The Meter, Main Circuit Breaker, and Service-Entrance Panel

The installation examples given in this section are for 100-amp services. The techniques used for larger services are basically the same except that larger-sized materials are used. When you select your service size, be sure to allow room for future expansion or amenities.

The Meter and Main Circuit Breakers

Meter sockets are selected for the size of the service. The two most common sizes are 100 and 200 amp. Larger services than these require special metering arrangements that use current transformers to reduce the cur rent in the metering circuit to a low value that’s proportionate to the actual amount of current being delivered to the service. The power company can tell you the type and size meter socket you’ll need for your ser vice. Local electrical suppliers can give you this information as well.

When the service-entrance panel is installed indoors and the main circuit breaker is in stalled outdoors, the breaker is sized to protect the service conductors and to limit the current to the mains to a safe value. A 100-amp service is protected by a 100-amp circuit breaker, and so forth. Some authorities allow a main fused switch to be used in place of a circuit breaker. Often, the meter socket and main disconnect are mounted in a common enclosure. If they’re separate, they should be mounted side by side.

All equipment enclosures used outdoors must be Type 3R, which means that they are constructed to provide an adequate degree of protection against falling rain and sleet and external ice formation. Outdoor enclosures are easily recognized because their tops extend beyond their front and sides to deflect rain. Weather- tight hubs must be used when conduit enters the top or sides of the enclosure. The circuit- breaker enclosures and fused switches to be used as service disconnects must be marked as being suitable for use as service equipment.

All electrical equipment must be firmly secured to the surface on which it's mounted. It’s unwise to mount equipment on the side of a building and depend only on the siding material for support, unless the siding is wood. Screws that pass through other types of siding into wood sheathing provide excellent mounting support. Sometimes it’s necessary to provide blocking inside a wall, or to cut a board into the siding and nail it to the studs to provide sufficient support. When mounting equipment on masonry walls, use masonry anchors and screws, not screws and wooden plugs driven into holes in the wall.

Outdoor enclosures have to be mounted in such a way that moisture can’t accumulate between the back of the enclosure and the surface on which it's mounted. The mounting holes in equipment enclosures are drilled through bumps that ex tend outward from the back of the enclosure. These bumps are there so that the enclosure won’t twist if mounted on an irregular surface and so the back of the enclosure won’t contact the surface on which it's mounted, which would allow moisture to accumulate. The top and sides of the enclosure must be caulked at the wall.

If the meter and main breaker are in a common enclosure, the black wires entering from the service conduit connected to the top lugs on the socket. The connections between the meter’s bottom lugs and the line side of the main breaker are factory-connected. The white wire connects to the neutral lug in the circuit break half of the enclosure. Two blocks are then used to connect the load side of the main breaker to the panel main lugs, and a white wire is used to connect the neutral lug to the panel’s neutral bus.

When the socket and main breaker are in separate enclosures they should be mounted side by side. The top of the socket is fed as in the previous example, and field-installed wires complete the connections between the bottom of the socket and the line side of the main breaker. The white connects to a lay-in lug in the socket and continues to the neutral lug in the breaker en closure. Final connections to the breaker panel are the same as in the previous example.

Specific requirements vary from locality to locality. Always contact your electrical-inspection department regarding particulars.

74 Meter and Service Entrances: Fuse type; Fuse drawer type; Breaker type

Service-Entrance Panel

The minimum allowable service size for a house is determined by using one of the calculation methods allowed by Article 220 of the Code (). These calculations take into consideration the size of the house, the required 120-volt circuits, and the 240-volt branch circuits that supply fixed loads such as ranges, water heaters, and clothes dryers. The service cur rent and the number of branch circuits needed for general lighting, which includes the permanent lighting and most of the convenience outlets in the house, also are determined by this process. To calculate the number of fuses or circuit- breaker spaces needed in addition to those for the general lighting load, add up the required small-appliance circuits, the laundry circuit, plus any other 120-volt individual branch circuits, such as for the dishwasher and the food disposer. Each of these circuits requires one circuit-breaker space or fuse. In addition, two spaces are needed for each of the 240- volt individual branch circuits. These are the circuits that feed the range, water heater, and clothes dryer. Add them all up to know how many circuit breakers the panel will need.

