Gr ou n din g Syst e m s a n d Th e ir I m ple m e n t a t ion
ByCh a r le s At k in son
Ca n a dia n Br oa dca st in g Cor por a t ion Tor on t o, Ca n a da
and
Ph ilip Giddin gs En gin e e r in g H a r m on ics
Tor on t o, Ca n a da
The original docum ent and figures m ay be found in t he Journal of t he Audio Engineering Societ y, Volum e 43 Num ber 6, June 1995. This version is © Philip Giddings 1995 and was revised Feb. 15, 1996.
Abst r a ct
The isolat ed st ar ground syst em is t he m ost popular im plem ent at ion of t echnical grounding for t he purposes of grounding sensit ive elect ronic
equipm ent . This approach has been in pract ice for m any years, and w hile it is not a perfect solut ion, it is t he solut ion t hat present s t he least com prom ises. This paper docum ent s t he current approach as im plem ent ed in a num ber of large inst allat ions and is part of an on- going AES effort t o docum ent
appropriat e pract ices w it h regard t o t he cont rol of noise in audio syst em s.
1 . I n t r odu ct ion
The purpose of grounding is t o provide safe, reliable and cost efficient power dist ribut ion. ( Not e t hat t he cost elem ent includes dam age t o t he equipm ent due t o a fault or light ning st rike.) These are t he goals of grounding from a power dist ribut ion viewpoint where elect rical noise int erference is not a considerat ion. I n t he case of sensit ive elect ronic syst em s, such as audio, video and com put er syst em s it is also necessary t hat t he grounding syst em provide a st able and low im pedance connect ion t o eart h t o cont rol
elect rom agnet ic int erference ( EMI ) . The isolat ed st ar ground syst em as docum ent ed in t his paper serves all of t hese purposes: safet y, reliabilit y, cost efficiency and cont rol of elect rom agnet ic int erference.
Grounding is only one m eans of cont rolling elect rical noise in audio and ot her t echnical syst em s. A syst em s approach t o cont rolling noise is recom m ended and readers should see [ 1] , [ 2] , [ 3] , [ 4] , [ 5] , [ 6] and t he references
cont ained t herein.
2 . Syst e m Con ce pt
The overall concept of t he isolat ed st ar ground syst em is show n in Figure 1. From t his draw ing w e see t hat t he t echnical ground w iring connect ions occur in four locat ions; t hese being t he service ent rance, t he sub dist ribut ion panel, t he area panels and t he final equipm ent connect ions ( branch circuit s) . These are discussed in t he follow ing paragraphs.
The dist ribut ion of non- t echnical ( safet y) equipm ent ground is show n on all t he drawings via t he conduit syst em , as perm it t ed by m any elect rical codes. I n som e cases, t his is, or m ust be, supplem ent ed w it h an added ground conduct or t o reinforce t he int egrit y of t he bonding of t he conduit syst em . Of course, in t he case of arm ored cable in t he branch circuit s, t he t hird ( ground) conduct or is st andard pract ice. Not e t hat equipm ent racks and large t echnical unit s are not considered part of t he equipm ent ground syst em . They are part of t he t echnical ground syst em and are discussed lat er.
The t echnical ground syst em is isolat ed from all m et allic building st ruct ures. To t his end all ground conduct ors are insulat ed ( green or green w it h yellow t race or as required by code) and ground bars in t he m ain and area ground boxes are isolat ed from t heir m et al housings.
2 .1 . Se r vice En t r a n ce
The w iring diagram for t he Service Ent rance ground is show n in Figure 1. At t his point only, t he t echnical ground is bonded t o t he m ain building ground connect ion w hich in t urn is bonded t o t he neut ral and t he eart h elect rode. Typically t he m et allic st ruct ure of t he building will have a connect ion t o ground via cont act w it h elect rical conduit s and ot her bonded elem ent s.
The m ain pow er dist ribut ion panel m ay be shared w it h regular pow er dist ribut ion syst em s in t he service ent rance as shown in Figure 2. For com plet eness regular pow er dist ribut ion has been show n t o highlight w iring differences.
2 .2 . Su b
The w iring diagram for t he Main Technical ground is det ailed in Figure 2. The Main Technical Ground is t he cent ral st ar point of a syst em . This is w here t he m ain t echnical ground bus resides. All t echnical grounds st em from t his single point .
