GUIDE FOR INVESTIGATION OF CUSTOMERS’ HIGH-BILL ELECTRICITY INQUIRIES ON THE CUSTOMERS’ PREMISES

As a representative of the company, an employee who is assigned to investigate a customer’s inquiry concerning his billing has a dual responsibility. First, make absolutely certain that all service used by the customer is being accurately registered on the meter. Attempt to explain some of the metering factors to a customer who does not understand them to assure the customer of the accuracy of the meter.

The following is a plan suggested for conducting metering investigations. Steps 1 and 2 are frequently performed by a representative of the commercial department of the company. In many companies, only Steps 3 and 4 are performed by meter department personnel.

Step 1
A. Upon arriving at the customer’s home or place of business, the company representative should introduce himself, show his identification card or badge when requested, and explain the purpose of his visit. He should also advise the customer that, in the process of checking, the electric service might be momentarily interrupted.

B. The meter readings should be compared with those on the last bill. If an error is apparent, it should be explained to the customer and reported to the billing section.

C. If the customer’s question concerning his bill cannot be explained from the aforementioned, the company representative should ask the customer if any appliances have been added recently. Inquiry about appliances that affect seasonal loads is particularly important.

These may include air conditioners, dehumidifiers, space heaters, and heating cables. It should also be determined whether the customer has replaced any major appliances recently. The replacement of a refrigerator with a newer, frost-free model may result in an increase in operating cost, and this should be explained to the customer.

D. Ask the customer if there has been an increase in the number of persons living in the household.

E. Ask the customer if situations have occurred that were out of the ordinary routine of the household. These would include such things as more entertaining than usual, guests visiting in the home, an illness in the family, and other factors that would increase the customer’s bill.

F. If the customer’s inquiry can not be explained after carrying out the parts of Step 1, proceed to Step 2.

Step 2
A. Check for causes of abnormally high consumption.
1. Dirt- or lint-clogged filters on furnace or air conditioning units.
2. Leaky hot-water faucets where electric water heaters are used.
3. Defective water pump.
4. Use of electric range units for space heating.
5. Heating water on range.

B. If the preceding investigation is sufficient, discuss these factors with the customer briefly, pointing out any reasons you have found for the increase in the customer’s electric bill.

C. If further investigation is necessary, proceed to Step 3.

Step 3
A. If there is a load on the meter, ask the customer to shut off all appliances and lighting at the appliance or light switch. Recheck if the meter continues to indicate a load and determine absolutely whether rotation is due to a missed load or loss to ground. If there is a loss to ground, this should be checked with a stop watch and the rate of loss established.

B. If possible, it should then be determined which circuit is grounded and, if convenient to the customer, the circuit should be disconnected by removing the fuse or opening the circuit breaker. The condition should be explained to the customer and he should be advised to have the condition corrected by a wireman before using the circuit again. If the loss to ground is found to be a defective appliance, it should be disconnected and the customer advised to have repairs made before reconnecting the appliance.

Step 4
If no explanation for the bill has been reached, the meter should then be checked for accuracy, creep, proper constant, and correct register ratio. The results of each check should be noted on the investigation order.

COST OF USING ELECTRICAL ENERGY BASIC INFORMATION

POWER CONSUMPTION COMPUTATION TUTORIALS

A watt-hour meter is always connected into some part of the service-entrance equipment to record the amount of energy used. Billing by the utility is generally done on a monthly basis.

The meter might be mounted on the side of the house or on a pedestal somewhere on the premise on the lot line. The utility makes this decision.

The residence discussed in this text has one meter, mounted on the back of the house near the sliding doors of the Master Bedroom. The kilowatt (kW) is a convenient unit of electrical power.

One thousand watts (w) is equal to one kilowatt. The watt-hour meter measures and records both wattage and time.

For residential metering, most utilities have rate schedules based on “cents per kilowatt-hour.” Stated another way: How much wattage is being used and for how long?

Burning a 100-watt light bulb for 10 hours is the same as using a 1000-watt electric heater for 1 hour. Both equal 1 kilowatt-hour.

kWh = WATTS X HOURS/1000 = 100X10/1000 = 1 kWh

In these examples, if the electric rate is $0.08 cents per kilowatt-hour, the cost to operate the 100-watt light bulb for 10 hours and the cost to operate the electric heater for 1 hour are the same—$0.08. Both loads use 1 kilowatt-hour of electricity.

EXAMPLE
Find the cost of operating a color television set for 8 hours. The label on the back of the television set indicates 175 watts. The electric rate is $0.10494 per kilowatt-hour.

