SE cable (Figure 19) has a flame-retardant, moisture-resistant covering. The neutral conductor (copper or aluminum) is twisted into a pigtail so that it can be clamped into the grounding system.
Figure 19. SE cable.
SE cable must be supported within 12 inches of the service head and all boxes, and then supported every 4 1/2 feet thereafter. When a service head is unavailable an expedient service head can be made. The SE cable is bent into a gooseneck and secured with tape (Figure 20). Service heads are located above the service drop to prevent water from entering the cable run.
Figure 20. Expedient head.
When installed as a service mast, an SE using rigid conduit provides protection for the conductors and a strong contact point for the service drop. A service-mast system is used when greater overhead roof clearance is needed (Figure 21).
Figure 21. Service mast using rigid conduct.
To provide adequate strength of the service mast, supports must be attached to the structure at critical points. A typical arrangement for supports is shown in Figure 22.
Figure 22. Mast supports.
The conductors are pulled through the rigid conduit to provide total protection of the SE from the service head into the power panel (Figure 23). A well-built service mast will hold up under all types of weather.
Figure 23. Service mast.
Power-panel (Figure 24) and service-drop amperages must match. A smaller amperage power panel cannot be used as a main disconnect for a larger amperage service drop. A 210-ampere cable must be used to feed a 200-ampere power panel.
Figure 24. Power panel.
Conductors carrying current within a building are disconnected at the main power panel (Figure 25). When the main switch or circuit breaker is in the OFF position, all branch circuits will be disconnected.
Figure 25. Main switch inside a power panel.
A building can have no more than six switches or circuit breakers mounted in a single enclosure that disconnects all power from the building (Figure 26). In an emergency situation, all power from this service to the building can be disconnected by using no more than six operations of the hand. When a main switch (breaker) is provided inside the same panel, 42 branch circuit breakers can be installed.
Figure 26. Switches in a power panel.
Two- or three-pole breakers that can be joined together with a tie handle or a master handle can be counted as a single switch if all conductors are disconnected with a single pull or push of a set of switches. By adding tie handles, the power panel in Figure 27 follows the six-switch-maximum NEC rule. Label each breaker to indicate the load serviced.
Figure 27. Breakers joined with a tie handle.
The NEC contains important exceptions to the maximum-switch rule (Figure 28). The rule can be exceeded for a fire pump or an emergency service such as a hospital, but the switch should be located away from the other disconnects and the power panel should be labeled.
Figure 28. Labeled power panel.
The code also states that up to 42 overcurrent devices can be put into one panel; however, the power must be disconnected from all circuits with six hand operations. For the 42-device role, a two-pole circuit breaker is counted as two circuit breakers (Figure 29). One main disconnect removes the power from all circuits in 'this panel. Not counting the main, there are ten circuit breakers in this panel and four of them are tied together.
Figure 29. 42 over-current devices in a power panel.
No circuit should be loaded greater than 80 percent of the breakers amperage capacity. In Figure 30, the breaker is rated at 20 amperes. Therefore, the ampere load to be applied cannot be greater than 16 amperes. Each heater uses 8 amperes. This circuit has the maximum allowable load.
Figure 30. Maximum ampere load.
Power panels must be accessible. This is accomplished by mounting the panel so that the top of the panel is no higher than 6 1/2 feet and the middle no lower than 4 12 feet (see Figure 31).
Figure 31. Panel mounting location.