Re: Is it legal to lock a main breaker box?

The meter box? Sure, you have no reason to go in there. It is not your box. The circuit breakers themselves? Different story, you may have to reset one and need access.

The actual meter is controlled by the power company. You can't put a padlock on it, it's their property. The power company attaches the thin wire lockout tags and if broken, they know it's been entered. Though it doesn't keep anyone out, they will hold the owner responsible. If you have a concern with people breaking in, notify them of the issue.

Locking one in a 1&2 family is largely unaddressed. Just be aware the fire department will get medieval on your cabinet if they want to get in. In multifamily the resident needs access to his own disconnect unless you have a 24/7/365 maintenance person in site. Can he lock his own? see above. This is just the NEC If you are multifamily or commercial you are not talking to an electrical inspector you see a fire marshall and they have a stack of other NFPA documents they use. They are all tougher than the NEC. He is also a guy who can padlock your business, not just fail an inspection and slow down a construction job.

Around here, they just pull the meter.