Electrical Trouble Shooting

1. Electrical Trouble Shooting

2. Electrical Trouble Shooting • Basic Electrical Thoughts • Back to Basics • Motor Starters • Trouble Shooting Electrical Drawings

3. Basic Electrical Thoughts • Understanding the electrical wiring diagrams and performing checks with the volt meter assists with diagnosing the electrical control circuit issues • It’s the understanding of the draws and unit operation, that requires the work • We find that many times performing the checks, we need to return back to basics with the understanding of those circuits • Reviewing the simple wiring diagram in this section will help as be progress into the later portion of this course • Throughout this presentation there are going to use some standard symbols and techniques we find in our industry used in the drawings.

4. Back to Basics With electrical control circuits, they can be broken down into three categories. By placing them in these three categories, it is easier to understand the function and operation • Power Device - the actual supply of power to the circuit. This would include line voltage to the unit, low voltage supplied from a transformer or DC voltage from a converter • Switching Device - any component that makes or breaks voltage to a circuit, ex. pressure or temperature switch, relay contacts • Load Device – any component that draws current and performs a task, ex. Relay or contactor coil. This includes the Volt Meter itself.

5. Back to Basics We must keep in mind electrons are flowing throughout the circuit. They flow from the supply side and return to neutral or ground. There is the path or conductor that allows the electrons to flow. In the illustration, the arrows indicate the path of flowing electrons

6. Back to Basics When the volt meter is placed across the power supplying the circuit, the voltage to the incoming circuit is measured. It’s knowing the amount of power required to the circuit that is needed. In this circuit, it is the transformer. Line voltage is supplied to the primary side of the transformer and reduced on the secondary 27.5 vac

7. Back to Basics When the volt/ohm meter is place across the load device, it is the same as placing two loads in parallel with one another. The voltage supplied to the loads, will equally travel and supply each loads. The voltage to each load should not be confused with the current. There are two loads shown in the diagram. Each shown on being controlled by different contacts 27.5 vac 0.0vac

8. Back to Basics When measuring voltage across contacts, the rules change. Remembering the volt meter is a load device and electricity always takes it’s path of least resistance. On open contacts, you will read voltage. On closed contacts, no voltage will be read on the meter. Two sets of contacts. One normally open, the other closed 0.0 vac 27.5 vac

9. Back to Basics • It is easier for the voltage to flow through the closed contacts, than it is for the voltage to flow through the meter. • This is the opposite for the open contacts. The voltage cannot flow through the open contacts, so it will only flow though the volt meter. • Keep in mind, when the voltage across the contacts is “0”, this can mislead you in thinking the contacts are closed. When in fact there may not be any voltage supplied to the circuit at all

10. Motor Starters

11. Motor Starters • Motor starters are a control/protection device used in conjunction with 3 phase motors. • They start and stop the motor operation through a contactor from either an outside control source and manual push buttons. • They provide protection to the motor through a over load device by monitoring the current of the motor. • By linking both items together, it makes up the motor starter.

12. Motor Starters - Contactor Contactor offers the control portion of the motor starter. By applying the voltage to the coil, the magnetic force introduced, pulls in on the main contacts. Auxiliary contacts are mechanically connected to the main contacts. The contacts are rated to carry the Full Load Amps of the motor along with a 30% service factor. The auxiliary contacts are normally rated for 10 amps. The voltage applied to the coil of the contactor is sized according to the control used for the motor starter.

13. Motor Starter - Overload The overload provides the protection to the motor windings. If the motor experiences high current situation because of in coming low voltage or single phasing, the heaters or electronics of the overload will detect this condition and open the pilot contacts shutting down the control to the contactor. Overloads are available in two types using preset heaters or adjustable. The adjustable are offered as a electronic version and may be a used for a wide range of amp settings. Using the heater type overload, the heaters must be sized according to the motor specs.

14. Motor Starter - Heaters Heaters are used in the preset type overloads. The heaters are set for a particular amp rating and should be sized according to the current draw of the motor. Heaters come in many different styles and designs. Some use a low melting solder so when the temperature of the heater increases, the solder melts and allows a cogged gear to release, tripping the overload. Other heaters apply heat to a by-metal surface and as the heat increases, the pilot switch in the overload will trip.

15. Motor Starter - Wiring Many of the motor starters found in the field will be stand-a-lone. Caution must be used in ordering the correct coil voltage to the control circuit being applied In this particular circuit, the coil is energized through a holding circuit. What type of wiring diagram is this? Answer- Pictorial

16. Motor Starter – Control Diagram The control voltage of the motor starter can vary depending on the source from the controller. The consideration of the coil voltage and wire type used will need to be altered when the control voltages changes. This drawing illustrates the design of the “Holding Circuit”. The start sequence must be initiated in order for the process to begin.

17. Trouble Shooting Electrical Drawings

18. ExampleDrawings The example drawings uses the symbol to indicate the volt ohm meter. The voltage of the point will be displayed above or below the meter symbol. The symbols displayed as safeties or switches in the drawings will be shown closed. If the condition exists in the circuit that the switch is open, than the volt reading will indicate it.

19. Example Issue 1 230 vac 27.5 vac 0.0 vac 27.7 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 27.4 vac 0.0 vac 0.0 vac Bad Compressor Contactor Coil 27.3 vac 27.4 vac

20. Example Issue 2 230 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac Faulty Transformer 0.0 vac 0.0 vac

21. Example Issue 3 230 vac 27.4vac 0.0 vac 27.6 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac Open safety switch 22.2 vac 22.4 vac

22. Example Issue 4 230 vac 27.4 vac 0.0 vac 27.6 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac Broken wire to compressor contactor coil 27.5 vac 27.5 vac

23. Example Issue 5 230 mvac 27.4 mvac 0.0 vac 27.6 mvac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 27.4 mvac 0.0 vac 0.0 vac No Power, Meter set on Auto Range 27.5 mvac 27.5 mvac

24. Example Issue 6 230 vac 27.6 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 22.1 vac 0.0 vac 5.0 vac Low voltage through switch, faulty safety switch 22.2 vac 22.1 vac

25. Example Issue 7 208 vac 21.2 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 21.1 vac 0.0 vac 0.0 vac Primary side of the transformer is connected to the incorrect line voltage tapping 21.2 vac 21.1 vac

26. Example Issue 8 230 vac 27.2 vac 27.1 vac 0.0 vac 0.0 vac 0.0 vac 0.0 vac 27.0 vac 0.0 vac Broken neutral wire 27.0 vac 26.8 vac