connects, to supply power to the device. The Load side of a GFCI receptacle is used to feed other devices, while offering them GFCI protection.
Find the line
Before you can figure out how to connect the device, you have to determine where the power is coming from, and where it's going to. To do this, you'll need a non-contact voltage detector, and a few twist-on wire connectors.
- Turn off the circuit using the circuit breaker or fuse.
- Verify the power is off using a non-contact voltage detector.
- Remove all the wires from the receptacle, and place a twist-on wire connector on each wire individually.
- Turn the power back on at the breaker/fuse.
- Carefully, move the non-contact voltage detector near each wire.
- When the meter lights up, mark the wire in some way.
- Turn off the breaker/fuse again.
In this procedure, only one wire should make the meter light up. If more than one wire caused the meter to light, contact a local licensed Electrician.
Now that you've located the ungrounded (hot) Line conductor, you'll have to also locate the Line grounded (neutral) conductor. To do this, simply follow the wire you marked in the previous step back to where it enters the box. You should notice that the wire is grouped with one to two other wires. The wire you found to be hot should be black, and it should be grouped with a white, and possibly uninsulated or green wire. These wires make up the Line feeder.
Hook it up
GFCI protection to downstream devices
- Connect the black wire from the Line feeder to the brass screw terminal on the Line side of the GFCI receptacle (The receptacle should be clearly labeled LINE), the white wire from the Line feeder to the silver screw terminal on the Line side of the receptacle.
- Next connect the black wire from the other group of wires to the brass screw terminal on the Load side of the GFCI receptacle, and the white wire to the silver screw terminal on the Load side of the GFCI receptacle.
- Connect all the uninsulated/green wires together with an extra bit of uninsulated/green wire (about 6" long), using a twist-on wire connector or crimp connector.
- Connect the other end of the extra bit of wire to the green (ground) screw terminal on the GFCI receptacle.
Once you restore the power to the circuit, all the devices downstream (on the Load side) from the GFCI receptacle will be GFCI protected. If this is not the desired outcome, please follow the steps below.
No GFCI protection to downstream device
- Connect the black Line feeder to the other black wire and an extra bit of black wire (about 6" long), using a twist-on wire connector.
- Connect the other end of the extra bit of wire to the brass screw terminal on the Line side of the GFCI receptacle.
- Connect the white Line feeder to the other white wire and an extra bit of white wire (about 6" long), using a twist-on wire connector.
- Connect the other end of the extra bit of wire to the silver screw terminal on the Line side of the GFCI receptacle.
- Connect all the uninsulated/green wires together with an extra bit of uninsulated/green wire (about 6" long), using a twist-on wire connector or crimp connector.
- Connect the other end of the extra bit of wire to the green (ground) screw terminal on the GFCI receptacle.
- Leave the sticker covering the Load side terminals of the GFCI receptacle.
WARNING: If you lack the tools, knowledge, and/or confidence to complete this task, please do not hesitate to contact a local licensed Electrician.
AFCI breakers are horrible with motor loads and even heavily loaded circuits with dimmers or ballast, to the point my state exempts circuits that have problems.
Why are they not able to tell the difference? Your miter saw creates tons of little arcs each time the brushes change from 1 commutator pole to the next, on top of pulling 3-5x the current for startup. This looks like arcs that could cause a problem. Dimmers and ballast change the wave shape causing harmonics that if a loaded circuit (well below the 80% standard) they will trip because they cannot tell the difference between the harmonics and an arc.
Using current code, you need GFCIs in the garage, not AFCIs, and if you want to cut with anything that has brush-based based motors or variable speed it will need to be less than 50& of the breaker value on some of the mfg info I have read.
Best Answer
From the comments posted above I understand....
You say that you measure a hot to neutral short at the electrical box for one particular circuit. On the other hand you say that no short is measured across hot to neutral at the outlet boxes.
This can mean one of two things.
(One) Something severed one or both of the wires between the outlet string and the breaker box and in the process caused the two wires to become simultaneously shorted on the breaker box side of the break.
(Two) The shorted pair from the breaker box is feeding a different circuit than you think it is.
For the first case you should really think about what has changed in your building between now and when the outlets used to still function properly. In most cases it is unlikely that wires spontaneously break and short together without there being some interposing disturbance of the wiring. This can give a clue of where to start looking. Did something get nailed or screwed to a wall someplace? Did a window get replaced?
I can think of one case where a wire break/short could happen and that is if there was a loose or high resistance connection that over time caused so much heat to be produced wherein the wires melted apart and also shorted due to the insulation burning off. This type of failure is most likely going to happen inside an electrical box itself where connections exist.
For the second case the obvious thing is that you need to guide your attention to the correct circuit. Note that I have seen many cases where the breaker function labels in the breaker box are incorrect. So double check the circuit carefully.
To aid in either case there is a simple technique where you can run a known good conductor from the destination point back over to the breaker box. Just lay it along the floor / ground. Then wire clip one end of it a wire in question at the destination and use the other end of the wire with your multimeter. This effectively makes one of the test leads of your multimeter long enough that you can look for continuity or opens between breaker box and destination without having to buy other types of test gear. This kind of testing should obviously only be done when all the power is turned off. Use a flash light or battery powered lamp if it gets too dark to see.
One other thing to think about....if not already being done....is that when testing for problems like this it is generally necessary to remove all connections from each wire run and test against wire ends that are free ended.