Bought a 1960s home with aluminum wiring.
I noticed that I have two sets multiwire branch circuit? (also known as "multiwire circuit", "multiwire branch circuit", "shared neutral", "two circuits fed from one 12-3 or 14-3 NM-B cable", "shared neutral circuit", etc).
Both hot feeds are connected to same side of the breaker panel (thus presumably NOT a split-phase MWBS, but a same-phase). I would think that this overloads the neutral line.
Sure enough, one single-gang SPST switch box started clicking and then smoldering (had to turn two non-adjoining breakers off before accessing).
Purple wire nut got burned thru that was connecting all the neutral (white) AWG10 wires together.
After much long-wire continuity tests to identify each 3-wire plus ground Romex cables going to other boxes, I've resisted repacking properly with purple Alumicon steel buses because ...
The lone neutral feed (AWG10 aluminum) wire would be computationally overloaded with 2x15A loads.
I've often wonder which approach is better repair method:
switch one of the two breakers covering the MWBS from same phase as the other to an adjoining slot having inverted phase.
drop two separate but new AWG12 3-wire + ground copper Romex
Also get a deeper single-gang box to accommodate the clunky 3-connector Alumicon steel lugs.
I obviously cannot pack this box until this resolution has been taken.
Old construction, mostly aluminum AWG10, some contractor re-work in AWG12 copper.
Slot Position 10 (phase A) and 18 (phase A) have shared neutral.
GE TX1612 panel box.
If one side is same phase and other side is inverted, I would swap 15 (left side) and 10 (right side).
If one of those fancy zigzag alternating phase on one side (Edited: every two rows, yes, starting at row having slot 7-8).