What You Need To Know About Electrical Service Masts
Rules and regulations regarding electrical service masts vary depending what part of the country you live in, so some of the information here may not be applicable in every situation. When in doubt, check with the local electric utility company and electrical inspector.
The Service Drop
The overhead service drop, or underground service lateral, are the electrical conductors that come from the utility pole, pedestal or ground-mounted transformer to the home. Changes to the service drop will always be completed by the utility company, and the cost for most changes are the responsibility of the customer. The major safety issue here is that the service drop conductors have no fuse, circuit breaker or any kind of overcurrent protection at their supply end; they are directly connected to the utility’s distribution grid and are energized at all times.
There are three conductors coming to the service mast in the overhead service drop, two ungrounded conductors (hot legs) and a separate grounded conductor (neutral). The hot legs have black thermoset, polymer or other nonmetallic conductor insulation. If all three wires are connected to the service mast that runs through the roof, and/or down the exterior wall of the house in a service-entrance conduit, you can usually assume there is 240–volt service for the house since each hot leg measures 120–volts from each hot leg to the neutral.
Who Owns What?
Power line regulations and responsibilities will vary from one municipality to another and will 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, the point of connection between the serving utility and the house premises 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. 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.
The Mast Has One Purpose
For safety reasons, do not attach television, telephone, cable or other wires to the service mast. Only the electric utility conductors are permitted to be attached to the service mast.
Be sure the overhead service drop conductors are free and clear of trees, limbs, debris and vegetation. Trees that grow up into service conductors can damage the conductors and attract lightning strikes, 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.
Clearances for Service Drops
- Except at the drip loop, at no time less than 12-feet above final grade
- Where overhead service drop conductors terminate at a through-the-roof raceway or mast, there is a maximum of 6-feet of conductor length over the roof
- A minimum of 18–inches of clearance above any part of a sloped roof
- The service mast must be no more than 4-feet from the edge of the roof measuring horizontally
- The service mast should not be more than 3-feet vertically above the roof line; most utilities will require bracing or guy wires for additional support of any mast that is taller than 3-feet.
- Flat roofs need to have at least 8-feet of clearance and balconies need at least 10-feet of clearance
- Overhead conductors must have a horizontal clearance of 3-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.
Additional Clearances for Overhead Service Drop Conductors
- When located near a swimming pool, the overhead service conductors must be at least 10-feet away from the pool horizontally and at least 22.5-feet high.
- If the home has a flat roof, there must be 8-feet of clearance, and if your home has a pitch roof of 4–inches in 12-inches, or greater, there must be a minimum of 3-feet of clearance.
- 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 buildings and the finished grade, walkways, decks, patios, etc. The clearance is raised to 12-feet where the voltage does not exceed 300 volts to ground, and raised to15-feet where the voltage to ground exceeds 300 volts.
- There must be an 18-foot clearance over public streets, alleys, roads, parking areas that may have truck traffic, driveways other than on residential property, and areas used by farming and construction vehicles.
Service Drop Drip Loop
The overhead service drop conductors are spliced to the service-entrance conductors at the home. This connection is called the drip loop. The drip loop is required to keep water from traveling along the length of the service-entrance conductors and entering the service-entrance conduit at the weatherhead. Overhead service-entrance conductors are attached to service masts with clamp-on porcelain or similar nonmetallic insulators. Overhead service-entrance 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.
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 be sure to use the right tools for the job and take the time to be sure it is properly sealed. Mast bracing must also be sealed with flashing at the roof line intersection.
Supporting a mast above the roof
The typical service mast consists of 2-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. This can be repaired 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 5-feet above the roof line before needing a guy wire for extra support. The brace must be installed at a minimum 45-degree angle.
Supporting a Mast Below the Roof
The service mast must be plumb (not leaning) and properly attached to the frame of the home by installing securely fastened metal conduit straps every 3-feet. Malleable pipe straps and 4-inch lag screws in studs may sometimes be substituted. There will be a raintight threaded conduit hub where the service mast enters the top of the meter socket enclosure.
Underground power lines
Utility companies install electrical distribution either below ground or above ground, and they make the decision on which one will be used in your installation. The long-term overall cost is less for overhead electrical distribution compared to underground distribution, but sometimes the utility will install underground distribution, but it comes with an additional installation and maintenance cost to the property owner. The location of the electric meter will be determined by the electric utility based on the size of the service, the type of service and the type of distribution equipment, such as a transformer or distribution pedestal.
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 attempt repairs to a service mast.
About the author
Lisa Archer, Owner of BPG/Memphis Inspections Service & Nationwide Pest Control