Basic Electrical
Basic Electrical
and
and
Safety Precautions
Safety Precautions
Prepared by: Prepared by: Engr.Objectives
Objectives
Be familiar it! t!e fundamentalBe familiar it! t!e fundamental
concepts of electricity. concepts of electricity.
Be familiar it! t!e effects ofBe familiar it! t!e effects of
electricity on t!e !uman body. electricity on t!e !uman body.
Be able to recogni"e commonBe able to recogni"e common
electrical !a"ards electrical !a"ards..
Be familiar it! electrical protectiveBe familiar it! electrical protective
devices. devices.
#$%&OD'(%#O$
#$%&OD'(%#O$
Electrical %e
Electrical %ermrminologyinology
(urrent )
(urrent ) t!e movt!e movement of ement of electrical c!argeelectrical c!arge &esistance ) opposition to current flo
&esistance ) opposition to current flo *o
*oltage ) a measure of ltage ) a measure of electrical forceelectrical force (onductors )
(onductors ) substances+ suc! as metals+ t!atsubstances+ suc! as metals+ t!at !av
!ave little resie little resistance to electricitystance to electricity
#nsulators ) substances+ suc! as ood+ rubber+ #nsulators ) substances+ suc! as ood+ rubber+ glass+ and ba,elite+ t!at !ave !ig! resistance glass+ and ba,elite+ t!at !ave !ig! resistance to electricity
to electricity
Grounding ) a conductive connection to t!e Grounding ) a conductive connection to t!e eart!
(oncept of Electricity
Voltage
- electrical pressure (water pressure) Amperage
- electrical flow rate (gallons/min)
Impedance
- restriction to electrical flow (pipe friction)
(oncept of Electricity
%o flo electricity must !ave a complete
pat!.
Electricity flos t!roug! conductors
• ater+ metal+ t!e !uman body
#nsulators are non-conductors
E = Voltage (volts)
R = Resistance (ohms)
E
I R
O!ms /a
I = Current (amperes)
Electricity isnt live until current flos
Electrical current ont flo until t!ere is
a complete loop+ out from and bac, to t!e poer source.
0o electricity or,s
(urrent flos from a generating
source t!roug! conductors+ to a load
(omplete
circuits are needed
0o electricity or,s
$ormal route is t!roug!
conductors
S!oc, occurs
!en t!e body becomes a
part of t!e electrical circuit
Service E2uipment
%!e necessary e2uipment+ usually consisting of a circuit brea,er3s4 or sitc!3es4 and fuse3s4 and
t!eir accessories+ connected to t!e load end of t!e of service conductors to a building or ot!er
structure+ or an ot!erise designated area+ and intended to constitute t!e main control and cutoff of t!e supply.
/ocation of Disconnecting
Means
Electrical Protective Devices
%!ese devices s!ut off electricity floin t!e event of an overload or ground-fault in t!e circuit
#nclude fuses+ circuit brea,ers+ and
ground-fault circuit-interrupters 3G6(#s4 6uses and circuit brea,ers are
overcurrent devices
• 1!en t!ere is too muc! current: – 6uses melt
(ircuit protective
devices
(ircuit protective devices include:
• fuses and circuit brea,ers
-protect conductors and e2uipment
• G6(#s - limit or s!ut off current
• Provided to protect E7'#PME$% not people
• Do not reset brea,ers it! a line
voltage !ig!er t!an 89* and only reset if you ,no !y it tripped
/ocation of (ircuit
Brea,ers
Ground fault circuit
interrupters
; fast-acting circuit brea,er t!at
senses small imbalances in t!e
circuit caused by current lea,age to ground
#f a ground fault rated <m; above is
detected t!e G6(# can s!ut off
electricity flo in as little as 8=> of a second+ protecting you from a
Permissible 'ses of 6le5ible
(ords
E5amples
Pendant, or Fixture Wiring Portable lamp, tool or applian!e Stationar" e#uipment$ to %a!ilitate inter!hange'se of 6le5ible (ords
• • • • • More *ulnerable t!an fi5ed iring
Do not use if a proper iring met!od can be used instead
6le5ible cords can be damaged by:
;ging
Edges of doors+ indos+ e2uipment frames
Staples or fastenings
;brasion from nearby materials 3roc,s+ t!e ground+ ot!er mac!inery4
;ctivities in t!e area
ro
e
ses
o
e5
e
(ords
E5amples
Subtitute %or %ixed &iring
Run through &all, !eiling, %loor,
door, or &indo&
'on!ealed behind or atta!hed to
(lues t!at Electrical 0a"ards
E5ist
%ripped circuit brea,ers or blon
fuses
1arm tools+ ires+ cords+
connections+ or junction bo5es G6(# t!at s!uts off a circuit
1orn or frayed insulation around
%amper ) &esistant &eceptacles
#nsertion of n object in ny one side does not open t!e s!utter 3left4+ but
to-bl ded plug or grounding plug compresses t!e Spring nd simult neously opens bot! s!utters 3rig!t4
Grounding
1!y Electrical Grounding and Bonding?
