Chapter Nineteen SpecialPurpose OutletsWater Pump Water Heater Objectives

Chapter Nineteen Special-Purpose Outlets—Water Pump, Water Heater

Objectives • After studying this chapter, you should be able to: – Understand the operation of jet pumps, submersible pumps, and their components – Understand the operation of electric water heaters and their components

Objectives (cont’d. ) – Be familiar with the NEC® requirements for designing the branch circuit, including conductors, cables, raceway, motor branchcircuit short-circuit ground-fault and overload protection, disconnecting means, and grounding for water pumps and electric water heaters

Objectives (cont’d. ) – Figure out various electrical connections for “Time-of-Use” metering – Calculate the effect of voltage variation on heating elements and motors – Understand the hazards of possible scalding – Discuss heat pump water heaters

Water Pump Circuit • In rural areas where there is no public water supply, dwellings need their own water supply • For the most part, submersible pumps dominate the residential market

Jet Pumps • A jet pump creates downward pressure that forces water up a discharge pipe into a water tank • The jet pump continues until tank pressure reaches 40 psi • When the tank pressure falls below 20 psi, the pump restarts

FIGURE 19 -1 Components of a jet pump. © Cengage Learning 2015

Submersible Pumps • Consists of a centrifugal pump driven by an electric motor • The pump and motor are contained in one housing • The pump is located at the bottom of a deep well pipe below the water line • The pump is controlled by a disconnect switch, pressure switch, and limit switches located near the water tank

FIGURE 19 -3 Submersible pump. © Cengage Learning 2015

Motor Circuit Design • NEC® Table 430. 52 lists different types of protection for motors • If values in Table 430. 52 are not at standard size, it is acceptable to select the next higher rating

Motor Circuit Design (cont’d. ) • Motor Overload Protection – Overload protection keeps the motor from dangerously overheating – Common installations require motor overload protection not to exceed 125 percent of FLA

Motor Circuit Design (cont’d. ) • Disconnecting means – The NEC® requires all motors to have a means of disconnect from electrical supply – Common installations require motor overload protection not to exceed 125 percent of FLA – Disconnect must be in sight 50 ft (15 m) of controller and motor

Grounding • Proper grounding of the well casing and submersible pump motor will minimize or eliminate stray voltage problems • PVC water piping is often used today • Sometimes a grounding electrode conductor is required between the neutral bar of the main service disconnecting means and the well casing

Water Heater Circuit • Typical wattage ratings range from 1500 watts to 5500 watts • Electric water heaters use a resistance heating element to raise water temperature

FIGURE 19 -5 Typical electric water heater showing location of heating elements and thermostats and electrical connection. © Cengage Learning 2015

Water Heater Circuit (cont’d. ) • Combination controls regulate the temperature of the water • Scalding water is avoided by an upper temperature limit of 120°F • Water heaters need a 240 -volt circuit

Electric Water Heater Branch Circuits • NEC® classifies the water heater to be a continuous load (422. 13) • Branch-circuit rating must not be less than 125 percent of the nameplate rating • NEC® 422. 11(E) states how to size the overcurrent device

Effect of Voltage Variation on Resistive Heating Elements • Heating elements in the water heater in this residence are rated 240 volts • A resistive heating element will only produce rated wattage at rated voltage • Always use rated voltage to calculate the resistance, current draw, and wattage of a resistive heating element

Effect of Voltage Variation on Motors • Formulas for inductive circuits such as an electric motor are complex • NEMA rated electric motors are designed to operate at ± 10 percent of their nameplate voltage

Heat Pump Water Heaters • Residential heat pump water heaters can save 50 to 60 percent over resistance-type electric water heaters • The heat energy transferred to the water is three to four times greater than the electrical energy used • Work in conjunction with resistance-type electric water heaters