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Safely? You don't. To tighten up the main lugs safely, the power has to be off. And the meter will have to be removed for that to happen. We can cut the tags, you can't. (not without risking a hefty fine) Around here, if you do it then call the power company to re-seal the meter (or when they find it unsealed) the power company will demand to see the invoice where you paid an licensed electrical contractor to cut the seal, and God have mercy on your soul if you can not provide such document, because they won't! This is one thing best left up to the pros, not so much as a safety concern, but as a financial issue. Here, it's a $10,000.00 (yes Ten thousand) fine if your caught cutting that seal. It's less than an hour job. $90.00 tops.

Electrical Panel Lugs

Even trained electricians get killed working on energized circuits. Every year there are families with no bread winner because someone took a chance.

Your best choice is to hire an electrician. If your lugs are loose, then you noticed a problem 1st and if the lugs are loose there is a good chance of damage.

Let a professional inspect for damage and properly torque the lugs.

lugs should have been torqued to specifications at install. if they need to be re-torqued, you really should call an electrician. a pro will have the gear to do it safely. arc flash dangers are very real. without proper gloves, shields, and clothing serious injury and/or death is possible

If it is a sub-panel, you need to kill the power to it, get out your set of allen wrenches and go to town on them. If it is your main panel, you are going to have to call the power company to kill the power to it before you do anything.

an allen wrench wrapped HEAVILY in electrical tape, or an insulated allen wrench(preferred) are you serious everyone? its the simplest thing to work on live with an insulated driver, come on!

You don't. Best leave this one up to the pros.