RSquirrel
Member
- Location
- Watsonville, CA, USA
- Occupation
- Mechanical Engineer (retired/consulting)
I am replacing an obsolete Zinsco ML12 panel (9-3/4” wide) with two “stacked” Square-D QO816L100DF panels (8-7/8” wide). Two panels are needed in order to provide enough circuits and to fit into the available space (14-1/2" wide panels are too large) without making structural changes to a load-bearing wall. The 100-amp feed will come into the bottom of the lower panel and all of the circuit feeds will exit out of the top of the upper panel. The upper panel will only contain 15- and 20-amp breakers.
My questions concern the best method to feed power from the lower panel to the upper panel.
Method 1: Install an appropriately-sized 2-pole breaker (e.g. QO260) in the lower panel, feeding power via 6-AWG THHN’s to the upper panel (in effect, the upper panel would be a sub-panell to the lower panel).
Method 2: Connect the two hot and the neutral lugs of the lower panel with those of the upper panel.
With either method, the two panels will be bonded together.
As it relates to method 2, I checked the diameters of the lug holes and they should be able to accept both the 3-AWG primary power feeds and the piggy-backed 6-AWG feeds to the upper panel.
Q1. Are both of the methods acceptable per the current NEC?
Q2. Other than avoiding the cost for the QO260 breaker, is there an advantage to one method vs. the other?
My questions concern the best method to feed power from the lower panel to the upper panel.
Method 1: Install an appropriately-sized 2-pole breaker (e.g. QO260) in the lower panel, feeding power via 6-AWG THHN’s to the upper panel (in effect, the upper panel would be a sub-panell to the lower panel).
Method 2: Connect the two hot and the neutral lugs of the lower panel with those of the upper panel.
With either method, the two panels will be bonded together.
As it relates to method 2, I checked the diameters of the lug holes and they should be able to accept both the 3-AWG primary power feeds and the piggy-backed 6-AWG feeds to the upper panel.
Q1. Are both of the methods acceptable per the current NEC?
Q2. Other than avoiding the cost for the QO260 breaker, is there an advantage to one method vs. the other?