HOUSING PIH-110
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Electrical Wiring for Swine Buildings
Authors:
Eldridge R. Collins, Jr., Virginia Polytechnic
Institute and State University
Gerald R. Bodman, University of Nebraska
LaVerne E. Stetson, USDA-ARS, Lincoln, Nebraska
Reviewers:
R.F. Espenschied, University of Illinois
Larry D. Jacobson, University of Minnesota
Vernon M. Meyer, Iowa State University
Proper design and installation of swine facility electrical
systems is crucial to using electricity efficiently, providing
safety for workers and animals, and minimizing potential fire
loss. A majority of all farm fire losses are related to electri-
cal system failure (Figure 1). Many wiring practices that are
acceptable for use in our homes are unsafe when used in livestock
housing because of exposure to dust, moisture, corrosive gases,
and physical damage. Inferior wiring causes hazardous conditions
for livestock and humans, expense of early rewiring of many
buildings, and possible fires. The losses from burning of even a
fully insured building can be disastrous; there may be months of
production loss before new buildings can be constructed and
animals phased back into production, and years of genetic herd
improvement can be forever lost. Even when fires do not occur,
poor wiring may contribute to higher maintenance costs because of
overheated motors and equipment and can result in costly
failures. The mere fact that a system ``works'' doesn't speak for
its safety. Special wiring methods and components are needed for
swine structures.
The guidelines given in this fact sheet will aid you in
evaluating potential wiring problems in an existing swine build-
ing, or in ensuring that a new building is wired to reduce danger
of wiring failure and fire loss. This leaflet does not provide
all information necessary to properly design and install an
electrical wiring system, nor does it describe all specialty dev-
ices, mechanical protection, and special requirements for feed
handling and grain storage facilities with severe dust problems.
For these you should consult with a qualified electrician having
training, experience, and knowledge of the National Electrical
CodeO (NEC) as well as understanding of importance of following
accepted proper wiring practices. Assistance is often available
from your power supplier in planning and installing the distribu-
tion system to your building. By being familiar with some of the
special problems and requirements of swine buildings, you can
better advise your electrician how you want your building wired;
and, you will be able to assure that the job is done so that it
will stand up to the harsh swine building environment. Some com-
panies will not insure buildings wired by older commonly-used
methods. Check with your insurance company before beginning con-
struction to determine their requirements.
WIRING STANDARDS
The standard for electrical work in the United States is the
National Electrical CodeO published by the National Fire Protec-
tion Association. The NEC is a guide to selection and safe ins-
tallation of proper materials. The NEC has become law in many
states, but there is often limited inspection or enforcement in
rural areas. In other states, agricultural structures are
exempted from national, state, or local codes, so NEC practices
are often not followed. Nevertheless, the NEC provides a minimum
standard (Article 547) for wiring swine buildings or other damp
corrosive environments. Good practices often go beyond the bare
minimum of the NEC to minimize fire hazards and reduce future
maintenance problems. Because of the potential impact a fire loss
can have on your total swine enterprise, it is in your best
interest to see that all wiring meets or exceeds the minimum
standard. The lowest priced electrical system is seldom the most
economical.
FARM BUILDING REQUIREMENTS
Dry farm buildings generally do not require special wiring
materials or procedures. Such structures include garages
(detached from houses), machine sheds, shops, and similar build-
ings. These buildings may normally be wired with the same materi-
als commonly used in residences and in accordance with standard
procedures and practices of the NEC.
Dust-ignition-proof wiring systems should be used in
extremely dusty feed processing areas. However, most small feed-
grain handling centers are not classified as areas requiring
dust-ignition-proof wiring and should be wired like swine struc-
tures described below.
Open and enclosed swine housing structures and other build-
ings that are washed periodically should be considered damp and
corrosive atmospheres. Ammonia, hydrogen sulfide, and other cor-
rosive gases, in combination with moisture and dust, hasten
deterioration of electrical components. Many existing swine
buildings have been wired using practices and materials that can-
not withstand these conditions. Many older buildings, including
those constructed since 1960, have electrical systems that have
deteriorated to the point of danger. The following discussion
will focus on practices that reduce electrical system deteriora-
tion and its associated fire hazard, and foster efficient and
safe use of electricity.
MATERIALS FOR WIRING
Equipment and methods necessary to meet the special require-
ments of swine housing are different from residential wiring.
