Rules and regulations regarding electrical service masts vary depending what part of the country you live in. When in doubt, check with the local electric utility company.
What to Know About Electrical Service Masts
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How Electricity Comes From the Power Company
Most residences have 240-volt service. If it comes from overhead, it’s supplied by three conductors coming to the service mast from the power line transformer in the form of two ungrounded conductors (hot legs) and a separate grounded conductor (neutral). This is known as the service drop.
Residential electricity is AC; it changes polarity cyclically, and it must have a standard frequency to be useful. “The regional power grid operators work tirelessly and silently around the clock to make sure that the voltage and 60-Hz frequency of the grid is stable and consistent,” says master electrician John Williamson. “This is something we all take for granted.”
Service drop conductors have no overcurrent protection fuse or circuit breaker. They are directly connected to the utility’s distribution grid and are energized at all times. That creates a major safety issue, and it’s why it’s crucial to leave repairs of the conductors themselves to the power company.
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Who Owns What?
Power line regulations and responsibilities vary from one municipality to another and depend on whether a power line is public or private. Public lines are installed and owned by a public utility company. Sometimes they are on public property, but sometimes they are on private property. Utility companies own everything up to the service point, which is the point of connection between the serving utility and the home’s wiring system, and the service point is often on private property.
Different utility companies define where that service point is exactly located, and it can vary greatly depending on whether the electrical service is overhead or underground, the size of the electrical service rated in amperes, where it originates at the utility equipment, and where it terminates at the customer’s equipment. In most cases, the service point is the electric meter, and when it is, the meter itself belongs to the power company. But, says Williamson, the meter enclosure belongs to the homeowner.
Privately owned electrical distribution lines are sometimes found in gated communities, apartment complexes, mobile home and RV parks, college campuses, large industrial facilities and elsewhere. So if a tree does fall on a mast or service drop, the chart above will give you an idea who is responsible for what, but it ultimately depends on where you live and which utility company services you.
Discover the reason behind colored balls hanging on power lines.
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The Mast Has One Purpose
For safety reasons, do not attach television, telephone, cable or other wires to the service mast. Only electric utility conductors are permitted to be attached to electrical service masts.
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Avoid Trees
The overhead service drop conductors must be free and clear of trees, limbs, debris and vegetation. Trees that grow into service conductors can damage the conductors and attract lightning, both of which cause many power outages every year. Remember, a 4-foot tall, 2-foot wide tree might grow to be 60-feet tall and 30-feet wide.
Some utility companies have instituted tree replacement programs to assist customers in properly planting the right trees in the right place to avoid future problems. For information about growth potential and planting near power lines, contact your utility company, your County Extension office, State’s Department of Agriculture office, District Forester, or local nursery.
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Clearances for Service Drops
The following rules apply to service drops:
- Except at the drip loop, conductors must be at least 12 feet above final grade;
- When overhead service drop conductors terminate at a through-the-roof raceway or mast, there can be a maximum of six feet of conductor length over the roof;
- There must be a minimum clearance of 18 inches above any part of a sloped roof. If the pitch is greater than 4/12, the minimum clearance is three feet from all parts of the roof;
- Electrical service masts can be no more than four feet from the edge of the roof, as measured horizontally;
- Electrical service masts should not more than three feet vertically above the roof line. Most utility companies require additional support, such as bracing or guy wires, for any mast that is taller than three feet;
- Conductors need to be at least eight feet above flat roofs and at least 10 feet of above balconies;
- Overhead conductors must have a horizontal clearance of three feet from all windows that can be opened, doors, porches, balconies, ladders, stairs, fire escapes, or similar locations. No one should be able to grab a service conductor from these areas.
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Additional Clearances for Overhead Service Drop Conductors
- When located near a swimming pool, overhead service conductors must be at least 10 feet away from the pool horizontally and at least 22 1/2 feet high.
- When the voltage to ground does not exceed 150 volts, there must be 10 feet of clearance from the lowest point of the drip loop at the electric service entrance to the finished grade and all surrounding buildings, walkways, decks or patios. The clearance increases to 12 feet for voltages up to 300 volts and to 15 feet when the voltage to ground exceeds 300 volts.
- Minimum clearance over public streets, alleys, roads, parking areas that may have truck traffic, driveways other than those on residential property and areas used by farming and construction vehicles is 18 feet.
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Service Drop Drip Loop
The drip loop is where overhead service drop conductors are spliced to the service-entrance conductors for the home. This gooseneck-like loop keeps water from traveling along the length of the conductors and entering the service-entrance conduit.
Overhead conductors that enter a roof-mounted service mast are secured by clamp-on porcelain or similar nonmetallic insulators. Overhead conductors that terminate at the side of a house, under a roof eave or on the roof fascia board are attached to screw-in porcelain or similar nonmetallic insulators.
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Flashing
Electrical service masts that penetrate the roof must have a roofing boot properly secured at the roof line to prevent water leaks. The roofing boot must be properly sealed, glued and screwed flush with the roof membrane. If nails are used, they must be sealed properly. Nails can corrode over time and the membrane can split, so Williamson advises using the right tools for the job and taking the time to be sure it is properly sealed. If your mast has bracing, “don’t forget to seal it with flashing at the roof line intersection,” he cautions.
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Supporting a mast above the roof
The typical service mast consists of two-inch rigid metal conduit. Sometimes, you’ll see a through-the-roof service mast that appears to be leaning from tension in the overhead service drop conductors. You can repair this yourself by adding a brace, tie back or guy-wire supports.
Masts over 36 inches usually require a mast brace or tie–back supports such as a No. 6 Copperweld Aircraft Cable; although some municipalities allow the mast to be as much as five feet above the roof line before needing a guy wire for extra support. The brace must be installed at a minimum angle of 45 degrees.
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Supporting a Mast Below the Roof
A service mast that extends below the roof must be plumb (not leaning) and properly attached to the frame of the home with securely fastened metal conduit straps spaced by three feet. Sometimes, you can substitute malleable pipe straps and four-inch lag screws driven into studs. There must be a rain-tight threaded conduit hub where the service mast enters the top of the meter socket enclosure.
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The Meter
Electric utilities often require the meter to be mounted four to six feet from the ground, which is a reasonable height for utility workers to do their job in a safe manner. This is important to for DIYers to know because, as Williamson states, it’s the homeowner’s responsibility to install the meter enclosure. Meter bases for the sockets are furnished at no cost in most areas.
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Underground power lines
Utility companies install electrical distribution either above or below ground, and they usually determine which one will be used in your installation. Overhead installation is usually cheaper because of the cost of digging and trenching. The power company also determines the location of the electric meter based on the size of the service, the type of service and the type of distribution equipment.
Safety
Utility companies are very strict when it comes to breaking seals or removing meters. In addition to the obvious safety hazards, liability and theft of electricity are major concerns for utility companies. Always consult with the utility company before accessing the interior of the meter socket enclosure or attempting repairs to a service mast.
About the Author
- Lisa Archer is the owner of BPG/Memphis Inspections Service & Nationwide Pest Control
901-826-7500.
Find out more about Xcel’s requirements here
About the Expert
- John Williamson is a master electrician and the retired chief electrical inspector for the Minnesota Department of Labor and Industry.