%!e most controversial and misunderstood concepts in t!e (ode.
%!e most neglected subject by electrical practitioners.
1!en improperly installed+ it may results to p!ysical injuries+ costly damage to electrical facilities or even deat! to individual.
Eac! utility 3poer+ telep!one+ cable %*4 !as its on grounding electrodes.
Electrical Grounding and Bonding circuit follos t!e basic las of electricity.
Grounding
Protects you from electrical s!oc,
Safeguards
against fire
Protects electrical e2uipment
Grounding
Grounding
%o %o types of types of grogrounding inclunding include:ude:
•
• Service or systemService or system ground
ground
•
Grounded conductor ) a system or circuitGrounded conductor ) a system or circuit
conductor t!at is intentionally grounded. conductor t!at is intentionally grounded.
Grounding (onductor ) a conductor used Grounding (onductor ) a conductor used
to connect e2uipment or t!e grounded to connect e2uipment or t!e grounded circuit of
circuit of a iring system to a groundinga iring system to a grounding electrode
electrode conductor.conductor.
!
! t t is is t!e t!e difdifferference betence beteeneen groun
groun ded ded conductor conductor nd nd grougrou ndingnding conductor?
Definition of Grounded (onductor
Definition of Grounded (onductor
Definition of Grounding
Definition of Grounding
(onductor
Grounded (onductor
#dentifying Grounded $eutral
Proper iring St rts it! t!e &ig!t (olor 'sed in (ond uctor 1iring
Grounding Electrode for
0ig! *oltage
Electrical
Grounding
6our Main %ypes of
Electrical #njuries
• Electrocution 3deat! due to electrical s!oc,4
• Electrical s!oc, • Burns
od! Area
"#$%
&r! %'in
*
+et %'in
,*
Internal "rgans -
Ear to Ear
,
0uman &esistance
. Volts
,* "#$ = . amps (. mA)
. Volts
, "#$ = . amps (. mA)
,-0 mA = shoc'* not painful 0-,. mA = 1ain
,.-2 mA = $uscle contraction
2-, mA = %evere pain 3 paral!sis of 4reathing muscles
,-, mA = Ventricular fi4rillation (5suall! cause death) 6 ,* mA = #eart stops
Electricitys
P!ysiological Effect
.8 amps .8< amps .9 amps .8 8.9 8<. Barely felt “let go” threshold Muscular paralysis Ventricular fibrillation 100 Watt light bulb
Dangers of Electrical
S!oc,
(urrents greater t!an @<
m;A can cause ventricular fibrillation 3rapid+
ineffective !eartbeat4
1ill cause deat! in a fe
minutes unless a
defibrillator is used
@< m; is not muc! current
) a small poer drill uses times as muc!
- m. / milliampere / 101,+++ o% an ampere
Electrical Burns
Most common s!oc,-related+ nonfatal injury Occurs !en you touc!
electrical iring or e2uipment t!at is improperly used or maintained
%ypically occurs on t!e !ands
*ery serious injury t!at needs immediate
6alls
Electric s!oc, can also cause indirect or secondary injuries 1or,ers in elevated locations !o0o is an electrical s!oc,
received?
1!en to ires !ave different potential
differences 3voltages4+ current ill flo if t!ey are connected toget!er
• #n most !ouse!old iring+ t!e blac, ires are at 88 volts relative to
ground
• %!e !ite ires are at "ero volts
because t!ey are connected to ground
#f you come into contact it! an
energi"ed 3live4 blac, ire+ and you are also in contact it! t!e !ite grounded ire+ current ill pass t!roug! your body and CO' 1#// &E(E#*E ; S0O(
0o is an electrical s!oc,
received?
3contd4
#f you are in contact it! an energi"ed ire or any energi"ed electrical
component+ and also it! any grounded object+ CO' 1#// &E(E#*E ; S0O(
Cou can even receive a s!oc, !en you are not in contact it! a ground
• #f you contact bot! ires of a 9>-volt
cable+ CO' 1#// &E(E#*E ; S0O( and possibly be electrocuted
Overload 0a"ards
#f too many devices are plugged into a circuit+ t!e current ill !eat t!e ires to a very !ig! temperature+
!ic! may cause a fire #f t!e ire insulation
melts+ arcing may
occur and cause a fire in t!e area !ere t!e overload e5ists+ even inside a all
Over!ead Poerline
0a"ards
Most people dont reali"e t!at over!ead poerlines are usually not insulated Poerline or,ers need
special training and personal protective
e2uipment 3PPE4 to or, safely
Do not use metal ladders ) instead+ use fiberglass
ladders
Beare of poerlines !en you or, it!
Grounding Pat!