Therefore, you will need to plan ahead. Many of the materials may
be available only from wholesale electrical supply houses. Use
materials of at least 20 ampere (A) rating. All materials and
equipment should bear a seal indicating they are listed by Under-
writers' Laboratories (UL), or by some other recognized testing
laboratory.
Cable and Conduit
Either type UF cable or conduit (Figure 2) can be used for
wiring circuits in swine buildings. All wiring should be attached
to interior surfaces of the building and not concealed within
wall cavities, ceilings, or attic spaces. Surface mounting elim-
inates the need to make holes in the continuous vapor barrier,
thus reducing the risk of warm, moist room air moving into wall
or ceiling cavities and attics with resulting condensation. Sur-
face mounting also reduces the risk of rodent damage and allows
periodic inspection and repair.
Damage more serious than simple wet insulation may occur
when electrical wiring is involved. Electrical boxes recessed in
walls or ceilings will be cold during winter, thus becoming
``condensation boxes.'' As a result, switches, wire junctions,
duplex outlets, and circuit breakers will corrode rapidly which
may result in a short-circuit. When cables or conduits are
extended into cold wall cavities or ceiling and attic spaces,
condensation follows the cable or conduit (by draining or wick-
ing) into electrical fixtures and boxes. When this occurs, corro-
sion and circuit resistancewith associated overheating of wiring
or equipmentare greatly increased. Cables and conductors with
nonwaterproof covering can also lead to current leakage through
the insulation, which may cause problems with stray voltage and
increased potential for electric shock.
Surface wiring with cable is relatively easy, saves materi-
als and labor, and is generally preferable to conduit except
where subject to physical damage. Type UF cable is recommended
because it is moisture resistant and allows use of weatherproof
connectors and fittings at box connections. Do not use Type NM or
NM-B cable in swine buildings.
Install cable where it will be protected from physical dam-
age. Normally it should be installed on flat surfaces of walls
and ceilings. Use nylon or plastic coated staples, or stainless
steel nails and nonmetallic straps at a maximum of 4.5-ft. inter-
vals and within 8 in. of each junction or fixture box. If the
building has exposed joists, beams, or trusses, run cable along
the joist, beam, or truss chord. If it must run perpendicular to
joists or ribs of metal ceiling or wall liners, install cable on
a 1- x 2-in. running board. Sharp bends should be avoided;
minimum bend radius is five times the cable diameter.
Conduit offers an alternative to Type UF cable, especially
where wiring is subject to physical damage or where conduit may
facilitate use of multiconductor control circuits. Otherwise, its
use is discouraged because inadequate sealing will allow entry of
vapor which may condense and contribute to system deterioration.
Rigid Schedule 40 PVC conduit is recommended. Provide extra pro-
tection in areas subject to physical abuse by animals or equip-
ment. PVC conduit is available in 10- and 20-ft. lengths and in
commonly used diameters of 1/2, 3/4, and 1 in. Larger conduit for
large motors or service entrances are also available. Single
strand wire rather than cable is used in conduit. Select wires
with a Type W designation (RHW, THW, THWN, or XHHW). Use a bare
or green insulated copper wire of the same size as line voltage
wires for grounding. All equipment MUST be grounded.
Mount conduit on the surface of interior walls or ceiling.
Conduit (1/2- to 3/4-in. diameter) should be supported at 3-ft.
(maximum) intervals with nonmetallic fasteners. PVC conduit
elbows and offsets are available, or straight conduit can be bent
using a ``hot box'' or hot air blower, but never use an open
flame. Maintain a circular cross-section of the conduit
throughout the bend. No more than the equivalent of four quarter
bends (360 degrees total) may be installed between junction boxes
and/or fittings.
PVC conduit can be cut with a fine-tooth saw or a special
cutter. Ream or file the ends smooth after cutting. Permanent
joints can be made using PVC connectors and solvent weld cement,
or temporary joints can be made using threaded adapters with
rubber washers or O-rings.
Allow for thermal expansion and contraction in each conduit
circuit. Expansion joints are available, but normal expansion is
compensated for by leaving bends unrestrained within 1 ft. of the
radius center.
Install conduit to prevent entry of dust, water, and vapor.
If the conduit must be exposed to widely differing temperatures,
such as where it passes through the outside wall of a heated
building or between two different rooms, the inside of the con-
duit must be sealed where it passes from a warm to a cool area,
using electrician's duct sealer. In this way, moisture in the
warm conduit will be prevented from entering the cold conduit and
condensing.
