I'm planning to install a 240v 30 amp circuit breaker in the open slots on the bottom left hand side of the panel. I need to punch a hole at the top of the box as the 10/3 NM will be going into the attic. How do I safely punch a hole in the knockout and run the 10/3 NM cable without touching the live main cables? Can I use a punchout on the top right side instead and wind it down the right side then over to the left, then up to the breaker?
Stay away from the metal parts above the main breaker. They are hot always.
If you haven't turned off the main breaker, also stay away from the bolts and buses right below it, and the buses down the middle that the breakers clip into will also be hot.
It helps to use gloves if you can get PPE in this day and age.
Note the way the last guy runted off all the wires so they can barely reach where they're going right now. Don't do that. Make each of your hot and neutral wires long enough to reach any breaker location in the panel, so you have freedom to move things around later, which you may well because your panel is full. Neutrals also need to reach the breaker in case you add AFCI/GFCI/??CI later. To make it "neat", run your wire along the edge, overshoot past your breaker then double back and pull in the way they have.
Best option is to disconnect the incomers, e.g. to ask the supplier if the breakers are not accessible. If that is not possible, these live saving points may help:
- Only when a second person is around this kind of work should be done. That person must be informed about the kind of work and has to be aware of the danger to help a person that is touching live parts - the helper has to wear gloves or has to make sure that he will not be affected as well.
- Work on live parts should never be done if tired or exhausted or under influence of sedatives or drugs reducing the capability to focus on the work. - Insulating gloves do help as proposed by Harper, f.e. new household rubber gloves which did never come into contact with detergents or other Ion containing fluids.
- Low humidity.
- A piece of polystyrene foam or similar to stand on for better insulation .
- Trying to not sweat helps.
- Trying to work with one hand only (other hand behind back) is also a known safety method.
- All metal jewelry, necklaces, big earrings etc. should be removed.
- Cover all metal parts that have live voltage with insulating plastic or dry cardboards.