Electricity is distributed to our homes from the main power grid by either overhead wires connected to a service entrance pipe on the side of the building or roof, or by special wires buried underground. In between the connection point and your electrical panel inside your home is the meter that measures your power usage.
If you find that water is entering into your Electrical Panel from the incoming wires, it is a very serious situation. The reasons this happen are different for homes that are supplied by overhead power lines and homes that have underground power feeds.
Homes supplied by Overhead Power Lines
If you have overhead wires, the power is attached to your house through a fitting at the top of the service entrance pipe (called the mast). This fitting is known as the mast head or the rain cap. It can get cracked by tree branch damage; external damage from a force put onto the overhead wires themselves; unknowingly damaged by roofers or cable and satellite installers or just plain old age. Cracks in the mast head or rain cap will allow water to seep down the mast pipe, into the meter box (called a meter base) and then into your electrical panel.
Rain can also enter directly through the meter base. Tree branch damage or vehicle damage are the most likely culprits, followed by just plain old age of the meter base. When water gets in to the meter base, it easily flows along the wires and into your electrical panel.
Homes supplied by Underground Power Lines
When your home’s power is supplied via underground, the incoming cable often runs from the meter base outside (typically on the side of the garage) under the floor of the garage, and then into the panel in the basement. The most common reason water gets in is because the ground settles under the garage floor slab and over the years water uses the path of this wiring to drain into the building and into the electrical panel. This was such a common problem that it is no longer acceptable to have wires come into the building below grade (according to the Electrical Safety Code latest edition).
Just like in the overhead power, a damaged or worn out meter base will allow rain water to enter and make its way to your electrical panel.
Water and electricity do not mix. This is a very serious situation. If you notice your Electrical Panel has water in it a licensed Electrician should be consulted for options to repair.