Use flexible wiring methods for fans and other equipment.
Liquidtight, flexible, nonmetallic conduit with stranded conduc-
tors is one option. The maximum length of liquidtight, flexible
conduit permitted is 6 ft.; thus, careful planning of the overall
electrical system is required. Ordinary bare metal flexible con-
duit is NOT permitted in livestock buildings. Flexible cords with
water and dust proof strain-relief fittings can also be used.
Select cords with a Type S outer covering.
Boxes and Fixtures
Corroded metallic boxes and fixtures often lead to electri-
cal system failure. Despite the higher cost and lack of ready
supply in some areas, molded plastic boxes and other components
are required. Gasketed covers are necessary on all boxes to seal
wire splices, switches, and other electrical contact surfaces
from exposure to dust, moisture, and corrosive gases. Moisture-
proof receptacle boxes with spring-loaded covers are required.
Standard metal boxes with screwed-in-place face plates (Figure 3)
are not permitted. Switches should also be moisture-proof, either
by means of spring-loaded covers, moisture-tight switch levers
(Figure 4), or moisture-tight covers with flexible press
switches. General use switches and controls are cheaper but are
prone to corrosion and early failure. Moisture- and explosion-
proof controls last longer and are safer. Do not use brown Bakel-
iteO fixtures in livestock buildings!
All connections should be moisture- and dust-tight. Where
surface wiring is used, totally nonmetallic cable-to-box connec-
tors are available with tapered hub threads and a neoprene,
rubber, or plastic bushing sized and shaped to fit the cable.
When connected to a box, the bushing is compressed to form a
seal. Select boxes that are made to fit the tapered hub connec-
tors. Moisture- and dust-tight connectors should also be used to
connect conduit to boxes and fixtures.
All cable or conduit should enter electrical boxes from the
side or bottom (Figure 5) if possible. Then, if condensation
occurs in or on the cable or conduit, or water accumulates during
washdown, it will not drain onto electrical contact surfaces or
leak into the box and corrode or short-circuit electrical com-
ponents.
Mount receptacles and light switches where they will be pro-
tected from animals and water. A rule of thumb is to place boxes
at least twice animal height, or at least 4 ft. above the floor
unless extra protection is provided. Provide 6 to 8 in. of wire
at each box to allow easy connections, plus a little extra in
case switches, outlets, or fixtures are later replaced. Avoid
placing boxes, cable, conduit, or fixtures on the ceiling within
6 ft. of ventilation air inlets that direct air across the ceil-
ing; otherwise the devices might deflect cold, fresh air onto
young pigs and chill them.
LIGHTING
Incandescent and fluorescent are the two types of lighting
most common in swine buildings. Each type of fixture has dif-
ferent properties of light output, color, and maintenance which
might make it more suitable for special tasks. However, for most
swine structures the decision between the two types will be based
on cost and service.
Incandescent fixtures have a low initial cost and operate
well in most conditions including low temperatures. Their light
efficiency is low, so it takes more fixtures to provide the
desired lighting level, and they are relatively expensive to
operate. Bulb life is also short, usually about 750 to 800 hr.
for 100 to 150 watt (W) bulbs. Porcelain sockets are mandatory
for heat lamps. Fixtures should be dust- and moisture-resistant
with a heat-resistant globe to cover the light bulb (Figure 2).
Fixture boxes can become quite hot when used with globed fix-
tures. Since the conductors in Type UF cable do not meet the tem-
perature limits for many fixtures, UF cable should not be
extended directly into globed fixture boxes. The safe way to
avoid wire insulation failure from heat buildup is to install a
junction box near the fixture and extend conduit and type SFF-1
conductors into the fixture box.
Fluorescent fixtures cost more than incandescents but pro-
duce 3 to 4 times more light per watt of electricity. If fluores-
cents are turned on and off frequently (less than a 10-minute
burn cycle), lamp life will be reduced; incandescents would be a
better choice for such use. But if light will be on for a long
time between switching, fluorescents provide higher efficiency.
Lamp life ranges from 7,500 hr. for short use cycles to 20,000
hr. for long use cycles. Fluorescents are best used indoors,
since standard units do not perform well below 50o F without spe-
cial ballasts. They are also more sensitive to relative humidity
higher than 65%. Because of the damp, corrosive conditions normal
in swine housing, fixtures should be nonmetallic with gasketed
enclosures over bulbs. Units designed and listed for mildly cor-
rosive industrial environments do well in swine housing. Heat
buildup is less of a problem in fluorescent lighting fixtures.
