Can I connect it to a sub panel that is rated for 70 amp? I just want to put 3 or 4 20 amp 120 breakers in. Is it safe to do it?

  • I am not sure how the sub-panel is configured, but if the sub-panel has a pair of 70 Amp main breakers and if something trips it will be the 40 amp breakers in the main panel, not the 70's. That means you will need to go all the way back to the main panel to reset. If this is in another building or a locked room ...... – Chris Taylor Feb 27 '19 at 0:05

Yes, that's fine. The breaker in the main panel needs to protect the wiring to the subpanel.

Obviously, a 70A panel will not be damaged by 40A of power.

Just one word; don't penny-pinch when buying panels. Buy the biggest panel you possibly can, so you can add circuits later. A 40A/240V panel can support as many as 10 or more 120V/15A circuits, presuming they won't all be heavily loaded at the same time. You might even be able to upgrade the power feed later. Many panels are sold as 4 spaces/8 circuits. Don't count on the second one, given today's requirements for GFCI and AFCI which don't fit in half spaces.

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