View Full Version : GFCI installation question

07-25-2009, 11:48 PM
The house inspector indicated that the kitchen needed a gfci, so I have the following questions.

1. I don't really need to replace all of the outlet with gfci right? All I need to do is the replace the outlet that is closest to the circuit breaker box? I was under the impression that a single gfci should protect everything downstream if plugged in correctly?

2. The gfci has a line and load section. It's important to install the line to the wire coming to the box and the load to the wire further downstream from the box? If I don't do this, the gfci will still work, but it won't protect the sockets downstream?

3. How do I figure out which wire comes from the box? I was thinking about turning off the power, disconnecting one of the 2 sets of wires and then switch it back on. If I have no power then I disconnected the wire coming from the box?



Speedy Petey
07-26-2009, 06:22 AM
1) Correct.

2) Yes, but newer GFIs will not work if wired incorrectly.

3) Basically, but a tester is the best way to be 100% sure.

07-26-2009, 09:52 AM
Hi Petey

Thanks for your prompt answer. Can you tell me what a tester is? I only have a non-contact voltage tester. I was planning to use that to test if the wire contains voltage. Is there a different tester?



07-26-2009, 02:04 PM
The non-contact one will work. Trip the GFCI with the test button, and see which leads still have power. Probe test lights, and multi-meters are also good tools to test things. An alternative is to install a GFCI CB in the panel.

07-27-2009, 05:43 AM
The location of the outlet relative to the main panel is not necessarily a good indicator of which outlet is the first one in the series. You will have to disconnect each outlet in turn until you find the one that is live when the others are dead.

07-27-2009, 05:52 AM
This is harder to explain than to do.

Turn off the breaker.

10' of wire measures about 25 milliohms and you can measure this resistance and thereby tell which outlets are upstream of which.

You measure between the outlet short slots. Here's how.

Borrow one of those hefty flashlights that use a 6v or 12v lantern battery with screw terminals that passes a few hundred milliamps through its large sealed beam lamp.
You put the wire under test in series with the lantern battery in series with the lamp and you measure the voltage between the short slots of each outlet.

If the path from outlet #1 to outlet #2 reads 10 mV and from outlet #1 to outlet #3 reads 20 mV then #1 and #3 are farthest apart and #2 is in the middle, and so on.
This assumes one outlet is cascaded after each other. If several outlets branch out from one in a star configuration it might get tricky and take many measurements.

Start with your voltmeter on the 12v or 6v scale and be careful that this tester is making solid contact with the wire under test, or you will be putting 6v or 12v into your 200 mV scale. Go from the higher scale to the lower and back again.
Nowadays some meters are protected against overvoltage, in any case.

The accuracy is terrible and the readings may change as the battery is loaded down but you only need to distinguish relative resistance measurements in 10 or 20 milliohm chunks.
Only pass current long enough to take your reading.