als lesson 5

8/21/2019 Als Lesson 5

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LESSON FIVE: ELECTRICITY

BASIC PHYSICS:

Q1: What are the three basic factors in

electricity?

A1: Potential, current, resistance.

Q2: How can water be used as an analogy?

A2: Voltage V !olts" is the #otentialHeight, #ressure or #ressure difference

in feet or #si"

$urrent % a&#eres" is the current 'low

in gallons #er &inute"(esistance ( oh&s or )" is the

resistance (esistance to flow in inches

#er 1**ft"

Q+: What is h&-s aw?

A+: /he for&ula which relates these factors.% 0 V(. /he greater the !oltage, the

greater the current. /he greater the

resistance, the s&aller the current.

Q: What are series resistances and #arallel

resistances?

A: When there are se!eral resistances inthe flow #ath or when there are #arallel

#aths with different resistances and flow

rates.

Q3: What is the for&ula for calculating

series resistances?A3: ( tot 4 ( 1 4 ( 2 4 ( + 4 5 4 ( n

Q6: What is the for&ula for calculating

#arallel resistances?A6: 1 ( tot 0 1( 1 4 1( 2 4 1( + 4 5 4 1( n

TRANSMISSION AND USAGE:

Direct CurrentQ1: What is direct current 7$"?

A1:

Q2: What is the e8uation for #ower in a 7$circuit?

A2: P 0 V 9 %

Alternatin Current

Q1: What is alternating current A$"?

A1:

Q2: What is the #ower factor?

A2:

Q+: How is the #ower factor e9#ressed?

A+:

Q: What is a three#hase circuit?

A:

Q3: What are ;ilowatts and &egawatts?

A3: <ilowatts are 1,*** watts= &egawatts

are 1,***,*** watts.

ELECTRICAL E!UIPMENT

Q1: What is a &otor?A1: A &otor is a &achine which con!erts

electrical energy into &echanicalenergy.

Q2: What is a generator?A2: A generator is a &achine which

con!erts &echanical energy into

electrical energy.

Q+: What is the basic #rinci#le behind

generating electricity?A+:

Q: What is the basic #rinci#le behind

electric &otors and electric solenoids?A:

Q3: What is a solenoid?A3: %t is a wire wound s#irally around an

iron core to #roduce a &agnetic field

which is used as an electro&agnetic

switch.

Generati"n "# P"$er

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Q1: What is a single#hase alternator?

A1: %t is the &ost basic for& of #owergeneration.

Q2: What is the ty#ical A$ #ower fre8uencyin the ?

A2:

Q+: What is it in >uro#e?A3+:

Q: What is the co&&on household !oltagein the ? %n >uro#e?

A: %n the it is 11* !olts= in >uro#e it is

22* !olts.

Q3: How is three#hase #ower generated?

A3:

Q6: What ha##ens if only one of the circuits

is connected?

A6:

Tran%#"r&er%:

Q1: What is a transfor&er?

A1: %t is a de!ice which changes the !oltageof an A$ circuit to a higher or lower

!alue.

Q2: What does a transfor&er consist of?

A2:

Q+: What are transfor&ers used for?

A+:

Q: What are ste# u# transfor&ers and ste#down transfor&ers?

A:

Q3: How do transfor&ers wor;?A3:

Q6: What is the ther&al rating of thetransfor&er?

A6: %t is the #roduct of the Voltage and the

A&#erage VA.

QB: Why should transfor&ers be !entilated

and isolated?

AB:

Tran%#"r&er C"nnecti"n%:

Q1: '(at are t(e )ri&ar* an+ %ec"n+ar*

$in+in,

A1: /he )ri&ar* $in+in i% u%e+ #"r

in)ut in a tran%#"r&er- while the

%ec"n+ar* $in+in i% u%e+ #"r "ut)ut.

Q2: What is a twowire secondary?A2:

Q+: What is a threewire secondary?

A+:

Q: What are the two ty#es of connections

called?A: '*e an+ +elta.

Q3: Why is t(e $*e %"&eti&e% re#erre+ t"

a% a /%tar0,

A3: Cecause the neutral c"ntact at the

crotch of the wye" #"r&% t(e center "#

a t(ree1)"inte+ %tar.

Q6: '(at 2"ltae %*%te& are re%i+ence%

li&ite+ t",A6: 12*2* !olt single#hase syste&s.

