The zig-zag is the safest connection. It may be done safely even if the number tags are missing from all of the leads.
Assume that the set is wire for either 120:208 Volts or 277:480 Volts and you want to change to 120:240 Volts or to 240:480 Volts.
No numbers are left.
Arbitrarily tag the leads "A", "B" and "C".
Tag the star point leads X0
Pick any one.
Lets start with "A"
Disconnect the neutral connections.
With a continuity tester find the X0 end of the "A" winding(s)
Tag that X0A.
Reconnect the other X0 leads to the star point.
Connect X0A to either "B" or to "C", tape up the connection and forget it.
The two remaining leads will be L1 and L2 and X0 will be the neutral.
Or, said another way, disconnect the star point and do a continuity check.
reconnect the star point with one lead or pair of leads left out.
Make and insulate one connection.
Done.
Collins, 120:208 Volts to 120:240 Volts only.
You have a permanent star point with leads 7, 8, 9 and 10.
Leads #1 and #4 connect to leads #7 and #10 respectively.
Leads #2 and #5 connect to leads #8 and #10.
Now you see a zig-zag,
Leads #3 and #6 connect to leads #9 and #10.
Now you see a zig-zag that is a mirror image of the first zig-zag.
Naming.
If you draw a vector sketch with the #1-#4 and the #7-#10 windings horizontal and on the left, the #1-#4 and the #7-#10 windings form a horizontal bar.
The right hand side of the sketch forms a diamond.
Hence Bar-Diamond.
An engineer and his friend Mr. Collins were having coffee together.
The engineer was preoccupied with some generator conversions and was absent mindedly doodling sketches on a napkin.
Mr. Collins, an old cowboy, looked at one of the sketches and remarked;
"That looks like the old Bar-Diamond brand."
Hence; The Collins connection.
Bill
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"Why not the best?"
Jimmy Carter
