AEN-70
l].|'R.s'Gt|t('s'ASs()ci4teh1'Iessof,A8iL.tlIturatf:t,8ineerin8;D,G.(,,efbults,Ass()ciateFtte,'si(ln{essllr.
F.ttcnsirn,PnlJi'ssor.AgiculhralEngincerittg:ttttdR,I''Fe|x.,Electr0nicTecbntiog1,Qy174i,Mtof,A8riculttl rotection from electrical surges is receiving morc attcntion with thc widesprcad adoption of clcctronic devices in agricultural facilities ranging from personal computcrs to environmental control systems and computcrizcd fecd mills. Incorp<lration of surge protection is advised as the cost of surge protecrion cquipment drops and the potential cost due to a singlc failure of electronic equipment increases.
Transient surgcs arise from many sources. C<>mmon sources includc lightning and load switching that inducc transients which enter through the electrical or tclcphone utility service. Load switching from other users on the electrical power grid and other facilities on a uscr's prcmiscs also are surge sources. rVhile the massive energy of a dircct lightning strike can clearly cause extensive damage. smaller transients from remotc strikcs and other sourccs also can create severe upsets in digital electronics wlthout any outward sign of damage. In fact, most transient surges have voltage magnitudcs under'6000 volts ((r kV). Protection against these surges is important and cost effective.
A properly installed transient surge suppression systcrn includes several levels of protection. The system starts at the utility service and progresses to each building's service panels, sub-panels and particular circuits with sensitive electronic equipment. Each protcctive level is clcsigncd to remove a portion of the surge that survived a preceding level. These levels of protcction are classified by Standards Organizations
(ANSI, IEEE, NEC) by thcir location within the site as
Oategory C (scrvicc cntrance panel), Category B (panel b<lards and large sub-panels) and Category A (branch pancls). Protection for individual circuits and for the utility service also are rccommended.
idealized representation illustrates all five levels of protection which are numbercd in ascending order for reference. In practice, many agricultural installations do not need all levels. It is important to note, however, that providing surge suppression only at the circuit to which sensitive electronic equipment is connect€d generally is insufficicnt for high-energy transients.
These surges can dcstroy this low level protection and still have sfficient cncrg)'renraining to damagc electronic equipmcnt.
A good grounding system for the building is essential for correct operation of surge arrestons due to how surge arrestors work. Once a transient is detected, the arrcstor short-circuits (shunts) thc transient to the ground. lf the ground is poorly established, the effectivencss of the surge arrestors is greatly diminished. Your electrical utiliq'can test the adequacy of your grounding bv mcasuring the resistance bctwecn the gr<tund rod and earth ncarby'.
Most surge suppressors arc made of either gas discharge tubes or solid state componcnts called metal oxide raristors (MOVs). rX/hilc both functionally provide similar capabilities, MOVs are becoming more prevalent.
Beware of imitations, such as silicon oxidc varistors, when selecting surge suppression devices. Look for ratings from an independcnt laborat<lrv (e.g.,
Underwriter's laboratory) that certiS the equipment t<t meet or exceed the ANSI/IEEE C62 4l tr;rnsient overvoltage test waveforms.
Lightning protection for buildings also is important if sensitive electronic or life-supporting equipment, such
National Fire Protection Agency (Batterymarck Park,
Quincy, Massachusetts) and the Farm Building Wiring
Handbook (published bv Midwest Plan Service and availablc through count)' Extension offices) arc excellent sources of infirrmation on lightning protection.
The following minimum surge suppression cquipment is recommended frlr agricultural facilities such as livestock buildings containing electr<tnic controls.
c Ligbtning an'estor on main senice lxtle.
o Adequate grcundfor sutrice entrance and mnin seruicepole.
. Category A or B arrestorfitr tbe building senice panel.
o Secondary arrestor (or Categrtry A) for tbe ind.itifunl circuit to ubicb tbe electronic conhrtls are attacbed.
LINMRSITY OF KENTUCT(Y o QQTIEGE OF AGRICLJLTLJRE e COOPERATIVE EXTTNSION SERVICE
Agriculture . Home Economics . 4H . Development

(lertainlv morc surgc protcction is helpful. but this minimum ler.cl is practical to install and should protect equipmcnt against m()st surges. Remember, no amount of surgc protection can guarantce ahsolute reliabiliw.
'lhus, equipmcnt tlrat perfrrrms critical functions should surge suppression.
This is a partial list of transient srlrge supprcssion
'fhe dcl'icc manufircturcrs. t Iniversity <lf Kentucky does n()t in an)'wa1'endorsc a manufhcturcr or product at thc cxclusion <lf <lthcr manuficturers or products; thc iutcnt is onl),to prol'idc a rcflercncc fbr interestccl partlcs.
General Electric Capacitor
(lustornef Sewice
( 5 l 8 1 r t 6 r ' t - t , ,
St'condln' Arrcstor: Moclcl 9l.l5I:( I - (l(X) |
Joslyn Electronic Systems Corporation
Santa Barbara Rescarch Park
P.(). llox tllT
(iolcta. (A 9-ll l6
( fio5 ) 96u .1551
Widc rangc of prirnltn rnd scconclarl'arrcstors.
Joslyn Manufacturing
Co.
t)2(X) W. Fullefton Avenuc
Kalglo Electronics Co., Inc.
(1584 Ruck Roa<J
( 2 1 5 ) 8 3 7 - 0 7 0 0 rVide range of telephone and data arrcstors.
MCG Electronics, Inc.
l2 llurt I)rivc l)cer Park, NY I 1729
( 5 1 ( r ) 5 l t 6 - 5 1 2 5
Vidc rangc <lf te lcplronc antl datlr urrcst()rs.
BUILDINC LIGHTNING
( S E E N F P A }
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GROUNOED
U T I L I T Y
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CATEGORYA
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ARRESTOR
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PROTECTIOII
LEVEL 2
LEVEL '
BUILDINO
GROUilO r*hernatic of a pnrtected building electrical scn"icc using the recommended cascaded system.
Although not shown, tclephone servicc is protccted in a similar fashion. Elecrrical utility scrvice arrcstor and ground are intended to absorb largc transients that originate from other protection levels are designed to further dissipatc outside transients as well as those generated from within the facility (motor switching, for example ). For very sensitive electronic equipment, surge suppressor strips are recommended as a sixth level of protection.
CATEGOFIES D€FIXEO
8Y 3T I{OARDS
A S A N S I , IE E E
F x l e n s r o n S e r v r c e U n r v . t r s r l V , ) l K e n l i r c k y C o l l e g e o l A q r r c u l l r r r e . L e x r n g t o n . a n d K e n t u c k y S l a l e U n r v e r s r l y . F r a n k f o r l