While not acceptable for incandescent lighting, type UF cable can
be extended directly into fluorescent fixtures if the conductors
are kept away from the ballast.
Provide enough light so inspection and work can be done
efficiently. Each room should have at least two lighting cir-
cuits; two rows of lights on separate switches will provide two
levels of lighting intensity. If ceiling and wall surfaces are
light, no reflectors are needed. However, if surfaces are dark,
provide reflectors. A guideline for light placement in swine
housing is to provide one row of lights over each row of pens or
stalls, and one row along the feed alley. At least one light
should be installed over every other pen partition. Table 1
recommends the amount of lighting for various building purposes.
For example, a 24-ft. wide nursery could be illuminated to 10
foot-candles with (0.28 x 24 x 1) = 6.72 watts (W) of fluorescent
lighting/ft. of room length, or (1.00 x 24 x 1) = 24 W of 150 W
incandescent lighting/ft. of room length. For a 25-ft. long room,
this would mean at least one double-tube 40-W fluorescent fix-
ture, or two single-tube fixtures (6.72 W/ft. of room length
times 25 ft. of length) on each side of the room, or two 150-W
incandescent fixtures (24 W/ft. of room length times 25 ft. of
length) on each side. For wider buildings, you may want to con-
sider additional rows of lighting. Observe wattage limitations on
incandescent bulb fixtures. Many of them have 60- or 75-watt lim-
itations.
Table 1. Light level for swine buildings.*
___________________________________________________________________
Standard
Foot-candle cool white Standard
illumination fluorescent incandescent
________________
Building level 40 W 100 W 150 W
___________________________________________________________________
Watt/sq. ft. of building area
Farrowing 15 0.42 1.72 1.50
Nursery 10 0.28 1.15 1.00
Growing/finishing 5 0.14 0.58 0.50
Breeding/gestation 15 0.42 1.72 1.50
Animal inspection/handling 20 0.55 2.29 2.00
Office 50 1.38 5.72 5.00
Feed storage/processing 10 0.28 1.15 1.00
___________________________________________________________________
* Space lighting uniformly.
Values assume monthly bulb cleaning and regular bulb replacement.
For infrequent cleaning, increase table values 40%.
Assumed 8-ft. ceiling height and 50% wall and 70% ceiling reflec-
tance.
Values based on ASAE Farm Lighting Design Guide, SP-0175.
CIRCUITS
Have an electrician or other knowledgeable person calculate
circuit sizes because of the special heavy uses of electricity in
hog buildings (heat lamps, portable motors, and other equipment).
Circuits should include both those for general purpose and those
for special equipment. General purpose circuits include lights
and duplex convenience outlets (DCO). Equipment circuits include
those for ventilation fans, heaters, fixed equipment, appliances
over 1,500 W, motors exceeding 1/3 hp., and special purpose
outlets (SPO) for uses such as high pressure washers.
As a guide, a general purpose circuit should be computed
allowing 1.5 A per light fixture or DCO if not used for motors or
heat lamps. Use the actual load value for DCOs and SPOs that sup-
ply motors, heat lamps, floodlights, or other large power users.
Use #12 AWG copper wire (Table 2) and a 20-A circuit breaker for
each 20 A of electrical load. Circuits may not be continuously
loaded to more than 80% of their designed capacity. Where cir-
cuits serve heating lamps, ventilation equipment, or other con-
tinuous or extended use equipment, the 80% load factor is
required by the NEC, so plan the number of circuits accordingly.
If each DCO will be used with heat lamps or other large resis-
tance loads, circuit load should be calculated as follows:
_______________________________________
|Table 2. Maximum current capa- |
|city of copper wire. |
| |
|____________________________________ |
| Ampacity |
| __________________________ |
| Type THW, |
|Wire size THWN, RHW, |
|AWG copperType UF cableand XHHW wire |
|____________________________________ |
| 12 20 20 |
| 10 30 30 |
| 8 40 50 |
| 6 55 65 |
| 4 70 85 |
| 3 85 100 |
| 2 95 115 |
| 1 110 130 |
| 1/0 125 150 |
| 2/0 145 175 |
| 3/0 165 200 |
| 4/0 195 230 |
|____________________________________ |
|_____________________________________|
Amps (A) = Watts (W) : Volts (V),
where
A = current flowing through the conductor
W = total power to be in service on circuit
V = 120 V or 240 V service
Remember, if the circuit will be continuously loaded, such as
with heat lamps, a 20-A circuit should be planned to carry only
16 A (80% of its actual rated load).
Branch circuits with only one motor should be sized for 125%
of the motor full load current rating. For example: for one 8-A
motor on a circuit, 8 x 1.25 = 10 A. If more than one motor will
be on a circuit, rate the largest motor at 125%, and add the oth-
ers at 100% of full load current rating. Additional loads on
this circuit should be added at 100% of their full load current.
