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HVACR216 - HydronicsHVACR216 - Hydronics

SchematicsSchematics

Diagrams and PictorialsDiagrams and Pictorials

Three Phase PowerThree Phase Power

Circuit ComponentsCircuit Components

SchematicsSchematics

Diagrams and PictorialsDiagrams and Pictorials

Three Phase PowerThree Phase Power

Circuit ComponentsCircuit Components

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SchematicsSchematics

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PICTORIAL & SCHEMATIC DIAGRAMSPICTORIAL & SCHEMATIC DIAGRAMS

Pictorial diagrams show how components are actually wired. However, pictorial diagrams become cumbersome when many components are involved.

Schematic diagrams present the logic of the circuit in an organized fashion. Schematic diagrams are less cluttered because they use symbols to represent components.

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4LADDER DIAGRAMSLADDER DIAGRAMS

A ladder diagram is arranged with the power supply lines drawn vertical as the legs of a ladder. Each horizontal line contains one load and its control switches. Each load line may be numbered for ease of identification.

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5READING A WIRING SCHEMATICREADING A WIRING SCHEMATIC

Reading a wiring schematic is easier if you follow a few simple rules.

• Schematics are read like a book, top to bottom, left to right.

•There must be a complete circuit for current to flow through a component.

•Electrical contacts and switches are always shown in their normal position (power off).

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READING A WIRING SCHEMATICREADING A WIRING SCHEMATIC

• When a relay is energized, all of its contacts will change position. Normally open contacts will close. Normally closed contacts will open.

• Switches or components that are used to provide the function of stop are normally closed and generally wired in series.

• Switches or components used to provide the function of start are normally open and wired in parallel.

• When a relay is energized, all of its contacts will change position. Normally open contacts will close. Normally closed contacts will open.

• Switches or components that are used to provide the function of stop are normally closed and generally wired in series.

• Switches or components used to provide the function of start are normally open and wired in parallel.

7START – STOP PUSH BUTTON CIRCUITSTART – STOP PUSH BUTTON CIRCUIT

Notice there is no complete circuit to motor starter coil “M” because the start switch and auxiliary contacts ( M ) are open.

When the start button is pressed, both “M” contacts will close and the motor will run.

The auxiliary contacts will serve as a hold-in circuit to keep the circuit complete when the start switch is released.

The circuit will remain energized until the stop button is pressed, interrupting current flow to the “M” coil.

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THREE PHASE CIRCUITSTHREE PHASE CIRCUITS

The power plant generator rotates three conducting loops, each spaced 120 degrees apart, through a magnetic field. The induced power pulses take turns changing polarity from positive to negative to zero at a rate of 7200 times per minute (60 times per second).

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THREE PHASE CIRCUITSTHREE PHASE CIRCUITS

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Each wire has the same voltage but different polarity ( + vs. - ).

The potential between any two wires is additive.

120 volts positive plus 120 volts negative equals 240 volts.

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SINGLE PHASE CIRCUITSSINGLE PHASE CIRCUITS

Some loads are designed to operate with just two hot wires from a three phase system. These two wires will alternate from positive to negative polarity. This “push-pull” effect can be obtained with any two phases.

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THE NEUTRAL WIRETHE NEUTRAL WIRE

The earth is always at zero potential (no voltage) and can be used to complete an electrical circuit. Many electrical loads operate with just one hot wire from a three phase source and another wire called the neutral. A potential difference exists because the hot wire has voltage and polarity but the neutral wire is connected to the Earth (grounded) which is zero volts. The neutral wire is a current carrying conductor, but has no voltage.

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THE SAFETY GROUND WIRETHE SAFETY GROUND WIRE

The safety ground is connected to the frame of a motor or appliance and provides an alternate pathway for electrons to travel to ground should a fault occur. The safety ground connects to the same terminal as the neutral wire at the service panel. The neutral wire normally carries current. The safety ground only carries current in the event of a short circuit.

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13CONDUCTORSCONDUCTORS

In general, any material that has three or less electrons in its outer orbit is considered a conductor. Copper is the most commonly used conductor. Wire size and type determine the current carrying ability.

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INSULATORSINSULATORS

Insulators offer high resistance to current flow. Materials that have five or more electrons in the outer orbit are considered insulators. The type of insulation determines where a conductor can be used safely.

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15CIRCUIT PROTECTIONCIRCUIT PROTECTION

Fuses and circuit breakers are used to protect a circuit against over current.

The amperage rating of a fuse must not be greater than the ampacity of the wires being protected.

Fuses and breakers are used to protect wires, not people.

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16LOADS AND SWITCHESLOADS AND SWITCHES

Manufacturers design devices with the correct amount of resistance for the device to perform the desired amount of energy conversion.

Electrical energy flows through the device and is converted to another form of energy ( light, heat, motion, etc.).

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LOADS AND SWITCHESLOADS AND SWITCHES

A load cannot operate unless the circuit provides a complete path for electrons to flow. Switches are used to control and / or provide safety protection. Switches are wired in series with the load.

A load cannot operate unless the circuit provides a complete path for electrons to flow. Switches are used to control and / or provide safety protection. Switches are wired in series with the load.

18LOADS AND SWITCHESLOADS AND SWITCHES

When more than one load is connected to a power source, switches are connected in series with each load and each load is connected in parallel with the power source. NEXT

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SINGLE PHASE TRANSFORMERSSINGLE PHASE TRANSFORMERS

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Transformers have two windings, a primary (incoming voltage), and a secondary (outgoing voltage).

Voltage at the secondary (step-up or step-down) is determined by the number of coils in the secondary versus the number of coils in the primary. Single phase transformers are rated by VA (volts x amps) at the secondary.

20THREE PHASE TRANSFORMERSTHREE PHASE TRANSFORMERS

Three phase transformers are wound in “wye” or “delta”configurations. Combinations of wye and / or delta primary and secondary coils provide a variety of voltage and current outputs.

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RELAYSRELAYS

A relay uses electromagnetism to operate a switch (or contacts). The electrical circuit to the relay coil is entirely separate from the circuit through the contacts. A relay allows high current loads to be controlled using low current control switches and safeties.

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22CONTACTORSCONTACTORS

A contactor is basically a large rely. The contacts are much larger and capable of carrying more current. Contactor components (contacts, coil, etc.) are replaceable, whereas a relay is generally replaced as a complete unit.

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Any number of switches may be located in the contactor coil control circuit.

23LINE STARTERSLINE STARTERS

A line starter, or motor starter, is basically a contactor with overload protection.

The overload contacts are connected in series in the circuit controlling the contactor coil. There is one overload in each leg of the three phase power supply to the motor. If an over-current should occur, the overload contacts interrupt the coil control circuit and the motor stops. NEXT

24THERMOSTATSTHERMOSTATS

One common type of temperature sensing device is a bimetal switch, in which two different types of metal are laid together. Because the metals expand at different rates, a change in temperature will cause the bimetal strip to bend, opening (or closing) a set of contacts.

A mercury switch may be attached to the bimetal strip. A small drop of mercury is sealed in a glass tube that also contains a set of contacts. Most mercury switches are designed as single-pole double-throw, allowing them to be used for heating and cooling. NEXT

25HEAT ANTICIPATORHEAT ANTICIPATOR

The heat anticipator is an adjustable resistance heater located near the bimetal coil in a thermostat. It functions to slightly heat the bimetal coil to prevent system overshoot. The heat anticipator is set according to the amperage draw of the heating control circuit.

If the anticipator is set at higher amperage, system overshoot will occur. If it set to lower amperage, system lag will occur.

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