Cost = 175 x 8 x $0.10494/ 1000
        =  $ 0. 146 9 (approx. 15¢)

NEC CONTINUOUS LOAD CALCULATION FOR ELECTRICAL SYSTEM DESIGN

Several NEC sections contain the very important requirement to size conductors and overcurrent devices at 100% of the noncontinuous loads plus 125% of the continuous loads. This takes into account heat buildup resulting from the current flowing through the conductors and overcurrent devices for an extended period of time.

These requirements are found in NEC 210.19(A)(1) for branch circuits, 210.20(A) for branch circuit overcurrent devices, 215.2(A)(1) for feeder conductors, 215.3 for a feeder overcurrent protection, 230.42(A)(1) for service conductors, 409.20 and 409.21 for industrial control panels, and 625.21 for electric vehicle charging system overcurrent protection.

It is not necessary to apply the 125% factor for grounded (often neutral) conductors that are not connected to an overcurrent device, NEC 210.19(A) (1) Exception No. 2, 215.2(A)(1) Exception No. 2, and 230.42(A)(2).

The logic of this Code exception is that the heat developed in the neutral conductor
will not contribute to the possible nuisance tripping of a circuit breaker or the opening of a fuse because
the neutral conductor is terminated on a neutral bus, not to the terminal of an overcurrent device.

A second exception provides that if both the overcurrent device and its assembly are listed for operation at 100% of their rating, it is not necessary to increase the ampacity of the conductors and overcurrent device by 25%. Be very cautious with this exception.

Most electrical equipment in the 600 volt class is not rated for continuous operation at 100% of its rating.
Store lighting is an example of continuous loads, whereas receptacle outlets typically are not considered
continuous loads.

There are two ways to compensate for continuous loads. One way is to apply a 125% factor to the
continuous load plus 100% of the noncontinuous load, and this becomes the minimum rating of the
conductor and the overcurrent device.

The second method is to limit the continuous load on the circuit to not more than 80% of the rating of the overcurrent device and the conductor.

BLONDEL'S THEOREM - MATHEMATICS OF ELECTRICITY METERING

The theory of polyphase watthour metering was first set forth on a scientific basis in 1893 by Andre E. Blondel, engineer and mathematician. His theorem applies to the measurement of real power in a polyphase system of any number of wires.

The Blondel's theorem is as follows:
If energy is supplied to any system of conductors through N wires, the total power in the system is given by the algebraic sum of the readings of N wattmeters, so arranged that each of the N wires contains one current coil, the corresponding voltage coil being connected between that wire and some common point. If this common point is on one of the N wires, the measurement may be made by the use of N-1 wattmeters.

The receiving and generating circuits may be arranged in any desired manner and there are no restrictions as to balance among the voltages, currents, or power factor values.

From this theorem it follows that basically a meter containing two elements or stators is necessary for a three-wire, two- or three-phase circuit and a meter with three stators for a four-wire, three-phase circuit. Some deviations from this rule are commercially possible, but resultant metering accuracy, which may be decreased, is dependent upon circuit conditions that are not under the control of the meter technician.

An example of such a deviation is the three-wire, single stator meter.

The circuit shown in below may be used to prove Blondel’s Theorem.

Three watthour meters, or wattmeters, have their voltage sensors connected to a common point D, which may differ in voltage from the neutral point N of the load, by an amount equal to EN. The true instantaneous load power is:

WattsLoad = EAIA + EBIB + ECIC

Inspection of the circuit shows:
EA = E'A + EN
EB = E'B + EN
EC = E'C + EN

Substituting in the equation for total load power:
WattsLoad = (E'A + EN)IA + (E'B + EN)IB + (E'C + EN)IC
WattsLoad = E'AIA+  E'BIB + E'CIC + EN(IA  IB  IC)


Since from Kirchhoff’s Law, IA + IB + IC = 0, the last term in the preceding equation becomes zero, leaving

WattsLoad  = E'AIA + E'BIB + E'CIC = W1+ W2+ W3

Thus, the three watthour meters correctly measure the true load power. If, instead of connecting the three voltage coils at a common point removed from the supply system, the common point is placed on any one line, the voltage becomes zero on the meter connected in that line.

If, for example, the common point is on line C, E'C becomes zero and the preceding formula simplifies to:

WattsLoad = E'AIA + E'BIB = W1+ W2

proving that one less metering unit than the number of lines will provide correct metering regardless of load conditions.