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[bkenobi]

If you were comfortable enough with it, you could open the panel and look at the wire colors leaving the main and entering the sub and then confirm which phase they were connected to.  Careful, it's hot in there!

[HA Man]

If you were comfortable enough with it, you could open the panel and look at the wire colors leaving the main and entering the sub and then confirm which phase they were connected to.  Careful, it's hot in there!

That was my first thought as well - and it works for the "local" sub-panels (that is, the ones located in the house) where the wires in the sub-feeder cables are color-coded.  Unfortunately, in the case of the sub-panels located in the other buildings, the sub-feeds are supplied via overhead "triplex" cables, which either don't have any identifying marks and/or the electricians weren't concerned about which "side" of the triplex got connected to which half-phase at the weatherheads.

So, that left things uncertain as far as which half-phase in the house goes with which half-phase in each of the other buildings, and I don't know of any practical way to identify which is which (via a measurement of some type).  I suspect there is some "trick" that can be used, but I don't know what it may be.

[guyl]

Unfortunately, in the case of the sub-panels located in the other buildings, the sub-feeds are supplied via overhead "triplex" cables, which either don't have any identifying marks and/or the electricians weren't concerned about which "side" of the triplex got connected to which half-phase at the weatherheads.

So, that left things uncertain as far as which half-phase in the house goes with which half-phase in each of the other buildings, and I don't know of any practical way to identify which is which (via a measurement of some type).  I suspect there is some "trick" that can be used, but I don't know what it may be.

If you can temporarily run a long extension cable from the main building to the other buildings, you could measure the voltage between the "hot" side of the extension cable (plugged into the main building) and a phase in the outbuilding. If you get 0 volts, then you're on the same phase. If you get 240 volts then you're on the opposite phase.

[bkenobi]

The sub will be fed by both phases so you just need to determine which red/black conductors are connected to in each.  Should be simple enough.

[HA Man]

If you can temporarily run a long extension cable from the main building to the other buildings, you could measure the voltage between the "hot" side of the extension cable (plugged into the main building) and a phase in the outbuilding. If you get 0 volts, then you're on the same phase. If you get 240 volts then you're on the opposite phase.

That's along the same lines - but safer, and perhaps easier - than what I was thinking of, which was to turn off the breaker for the sub-feed in the main panel, then put a jumper between the neutral and one of the "hots" on the sub-feed, and then check the continuity between neutral and hots in the sub-panel.  Should work - but with some risks and hassles.  The extension cord method could be done without removing the covers of either breaker panel (because measurement could be made between the cord and an outlet or fixture in the out-building - which is on a known phase in the building's sub-panel).  Thanks for the idea!  (Now, to find some looong extension cords... ;-) )

[HA Man]

The sub will be fed by both phases so you just need to determine which red/black conductors are connected to in each.  Should be simple enough.

Right... but that's the problem:  How to reliably trace the conductor connections (see my previous reply).  With the way things were installed, it would be non-trivial - and perhaps impossible - to visually trace the conductors through the entire sub-feed path.  So, a measurement of some sort seemed to be easier/more reliable - or perhaps the only option.  I just didn't have any ideas about a quick and safe way to make the necessary measurement(s).

[bkenobi]

I didn't see initially that you had an aerial run which makes it more complicated.  If you can't use the conductor type, then you'd have to trace it some other way.  I would still have expected the electrician to use a single run if possible but I suppose you never know.  There are devices that let you trace a wire, but I don't know how reliable/feasible that is over that distance nor if it would be safe with an energized conductor.  Using the extension cord method suggested earlier is probably easier if you have sufficient length.

[HA Man]

I didn't see initially that you had an aerial run which makes it more complicated.  If you can't use the conductor type, then you'd have to trace it some other way.  I would still have expected the electrician to use a single run if possible but I suppose you never know.  There are devices that let you trace a wire, but I don't know how reliable/feasible that is over that distance nor if it would be safe with an energized conductor.  Using the extension cord method suggested earlier is probably easier if you have sufficient length.

Yeah, the overhead triplex cable is sort of the crux of the problem.  It has a bare stranded aluminum over steel core conductor that's either used for the neutral (for a split-phase feed) or for the bond (for a single-phase feed that doesn't have it's own "local" ground rod.  That bare conductor is also used to support the whole cable, with hangers attached to the anchors on the buildings, poles, etc.  The other two stranded aluminum conductors in the triplex cables have insulating jackets but appear to be identical, with no identifier markings that I can find.  So, even though the weatherhead cables that attach to each end of the triplex have their insulated conductors clearly marked with white or red stripes, there is no "carry-through" of identifier markings on the triplex, so I don't know how to visually tell which one is which at the other end of the cable.  Makes little sense to me that the weatherhead cables would be clearly marked, when they just attach to (apparently) unmarked triplex cables.  Perhaps I'm just missing some indicator, but if there is any, it's certainly not apparent, and definitely not "obvious" like the stripes on the weatherhead cables.  Maybe somebody reading this can clue me in?  Anyway, thanks for your reply.

[bkenobi]

The only other things i can think of are trying a battery or using a wire tracer.

If you can disconnecting the conductors at the main panel and attach each to a dc voltage source, you can use a meter at the sub to see which is which. Triplex should have 3 conductors and a neutral (3-1 I'm assuming). So if you have 3 conductors, 1 will be no connection, 1 will be positive, and 1 will be negative. If you only have 2 conductors then it'll just be +/-.

Alternately you can use a wire detective or similar to send a signal down the wire and hopefully see the signal at the main panel.  I used a couple variants of these to trace my circuits as well as locating the dead ends of a pre-wired (never installed) security system in my house. Takes patience but did work. Not sure it would help here though since both conductors run unshielded in parallel for a long distance so may just have the same signal.

[brobin]

Ususally one of the insulated conductores will have a yellow stripe but if not, examine the conductors very carefully to see if one has a raised ridge. Also examine a couple feet of the cable to see if there are any embossed markings which typically repeat every foot or two - you might need to brush some chalk dust on it like looking for fingerprints!