Post on 04-Apr-2018
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NATIONAL ELECTRICAL CODE (NEC) AND PHILIPPINES ELECTRICAL CODE (PEC)
RULES AND REGULATIONS ON DIFFERENT WIRING METHODS
I. NON METALLIC RACEWAY OR WOODEN MOLD WIRING
A. Definition
Non metallic raceway or wooden mold wiring is a
wiring method where conductors are installed in a surface
container which lay out along the surface of ceiling and
walls and not concealed (or not hidden).
B. Use
The use of this wiring shall be permitted only in dry
locations (places not affected by rain or moisture). It
shall not be used, however:
1. When or where concealed.
2. Where subject to severe physical damage unless approved
for the purpose.
3. When voltage is more than 300V between conductors.
4. In hoist ways.
5. In hazardous location.
6. Where subject to ambient temperature exceeding 50C.
C. Size of Conductors
No conductor larger than that for which the raceway is
design shall be installed in non metallic surface raceway.
D. Number of Conductors in Raceway
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The number of conductors installed in any raceway
shall be no greater than the number for which the raceway
is designed.
E. Fittings for Taps and Joints
Any junction point requiring joints and taps shall use
porcelain tee or porcelain cross with base. When junction
points come from one direction from top or from below, the
run wire porcelain tee is used. Where taps come from both
direction, porcelain cross is used.
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F. Need for Porcelain Tube or Flexible Circular Loom
Where conductors are entering switches, convenience
outlet, lamp socket, cutout box, and safety switch shall be
protected by circular loom.
If the wire or wires passing through walls porcelain
tube or circular loom may be used. Where circular loom or
mica tube is used at the end of the wooden mold or raceway
a V cut or M cut must be made the molding end.
G. Wall Switch, Convenience Outlet and Lamp Holder
Wall switch and convenience outlet used must be of the
surface type. In case of the wall switch is must be mounted
on a switch base when installed. The lamp holder used must
be of the cleat type.
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II. OPEN WIRING OR INSULATOR OR EXPOSED KNOB AND TUBE WIRING
A. Definition
Open wiring or insulators is a wiring method usingknob tubes, cleats and flexible tubing for the protection
and support of insulated conductors run is and on building
and not concealed by the building structure.
B. Use
1. The wiring method may be used for or outside the
building.
a. Exposed work, either inside or outside the building.
b. In wet or dry location
c. When subject to corrosive
2. This wiring method, however shall not be used
a. Commercial garage
b. In theater or movie houses
c. In motion picture studios
d. In hazardous location
C. Conductors
Any conductors shall be insulated. Only single
conductor may be used on a knob (split or solid) or tubing
hence conductor such as TW, THW, RW, RHW, etc. are
permitted.
In figuring the ampacities (meaning current carrying
capacity of wire) allowed, the table for copper or aluminum
conductor must be consulted.
D. Supports
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1. Conductor must be separated or must not take contact with
any object over than its insulating supports. The
supports shall be non combustible and non absorptive.
a. Under ordinary conditions and conductor support shall
not be more than 4 feet apart or closer as the
condition warrants.
b. Conductors of number 8 or larger that are installed
across open space where they are not liable to be
disturbed may have the support spaced is feet apart.
However, non combustible, non absorptive support
shall be speed at interval not to exceed 4 feet apart
and a minimum spacing of 2 inch between conductors.
c. In buildings of mill constructions where feeders of
number 8 or longer are used and a minimum spacing 6
between conductors maintained the conductors may be
supported at the timbers only.
2. Exceptions:
a. Approved flexible non metallic tubing may be used to
cover the conductor in a continuous length not to
exceed is 15feet when not exposed to physical damaged
and in a dry location and shall be secured by straps
not more than 4 feet apart.
b. Conductors of number 8 or larger that are installedacross open spaced wire. They are not liable to be
disturbed may have the support spaced is feet apart.
However, non combustible, non absorptive support
shall be speed at interval not to exceed 4 feet apart
and a minimum spacing of 2 inch between conductors.
c. In buildings of mill constructions where feeders of
number 8 or larger are used and a minimum spacing of
6 between conductors maintained the conductors may be
supported at the timbers only.
E. Conductor Separation
1. For voltage not exceeding 300V between conductors
a. A minimum of 2 inches separation between conductors.
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J. Protection from Physical Damage
Open conductors exposed to physical damage they shall
be separated by any of the following:
a. By guard strip not less than inch in thickness and as
high as the insulating support place on each side.
b. By substantial running board at least inch thick or by
wooden molds.
c. By metal strips or metal mold.
d. By conduit pipe in continuous length.
