Electrical Service Run to 100A Sub-panel

Question

I have 2 x 240V 150A main panels next to each other in my house.

I want to install a 40A 120V breaker in each panel to feed a 240V sub-panel so I would have a total of 80A feeding into a 240V sub-panel.

Do I run a Neutral wire from each main panel and tie into the new sub-panel bus bar?

Do I run a bare copper wire from each main panel and tie it into the neutral bus bar?

You're talking about a very significant modification to your electrical panels, and you have an odd setup (two main panels?) and odd requirements (feed a subpanel from two main panels via two circuits?). Can you explain what your goal is here, e.g. in terms of adding branch circuits, and why it's currently set up that way? — Shimon Rura, Commented Aug 8, 2016 at 21:16
There's nothing weird about two main panels. This is done when a house has more service than one panel can carry. They are right next to each other and right behind the meter. A friend has a heat pump system (70A by itself) with an auxiliary electric heater (70A additional) since heat pumps can't work below freezing. That dominates one panel. His house is literally all electric. — Harper - Reinstate Monica, Commented Aug 8, 2016 at 22:10
Is there a reason you simply can't condense this into a single main panel? 300A panels are a thing, at least for Square-D (QON42MS300) and Eaton (CH42PM300 or BR4242B300F)... — ThreePhaseEel, Commented Aug 8, 2016 at 22:24
@Harper: Heat pumps work fine below freezing. The highest efficiency systems are quite efficient even at 15F/-10C. Maybe they are old units (like pre-1980)? — wallyk, Commented Aug 8, 2016 at 22:43

Harper - Reinstate Monica · Accepted Answer · 2016-08-08 22:01:19Z

5

You absolutely, positively cannot do that. Period.

Both hots and the neutral must all come from the same panel and one, only one, 2-pole breaker.

If you think you have a balancing problem, you could move some circuits around - but honestly, you'll want to get some help with that. Seriously.

answered Aug 8, 2016 at 22:01

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