General purpose circuits wired with #12 AWG copper wire
should have no more than a 20-A connected load; #14 AWG copper
wire circuits should have no more than a 15-A connected load. New
general purpose circuits smaller than 20-A (#12 AWG, copper)
capacity are not recommended except for specific loads.
Size all conductors based on length of run as well as con-
nected load. Long runs of undersized wire result in wasted
energy and reduced performance of lights and electrical equip-
ment. Branch and feeder circuits should not exceed 2% voltage
drop, and should never be smaller than #12 AWG (copper). Maximum
combined voltage drop for service drops, feeder and branch cir-
cuits should not exceed 5% to the most distant DCO. The relation-
ships between current, circuit length, voltage drop, and wire
size are given in Tables 3 and 4.
Table 3. Minimum copper conductor size for branch circuits using
Type UF cable (based on maximum conductor capacity or 2% voltage
drop, whichever is limiting).
____________________________________|_______________________________
Nominal 120 V service | Nominal 240 V service
AmpereConductor length, ft. (one way)Conductor length, ft. (one way)
______________________________________________________________
load 30 4050 6075 100125 150 175200|5060 75100125 150175200 225250
____________________________________________________________________
American wire gauge | American wire gauge
5 12 1212 1212 12 12 10 10 10|1212 1212 12 12 12 12 12 12
7 12 1212 1212 12 10 10 8 8 |1212 1212 12 12 12 12 10 10
10 12 1212 1210 10 8 8 8 6 |1212 1212 12 10 10 10 10 8
15 12 1210 1010 8 6 6 6 4 |1212 1210 10 10 8 8 8 6
20 12 1010 8 8 6 6 4 4 4 |1212 1010 8 8 8 6 6 6
25 10 10 8 8 6 6 4 4 4 3 |1010 10 8 8 6 6 6 6 4
30 10 8 8 8 6 4 4 4 3 2 |1010 10 8 6 6 6 4 4 4
35 8 8 8 6 6 4 4 3 2 2 |8 8 8 8 6 6 4 4 4 4
40 8 8 6 6 4 4 3 2 2 1 |8 8 8 6 6 4 4 4 4 3
45 6 6 6 6 4 4 3 2 1 1 |6 6 6 6 6 4 4 4 3 3
50 6 6 6 4 4 3 2 1 1 1/0|6 6 6 6 4 4 4 3 3 2
60 4 4 4 4 4 2 1 1 1/02/0|4 4 4 4 4 4 3 2 2 1
70 4 4 4 4 3 2 1 1/0 2/02/0|4 4 4 4 4 3 2 2 1 1
80 3 3 3 3 2 1 1/0 2/0 2/03/0|3 3 3 3 3 2 2 1 1 1/0
90 2 2 2 2 2 1 1/0 2/0 3/03/0|2 2 2 2 2 2 1 1 1/01/0
100 1 1 1 1 1 1/02/0 3/0 3/04/0|1 1 1 1 1 1 1 1/0 1/02/0
____________________________________|_______________________________
Source: Adapted from Agricultural Wiring Handbook, 8th Ed.,
National Food and Energy Council, Inc. 409 Vandiver West, Suite
202, Columbia, MO 65202.
Table 4. Minimum copper conductor size for branch circuits using
Type THW, THWN, RHW, and XHHW wire (based on maximum conductor
capacity or 2% voltage drop, whichever is limiting).