K. Entering Spaces Subject to Dampness
All conductor of open wiring that enter or leave a
damp wet or corrosive space shall have drip loops and the
tube entering the walls shall be non combustible and non
absorptive mounted on a slope so that the moisture will
not enter other parts of the building.
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III. CONCEALED KNOB AND TUBE WIRING
A. Definition
Concealed knob and tube wiring is a wiring methodusing knobs, tube and flexible non metallic tubing for
the protection and support of insulated conductor concealed
or hidden in hallow spaces of walls and ceilings of
buildings.
B. Use
This type of wiring shall be use in hallow spaces of
walls and ceilings it shall not be use in:
1. The commercial garage
2. Theaters
3. Motion picture studios
4. Hazardous location
C. Conductors
The same provision as that in open wiring or
insulator.
D. Supports
The same provision as that in open wiring or
insulator.
E. Conductive Separation
a. Conductor shall be separated at least 3 and maintained
at least 1 from the surface wired over.
b. At distributing center outlets, switches or other places
where spaces are limited each conductor shall be encased
in a continuous length of flexible tubing.
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F. Separation from Other Objects and Protections
The same provision as that in open wiring or
insulator.
G. Boxes of Insulating Materials
The use of non metallic boxes is permitted. Provided
that the conductors are supplied with in 8 inches of the
box.
H. Switches
The same provision as that in open wiring or
insulator.
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IV. METAL MOLD OR SURFACE METAL RACEWAYS
A. Definition
Surface metal raceways provide in wiring method thathas many advantages. This wiring method not intended for
new construction, but is quite valuable in additions to
existing wiring systems that must be expanded without
cutting into the existing building to add conduit and other
component surface metal raceway have been use for many
years and have been found quite satisfactory for the
purpose for which they are intended.
B. Use
Surface metal raceways may be installed in dry
location in most any case except the following:
1. Where concealed except that it may be used for under
paster extensions when approved for that purpose.
2. Where exposed to severe physical damage unless approved
for that purpose.
3. Where the voltage between conductors exceed 300V.
4. Where subject to corrosive vapors.
5. In hoist ways.
6. In hazardous areas.
C. Grounding Metal Enclosures
Metal raceways, boxes, cabinets and fittings shall be
grounded.
D. Electrical Continuity of Metal Raceways Enclosures
Metal raceways or metal enclosures for conductors
shall be metallically joined together into a continuous
electrical conductor.
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E. Secured Place
All raceways, boxes, cabinets and fittings shall be
securely fastened in place with approved screws.
F. Mechanical Continuity of Raceways and Conductors
Raceways and other assemblies shall be continuous from
outlet to outlet and from fitting conductors shall be
continuous between outlet and devices. No splices shall be
permitted in raceways.
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V. ARMORED CABLE OR BX WIRING
A. Definition
Armored cable wiring is a wiring method using afabricated assembly of insulated conductors in a flexible
metallic enclosure.
B. Use
Armored cable wiring may be use in the following:
1. For dry location
2. Under plastic extensions
3. Embedded in plaster finish
4. Embedded in brief or other masonry except in wet or damp
location.
5. May be run or fish in air void, of masonry block of the
walls that are not exposed to moisture or dampness are
below grade lines.
6. In damp places and where exposed to oil or other
conditions that might deteriorate the insulation if thearmored cable is of the ACL type (lead - covered)
Armored Cable may not be use in:
1. Theaters
2. Motion pictures studios
3. Any hazardous locations
4. Crane or hoists
5. Storage battery rooms
6. Where exposed to corrosive vapors
7. To hoist ways of elevators
8. Commercial garage
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C. Types
There are numbers of types of armored cable such as
type AC, type ACL, type ACI, etc.
Armored cables are for branch circuits. This cable are
made of flexible metal type but an internal strips of
bonding composed of copper or aluminum shall be continue
throughout the length and
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D. Conductors
The insulated conductors shall be of the following
types:
1. Rubber
2. Thermoplastic
3. Varnished cloth
4. Asbestos varnished cloth
5. Special type approved for the purpose
E. Supports
All supports for armored cable must be of the approved
type and must be installed so as not to damage the cable.
Armored cable shall be secured at interval not to
exceed 4 feet and within 12 may be extended to not over
24 at terminal where there is a necessity for flexibility.
F. Bends
All bends are to be made so as not to damage the
cable.
The bend radius shall not be less than 5 times the
diameter of the cable.
G. Electrical Continuity of Armored Cable and Enclosures
The armor of armored cable shall be metallically
joined together into a continuous electrical conductor. The
armor covering shall be securely and effectively connected
to boxes fittings and cabinets locknuts and connectors
supply this continuity.
