Friday, March 4, 2011

GFCI

What do you see that is unusual about this outlet?  It is not the normal shape.  It is in fact a GFCI outlet.  Those initials stand for Ground Fault Circuit Interrupter, and they could save your life.

Concealed in the tiny device is some pretty neat magic.  The GFCI continuously monitors the amount of current in the supply (hot) and return (neutral) lines.  If they are not identical, it trips, stopping the current flow.  How could they not be identical, you ask rhetorically?  If there were an internal short in an appliance causing you to receive an electrical shock, some of the current that should have been returning via the neutral wire would be instead passing thru your screaming body to ground.  The GFCI would detect this and open the circuit.  I talked about these in the middle of an earlier electrical rant.  But the subject is important enough to bear repeating, in its own post.

Ground Fault Interrupters are now, like in houses, required equipment on all circuits on a boat near water:  the galley and the heads.  But realistically speaking, isn't any circuit on a boat near water?  All your AC outlets should be GFCI protected.
WARNING:  This procedure will have you working with lethal voltage, and could result in your death or the consumption of your boat by fire if done improperly or without common sense.  If working with electricity makes you uncomfortable, or if you have any doubts at all about your ability to safely complete this installation, you must hire a qualified electrician to do this work.

Disclaimer:  I am not in a position to judge your abilities or skills.  If you choose to proceed, you do so having determined yourself that you have the necessary abilities and skills.

The biggest problems I have encountered on boats are electrical wiring issues, done by obviously unqualified people.  Be part of the solution; do not contribute to the problem.
This is an ideal Small Boat Project™.  It is inexpensive and can be completed in a short time, yet has significant benefits.  How many AC outlet circuits do you have on board?  One?  Two?  Three?  Well then you just need to go to Home Depot and buy one/two/three GFI outlets - one for each circuit.  In boats as well as houses, multiple outlets are typically wired on a single circuit in a daisy-chain fashion.  And GFCI outlet manufacturers know this and have provided for it.  If you install a GFCI outlet in a circuit, all outlets downstream of the GFCI outlet in the daisy chain will also be protected.  Obviously then, you want to make the GFCI outlet the first one in the chain.

So then, how to find the first outlet?  Think like an electrician.  How would he have wired your boat?  He would have run a wire from the power panel to the closest outlet, and then from that outlet to the next one, and so on.  If the wiring is concealed, then this would be your best bet:  the first outlet in a circuit will be the one closest to the panel.

But you should actually confirm this.  Here's how:  Turn off the circuit and remove the outlet you suspect to be the first in a chain from its outlet box (you were going to need to do this anyway).  You will find two cables enter the box - each cable will contain a white wire, a black wire and a green ground wire.  The two ground wires will be bonded together, with a single connection going to the outlet.  Remove all the wires from the outlet and tape the ends of the black and white wires well to prevent inadvertent contact with the bare ends.  Turn the circuit back on and check the rest of the outlets on the circuit - all those that are now dead would be protected if the GFCI were installed in that outlet box.  Turn the power off again.

This next step is important.  Of the two cables in the box, one goes back to the power panel and is the supply for the whole circuit.  The other goes to the downstream outlets in the daisy chain.  Each set of wires has its own dedicated terminals on the GFCI - for it to work properly, they cannot be mixed up.  If you can access the back of the panel in which the outlet box is installed, it may be obvious which cable goes back to the panel.  If not, then you will need to do a LIVE WIRE check.
DANGER:  This task has you working with LIVE WIRES and LETHAL VOLTAGE.  If you are uncomfortable with your level of knowledge or your ability to safely complete this task, STOP.  Hire an electrician to complete the work.
Remove the tape from one pair of black/white wires.  Position the bare ends so that they are not at risk of touching anything (including you), and turn the breaker on.  Use your voltmeter to check for the presence of 110 VAC between the wires.  Turn the breaker back off.  If power was found, then this is the power source wire set.  If not, then the other set must be the power source.  Confirm this by retaping the exposed wires, and then proceeding as above with the other pair of wires.  Turn the breaker off.

TURN THE BREAKER OFF.

Now install the GFCI outlet.  Connect the ground wire to the green terminal.  Connect the power source wires to the power source terminals on the GFCI, black wire to the copper-colored screw and white wire to the silver-colored screw.  If your boat was wired properly, the wires will be stranded marine wire and will have been terminated with crimped on terminals - probably ring terminals.  You will find that the screws on the GFCI cannot be entirely removed.  If your wire terminals are ring terminals instead of J terminals or flanged spade terminals, they will have to be cut off, and J terminals or flanged spade terminals securely crimped on.
Make no mistake - an improperly crimped terminal is a fire hazard.  If you are unsure about your ability to properly install a crimp terminal, or even what a properly crimped terminal looks like, STOP.  Hire an electrician to complete the work.

Remove the protective cover from the other set of terminals on the GFCI and connect the downstream outlets to these terminals, as above, black to copper and white to silver.

Be sure that nothing can come in contact with the exposed connections on the GFCI.  Turn on the breaker.
  • First of all, the breaker should not have immediately tripped.  If it did, do not attempt to reset it - you have made a serious wiring mistake.
  • The GFCI may need to be reset - reset it if necessary.  
  • Check to see that the GFCI and all the downstream outlets are powered.
  • Trip the GFCI (use the 'TEST' button).
  • The GFCI and all downstream outlets should now be dead.

TURN THE BREAKER OFF.

Now it is necessary to stuff everything back into the outlet box.  Because the GFCI outlet is physically larger than the old outlet, this will be difficult.  First, push the ground wires into the back of the box, as tightly against the back and out of the way as you can.  Now push the remaining wires into the box, followed by the GFCI.  Reinstall the retaining screws and the cover plate.  Turn on the breaker.
  • The breaker should not have immediately tripped.  
  • The GFCI may need to be reset - reset it if necessary.  
  • Check to see that the GFCI and all the downstream outlets are powered.
  • Trip the GFCI (use the 'TEST' button).
  • The GFCI and all downstream outlets should now be dead.
All the downstream outlets on that circuit are now protected - apply the little stickers included in the GFCI packaging to the downstream outlet covers to attest to this. 

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