Is there a simple way to figure out which is the first recepticle on a circuit? I have an older house - the two upstairs rooms are on the same circuit and are not grouned. Id like to add a GFCI plug on the first recepticle on that circuit, so every recepticle downstream is protected.
The brute force method would be to guess which recepticle is the first, remove the outgoing wires, and test every other outlet for power - rinse (hook back up the wires), repeat, until ive found the recepticle that has power and all the others that dont. :) However this will take awhile - most arent easily accessible - behind furnitire, beds etc.
I have at my disposal the standard home repair tools - volt meter, etc.
Nehmo - I don't know exactly how to do it in practice, but in theory?
Unplug everything on the circuit.
At the circuit breaker box, with the breaker off, connect what would have been the hot wire of the circuit to the neutral. Leave the neutral connected normally.
Measure between one slot and the other at each receptacle.
At each receptacle, the measurement of the resistance and inductance will be different. They will be lowest at the first, and highest at the last.
14 gauge wire only has a resistance of 2.6 ohms per 1,000 feet, so the difference in resistance will be difficult to measure. But the inductance should be substantially different at each receptacle. At higher frequencies, the measurement should be easy.
Or
Get something that detects AC _current_ in a wire without electrically connecting to the wire. Perhaps a pick-up coil attached to an amplifier or perhaps a large coil simply connected to an earphone. I'm not used to the commercial non-contact detectors, but one of them would work. You want something that makes a different indication for a current flowing wire and just a hot wire. After you have your detection tool, experiment with it. Learn to detect a current-carrying wire.
With the circuit breaker on, plug-in a high-wattage lamp in what you suspect to be the first receptacle. You should not be able to detect current moving through the wires at any other receptacle. If you detect current at a receptacle, it's at a position before the lamp receptacle.
Unplug the lamp and plug it in what you suspect to be the last receptacle. You should be able to detect current at every receptacle.
Note I'm making a distinction between a receptacle with current going through the wires connected to it and a receptacle that's just hot. All of them should be hot. The electromagnetic field will be much stronger around a current carrying wire.
Or
Get a really high-wattage load, perhaps a big electric heater, something with a high enough wattage to heat its supply wires detectably - but not dangerously. Use the same system as the current detector. Plug in the load at the (believed) last receptacle. Check the earlier receptacles for warm wires. You get the idea.
Fire the circuit up with DC (use a rectifier by the circuit breaker box). Put a low-resistance load on the circuit at some receptacle. With a sensitive voltmeter, measure between a hot slot of one receptacle and the hot slot of another. The existence and the polarity of this tiny voltage drop will show the relative position of the receptacles. If you draw a diagram, you'll understand.
You could do this with the regular AC too, but you wouldn't get the polarity info. You still could figure out which receptacle is first. You're testing for a voltage drop across a load, which in this case is just a piece of wire between receptacles. The voltage drop will not be much.
For broad protection, GFCI circuit breakers may be added in many panels of older homes to replace ordinary circuit breaker. For homes protected by fuses, ...
afaik, those breakers are pretty expensive. But ill check today and possibly pick one up.
Thanks for the comments all. Nehmo - your post alluded to a method I had considered, but im not skilled enough to know exactly what to do :) What you say makes sense, but I think ill either go with a breaker, or the method I talked abut.
If you go to RatShack and buy one of their little amplified speaker boxes (looks like an old transistor radio) and a telephone pickup coil, that combo can ge used to hear 60 Hz magnetic fields near wires.
So connect some load gadget to the various outlets one at a time. Something that has nasty current harmonics, like a PC or a tv set, is best... makes the current distinct and more audible. Now you can trace the wires in the walls and figure where the current is going. You may wish to kill other breakers in the house, or have somebody cycle your test load, if things get confusing.
Well, as long as I have your attention, it makes absolutely no difference whatsoever which outlet on a main line has a GFCI - each one only protects itself and what's plugged into it, and couldn't care less what's happening downstream:
What has been suggested, (sorry, don't remember by whom - jalegris?) is to use a GFCI circuit breaker, which goes on the left: . . ------- . Mains Hot --| GFCI |----+-------------+-------------+ . Mains Neut.--| C.B. |----|--+----------|--+----------|--+ . ------- | | | | | | . Ordinary Ordinary Ordinary . Outlet Outlet Outlet
That's "on the left" in my attempt at a diagram - in real life, it goes in the breaker panel.
Or, of course, you could upgrade your wiring - it will increase the resale value of the house considerably! :-)
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