forced air

How is it wired? Cool anti

-Wired in parallel to cooling contacts

What is a GFCI?

-ground fault circuit interrupter, (similar operation as circuit breaker), high amps cause strong field that operates armature and trip circuit (protects the individual), installed in wet/damp locations where accidental over current (short) is more likely(kitchen, bathroom), in a wall plug receptacle typically(residential)

O/B is what?(t-stat)

-if wires coming from O/B terminals then system has a heat pump, controls reversing valve on heat pump*

What is auto ranging?

-process in which instrument has the capability to to automatically switch to settings anywhere along a specifically identified range.

What does "at rest" mean?

-switch at rest is not calling in any mode or being acted upon by any outside forces, switches at rest either N/o or N/C,

Give an example of an indirect control

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How could it be used as a modulating control? (bulb and bellows)

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What are the two different types of primary control systems?

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Give examples of A helix style bimetal is used in what control?

Circuit breaker , fan limit

How does a clamp on meter work?

Instrument that is used to measure the current flowing through a conductor. An AC clamp meter basically consists of a current transformer in its jaws, bar CT usually. When clamped on conductor, conductor acts as primary and the magnetic flux due to current flowing through conductor cuts the secondary of the CT, current in secondary of ct is converted to voltage using current to voltage convertor.

Explain the purpose of the cooling anticipator

Is a resistance heater (usually not adjustable) it is on when the current is off, adding heat to shorten the off cycle. Add false heat to stat bimetal element same as heating, but cooling are not adjustable they are sized by manufacturer of stat.

temperature disc. Also known as?-

Klixon

How do they each work? Float type

N/O RA held closed by float on top of water. If water level falls below predetermined point, the float mechanism lowers and breaks the electrical contact

How do they each work? Probe Type:

NO switch, has an electronic circuitry that uses boiler water to conduct current between the terminals on the ends of the probe. If water falls below the level of probe, the electronic circuit between the terminals is broken. In response to no circuit, the low water cut off switch opens cutting off power to man GV.

How is it wired? Heat anti

Wired in series to heating contacts

What is bonding?

act of joining two electrical conductors together, (two wires, wire and pipe etc.) connect all metal parts that are not supposed to be carrying current during normal operations thus bringing them to the same electrical potential. Help create low impedance path back to source, force of large current flow will trip breaker (if conductor touches external metal.)

What are the two types of low water cut off?

actuates in response to fluid movement, if water level in boiler falls below min level, low water cutoff switch opens its contact and cuts off power to main gas valve. Two types: Float and Probe type.

Explain the purpose of a heat anticipator

added in stat to reduce operating differential of system (diff between highest and lowest temp actually obtained.) is a small resistive heater in the stat itself which heats when the system if on. The heat produced by anticipator raises the internal stat temp slightly faster than the surrounding room temp. This allows stat to shut off the heating system sooner than it would if affected by room temp only, in other words. The stat anticipates the need to shut off the heating system. (4 times/hr), produces false heat in stat to prevent extreme temp changes within a space. The false heat created by resistance increase the stat rate of response, the state receives false heat which shuts down heating source before stat reaches desired temp. (reduces over shooting and more efficient.)

What is Cold Flow?

causes loose connections. An aluminum conductor secured by a terminal screw will gradually lose its resistance to the pressure of the screw and cold flow away from the point of contact. The resulting reduction in contact pressure produces a loose connection. The increased resistance to current flow at the loose connection will cause overheating, damaging the connection and the surrounding insulation.

What is Electrolysis?

chemical decomposition produced by passing an electric current through a liquid or solution containing ions. Process in which chemical is broken down into its component chemicals using electricity.

Define "Direct Acting"-

closes on fall past the medium

Define "Reverse Acting"-

closes on rise past the medium

What is grounding?

connecting live part(part which carries current under normal condition to the earth. Ex neutral of transformer, to provide effective return path from machine to power source. Refers to neutral, once all metals are bonded, then can get grounded to earth.

What is the "control range"?

cut in and cut out points

What is the "control differential"?

difference between cut in and cut out

How does "at rest" differ from "de-energized"?

ex to make furnace fire need to energize first then call for heat. If t stat is adjusted without energizing circuit then circuit is calling meaning no longer at rest but remains de-energized. De-energized circuit no potential (volts) applied , when no potential diff, then current flow impossible. Ex. Funace is energized by power source but still at rest since stat as not been adjusted to call for heat

What is liquid tight?

flexible metal conduit, outer liquid tight, non-metallic, sunlight resistant jacket over flexible metal core.

Why is a flow switch needed on a boiler?

flow switches actuate in response to water movement. They ensure the pumps are circulating water in the piping system and the boiler before the main burner can fire. Boilers that require flow switches have small water capacities and their water may turn to steam if the flow of water is inadequate.

What are "anti-shorts"?

install anti short bushing to protect the wires. Tab on bushing helps inspectors see that it's installed., red split, plastic sleeve placed between the wires and the rough edge of the armor in AC.

What does it protect?(fuse)

live conductor ,load, specifically designed and sized for wire

When is C used?(t-stat)

need not to be run out to the t stat however if stat requires power, the c wire should be routed to the thermostat, even if current stat does not require external power good idea to brin c wire out to stat in anticipation of future install of a stat that requires power

Explain the thermal expansion of liquids

only one related to volume expansion dependant on the temperature. Expansion of liquid is much greater than solids.

explain catridge type

operates directly in line with conductor three types, ferrule(round ends that snap , holds receptacle), knife blade(thin metal; blades snapping into thin holder designed for fuse), and bolt(similar to knife, but contact point secured with bolts/screws)

When/why is it used?(LIQUID TIGHT)

permitted to be used for exposed or concealed work, in dry, damp or wet locations indoors and outdoors. Exception of Class 1 division1 locations can be used in hazardous class 1 div 2 locations.

What are the different types?(fuse)

plug type Cartridge type

What is a temperature disc?

responds to temp changes by moving from concave to convex shape, touching electrical contacts and completing a circuit, can be used in a thermal relay.

explain plug type

round fuse screw into receptacle of some for max allowable amp rate 30 amps, max potential applied across conductors is 125 V

What is a fuse?

specifically to protect the live conductor leading to the load(conductor sized according to load)

Explain the 'bulb and bellows' system

temp sensing bulb, capillary tubing and bellows are filled with temp sensitive liquid. Change in temp at the bulb contract the liquid on temp fall and expand it on temp rise, causing the bellows to shorten/lengthen. This movement is transmitted to the valve assembly by horizontal pivot arm, the modusnap modulating valve is used for space temp control. Liquid immersion model is similar but it has larger top casing to accommodate larger bellows.