H. Mechanically Continuity of Armored Cable
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D. Wet Locations
All supports volts straps concrete shall be of
corrosion resistant materials or protected against
corrosion by approve corrosion resistant materials. In
exposed work under wet or damp location it is required that
a air space between the conduit system (including boxes
and fittings and the surface wired over).
E. Minimum Sizes
For practical purposes inch trade size rigid conduit
is the smallest allowable however for under plaster
extensions conduit with a minimum inside diameter of 5/16
is permitted in some cases.
F. Number of Conductors in Conduit
A table for a minimum number of conductors in table
sizes of conduit shall be consulted. Example is given below:
Wire
Type
Conductors
Size
1/2 3/4 1 1/4 2 2
TW,
THW
14 9 15 25 44 99 142
RW,
RHW
10
12
8
7
5
2
12
9
4
19
15
7
35
26
12
78
60
28
111
85
40
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VII. Non Metallic Sheated or Loomex Cable Wiring
A. Definition
Non metallic sheated, which is commonly termed asloomex cable is a factory assembly of two or more insulated
conductors having an outer sheat or moisture resistance,
flame retardant or sometimes corrosion resistant, non
metallic material.
B. Use
This type of wiring either for exposed or concealed
wiring it maybe regarded as a substitute for open wiring on
insulator or exposed knob and tube work, and has the
advantages that continuous protection is provided over the
entire length of the conductor. In addition to the
insulation supplied to ordinary thermoplastic were in the
case of armored cable no insulating supports are required
and only one hole need be bared when the cable passes
through a timber.
Insulating bushing or grommets shall be used where the
cable passes through holes in metal part or similar members.
C. Types
Non metallic sheated cable are manufacture in the
following types, type NM which has an overall covering of
the flame retardant materials and the type NMC which has an
overall covering of flame retardant, moisture resistance,
fungus resistant and corrosion resistant materials.
Both types are emitted to be used in one and two
familiar dwelling and other structure exceeding three
floors.
Type NM, non metallic sheated cables are permitted
to be installed for exposed and concealed work in normally
dry location. It is also permissible to be ferned in air
voids, in masonry blocks on tiles, walls where such walls
are not expose on suggested to excessive moisture or
dampness. This cable (type NM) shall not be installed in
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Both types however shall not be use at
1. Service entrance cable
2. In commercial garage
3. In theaters
4. Motion picture studios
5. Hoist ways
6. Hazardous location
7. Embedded in poured cement or concrete
D. Supports
Non metallic sheated cable shall be seaved by wire
staple strap or similar fittings so designed and installed
as not to injured, the cable shall be secured in place at
interval not exceeding 4ft. and within 12 from every
cabinet, box or fittings.
E. Bends
Bends in cable shall be made so that the protective
covering of the loomex not allowed the cable must be
injured. No bends shall have the radius less than five
times the diameter of the cable.
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RULES AND REGULATION ON SERVICE ENTRANCE INSTALLATION
1. Service conditions supplying a building or other structureshall not pass through the other interior or another
building.
2. Service conductors shall normally with stand exposure to
atmospheric and other condition of use without deter mental
lockage of current.
3. Ungrounded conductors of service entrance for limited loads
of a single branch ckt. shall be number 12 or number 1 but
it is no case smaller than the branch ckt. conductors.
4. Service entrance conductor shall not have be splice.
5. Service raceways or tubing shall be equipped with a rain
tight or weather head.
6. Drip loops shall be formed on end service entrance
conductor to prevent entrance of water and moisture.
7. Any service entrance raceway tubing or cable shall
terminate at the
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RULES AND REGULATION ON SERVICE, SWITCH FEEDER AND DISTRIBUTION
BOARD INSTALATION
1. Conductors and bus bars on a distribution board shall be located
as to be free from physical damage and shall be held firmly in
place.
2.The arrangement of bus bars and conductors shall be such as to
avoid over heating due to inductive effect.
3.Feeder conductor shall have an ampacity not lower than required
to apply the load.
4.Feeder conductor shall not be smaller than number 10 where the
load supplies consist of the following number and types of
circuit
a. Two or more two wire branch circuit supplied by a two wire
feeder.
b. More than two wire branch ckt. supplied by three wire feeder.
c. Two or more three wire branch ckt. supplied by three wire
feeders.
5. Feeder conductors ampacity shall not be lower than that of
the service entrance conductor.
6. Service switch, containing the main protective devices such
as fuse or circuit breaker must be installed as near as
possible to the point of entrance.
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