If your initial service-current calculation is just a little less than a standard service size, 100, 150, or 200 amp, you should think about going to a larger-than-required service to allow for future expansion. Also, consider the number of circuit-breaker spaces your planning calls for. One-hundred- amp panels are generally limited to 20 spaces, so more spaces means a larger panel and associated service wiring.

Installation Techniques

Panels should be mounted on wood surfaces for soundness and ease of fastening. Often, a large piece of ¾-inch plywood is fastened to a basement masonry wall with anchors or concrete nails, then the panel is secured to the plywood with wood screws. The plywood should be wider than the panel and should extend at least 1 foot above and , if necessary, 1 foot below the panel in order to provide a surface to anchor the cables and conduits that run to the panel. Remember to provide adequate space behind the panel for air circulation. If the bumps alone aren’t sufficient, run the mounting screws through ¼” nuts held between the panel and the board, which will guarantee more standoff from the wall. A 1¼-inch conduit is run from the bottom of the meter socket into an SLB at the nm joist. A hole would be sawed at the rim joist where a conduit elbow would pass through it to connect the SLB to the panel.

[[ Sizing and Installing the Service Conductors: The size of the service conductors is determined by the size of the service panel you’ve chosen. The nominal size of copper service wires used with 100-amp services is No. 4 with a temperature rating of 194° F (90° C). No. 1 is used with 150-amp services, and 2/0 (two-ought) with 200-amp services. if you use aluminum wire, larger sizes are needed to provide the required ampacities.]]

Studs provide excellent mounting for flush-mounted installations. Provide blocking above and , if needed, below the panel for cable anchoring.

A panel in a garage is commonly mounted between studs, with the top edge about 5 feet above the floor. Most modern panels are about 14% inches wide, so they fit perfectly between studs that are 16 inches on center and can be secured in place with two screws through each side of the panel. Begin by removing a 1.25” top knock out from the rear of the panel and tracing its outline on the wall in the desired position. Using a hole saw or dial saw, cut a 2½-inch hole through the wall at the center of the traced outline.

75 Wiring a Meter Socket: Incoming conduit from overhead service; 1. Connect 2 hot wires from service head to upper screw clamps; 2. Connect neutral— wire to screw clamp at the center; Hub; Incoming conductors still enter meter socket from the top; Incoming conduit from underground service panel and main disconnect switch

Go to the exterior side of the wall and open a 1%-inch bottom knockout in the back of the meter socket. Thread lock- nuts completely onto both ends of a 1 by 2½-inch conduit nipple and insert one end into the knockout. Thread another locknut and then an insulated grounding bushing tightly onto the nipple on the inside of the socket enclosure. Push the nipple into the center of the hole in the wall, square up the enclosure and secure it in place with wood screws.

Back in the garage, pack the hole in the wall with caulk and slip the panel over the nipple. Thread a locknut and then an insulated grounding bushing tightly onto the nipple, plumb the panel, and fasten it in place with wood screws.

Outdoor installations must be caulked where the panel top and sides meet the wall, but you can leave the bottom open.

Replacing an Existing Service Panel

Replacing an old fuse panel with a new, larger circuit- breaker panel is usually best left to a licensed electrician. Many municipalities also re quire the addition of small- appliance circuits to the kitchen when the service in an older home is upgraded. No two fuse-to-circuit-breaker changeovers are alike.

If your main disconnect is in the panel, the power company must remove your meter to disconnect the power to your panel before you begin. Then, after your changeover is complete and has passed inspection, call the power company again to reinstall the meter.

Install any required additional circuits and drive an 8- foot ground rod near the point where the service conductors enter the house, if one isn’t already there, before beginning the actual panel changeover. Then have the utility company disconnect your power at the pole and remove your meter.

If the existing service conduit is 1 inch or larger, it won’t have to be changed; if it's less than 1 inch, remove it.

Identify the branch-circuit wires with color-identification tape or wire markers. Then disconnect the wiring inside the panel, swing the cables or conduits out of the panel, and re move the panel itself. Install the new service conduit, if necessary, and fit the new panel to the service conduit and secure it in place. Pull in and connect the new service wires, and also install a grounding-electrode conductor from the ground rod to the neutral bus in the service panel. When the service installation is complete, call the building-inspection department that issued your permit to schedule an inspection. After the installation is approved, you or the inspector (depending on local practice) call the electric utility company to re quest an immediate hookup.