QB: What do larger loads such as air

conditioners, refrigerators and electric

ranges" use?

AB: arger loads use the linetoline !oltageof 2* !olts.

QB: What do rece#tacles and light switches

use?AB: (ece#tacles and light switches use the

linetoneutral !oltage of 12* !olts.

Electric Heater%:

Q1: How do electric heaters wor;?

A1: A length of stainless steel wire for&ed

onto a coil and su##orted on insulated #rongs acts as a resistance to the

current, which generates heat.

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Q2: '(* are electric (eater% 3445

e##icient,

A2: E2er* 6it "# electrical ener* i%

c"n2erte+ t" (eat.

Q+: '(* i% it ine##icient t" u%e electricit*

t" (eat a %)ace,A+: Duch of the electricity in the is

generated by using heat to generate

stea&, which generates electricity at

about +*E efficiency.

Q: Why is it efficient though to use electric

heat as a radiant heat source?A: (adiant heat only heats #eo#le, not air.

Electric Li(tin:

Q1: What is a fourway switch?A1: When &ore than two switches are

necessary, two of the switches &ust be

threeway switches and the re&aining

additional switches &ust be fourwayswitches

M"t"r%:

Q1: What ty#es of &otors are in generaluse?

A1: 7$ &otors, single#hase A$ &otors,three#hase induction &otors anduni!ersal &otors.

Q2: What is the 7$ &otor used for?A2: &all scale a##lications and ele!ators,

where continuous and s&ooth

acceleration to a high s#eed isi&#ortant.

Q+: What is the uni!ersal &otor?

A+: %t runs on either 7$ or A$ current but!aries in s#eed based on the load.

/hese &otors are often found in &i9ers,

hand drills and si&ilar a##liances.

Q: How can &otors be #rotected fro&

o!erheating?A: Cy ther&al relays. /he #ower gets shut

off when any #art of the &otor or

housing o!erheats.

Ca)acit"r%:

Q1: What are ca#acitors used for?A1: /hey are used to i&#ro!e the #ower

factor in a circuit. /his i&#ro!es

efficiency and #erfor&ance.

Q2: How does a ca#acitor wor;?

A2: /he si&#lest ca#acitor is a set of two #lates se#arated by a s&all insulating

layer. $urrent is FstoredG on one #late

and later the entire stored a&ount is

discharged.

Rece)tacle%:

Q1: How should outlets be installed in

residential construction?

A1: 12 ft a#art= all outlets should be three #rong, where the third #rong is

grounded= outlets should not all be onthe sa&e circuit.

Panel6"ar+%:

Q1: What is a #anelboard?A1: %t is a set of fuses or circuit brea;ers

which control the circuit loading in a

building fro& a central #oint.

Q2: How are brea;ers sied?A2: >ach brea;er ser!es a single circuit, and

the o!erload #rotection is based on thesie and currentcarrying ca#acity of the

wiring in that circuit.

'irin:

Q1: '(at i% t(e %&alle%t %i7e "# electrical

$irin t(at %("ul+ 6e u%e+ #"r

6uil+in $irin,

A1: 38 aue.

Q2: '(* (a% alu&inu& $irin #"r %&allae% 98 "r le%%; 6een +i%c"ntinue+,

A2: F"r %a#et* an+ )er#"r&ance rea%"n%.

Q+: '(at i% t(e %tan+ar+ #"r 6ranc(

circuit%,

A+: C"))er $ire.

Q: H"$ are circuit% "2er%i7e+,

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A: B* a6"ut <45 "# t(e ca)acit* $(ic(

#ee+% t(e&.

C"n+uit:

Q1: Why is conduit used?

A1: T" )(*%icall* )r"tect $ire%

Q2: How is conduit sied?

A2: %t is designated by its interior dia&eter./he nu&ber of wires which can fit into

a conduit is s#ecified by code.

Q+: '(at are t(e c(aracteri%tic% "# rii+

c"n+uit,

A+: It i% t(e %a#e%t c"n+uit an+ (a% t(e

%a&e $all t(ic=ne%% a% Sc(e+ule 84

)lu&6in )i)e. All c"nnecti"n% are

rii+ an+ t(rea+e+. It &u%t 6e

al2ani7e+ #"r e>teri"r a))licati"n%.

