Parallel feeder sets, and why they must stay matched.

A paralleled service divides current across several conductors of the same size instead of using one very large one. That keeps each conductor within a size that can be bent, pulled and terminated with ordinary equipment, and it lets a large service be built from cable a crew can actually handle on a roof or inside a vault.

Code requirements for paralleled conductors set the conditions: conductors of 1/0 and larger, identical in length, material, size and insulation, arranged so current divides evenly. The physics is unforgiving. If one run is shorter or a size different, it carries more than its share and the set runs hotter than the design intended.

Five properties make a set, and each one is checked at removal rather than assumed from the drawing. A group that was matched in design can lose that status in a warehouse, on a truck, or in a single afternoon when one reel is borrowed for another job and never comes back.

Insulation is the property most often overlooked. A set built from XHHW-2 and later extended with a length of THHN is no longer a set, even where the sizes agree, because the temperature rating and the wet-location suitability differ. The lowest-rated conductor in the group sets the limit for all of it.

Tag every reel in a set with the same group reference and the position it held, then keep them on one pallet or in one bay. The moment a reel goes to a different job, the set becomes a collection of reels. Paint the group reference on the flange as well as on a card, because cards fall off.

When a set comes out of service, cut the ends long and keep the phase identification intact. Cable that was taped at both ends is far easier to re-use than cable cut into anonymous lengths, because the tape is the only record of which run was which.

A matched set of four is one lot, not four. If a reel in the group is missing or unmatched, say so at the start, because the review changes from a set to individual lengths.

Removals rarely preserve sets. A crew pulling out a service cuts at the terminations, coils each run separately and loads them in the order they come free. By the time the reels reach a yard the only evidence of the group is matching lengths and matching print, and often some of that has been cut away.

That does not make the cable worthless. It means it is reviewed as individual lengths rather than a matched set, and that the lengths are measured rather than assumed. A buyer told the history can usually still use the cable; a buyer told it is a set who finds four different lengths will question the rest of the list.