Prolly
December 28th, 2008, 09:29 AM
so you can put the GFI upstream.
This assumes the outlets are each one downstream of the other, not having parallel branching off of one or more outlets.
Let's say there are 2 outlets on a circuit. Put a 10A load on one of the outlets.
If it's on the upstream outlet, the voltage drop between the short slot of this outlet and the short slot of the other outlet will be zero (since there is no current flow).
If it's on the last outlet, the voltage drop between the short slot of this outlet and the short slot of the other outlet will not be zero. It will be 10A x the resistance of the Romex, about 130 mV for 5' of cable.
Using this method you will be able to sort all the outlets in a circuit. It's easier to do than to say.
Using a voltmeter and a 10A load, figure out what order three outlets (arbitrarily numbered 1, 2, & 3) are in and how many feet of #14 copper Romex are between each outlet.
Plugging the load into #1, #2 reads 0v and #3 reads 468 mV, so #2 is downstream of # 1 and #3 is 18' upstream of #1.
Plugging the load into #2, #1 reads 260 mV and #3 reads 728 mV, so #1 is 10' upstream of #2 and #3 is 28' upstream of #2.
Plugging the load into #3, #1 and #2 read 0 so they are both downstream of #3.
The order is: #3 is farthest upstream, then #1 is18' downstream, then #2 is 10' downstream of #1.
This assumes the outlets are each one downstream of the other, not having parallel branching off of one or more outlets.
Let's say there are 2 outlets on a circuit. Put a 10A load on one of the outlets.
If it's on the upstream outlet, the voltage drop between the short slot of this outlet and the short slot of the other outlet will be zero (since there is no current flow).
If it's on the last outlet, the voltage drop between the short slot of this outlet and the short slot of the other outlet will not be zero. It will be 10A x the resistance of the Romex, about 130 mV for 5' of cable.
Using this method you will be able to sort all the outlets in a circuit. It's easier to do than to say.
Using a voltmeter and a 10A load, figure out what order three outlets (arbitrarily numbered 1, 2, & 3) are in and how many feet of #14 copper Romex are between each outlet.
Plugging the load into #1, #2 reads 0v and #3 reads 468 mV, so #2 is downstream of # 1 and #3 is 18' upstream of #1.
Plugging the load into #2, #1 reads 260 mV and #3 reads 728 mV, so #1 is 10' upstream of #2 and #3 is 28' upstream of #2.
Plugging the load into #3, #1 and #2 read 0 so they are both downstream of #3.
The order is: #3 is farthest upstream, then #1 is18' downstream, then #2 is 10' downstream of #1.