Home Improvement → Circuit Short

The problem could be in one of the things you unplugged, if I understand your description.

All three (white, black, and green, right?) show continuity to each other. Strange. I don't know how a single short would cause that.

You determined that the fault was before the box at the lower right of your drawing. Try breaking the chain in another box next. Can you open the box to the left of the 12 ft label, and disconnect those lines to further isolate?

You did not say whether there was continuity to ground.

Here is another test that you might consider: rig up something that will put a limited 1 amp to 10 amp to the wires. Maybe use a 200 watt light bulb or 200 watt soldering iron in series or a 500 watt hair dryer. With your voltmeter, measure the voltage at each outlet downstream. It may only measure millivolts. Let's say the short is in the farthest outlet box. The number of millivolts will decrease as you approach the short. Alternatively, suppose the short is midway down the line. The millivolts will go down as you test your way farther from the power source. If you pass the short, all of the subsequent outlets should measure about the same millivolts, because the wires past the short are not carrying current.

There is no way to apply power to the circuit as it trips the main breaker when on.

There is no way to apply power to the circuit as it trips the main breaker when on.

Also the fact that the ground wire has continuity with the drain pipe is to be expected unless you actually disconnect the ground wire during testing (I would leave it connected and just focus on hot and neutral wires). Both the metal pipe and the ground wire are supposed to be connected to ground.

I would start about the middle of the circuit and disconnect the wire.

As far as what shorts, the Fluke (hah!) reports continuity across all wires. The strange part is that this setup has been untouched since the early 70's for the most part.

Perhaps a case of backstab pulling out inside a grounded metal box and touching the box.

Can you please describe in a bit more detail exactly what steps you have taken while troubleshooting so far ? As nice as digital multimeters look, this is one of the situations where a high impedance does not help (and can easily lead to wrong conclusions).

Your circuit diagram does not only show wall outlets but also light fixtures. The "nothing plugged in" statement is probably true (unless there are more outlets you are not aware off) but the conclusion that this means that there are no loads on the circuit is not. You might be measuring continuity across a light fixture (very low resistance for incandescent bulbs).

Also the fact that the ground wire has continuity with the drain pipe is to be expected unless you actually disconnect the ground wire during testing (I would leave it connected and just focus on hot and neutral wires). Both the metal pipe and the ground wire are supposed to be connected to ground.

How about a completely different track - In the last few days did you do any of the following?

Hang up a new picture or anything else on the walls?
Did you plug in new equipment or move plugs around for existing equipment?
Plug in a sweeper, fan or anything else?

If you did any of that, check those outlets first.

Low ohm reading, but the outlets are inaccessible and will be for a couple days probably.

As nice as digital multimeters look, this is one of the situations where a high impedance does not help (and can easily lead to wrong conclusions).