Q: '(at i% inter&e+iate &etallic c"n+uit

9IMC;,

A: It i% a %teel c"n+uit $it( t(inner $all%

t(an )lu&6in )i)e- le%% e>)en%i2e

an+ a% acce)ta6le a% rii+ c"n+uit.

Q3: '(at i% electrical &etallic tu6in

9EMT; "r t(in $all,

A3: It i% t(e t(inne%t "# t(e %i&)le &etal

c"n+uit%. It i% al2ani7e+- an+

c"nnecti"n% are &a+e $it( a %)ecial

cla&)in %*%te&.

Q6: '(at i% #le>i6le &etal c"n+uit 9"r

?#le>@ "r Green#iel+;,

A6: It i% a2aila6le $it( an+ $it("ut a

#le>i6le $ater)r""# ac=et. It can 6e

u%e+ e2er*$(ere e>ce)t

un+err"un+.

QB: '(at i% interl"c=e+ ar&"re+ ca6le "r

B ca6le,

AB: It i% #act"r* a%%e&6le+ an+ n" $ire%

can 6e a++e+. It cann"t 6e u%e+

un+err"un+ "r e&6e++e+ in

c"ncrete.

QI: '(at i% R"&e>,

AI: %t is an alternati2e t" c"n+uit #"r

re%i+ential c"n%tructi"n an+ c"n%i%t%

"# t$" in%ulate+ li2e $ire% an+ "ne

r"un+ $ire- all enca%e+ in a )la%tic

%(eat(. %t is designated ty#e @D or

@D$ cable. It &a* n"t 6e u%e+ in

c"&&ercial arae% "r 6e e&6e++e+

in c"ncrete.

CALCULATIONS:

Q1: What is the allowed !oltage dro# due to

the resistance of the wire in a gi!en

circuit?A1: %t should not be &ore than +E in

lighting circuits and 3E in circuitssu##orting &otors.

L"a+ E%ti&ati"n:

Q1: How can the o!erall electrical load in a #roJect be esti&ated?

A1: Cy esti&ating the wattage #er s8uare

foot.

SAFETY CONSIDERATIONS:

S("rt Circuit%:

Q1: When does a short circuit occur?

A1: '(en a current #l"$% 6et$een t$"

a+acent c"n+uct"r%.

S(ut"## De2ice%:

Q1: How do fuses wor;?

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A1: /hey are co&#osed of a soft &etal lin;

in a glass #lug or fiber cartridge, whichare rated at a certain current flow.

When the current e9ceeds the rate, the

&etal lin; gets hot and brea;s thecircuit.

Q2: How do circuit brea;ers wor;?A2: /hey disconnect a circuit when the

current is e9cessi!e.

Q+: What is a K'% or K'$%?A+: /he K'% detects a continual current lost

to ground and brea;s the circuit.

Gr"un+in:

Q1: What is grounding?

A1: A ground wire is fastened to an ele&ent

which #ro!ides a directly to the ground,thus dissi#ating the electric current and

a!erting #ossible inJury. Dany

a##liances are housed in &etal casings

which are grounded.

Q2: '(at are t(e c(aracteri%tic% "#

r"un+ $ire%,

A2: T(e* are c"2ere+ $it( reen

in%ulati"n 9"r &a* 6e 6are;.

SERVICES

Q1: What is the ser!ice dro#? What does it

consist of?

A1: All the ser!ices arri!ing on the site. %tconsists of the wires fro& he &ain line,

a transfor&er, a &eter and a disconnect

switch.

Meter%:

Q1: How is the electric usage in a building

&easured?A1: %n residential buildings the total

consu&#tion is &easures in ;wh". %n

larger buildings the #ea; de&and is

&easured as well.

Q2: What is the de&and surcharge?

A2: %t is the charge associated with the #ea;

de&and..

E&erenc* P"$er S"urce%:

Q1: What is e&ergency #ower used for?

A1: %t is used for lighting e9it #assages ande9it signs.

Q2: How is bac;u# #ower #ro!ided?

A2: 'or lights it is often #ro!ided by

batteries that are recharged while #ower is on. A diesel generator is #ro!ided for

larger e8ui#&ent.

BUILDING AUTOMATION

Q1: '(at are %"&e e>a&)le% #"r 6uil+in

c"ntr"l%,

A1: ighting can be controlled by a ti&ecloc; or #hotocell= fire e8ui#&ent can

be auto&atically acti!ated and

controlled.

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als lesson 5

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