Wiring a Service Panel:

1. Run cable from meter into service panel

2. Connect 2 hot wires from meter to screw terminals on main disconnect switch; Main disconnect switch

3. Connect neutral wire from meter to neutral bus bar

4. Connect ground wire to ground bus bar and cold-wafer pipe and grounding electrode

5. Connect neutral wires from house circuits — to neutral bus bar

Bonding screw; Cables to house circuits; Circuit breakers; 3-wire cables to 240v appliances connect to double breakers; Bonding screw; Space for 6 more breakers; Ground bus bar (ground and neutral bus bars are often contiguous)

Reconnect the branch-circuit wiring if it wasn’t required for your final inspection. As you work make a note of which circuit goes to which breaker so that you can properly fill out the circuit directory for the panel when you’re through. Often, because the new panel is physically larger than the old one, some of the wires won’t reach their circuit breakers. Splice extensions to the old wires inside the panel when this happens.

Types of Overcurrent Devices

Unlike fuses, which use nation ally standardized thread designs, circuit breakers are designed by panel manufacturers to be used in their panels only and are generally not interchangeable.

Breakers used in residential panels are either single-pole, for 120-volt circuits, or two- pole (double-pole), for 240-volt circuits. Common ampere ratings for single-pole breakers found in the home are 15 and 20 amp. Some common two- pole ratings are 15, 20, 30, 40, and 60 amp, plus 100, 150, and 200 amp main circuit breakers.

Full-width single-pole circuit breakers are about 1 inch wide, but some manufacturers have made ½-inch-wide breakers. “Piggyback” and “twin” circuit breakers are available for some panels to allow additional circuits to be powered from an already full panel. GFCI circuit breakers are also available. Circuit breakers make an electrical connection to the main bus of the panel as well as a mechanical non-conducting attachment to a rail or bar which holds them firmly in place.

Buses

Competitively priced panels use aluminum main buses.

These are fine in most parts of the country, but premium cop per bus panels should be used in coastal areas where salt air can have a damaging effect on aluminum.

The neutral bus in a service is bonded to its enclosure so all branch-circuit grounding wires as well as all neutral conductors are connected to it. A subpanel differs from a service panel in that the neutral bus of a sub- panel isn't bonded to its enclosure, and a separate grounding bus must be provided for the branch-circuit cables being powered by it. A grounding bus, or grounding bar kit, can be installed for convenience in a service panel, but it isn't required.

Installing Circuit Wires in the Service.

Entrance Panel

Service panels are much larger now than they were in the past because of recent NEC changes in wire-bending space requirements. The increased space available means that panel wiring can be more systematic and easier to trace than it was in the past. It’s best to strip the cable jacket to within ½ inch of where the cable enters the en closure; then route the individual conductors to the rear and side of the panel to a point level with where they’ll attach to a circuit breaker or the neutral bus. At this point bend the wire so that it points straight out at a distance out from the back of the panel that's equal to the distance out to the terminal. Bend the wire toward the terminal, cut it to fit, strip, and connect it.

Be sure to accurately fill in the circuit directory for the panel. It can save a lot of confusion and uncertainty when there is trouble.

Fuses and Circuit Breakers

Three styles of circuit breakers by different manufacturers. The double breaker (at right) has a bar connecting the 2 handles and is used to protect 240v circuits.

Some breakers go to the off position when tripped. Some go halfway to off or (as shown above) to a tri position. These must be switched to off then on to restore service.

You can replace your screw-in fuses with this type of breaker (at the same rating). An overload will cause the button to pop out, exposing a colored band. To restore service, just push in the button.

78 Circuit Breakers

Bonding screw or ground wires connected to neutral bus; A GFCI breaker installs just like a regular breaker, except that the neutral wire from the circuit cable connects to the neutral lug of the breaker, and the neutral pigtail on the breaker connects to the neutral bus bar in the panel.

Here is how a typical circuit is connected to the breaker and the panel. For clarity, we show only 1 circuit. The breaker has contacts that connect it to 1 of the power buses and the neutral bar when it's snapped into place.

To remove a breaker loosen the load power lug screw and remove the power wire. Grip the breaker with your thumb and index finger, pull up on the end opposite the load power lug screw, and it will snap out.