____________________________________|_______________________________
Nominal 120 V service | Nominal 240 V service
AmpereConductor length, ft. (one way)Conductor length, ft. (one way)
______________________________________________________________
load 30 4050 6075 100125 150 175200|5060 75100125 150175200 225250
____________________________________________________________________
American wire gauge | American wire gauge
5 12 1212 1212 12 12 10 10 10|1212 1212 12 12 12 12 12 12
7 12 1212 1212 12 10 10 8 8 |1212 1212 12 12 12 12 12 10
10 12 1212 1210 10 8 8 8 6 |1212 1212 12 10 10 10 10 8
15 12 1210 1010 8 6 6 6 4 |1212 1210 10 10 8 8 8 6
20 12 1010 8 8 6 6 4 4 4 |1212 1010 10 8 8 6 6 6
25 10 10 8 8 6 6 4 4 4 3 |1010 10 8 8 6 6 6 6 4
30 10 8 8 8 6 4 4 4 3 2 |1010 10 8 6 6 6 4 4 4
35 8 8 8 6 6 4 4 3 2 2 |8 8 8 8 6 6 4 4 4 4
40 8 8 6 6 4 4 3 2 2 1 |8 8 8 6 6 4 4 4 4 3
45 8 8 6 6 4 4 3 2 1 1 |8 8 8 6 6 4 4 4 3 3
50 8 6 6 4 4 3 2 1 1 1/0|8 8 6 6 4 4 4 3 3 2
60 6 6 4 4 4 2 1 1 1/02/0|6 6 6 4 4 4 3 2 2 1
70 4 4 4 4 3 2 1 1/0 2/02/0|4 4 4 4 4 3 2 2 1 1
80 4 4 4 3 2 1 1/0 2/0 2/03/0|4 4 4 4 3 2 2 1 1 1/0
90 3 3 3 3 2 1 1/0 2/0 3/03/0|3 3 3 3 3 2 1 1 1/01/0
100 3 3 3 2 1 1/02/0 3/0 3/04/0|3 3 3 3 2 1 1 1/0 1/02/0
____________________________________|_______________________________
Source: Adapted from Agricultural Wiring Handbook, 8th Ed.,
National Food and Energy Council, Inc. 409 Vandiver West, Suite
202, Columbia, MO 65202.
Stationary equipment should be permanently wired into
moisture-proof boxes as described earlier. This will minimize
problems of moisture and dust entering the wiring system.
Suspended appliances, lighting fixtures, and heating equipment
should be provided with mechanical support such as chains and not
suspended by their electrical supply wires, conduit, or cords.
Minimize the use of extension cords.
Circuits servicing high pressure washers must be equipped
with a ground fault interrupter (GFI) device unless a GFI is
built into the washer. Installing a ground rod at the receptacle
is not an allowed practice by itself, though a ground rod may be
used to complement proper wiring techniques.
ELECTRICAL SUPPLY SYSTEM
The electrical supply system is the ``heart'' of the build-
ing electrical system and consists of service conductors from the
power supply, the main disconnect, one or more distribution
panels (DP), and associated equipment. Often the main disconnect
and DP will be in the same panel. Be sure that service conductors
and equipment are large enough to provide electrical capacity for
present and future needs. Minimum supply service for farm build-
ings is 60 A, but most modern buildings require at least 100 A;
your power supplier can help in determining the proper service
supply. An undersized service supply is unsafe and inefficient
and reduces the longevity of the system and equipment.
Where building openings such as doors, hatches, or windows
are used for transfer of materials between the inside and outside
of the building, overhead service conductors must be out of
reach. Portable elevators and other equipment must be maneuver-
able into openings with minimal risk of contacting overhead
wires. Therefore, have the point of attachment of overhead ser-
vice conductors or other wiring no closer than 10 ft. on either
side of the opening, and at least 3 ft. above. Under no cir-
cumstance should the point of attachment be below such openings.
A minimum clearance of 18 ft. should be provided above all drive-
ways. Remember: clearance will decrease in warm weather as ther-
mal expansion causes conductors to sag. Contact of conductors
with equipment can kill!
Each circuit should be protected in the DP with its own fuse
or circuit breaker selected to correspond to the size of the con-
ductors used in the circuit. Do not load circuits to more than
80% of their current-carrying capacity (Table 2). This limitation
is especially important for circuits loaded continually for long
periods of time as with fans or heat lamps. Where fuses are used,
they should be of the Type S kind sized for the current-carrying
capacity of the circuit conductor. Type S fuses prevent the ins-
tallation of a larger capacity fuse when a properly selected fuse
fails.
Location of the DP can affect its rate of deterioration.
Never install a DP recessed into an outside wall. Lack of ade-
quate insulation behind the panel can result in condensation
within the box and rapid corrosion of electrical equipment. Even
surface mounted DPs, if possible, should not be mounted on the
inner surface of an outside wall for the same reason.
