The Electric Motor

Introduction To Electric Motors


Electric motors power the majority of hot water pressure Inflatable bouncers Costco cleaners in service today. Many electric motors suitable for use in high pressure cleaning are available. Unsuitable motors, however, are often used. The most suitable motors are totally enclosed or washdown duty motors especially designed for use in damp environments.


Motor Operation

All electric motors use changes in magnetic fields to turn a shaft, converting electrical energy into mechanical energy. Changes in polarity of magnetic fields in the stationary portion of the motor – called the stator – interact with induced magnetic fields in the motor’s core or rotor to turn the motor’s shaft.

Current Needs

Electric motors may be classified according to the type and amount of current they require to run. Motors can be powered by either direct or alternating current.

Current Types


All electrical current has a positive and negative polarity. Direct current always has the same directional orientation of positive and negative charges. Alternating current changes polarity at a constant rate. Alternating current supplied in the United States changes direction 120 times a second or 60 full cycles per second.

Alternating Current

Most electric-powered cleaners have motors which require alternating current. Some direct current motors are used in power fuel pumps and burner blowers. This motor is generally driven by a transformer operating on alternating current.

Note: Some DC motors can run on alternating current. These are called universal motors.

The change of direction in alternating current flow powers the changing magnetic field which turns the rotor inside the stator. As the flow of current changes direction, the magnets which make up the stator change polarity. This makes the magnetic fields in the stator have the same effect on the rotor as if they had moved.

Windings, Poles And RPM

The stator is made up of one or more wire windings which becomes an electromagnet when power passes through it. Each magnet is designed so its poles are directly opposite each other. Motors are classified according to how many poles are possessed by all its stator windings. One with a single winding has only two magnetic poles and is called a two-ole motor. A motor with two stator windings is a four-pole motor. A two-pole motor turns its rotor at about 3500 rpm while a four-pole motor turns the rotor at about 1750 rpm. Four-pole motors were once predominant in the industry but are being replaced by two-pole motors. Pumps designed for direct drive by an electric motor are consequently designed to turn at either 3500 or 1750 rpm.

Single-Phase Electric Motors


Single-phase motors produce magnetic fields of alternating polarity in the stator windings. Induced current in the rotor produces a stationary field which turns as the stator field alternates polarity.

Most electric motors used in high pressure cleaners have what are called squirrel cage rotors made up of two end rings connected by metal bars. The metal bars themselves function as the windings in the squirrel cage motor. The surrounding stator windings induce an alternating current in the bars, causing the rotor to spin in interaction to alternations in stator magnetic field polarity.

Three-Phase Electric Motors


A three-phase circuit is easiest to visualize as three single-phase power supplies. The three-phase stator gives each phase its own set of windings. Most, in fact, have two windings per stage. The sets of windings are spaced at equal distances around the stator. Current flow changes direction in each set of windings at a different time. The change of direction of current flow in each phase occurs in the same order. The time interval between each change is always the same.

This alternation of direction change acts against the induced field in the rotor, causing the rotor to turn. Three-phase motors are used in heavier cleaning applications.

Running In Reverse

Most motors are reversible either by electrical connection or physical orientation. A single-phase motor is generally capable of running in either a counterclockwise or clockwise direction. The offset of the starting windings from the running windings determines the direction in which the motor starts and runs.

Single-phase motors usually have the input or line leads on the outside of the motor which are connected in a particular way for the motor to run clockwise. A diagram on the nameplate shows how to connect the leads to reverse the motor. Some motors have a double-ended shaft and can simply be turned around. Proper rotation should be checked when a motor is set up or wired. Reversing two of the power leads will cause a three-phase motor to turn in the other direction.

Different Voltages

Some motors are rated to operate on more than one voltage. This is indicated on the motor nameplate. Typical dual ratings are 115/230V and 230/460V. The motors must e rewired if the power supply voltage is changed. The name plate shows how to connect the leads for rated voltages. Warning: If the supply voltage is changed, other changes may need to be made in the system besides reconnecting the motor.

Service Factors

Electric motors are available in 1.0 or NEMA service factors. A motor with a 1.0 service factor will perform as rated on the nameplate. A motor which conforms to the NEMA service factor standard will perform periodically at higher than rated horsepower capacity. For 1 and 1/2 or 2 hp rated motors the NEMA service factor is 1.15. This means the NEMA-rated 2 hp motor is capable of producing 2.3 hp on demand. A 1.5 horsepower motor confirming to the NEMA service factor standard is capable of producing 1.725 horsepower on demand.

