The term "weatherhead" when applied to a residential electrical system refers to the rounded metal or plastic cap where the utility company's overhead service wires turn downward through the service mast toward the electrical meter and the service entry point into your home. You will not find this feature in communities where electrical service is run through underground cables, but in traditional overhead service delivery, each home will have a weatherhead that sits atop the service mast through which the service wires reach the home's entry point.
The weatherhead's rounded cap is essential to protecting the service wires and preventing water, dirt, and pests from infiltrating the service mast and damaging the service wires.
What Is a Weatherhead?
The term "weatherhead" is sometimes mistakenly used to refer to the entire cable loop, cap, and masthead where the utility's service wires turn downward toward the electrical meter and entry point into the home. Technically, however, the weatherhead is just the metal cap that sits atop the mast. This cap must be angled at least 45 degrees toward the ground, and it often has a rubber gasket that seals around the individual service wires that pass through it into the mast. The shape of the weatherhead, along with its gasket, helps protect the service wires from weather, birds, and any other elements that may harm the wires.
The Service Entrance Components
The assembly of structural parts and wiring that connects your home to the utility power grid is known collectively as the service entrance. The service entrance starts at the transformer on the utility's power pole. The heavy insulated wires and metal cable strung overhead from the transformer to your house are called the service drop. The service drop is either anchored to a metal pole rising through the roof or attached to the exterior of the house. The pole is called the mast or riser and it contains a large cable or individual wires known as the service entrance conductors (or service entrance cable). These horizontal conductor wires enter the mast through the weatherhead, which is dome-shaped so that the conductors then turn downward as they continue toward the electrical meter.
In some situations, there may be no service mast, and the service wires will simply anchor to the side of the home. In this case, there will still be a weatherhead that protects the point where the horizontal service wires turn downward into an insulated cable anchored to the outside wall of the home.
How the Weatherhead Works
The shape of the weatherhead, with its rounded dome, downward-facing face, and rubber gasket, helps keep rain and snow out of the mast in more ways than you might expect. First, it simply covers the mast to prevent rain and snow from falling in. Second, the way in which the service drop is anchored to the mast allows for a slight downward-facing curve in the individual wires, known as a drip loop. Thanks to this shape, any rain that clings to the service drop wires flows downward, then falls off the bottom of the drip loop—not into the service mast where it can do damage.
The overhead point where the service drop wires connect to the service entrance conductors inside the vertical mast is known as the service point, and it usually represents the point of official transfer between the utility provider and the utility customer. Everything on the house side of the service point (with the exception of the meter) typically is installed by an electrician hired by the homebuilder or homeowner. Everything on the utility side of the service point is installed and maintained by utility personnel.
Not all weatherheads mount to the top of hollow masts. In instances where the electrical entry point into the home is high above the ground, the weatherhead can be attached directly to the outside of the home. In this instance, the weatherhead cap will have a special clamp that securely holds the service wires to the cap, rather than to a service mast.
When a traditional service mast is used, the service wires are secured to the mast itself, allowing the wires to form the downward drip loop before they enter the weatherhead.
A weatherhead affixed atop a traditional mast can either be secured to the mast with clamps, or it can use threaded fittings. The mast is usually a rigid metal electrical conduit, either rigid metal conduit (type RMC) or intermediate metal conduit (type IMC). Some weatherheads can be used with nonmetallic (usually PVC plastic) pipes. All of these specifics are governed by the local building authority and/or the utility company, and rules vary from location to location.
Maintaining and Repairing a Weatherhead
A properly installed weatherhead may never need any attention, but it's possible for high winds, ice storms, or other natural events to cause damage to the weatherhead. Falling tree branches can crack a weatherhead, for example, or loosen the connections that anchor the service mast to the home. Over many years, the rubber gasket sealing the service wires within the weatherhead opening can crack or loosen.
If you notice any kind of damage to the weatherhead or mast, your first call should be to the utility company, who will inform you if such a repair is their responsibility or yours. In most cases, it will be your responsibility to hire an electrician to do the work. The electrician will coordinate with the utility company to shut off power while they detach the service wires to replace the weatherhead. Average costs for having a weatherhead replaced run from $400 to $1,700, depending on the availability of qualified electricians in your area.
While replacing a weatherhead is not a complicated process, you should never attempt such a repair, as it involves working with wires that carry high voltage high above the ground. And your building inspection office may prohibit homeowners from doing such work themselves. Whoever replaces the weatherhead will need to apply for a permit and have the work inspected upon completion.