F3: Switches and Relays

Question 1

What is the heart of operational systems?

Answer 1

Switches and relays

Question 2

What is a switch?

Answer 2

a device that makes or breaks (aka closes or opens) a path in an electrical circuit to allow loads.

Question 3

What is an example of a manual switch?

Answer 3

a light switch for a room

Question 4

What happens when a switch is manually moved (aka thrown)?

Answer 4

The pole (moving part) changes

Question 5

How are switches referred?

Answer 5

by the number of poles / throws they have

Question 6

What is this?

Answer 6

Single pole, single throw switch

Question 7

What is this?

Answer 7

Single pole, double throw switch

Question 8

What is this?

Answer 8

Double pole, single throw switch

Question 9

What is this?

Answer 9

Double pole, double throw switch

Question 10

What is this?

Answer 10

7 pole (rotary) switch

Question 11

What is a momentary switch?

Answer 11

a switch that must be pushed or tuned / held in order for the contacts inside to close.

Question 12

Are momentary switches spring loaded?

Answer 12

Yes, snap open when released.

Question 13

What type of switch is used to sense, measure / react to conditions (temp, pressure, flow, liquid level / position)

Answer 13

Automatic switches

Question 14

How are automatic switches classified?

Answer 14

1) what they measure
2)condition that causes them to react

Question 15

What type of switch is a thermostat?

Answer 15

open or rise automatic switch

Question 16

What would a cooling thermostat be classified as?

Answer 16

a close on rise switch

Question 17

How does a close on rise switch work?

Answer 17

as the temp rises - thermal element expands / closes its contacts to bring on the cooling system

Question 18

What is an aquastat?

Answer 18

a switch that does for water what thermostat does for air

Question 19

What is a thermowell?

Answer 19

It is a well that is inserted into an opening in the piping system

Question 20

What does differential mean for switches?

Answer 20

They have variance between their open and closed positions

Question 21

What is the fixed differential of an Aquastat?

Answer 21

15F (8.33C)

Question 22

What is the differential pre-set of a pressure switch?

Answer 22

20 psi

Question 23

A flow switch is what type?

Answer 23

a single pole, double throw switch

Question 24

How does a flow switch operate?

Answer 24

When there is flow the paddle moves = causes pole to be pushed from one throw and pulled to another throw

Question 25

Where is a pressure switch used?

Answer 25

on mid and high efficiency gas equipment

Question 26

How does a pressure switch operate?

Answer 26

contacts close when the correct pressure is sensed.

Question 27

When replacing a pressure switch, you should use one that has the same what?

Answer 27

pressure setting

Question 28

What are float switches used for?

Answer 28

To monitor the level of liquids in a vessel

Question 29

A float switch will open or close to control what?

Answer 29

a pump supplying water to a cooling tower sump, or to shut off the burner in a steam of hot water boiler whose water level has dropped to an unacceptable point.

Question 30

What is another name for a float switch?

Answer 30

Low water cutoff

Question 31

What is this?

Answer 31

Float switch

Question 32

Where are End switches used?

Answer 32

used if the position of a piece of mechanical equipment has to be proven before the next step in a sequence of operation can take place.

Question 33

What prevents Dead - heading?

Answer 33

A zone valve that has to be proven to be open before the pump tried to move water through it

Question 34

What does a 4 wire zone valve have?

Answer 34

end switch wired across 2 of the wires which typically have red insulation

Question 35

What else is an End switch used for?

Answer 35

operations of the dampers on the inlet to a direct-fired makeup unit (DFMA)

Question 36

A dimmer switch functions as an?

Answer 36

On / off switch w/ the addition of a variable resistor built into it

Question 37

Where should a switch be located?

Answer 37

ALWAYS be located in the "hot" leg of the circuit positioned between the source (power supply) / the load (device that turns electrical energy into work)

Question 38

What do the volts and amps have to be?

Answer 38

at least as high as those it will be exposed to

Question 39

What does a relay do?

Answer 39

allows low volts to operate high voltage equipment equipment w/o the two touching each other

Question 40

What are the 2 varieties of relays?

Answer 40

1) electromagnetic relays (EMRs) 2) solid - state relays (SSRs)

Question 41

What is the job of the 2 kinds of relays?

Answer 41

use a circuit w/ low power to operate equipment that uses a higher voltage power source.

Question 42

What is the SSR about?

Answer 42

silent in operation has no moving parts Wear and tear isn't an issue

Question 43

What is EMR about?

Answer 43

has a moving armature / moving contacts Can not be used in a volatile environment

Question 44

What is a downside of a SSR

Answer 44

limited to operating one circuit only

Question 45

Can EMRs operate multiple sets of contacts?

Answer 45

Yes

Question 46

Where are SSRs found?

Answer 46

on furnaces / boiler modules, solid state fuse / relay panels in vehicles.

Question 47

Most relays that are used in hydronic systems will be of what type?

Answer 47

EMR

Question 48

Most relays that are used in hydronic systems are of what type?

Answer 48

EMR

Question 49

What do relays consist of?

Answer 49

a Coil = temporary electromagnet A single or multiple sets of spring loaded electrical contacts

Question 50

When a relay coil is energized and de-energized what can be heard?

Answer 50

an audible click

Question 51

What voltage values are relays capable of?

Answer 51

600V

Question 52

In a nutshell, how does a relay work?

Answer 52

It's a magnetic switch = uses electromagnetism as the force that operates the switching mechanism

Question 53

What does SSR stand for?

Answer 53

Solid state relays

Question 54

What does EMR stand for?

Answer 54

Electromagnetic relays