Installing GFI Receptical

[Parfait's Provider]

OJ,

I know there are thermal and magnetic breakers, but I believe that GFIs come in only one flavor in terms of their sensing an imbalance. There are GFIs to protect people and GFIs to protect power distribution systems, but the ones we are talking about need to respond quickly to small imbalances and a thermal sensor just isn't going to get it.

For an interesting treatise on AC wiring and safety that has nothing to do with boats try http://www.chemistry.ohio-state.edu/ehs/electric.htm In that piece there is some information on GFIs and other practical information.

[Leo CD33]

Hi All,

Ken, Rich, OJ, are correct. ‘For a Ground Fault Interrupter’ (GFI) or ‘Ground Fault Interrupter Device’ (GFID) to work as designed it must be first receptacle in the line (closest to the power source) AND has to be wired CORRECTLY. That is with the ‘Line’ labeled connections to the supply wires and the ‘Load’ labeled connections to the downstream wires.

The GFID senses a difference in the hot or LINE (120 VAC, usually the BLACK wire) current and the ‘Grounded Conductor’ (ground potential, usually the WHITE wire) current. At ~ 5 milliamps delta it trips the GFID (a GFI Receptacle or a GFI Breaker.)

Note: Only a breaker or fuse will give circuit overload (over current) protection. A GFI Receptacle will NOT.

For a primer look at: http://hyperphysics.phy-astr.gsu.edu/hb ... c/gfi.html, and/or try a web search for “Ground Fault Interrupter Device”

Fair Winds,
Leo MacDonald
S/V Evening Light
Pine Isl. Bay, Groton, CT

[Andy Denmark]

Well, Ken,

Looks like I owe you the Dark & Stormy (more than one if necessary:!:

My on-the-boat testing proved me wrong. It's a good thing to know, too. At some point I may have assumed a receptacle was protected only to find, too late, that it wasn't. That would really be learning the hard way.

The deceptive thing was that I assumed the receptacle closest to the main panel was "the first" in the string when it was electrically really "downstream" from the GFCI receptacle. What had me confused was that the wiring from the main panel does not proceed linearly (SP?) down the side of the boat (there's a separate main panel breaker for both port and starboard AC outlets on the Bowman) but goes to the GFCI first and then parallels from there to the other outlets, both forward and aft, of the GFCI location.

On Rhiannon, there are only three receptacles and the first is a GFCI with the other two paralleled past that one (one in the head for hair dryers, etc. and another at the ham rig). Of course, there's a breaker at the Paneltronics AC panel ahead of all of these. A fault in any of these "downstream" outlets trips the GFCI so there's no problem.

My mistake, for sure, and one I'm glad to learn from the board rather than in a real life accident. Certainly worth a round of D & S's!

Thanks all for straightening me out.

Andy
________
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[Guest]

Andy,

Glad to know that you were able to trace the wiring and, so to speak, get the cart behind the horse. Like you, I assume that I know how Parfait's AC is routed, but it does seem strange that the GFI is in the head, so maybe that is the common point for all four outlets. I have had so much fun working on the panel and upgrading DC circuits that I haven't looked very far into the AC side.

BTW, we sailed with the autopilot, RADAR, and chartplotter ON the other day and ran out of juice for the starter after several hours. Second battery brought things back under control, but it looks like I really do need to get that DC shunt hooked up so I can see what the current draw really is. I suppose it would have been wise to look at the voltmeter and battery monitor too.....

You didn't have to accept that bet, but I'll be happy to join you for a DnS if we can ever get to the same place simultaneously.

[Oswego John]

Hey, Mr Ken,

Bingo. You picked right up on that test . Of course GFIs wouldn't be thermal. Not if they react in 50 milliseconds or thereabouts. They do have magnetic and thermal circuit breakers though.

Keep watching your mailbox. If the spirit ever moves me, I'm going to send you a gold star. Good catch.

O J