Avoid problems by locating the DP outside the dusty, humid,
and corrosive environment of the animal housing. The environment
is less likely to be harsh in an entry hall, office, or utility
room, and the DP could be located there using a NEMA 3R enclosure
with corrosion-resistant finish. If the DP must be located in a
room with animals, use a moisture-tight nonmetallic unit (NEMA 4
or 4X enclosure). For safety and convenience, be sure to provide
at least 3 ft. of open, accessible work space in front of the DP.
The door or cover must be capable of being opened a full 90
degrees.
Where possible, place DPs near the largest electrical loads.
This will minimize requirements for long runs of larger, more
expensive conductors and eliminate energy-wasting voltage drops.
Surface mount DPs on a fire resistant surface such as con-
crete or 26 gauge (minimum thickness) galvanized steel over a
fire-resistant material. Use spacers to provide a gap of at least
1/4 in. between the DP and wall (Figure 6). If overheating does
occur with this installation, the air space will help protect the
combustible wall of the building. The spacing arrangement will
also help maintain the DP at room temperature, reducing the pos-
sibility of condensation, and will eliminate entrapment of mois-
ture, dust, manure, and other corrosive matter.
As noted earlier, service conductors and branch circuit con-
duit or cable should enter at or near the bottom of the main
disconnect or DP. In this way, draining of water and condensate
down the cable or conduit and into the panel can be more easily
avoided.
Where existing DPs have been installed so that condensation
may develop during cold weather, a small amount of heat installed
around, on, or in the DP may help alleviate the problem. If pos-
sible, first install some insulation behind the panel. If the DP
is surface mounted, it may be possible to wrap the perimeter with
a heat tape. Another alternative during cold weather is to mount
a heat lamp in a holder outside the panel directed to warm the
DP. Take care that the bulb is not close enough to wires, walls,
or other materials that it might cause damage or fire.
Since some corrosion may develop on contact surfaces of DP
circuit breakers, a monthly schedule to switch circuit breakers
off and on should be established. This will help wear away minor
amounts of corrosion which may develop at the breaker contact
surface, and which could contribute to electrical resistance and
overheating. Circuit breakers that are not switched off periodi-
cally are frequently found ``frozen'' into the ``on'' position.
In such cases, it is unlikely they would trip under high current
load, so the intended safety feature no longer exists.
GROUNDING
Safety requires two systems of grounding:
1. System groundingthe connection of the ground service con-
ductor through an acceptably sized (based on service capacity)
conductor to an acceptably sized grounding electrode. This
grounding electrode conductor must be connected at the terminal
or bus bar to which the grounded service conductor (commonly
called the ``neutral'') is terminated in the main disconnect.
Grounded conductors carry current during the normal operation of
115-V equipment and must have white or gray insulation or mark-
ing.
2. Equipment groundingthe grounding or bonding of noncurrent
carrying equipment such as motor frames back to the service
entrance panel grounding bar. Failure to provide proper equipment
grounding may contribute to stray voltage problems causing stress
and danger to animals and humans. The NEC requires that grounding
conductors be bare or have a green or green with yellow stripe
insulation. This conductor is designed to carry current ONLY
under fault conditions and is commonly referred to as the
``ground'' wire.
Grounding electrodes are required at all service entrances,
using approved bonding (clamps) properly sized, based on service
capacity. Rods of 8 ft. (minimum) are commonly used, but the NEC
does allow other methods. The grounding conductor from the ser-
vice entrance disconnect to the grounding electrode should be
protected from physical damage and should be continuously main-
tained. Resistance from the grounding electrode to surrounding
soil must be 25 ohms or less. If more than one electrode must be
used to get this resistance, rods should be spaced at least twice
the length of the ground rods and interconnected with a noncorro-
sive conductor and ground rod clamps approved for that purpose.
Use clamps designed and rated for direct burial.
To minimize danger from electrical faults, the NEC requires
all metallic equipment including building components within 8 ft.
of the floor or soil surface to be bonded to the system grounding
electrode through the branch circuit grounding or other appropri-
ate grounding conductors. Although separate grounding rods may be
used in these cases, they must be in addition to and bonded to
the main system electrode. All metallic water lines, gates,
flooring materials, animal crates or pens and similar equipment
must be bonded together and to the electrical system grounding
electrode.