The m ain t echnical ground and associat ed AC panel w ould t ypically be locat ed at t he m ain t echnical equipm ent cent er of t he facilit y, such as a m ast er
cont rol room in a broadcast cent re.
enclosure.
2 .3 . Ar e a
The w iring diagram for a t ypical Area Technical Ground is show n in Figure 3. Locat ed t hroughout t he facilit y or adj acent t o t he m ain equipm ent cent res ( such as st udio cont rol room s) will be t echnical power branch panels fed from t he t echnical power sub dist ribut ion panel. The area t echnical grounds are wired in a sim ilar m anner t o t he m ain t echnical ground panel - - t here is an isolat ed ground bus in a separat e box locat ed below t he elect rical panel. This isolat ed ground bus receives it s ground reference from t he ground bus in t he t echnical sub dist ribut ion panel. The area t echnical ground bus provides t he ground reference for t he equipm ent or branch t echnical circuit s in t he adj acent area.
2 .4 . Equ ipm e n t or Br a n ch Cir cu it s
The w iring diagram s for t he Equipm ent or Branch Technical Grounds are show n in Figures 3, 4 and 5. The branch circuit s are AC isolat ed ground recept acles for t he use of st and- alone or port able equipm ent and are det ailed in Figure 3. The drawing shows t he difference in t he wiring pract ices bet ween t echnical recept acles and regular recept acles. No m ore t han t wo recept acles are looped t oget her on a single conduct or from t he ground bus. I n Nort h Am erica, isolat ed ground recept acles are salm on or orange colored and m ay have a t riangle sym bol on t he front face ident ifying t hat t he ground t erm inal is isolat ed from t he casing and hence t he box it is m ount ed in.
Figures 4 and 5 dem onst rat e how t he equipm ent racks and large t echnical unit s ( such as audio consoles) m ust be isolat ed and receive t heir ground connect ion only from t he incom ing insulat ed t echnical ground conduct or. All racks are m ount ed on an insulat ing plint h ( base) . I n t he case of a m ult iple rack inst allat ion t hey are bolt ed t oget her t o provide an equipot ent ial plane. All st and- alone equipm ent m ust be isolat ed t o prevent t he possibilit y of
inadvert ent ground cont act w it h m et allic building st ruct ures. I n t he case of m ult iple equipm ent racks and audio consoles t he separat e ground conduct or from t he j unct ion box t o t he equipm ent should have an overall prot ect ive sheat hing t o elim inat e inadvert ent insulat ion dam age. Junct ion boxes " J" as shown in t he figures m ust be isolat ed from t he t echnical equipm ent housings and are wired t o t he t echnical equipm ent via insulat ed sheat hed cable.
3 . Con du ct or Te r m in a t ion
barrier. Alum inum w ire and t erm inat ion hardw are and alum inum bus bars should not be used.
4 . Con du ct or Siz e s
4 .1 . Sa fe t y Con side r a t ion
The isolat ed conduct ors also serve as t he equipm ent ( Safet y) ground for t he t echnical equipm ent housings as required by t he elect rical code. As a
m inim um requirem ent , t hese conduct ors m ust sat isfy t he elect rical code. The m inim um equipm ent ground conduct or sizes required by t he Nat ional
Elect rical Code in t he Unit ed St at es and t he Canadian Elect rical Code in Canada are given in t he follow ing t able. Ot her count ries have sim ilar w iring regulat ions.