Motor Housings

Electric motors are available in many different types of enclosures. Since high pressure cleaning often takes place in a damp environment, the type of motor enclosure can be critical to electrical safety.


Types of motor enclosures include:

Open Drip-Proof. Drip-proof motors have open-ended enclosures designed to prevent water from dripping directly downward into the motor windings. The open ends allow cooling air to enter and circulate through the motor. There is no protection against water splashed or sprayed into the ends of the motor. These motors are designed for use indoors in clean, dry environments.

Totally Enclosed. Totally enclosed motors used in the high pressure cleaning equipment industry are usually fan-cooled and these motors are referred to as TEFC (totally enclosed, fan-cooled) motors. TEFC motors are designed for damp or dusty environments. Totally enclosed motors that are not fan-cooled are called totally enclosed, air-over motors.

Washdown. These motors are thoroughly waterproofed but not necessarily fully enclosed. They are ideally suited to damp environments and can be washed off while in operation. They are constructed of corrosion-resistant materials as well. Washdown motors are designed to be waterproof. Even the windings are sealed and can be washed while the motor is in operation.

Explosion Proof. Explosion proof motors are fully enclosed and designed for operation in hazardous atmospheres which contain explosive gases or heavy concentrations of potentially explosive dust. These motors are sealed to prevent vapors or potentially explosive dust from entering the motor housing where sparking occurs. The enclosure also prevents sparks from escaping the motor housing.

General And Special Purpose

Different types of motors find wide use in high pressure cleaning equipment. General purpose motors are normally used to drive the pump. The motors conform to specific NEMA ratings. They are ruggedly constructed and, if supplied proper power, will operate with little maintenance for thousands of hours.

Special purpose and definite purpose motors are designed for specific applications. The motor driving the oil burner may be a definite or special purpose motor.

The Nameplate

Relevant information about an electric motor is included on the motor nameplate. The information supplied on the nameplate classifies the motor according to National Electrical Manufacturers Association standards. The nameplate rates the motor’s expected performance as measured by NEMA standards and gives information about the motor manufacturer, motor size, and motor wiring.

The manufacturer’s name and address are given at the top of the nameplate. Other information supplied on the nameplate and captions of the blanks in which the information falls include:

(MOD) Model number.

(HP) Rated horsepower.

(PH) Whether one-or three-phase power supply required.

(RPM) Motor shaft rotation in revolutions per minute.

(HZ) Number of cycles per second for AC motors or Hertz.

(INS) Insulation classification.

(SF) Service factor or percentage of rated horsepower the motor is capable of producing.

(FR) Frame size expressed as a number which (for fractional motors) gives the shaft center line height when divided by 16.

(KVA CODE) KVA code expresses locked rotor current draw as a code letter.

(V) Voltage, including whether the motor will run at multiple voltages and the voltage spread.

(MAX. AMB.) Maximum ambient temperature at which the motor will operate expressed in degrees Centigrade.

(FLA) Full load amp draw or amp draw during normal operation.

(TEMP RISE) Temperature above ambient at which the motor can operate under full load.

(SFA) Service factor amp draw or draw when the equipment is operating at its service factor load.

Other information which may appear on the nameplate may include the type of enclosure, type of mounting, type of thermal protection, bearing style, and line connections which may be diagrammed on the nameplate.

Motor Starting

It takes more current to start a motor than it does to keep it running. This is especially true if the motor is starting with a load such as a pump attempting to move water. Single phase motors generally require some sort of help to start. Three phase motors are essentially self starting. Rotation between the phases (each with its own stator winding) causes the motor rotor to begin turning.

Capacitor Start

Single-phase motors generally rely on a separate, additional set of rotor windings to get the motor turning. These windings are offset from the running windings. Interaction between the offset magnetic fields in the starting and running windings get the rotor to begin turning. Power may be supplied to the starting winding by a starting capacitor. Motors with a starting capacitor are called capacitor-start motors. These will always be single-phase motors. Capacitor-start/capacitor run motors have an additional capacitor for the running windings.

Amp Draw For Various Horsepowers


Values are for motors running at usual speeds and with normal torque characteristics. The above values are the approximate maximums you will encounter for properly functioning electric motors.


Different types and makes of motors may vary considerably above or below values in this table. Newer, low amperage, high efficiency motors will have substantially lower full load amp draws as indicated in the table below for definite purpose, single phase 3600 rpm motors marketed to the high pressure cleaning equipment industry by Marathon Electric.

Electric Motor Troubleshooting

Generally, the reason an electric powered cleaner will not start is that power is not getting to the motor.

Ask, “Is the cleaner getting proper electrical power?”