%!e pat! to ground from circuits+
e2uipment+ and
enclosures must be permanent and
continuous
*iolation s!on !ere is an e5tension cord it! a missing
Guarding of /ive Parts
Must guard live parts of
electric e2uipment operating at < volts or more against accidental contact by:
• ;pproved
cabinets=enclosures+ or
• /ocation or permanent partitions ma,ing t!em
accessible only to 2ualified persons+ or
• Elevation of ft. or more above t!e floor or or,ing surface
Guarding of /ive Parts
Must enclose or guard electric e2uipment in locations !ere it
ould be e5posed to p!ysical damage
*iolation s!on !ere is p!ysical damage to
(abinets+ Bo5es+ and
6ittings
Function bo5es+ pull
bo5es and fittings must !ave approved covers
'nused openings in
cabinets+ bo5es and
fittings must be closed 3no missing ,noc,outs4
P!oto s!os violations
of t!ese to re2uirements
%!e ;EG( program is an
inspection program covering:
• all cord sets
• receptacles t!at are not part of a
permanent iring structure
• e2uipment connected by cord and
plug
;ssured E2uipment
Grounding (onductor
program
E2uipment must be visually
inspected for damage=defects before eac! days use
;ssured E2uipment
Grounding (onductor
program
%ests must be performed:
• before t!e first use of ne
e2uipment
• after suspected damage to
e2uipment
• at t!ree mont! intervals
– continuity test
– grounding conductor test
;ssured E2uipment
Grounding (onductor
program
/oc,out=%agout
Electrical e2uipment
deactivated for repair must be loc,ed out and tagged at t!e
point !ere it can be energi"ed
Protects maintenance or,ers
1arns ot!ers t!at or, is being
/oc,out=%agout
Only t!e person !o
loc,ed=tagged t!e e2uipment can turn it bac, on
Before e2uipment is energi"ed+ a 2ualified person must conduct tests and visual inspections
/oc,out=%agout
Eac! loc,=tag must be removed
/oc,out=%agout
#f t!e employee is absent+ t!e loc,=tag can be removed by a 2ualified person if:
• t!e employee !o applied t!e loc,
!as left t!e premises
• it is visually determined t!at all employees are clear of t!e
Guarding re2uirements
;ny live parts of electrical
e2uipment operating at < volts or more must be guarded to
Guarding re2uirements
Entrances to areas it! live
electrical parts must be mar,ed it! arning signs
Signs s!ould
forbid entrance e5cept by
#nsulation
(!ec, e2uipment daily for
insulation brea,don (!ec, for:
• e5posed ires
• bro,en ires
• scuffed insulation on e5tension
Dos and
Donts
Dos and
Donts
lug poer e2uipment into all
receptacles it! poer sitc!es in t!e Off position.
unplug electrical e2uipment by
grasping t!e plug and pulling. Do not pull or jer, t!e cord to unplug t!e
e2uipment.
Do not drape poer cords over !ot
Dos and
Donts
Dos and
Donts
Do c!ec, t!e receptacle for
missing or damaged parts.
Do not plug e2uipment into
defective receptacles.
Do c!ec, for frayed+ crac,ed+ or e5posed iring on e2uipment
c!ec, for defective cords clamps
at locations !ere t!e poer cord enters t!e e2uipment or t!e
attac!ment plug.
E5tension cords s!ould not be used
in office areas. Generally+ e5tension cords s!ould be limited to use by
maintenance personnel
Dos and
Donts
Dos and
Donts
Dos and
Donts
Dos and
Donts
H(!eater plugsI+ e5tension
cords it! junction bo5
receptacle ends or ot!er injury-rigged e2uipment s!ould not be used.
Dos and
Donts
Dos and
Donts
(onsumer electrical e2uipment
or appliances s!ould not be
used if not properly grounded. 3/oo, for t!e '/ /abel4
Employees s!ould ,no t!e location of electrical circuit brea,er panels t!at control
e2uipment and lig!ting in t!eir respective areas. (ircuits and
e2uipment disconnects must be identified
Dos and
Donts
Dos and
Donts
Dos and
Donts
Dos and
Donts
%emporary or permanent storage of
any materials must not be alloed it!in feet of any electrical panel or electrical e2uipment.
;ny electrical e2uipment causing
s!oc,s or it! !ig! lea,age
potential must be tagged it! a Danger tag or e2uivalent.
Myt!s and
Misconceptions Myt!s and
Misconceptions
Electricity ta,es t!e pat! of least
resistance.
Electricity ants to go to ground.
#f an electric tools falls into a sin, or
Myt!s and
Misconceptions
Myt!s and
Misconceptions
;( reverse polarity is not !a"ardous.
#t ta,es !ig! voltage to ,illJ 89 volts is not dangerous.
Double insulated poer tools
are doubly safe and can be used in et and damp locations.
#nsulation
'se non-conducting mats+
s!ields+ or barriers !en necessary
'se
non-conducting coatings on !and tools
Personal protective
e2uipment
Employers must provide
electrical protective e2uipment to employees
!o or, near electrical
Personal protective
e2uipment
'se appropriate e2uipment for
t!e !a"ards+ including:
• !elmets
• eye and face
protection
• gloves and
sleeves
• aprons