M in im u m Equ ipm e n t Gr ou n d Con du ct or Siz e s ( ba se d on N a t ion a l Ele ct r ica l Code t a ble 2 5 0 - 9 5 " M in im u m Siz e Equ ipm e n t Gr ou n d Con du ct or s for Gr ou n din g Ra ce w a y a n d Equ ipm e n t " )
Ra t in g or Se t t in g of Au t om a t ic Ove r cu r r e n t D e vice in Cir cu it Ah e a d of Equ ipm e n t , N ot Ex ce e din g
( A)
Coppe r W ir e AW G ( squ a r e
m illim e t e r s)
Alu m in u m or Coppe r cla d Alu m in u m
W ir e AW G ( squ a r e m illim e t e r s)
15 14 ( 2.081) 12 ( 3.309)
20 12 ( 3.309) 10 ( 5.261)
30 10 ( 5.261) 8 ( 8.366)
40 10 ( 5.261) 8 ( 8.366)
60 10 ( 5.261) 8 ( 8.366)
100 8 ( 8.366) 6 ( 13.30)
200 6 ( 13.30) 4 ( 21.18)
4 .2 . Te ch n ica l Con side r a t ion
The sizing of t he conduct or w it h regard t o t he requirem ent s for Elect ro-Magnet ic I nt erference ( EMI ) cont rol is m ore difficult t o det erm ine. The
appropriat e w ire gauge for EMI reasons is influenced by t he sensit ivit y of t he syst em and t he ant icipat ed level of elect rom agnet ic int erference. Obviously syst em s of low dynam ic range such as paging and background m usic syst em s do not have st ringent requirem ent s for t echnical grounding whereas broadcast and post - product ion com plexes are m ore crit ical. Wire gauges t ypical of a broadcast inst allat ion are shown in t he figures. The follow ing t able gives suggest ed values [ 1] .
Only) device of it s associat ed power conduct ors.
5 . Con du ct or Se pa r a t ion a n d Rou t in g
The elect rical code requires t hat t he ground conduct or m ust be rout ed w it h it s associat ed power conduct ors. Except ions have been m ade in som e cases, but special approvals m ay be required. The aut hors have not been able t o
det erm ine whet her t here is any benefit from running ground conduct ors separat ely. Furt her w ork w ill follow in t his regard.
As t he ground conduct or is sensit ive t o EMI t he rout ing of t he t echnical pow er and ground conduct ors should be done w it h som e care and should be rout ed aw ay from ot her m aj or high volt age feeders, t ransform ers, large m ot ors and ot her EMI sources in t he building.
6 . Con clu sion
The m ost widely accept ed approach t o t he im plem ent at ion of a isolat ed st ar ground syst em has been present ed. I t is suggest ed t hat from a value
problem " ) and overall syst em s design.
7 . Re fe r e n ce s
[ 1] Giddings, P. 1990. Audio Syst em s Design and I nst allat ion, I ndianapolis: How ard W. Sam s.
8 . Bibliogr a ph y
[ 2] Muncy, N. A. 1994. " Noise Suscept ibilit y in Analog + Digit al Signal
Processing Syst em s" . Present ed at t he 97t h AES Convent ion, San Francisco.
[ 3] Macat ee, S. R. 1994. " Considerat ions I n Grounding and Shielding Audio Devices" . Present ed at t he 97t h AES Convent ion, San Francisco.
[ 4] Whit lock, B. 1994. " Balanced Lines in Audio Syst em s - Fact , Fict ion, and Transform ers" . Present ed at t he 97t h AES Convent ion, San Francisco.
[ 5] Windt , J. 1994. " An Easily I m plem ent ed Procedure for I dent ifying Pot ent ial Elect roMagnet ic Com pat ibilit y Problem s in New Equipm ent and Exist ing
Syst em s - The Hum m er Test " . Present ed at t he 97t h AES Convent ion, San Francisco.
[ 6] Perkins, C. 1994. " Aut om at ed Test & Measurem ent of Com m on I m pedance Coupling I n Audio Syst em Shield Term inat ions" . Present ed at t he 97t h AES Convent ion, San Francisco.
[ 7] Morrison, R. and Lewis, W. H. 1990. Grounding and Shielding in Facilit ies, New York: Wiley I nt erscience.
[ 8] Giddings, P. 1989. " An I nt roduct ion t o Elect rom agnet ic Com pat ibilit y ( EMC) and Elect rom agnet ic I nt erference ( EMI ) for Audio Syst em Designers" , J. Audio Eng. Soc., Vol. 37, No. 7/ 8.
[ 9] Burdick, A. H. 1986. A Clean Audio I nst allat ion Guide, Nort h Syracuse, N.Y.: Benchm ark Media Syst em s, I nc.
[ 10] Davis, C., and Davis, D. 1985. " Grounding and Shielding Workshop" , Tech Topics, Vol. 12, No. 10. San Juan Capist rano: Syn Aud Con.
[ 11] Morrison, R. 1977. Grounding and Shielding Techniques in I nst rum ent at ion, 2nd ed., New York: Wiley I nt erscience. Cont ains int erest ing inform at ion.