One easy way to determine if the motor is getting power is to listen. If there is a humming noise, then the motor may be getting power but not driving the pump. If there is such a humming sound, check to see if the motor shaft is turning and inspect the pump drive for damage or malfunction.

Note: As in most cases in which a diagnosis is being made, simply observing the equipment and its environment can give you important clues about potential equipment problems.

Example: If a cleaner with a metal frame is standing in water and the cleaner is equipped with a GFCI, checking the GFCI might be a good idea. If a cleaner is in a shop where there are a number of other pieces of equipment with high power demands, a good first step might be determining if any of the other pieces of equipment are on the same circuit with the cleaner. To trace the path of power to the motor, start with the power source.

Check For Proper Voltage

Ask, “Is the proper voltage being delivered at the outlet?”

Use your multimeter to check the outlet or electrical receptacle to make sure the proper voltage is being delivered. To check for 115 voltage at the supply box, insert one lead in each of the two vertical slots. The meter will usually read about 114 to 115 volts. The equipment will normally operate with voltages ranging from 105 volts to 124 volts. To check for 230 voltage at the supply box, insert one lead in each of the two blade slots. This should read in the 220 to 230 voltage range. Leave one lead in place and move the other to the neutral. This should read in the 110 volts range. Each leg should read around
110 to 115 volts when paired with the neutral.

Note: Sometimes skipping a series of steps can save time. If the cleaner is getting power, check the thermal reset on the motor (if applicable). (An extension cord too small may have caused the motor to overheat and the thermal reset may have tripped.)

Improper Voltage

If the proper voltage is not being delivered at the box, here are some things you can look for.

Ask, “Why is power not being delivered?”

Check the circuit breaker. Make certain the breaker has not been tripped. Try to determine if there is other high draw equipment on the circuit and operating. Generally such equipment will include fans, air compressor, coolers and power tools. Turn the equipment on and see if the breaker trips. Again, eliminate all other equipment operating on the circuit. If the breaker still trips, a short circuit in the cleaner is indicated.

Note: If there is no breaker or if power will not come back on after a breaker trips, check to see if there is a screw-in fuse in the circuit.

Check The Voltage At The Switch

Ask, “Is the proper voltage being delivered at the switch?”

If the voltage was correct at the supply box, use the multimeter to check the voltage at the switch. If the cleaner is a 115 volt machine, check across the two leads. You should get a reading in the 115 volt again. If the cleaner is a 230 volt cleaner, check each leg of the switch against the cleaner’s frame. You should get a reading in the 115 volt range from each leg grounded against the cleaner frame.

No Voltage At The Switch

If no voltage is being delivered to the switch, and there is voltage at the power box, then the problem has to lie between switch and the power supply box.

Ask, “Why is power not being delivered to the switch?”

First, make sure the cleaner is plugged in. If the equipment is equipped by a Ground Fault Circuit Interrupter, check the interrupter. Examine the power cord for visible damage.

If the equipment is operating on an extension cord or cords, eliminate the cords by plugging the cleaner straight into the power source. Potential problems include bad cord connections, bad cord or cord that is too small for required power and distance of power delivery.

The Magnetic Contactor

Ask, “Are the magnetic contactors in good condition and operating properly?”

If there is voltage at the switch, then check the magnetic contactors visually for damage or reasons for improper operation. Generally there will be only two leads but three contactors. One of the leads can be switched if a contactor is bad.

At The Motor

Ask, “Is the motor receiving the proper voltage?”

Use the multimeter to check the connections at the motor to make sure that the motor is now receiving the proper voltage. If the proper voltage is now arriving at the motor, check the thermal reset button again.

The Start Capacitor

Ask, “Is the starting capacitor good?”

Use the multimeter to check the starting capacitor. If the capacitor is good, the voltage will rise as the capacitor charges. After about five seconds, reverse the leads and the capacitor should discharge proportionately.

Motor Malfunction

If proper voltage is reaching the motor and the motor will not operate, it is likely that the motor is frozen or burned up.

NOTE: This will not always be the case; the belt or belts driving the pump may be broken or slipping so much that the pump will not operate. By tracing the flow of electrical current from the power supply box to the motor, you have eliminated or remedied any problems which might have kept the proper voltage from reaching the motor. If the motor is defective, it should be replaced.

NOTE: In some equipment configurations, especially with full-featured equipment, the path of power to the motor may be interrupted by some type of timed or safety shutoff control. Whenever tracing the flow of electricity, check the manufacturer’s electrical diagrams or schematics to determine the wiring connections and devices included in the circuit.

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