Safety Tips for Working with 120V Breaker Panels

Because these panels are in our homes and offices — and because they tend to use small molded case breakers — the dangers they pose are easy to overlook. Yet, when conditions are ripe for a disaster, a mistake during a service call can produce exactly that. A disfiguring or blinding arc flash, a lethal jolt of current, or a severe “secondary injury” from a reflexive coil back are all possibilities.

Before accessing the panel

• Ensure you have adequate working space. If this means physically moving things out of the way, notify the area supervisor before moving those things. Try to get the area supervisor to instruct his people to move things so that you are not liable for any incidents with moving things and so they understand they aren’t supposed to put those things there in the first place. But don’t proceed until those things are moved.
• Ensure you have adequate lighting.
• Inquire about any breakers that are open. Is there some danger if breaker no. 13 is subsequently closed? Which load(s) does it supply? If it’s the middle of August and that breaker supplies an electric line heater, you should leave it off. If it’s late December and you’re in Michigan, odds are the automatic lawn sprinkler system doesn’t need to operate now.
• Investigate any breakers that are tripped. Don’t merely reclose a tripped breaker, as there could be a dead short or an operational reason it’s open (despite not being properly tagged). If the trip identifier is showing, identify the likely sources of the trip. Raise the issue with your foreman and/or the owner/operator of the connected load(s).
• Note any issues with the panel cover, such as an open slot (a knockout that ended up not being used).
• Read the circuit directory. Note any issues, such as unidentified breakers.
• If cover screws or other hardware used for securing the panel cover are missing, obtain replacements before proceeding.
• As you remove the cover screws, place them into a container that you brought especially for that purpose.
• Sometimes, getting a cover off results in operation of a breaker. Go back to your list of tripped and open ones. You’ll have to address those now. If you opened one that was closed, don’t simply close it right away. In a commercial or light industrial setting, you might cause adverse operation of equipment, get someone hurt, or destroy something. Make sure you know what will happen if you close that breaker again. For example, if it’s a lighting circuit, there’s no problem. But it could be a motor that needs to cool for a few minutes before restarting; for example, an HVAC blower motor or a refrigerator motor.

Opening the main

• Before opening the main, open the other breakers. Before opening a breaker, turn off its load. This way, you don’t make an arc across the breaker contacts. This is often impractical and unnecessary for “smaller” loads, such as those 20A or less. As the volt-amp (VA) level increases, this becomes more important to do.
• In a residential panel, don’t simply open the HVAC breaker(s) just because the HVAC is not running at the momentt. Use the thermostat to ensure the system won’t automatically start. If the thermostat is programmable, don’t just increase the setting manually; move the switch to the OFF position. Then, as a backup, open the local shutoff switch at the unit’s blower section (the interlock will also prevent the unit from automatically starting).
• Before turning any of these circuits back on, you close the main. This way, you are again not making an arc across the breaker contacts.

With the panel cover removed

• Use a DMM, not a “voltage pen” to determine the absence of power.
• If using a DMM, clip one lead to ground or neutral, and use the other lead to measure.
• Visually inspect breakers for signs of arcing, especially where the load wire is connected. Inspect load wiring for signs of damage to the insulation. Shine a light along the sides and the bottom of the enclosure looking for signs of water ingress, rodents, or insects.
• Always update the panel directory if a circuit has been added, removed, or modified.

Some general notes on owners and tenants

• All of that wasted space in front of an office panel is a perfect place to put a few filing cabinets — or so some believe. Similar logic is used to justify putting up shelves for cleaning supplies or record storage right next to the service panel that’s in the utility room of a commercial unit. Don’t put these things back when you’re done working. Tape a note to each offending item citing the OSHA regulation (which is 1926.403; consider writing that on your hardhat).
• They may not understand why this particular task requires turning off the main. It may be awfully inconvenient for them if you shut off the main just to replace a nuisance tripping breaker with a new one, but convenience is not a factor to consider in this safety condition. That said, most panels are designed to eliminate this need. You can flip out (remove) a breaker while the main is closed. And, of course, if the breaker is open, you can connect or disconnect its load wiring. If you cannot flip the breaker out, you will have to open the main.
• While their super important, high-skill job requires focus, yours apparently does not. Anybody can work with electricity while not paying complete attention! If that’s the attitude they seem to project by wanting to talk to you while you are working, stop working. A single distraction can cause you to do the last thing you’ll ever do. In an office or commercial setting, you could ask the person, “What is it you do here?” Then say that sounds like an important, high-skill job that requires concentration, kind of like electrical work. If you say this with the right tone and a genuine smile, you’ll get your message across while simultaneously showing respect for the other person.
• Always confer with your supervisor, sales manager, or project manager regarding any OSHA or NEC violations. You may be instructed to fix these at no charge, or they may require the customer to agree to pay for the additional work. For example, a missing knockout is easily and cheaply corrected, but an evident neutral-ground bond that you haven’t yet located may take time to get sorted.
• If the preceding step is impractical or impossible, review any OSHA or NEC violations with the tenant, and make that person aware that per company policy, you must note these things on the paperwork that will be reviewed by the person authorized to sign off on the job. The verbal and written notices are not for your safety, but for the safety of the tenant and the potential liability of the owner and your company.