Load Balancing Now that you have installed the branch circuit conductors and breakers, you must balance the load. Conductors cannot be connected to a panelboard by

attaching each one as you come to it. The arrangement or sequence of attaching conductors to the panelboard is determined by the arrangement of the bus bars in the panelboard, whether the circuits are 240 volts or 120 volts, and the need to balance the load on the phase conductors. Bus bars are installed into panelboards in one of several ways. Most of the time, the bus bars are run in a vertical configuration. In one arrangement, a split-bus panelboard is used that has all the 240-volt circuits in the upper section and the 120-volt circuits in a lower section. Another type of split-bus panelboard uses one main circuit breaker to feed one set of branch circuits and a second main circuit breaker to feed a second set. In many cases, panelboards are designed so that any two adjacent terminals can be used to provide 240-volt service. This arrangement also means that two 120-volt circuits attached to adjacent terminals are connected to different phase conductors. Since there are so many panelboard layouts, you must look at the panelboard to see how it is set up for 240-volt service, and you must be sure you get the conductors for 240- volt circuits connected to the proper terminals.

5-36 Loads that are connected to a panelboard should be divided as evenly as possible between the supply conductors. This process of equalizing the load is commonly referred to as load balancing. The purpose of load balancing is to reduce voltage drop that results from overloading one side of the incoming service. It also prevents the possibility of overloading the neutral. A perfectly balanced load between the supply conductors reduces current flow in the neutral to zero.

Load balancing is no problem for 240-volt circuits on a three-wire, single-phase system since the load has to be equal on each phase conductor. However, the 120- volt circuits are a different matter. These must be connected in such a way that the loads tend to equalize. Generally speaking, the simplest way to balance the load on a panelboard is to connect an equal number of branch circuits to each phase conductor. But this method does not necessarily give you a balanced load as will be evident if you will look at the top of figure 5-68.

As you can see, the indiscriminate connection of branch circuits without consideration of their loads can cause you to end up with an unbalanced condition. On the other hand, you can connect the circuits so that one with a heavy load is offset by one with a light load, which does result in the balanced condition shown in the bottom of figure 5-68. Most of the time, you should be able to connect half of the lighting circuits and half of the appliance circuits to each phase conductor to give you a reasonably well-balanced load. Spare circuits should also be equalized There is one more thing to consider: When there are appliance circuits where the loads are known to be heavy, these circuits must be divided between the phase conductors.

TROUBLESHOOTING AND REPAIR OF INTERIOR WIRING SYSTEMS Electrical troubleshooting is an important part of your job. Your ability to find a faulty condition quickly can play an important part in shortening the downtime caused by failure. To find faulty conditions in circuits, you must do some inspecting, some calculating, and some instrument testing. A few moments spent studying the circuit diagrams before you start actual troubleshooting will simplify the task of isolating the trouble. If a circuit fails to function, use logic when you check for the fault. The trial-and-error method of finding faults in circuits is inefficient and time-consuming.

The first step to take in troubleshooting circuits is to inspect the circuit visually. Check for loose connections, loose wires, abraded wires, and loose fittings. An overloaded circuit is a serious problem.

Many times the electrical demand on a circuit is so great that the circuit fuses blow or the circuit breakers trip. In some cases, the wrong fuses or circuit breakers are used, and the wires overheat and burn off the insulation. This condition causes shorts and grounds and sets up potential fire hazards.

OPEN, SHORTED, AND GROUNDED CIRCUITS

An OPEN CIRCUIT occurs in a wiring system when one or more conductors in a circuit are broken or otherwise separated. An open circuit is determined by the failure of a part or all of an electrical circuit to operate, even though the fuses may not be blown. Use the following maintenance procedures for locating the source of the trouble: 1. Initially, you should make a visual check for a broken or loose connection at the first dead (nonoperating) outlet in the circuit. If a defective connection is found, tighten or repair the connection

Figure 5-68.- Load balancing.

2. If you do not find the trouble, or open, by a visual check, use a voltmeter to determine whether the circuit is live (operating) up to the point of the component.

A SHORT CIRCUIT results when two bare conductors of different potential come into contact with each other. If a conductor inadvertently contacts a metallic part of a wiring system, such as a motor frame or conduit, the system is sometimes said to be GROUNDED instead of having a short circuit. Grounds or short circuits can be (1) solid, (2) partial, or (3) floating. This situation presents a serious safety hazard because the machinery may be in operation, even though it has a short circuit. This condition is especially true in motors and some appliances. A solid ground or short circuit is one in which a full-voltage reading is obtained across the terminals of a blown fuse when the load is disconnected from the circuit. The circuit resistance, in this case, is quite low, and the current is quite high so that the fuse will blow.

A partial short or ground is one in which the resistance between the phase wires, or between the phase wire and the ground, is partially lowered. However, enough current still remains to blow the fuse.

Grounds of this type are generally more difficult to locate than are solid grounds.

A floating ground is a condition in which the resistance of the defect in a system varies from time to time. Grounds of this type may be present in an electrical system for some time before their existence becomes known. A floating ground is indicated when fuses are blown on the phase side of a circuit a number of times, and a circuit test shows no defects in the system. In grounds of this type, fuse trouble may not occur for several days. Then the ground recurs, and the fuses are blown again.

The procedures used to repair the troubles mentioned thus far are usually fairly simple. In the case of an open, short, or ground in NM cable, the bad section from box to box can simply be replaced using the same procedures outlined for installation. Another method would be to cut the cable at the trouble spot, install junction boxes, and add a short piece of cable to replace the bad section. Although the latter is the cheapest, it may not be possible if the trouble is concealed. Remember, you must have at least 6 inches of free conductor in a junction box to make the splices.

Once you find out where the trouble is in a conduit system, the repair procedure is even easier. All that is required is to pull the open, shorted, or grounded conductor out and replace it with a new one. This replacement can be done by attaching the new conductor to the one that is to be removed. In any case, a little common sense and knowledge of the NEC(c) requirements will dictate the action you should take.