All new wiring should include equipment grounding conduc-
tors. Equipment such as motors or electrically-heated waterers
should be grounded by means of an equipment grounding conductor
connected to the grounding bus at the DP. Installing a ground
rod at such equipment as a substitute for an equipment grounding
conductor is not permitted, but a ground rod may be installed as
a complement to the grounding conductor.
FANS
No more than two fans should be wired per circuit in an
environmentally controlled swine room. With fractional horsepower
motors, or when more than one fan is included on a branch cir-
cuit, secondary fusing is necessary to provide adequate over-
current protection of individual fan motors with a locked rotor.
The use of automatic reset fans is not recommended because fans
often continue to restart until they finally burn out the motor.
Also, there is risk involved since a person who sees a fan not
operating could begin to check to determine why it is not running
and the automatic restart could re-engage, causing personal
injury. The manual reset is a much preferable and safer protec-
tive measure for motors that operate fans, feed, and material
handling systems.
A fused switch installed in a corrosion resistant box, and
located within 5 to 10 ft. of each fan is required for safety
during cleaning and maintenance. Fused switches are available to
meet both individual fan fusing and switching requirements. Use a
time-delay fuse sized at 150% (125% for motors without thermal
protection) of the motor full load current rating. At least two
fan branch circuits from opposite sides of the 230 V entrance
panel should be provided in each environmentally-controlled room.
Then, if one circuit fails, the room can still be ventilated.
Because of dust and corrosion, use only totally-enclosed
motors for swine buildings. Open motors are more prone to early
failure and more apt to cause fire and explosions and are not
allowed in livestock buildings.
INSPECTIONS
Few states require the inspection of agricultural electrical
systems. However, some power suppliers require an inspection
before electrical service will be provided. Some insurance com-
panies require inspections, while others offer reduced premium
rates for buildings that are inspected and verified as meeting
NEC requirements. Consult your power supplier and and insurance
company, and use available inspection services before putting
newly wired facilities into use.
SUMMARY
Quality electrical wiring practices are often overlooked
when remodeling or constructing new swine buildings. The moist
and corrosive conditions in these buildings necessitate suitable
practices and materials to increase the life of the electrical
system and to reduce the likelihood of loss of property, animals,
and income, or personal injury caused by electrical failure.
ADDITIONAL REFERENCES
_________________________________________________________________
Agricultural Wiring Handbook (Eighth Ed.). National Food and
Energy Council, Columbia, MO 65202.
Electrical Wiring Systems for Livestock and Poultry Facilities.
National Food and Energy Council, Columbia, MO 65201.
Farm Buildings Wiring Handbook, MWPS-28. Midwest Plan Service,
Iowa State University, Ames, IA 50011.
National Electrical CodeO. Published by and a registered trade-
mark of the National Fire Protection Association, Quincy, MA
02269.
_________________________________________________________________
Reference to products in this publication is not intended to be
an endorsement to the exclusion of others which may be similar.
Persons using such products assume responsibility for their use
in accordance with current directions of the manufacturer.
NEW 6/87 (5M)
_________________________________________________________________
Figure 1. A majority of all farm fire losses are related to elec-
trical system failure.
Figure 2. Either conduit or Type UF cable wiring circuits may be
used in swine buildings. Wiring should be attached to interior
surfaces of buildingnot concealed in wall, ceiling, or atticto
reduce condensation and rodent damage and facilitate periodic
inspection.
Figure 3. Standard metal boxes are not suitable for swine housing
because of susceptibility to corrosion and subsequent electrical
system failure. Boxes are required to be moisture-proof and have
spring-loaded covers.
Figure 4. Switches should be moisture-proof, either by means of
moisture-tight levers, spring-loaded covers, or moisture-tight
covers with flexible press switches.
Figure 5. All cable or conduit should enter electrical boxes and
distribution panels from the side or bottom if possible.
Figure 6. A 1/4-in. gap is required between distribution panels
and walls to reduce fire hazard if overheating occurs. Spacing
also helps to maintain panel at room temperature, reducing con-
densation, and reduces entrapment of dirt (Note: Normal operation
would assure that panel cover is in place).
% Figures are available in hard copy.
_________________________________________________________________
Cooperative Extension Work in Agriculture and Home Economics,
State of Indiana, Purdue University and U.S. Department of Agri-
culture Cooperating. H.A. Wadsworth, Director, West Lafayette,
IN. Issued in furtherance of the Acts of May 8 and June 30, 1914.
It is the policy of the Cooperative Extension Service of Purdue
University that all persons shall have equal opportunity and
access to our programs and facilities.
.