411.3.2.3 In TN systems, a disconnection time not exceeding 5 s is permitted for distributioncircuits
tiu chun vit nam
TIU CHUN VIT NAM
TCVN 46: 1984CHNG ST CHO CC CNG TRNH XY DNG - TIU CHUN THIT K,
THI CNGLightning protection for buildings - Standard for design and
construction.
Chng l
QUY NH CHUNG1.1. Tiu chun ny p dng thit k thi cng, nghim thu v
qun l thit b chng st cho cc cng trnh xy dng dng mi, ci to hoc m
rng.
Khng p dng tiu chun ny i vi cc cng trnh sau:
a. Cng trnh ngm, cng trnh di ng, cc cng trnh c bit v qun s (trm
ra- a, trn a tn la, pho...) v cc kho cha vt liu n.
b. Cc ng dy ti in, mng tip xc, in tn, in thoi, truyn thanh,
ng-ten ca cc i thu- pht sng v tuyn in, v tuyn truyn hnh v cc kho
xng du.
1.2. Tu theo chc nng s dng, cc cng trnh xy dng phi c chng st
theo s phn cp nh sau:
Cp I- Nhng cng trnh, trong c to ra cc cht kh hoc hi chy, cng nh
cc bi hoc si d chy chuyn sang trng thi l lng v c kh nng kt hp vi
khng kh hoc cht xy-ho khc to thnh cc hn hp n, c th xy ra ngay trong
iu kin lm vic bnh thng k c iu kin lm vic bnh th-ng ngn hn (m hoc ng
cc thit b, cha hoc rt cc cht d bt la hoc cc cc cht lng chy qua li
cc bnh h...).
Khi xy ra n s gy ra nhng ph hoi ln v lm cht ngi.
Cp II- Nhng cng trnh, trong c to ra cc cht kh, hi, bi hoc si chy
v c kh nng kt hp vi khng kh hoc cc cht xy-ho khc to thnh cc hn hp
n. Nhng kh nng ny ch xy ra khi c s c hoc lm sai quy tc, khng th xy
ra trong khi lm vic bnh thng. Khi xy ra n ch gy ra nhng h hng nh v
khng lm cht ngi.
Cp III- Tt c nhng cng trnh cn li.
Ghi ch: Mt s cng trnh cp III, theo nguyn tc phn cp trn, nhng c
tm quan trng c bit v chnh tr hoc kinh t th c php nng ln cp II.
(V d: Nh Quc hi, i pht thanh, nh my in, nh , nh lm vic ca lnh
t...)
1.3. Cc cng trnh xy dng cn bo v theo cp I hoc cp II phi p dng
bin php chng st nh thng, chng cm ng tnh in v cm ng in t, chng in p
cao ca st lan truyn t h ng dy, ng ng bng kim loi t ni v t ngm bn
ngoi dn vo.
Cc cng trnh xy dng cn bo v theo cp III phi p dng bin php chng st
nh thng; chng in p cao ca st lan truyn t h ng dy, ng ng bng kim loi
t ni bn ngoi dn vo.
Trng hp cng trnh (k c ba cp) c chiu rng t 60m tr ln, phi p dng
bin php san bng in p bn trong cng trnh - xem iu 2.15.
1.4. Nhng thit b t ngoi tri cn bo v theo cp II phi p dng bin php
chng st nh thng v chng cm ng tnh in.
Nhng thit b t ngoi tri cn bo v theo cp III phi p dng bin php
chng st nh thng.
1.5. i vi cc cng trnh xy dng c nhiu phng, trong c mt s phng cn
bo v theo cp I v II hoc I v III th ton b cng trnh nn chng st theo
cp I.
i vi cng trnh mt tng, khi din tch cc phng cn bo v theo cp I nh
hn 20% din tch ca ton b cc phng trong cng trnh, v i vi cng trnh
nhiu tng khi din tch cc phng cn bo v theo cp I ca tng trn cng nh hn
20% din tch ca cc phng tng trn cng thuc cng trnh , th ton b cng
trnh c th thc hin chng st theo cp II. Trong trng hp ny ton b cc ng
dy, ng ng bng kim loi t ni v t ngm c bn trong cng trnh, v tr u vo
cc phng cn bo v theo cp I phi ni vi mt b phn ni t ring, t pha ngoi,
c in tr tn dng in tn s cng nghip t 10 m tr xung.
1.6. i vi cc cng trnh xy dng c nhiu phng, trong c mt s phng cn
bo v theo cp II v III th ton b cng trnh nn chng st theo cp II.
i vi cng trnh mt tng, khi din tch cc phng cn bo v theo cp II nh
hn 20% din tch ca ton b cc phng trong cng trnh, v i vi cng trnh
nhiu tng, khi din tch cc phng cn bo v theo cp II ca tng trn cng nh
hn 20% din tch ca cc phng tng trn cng thuc cng trnh , th ton b cng
trnh c th thc hin chng st theo cp III. Trong trng hp ny ton b cc ng
dy ng ng bng kim loi t ni v t ngm c bn trong cng trnh, v tr u vo cc
phng cn bo v theo cp II phi ni vi mt b phn ni t ring, c in tr tn
dng in tn s cng nghip t 10 m tr xung.
1.7. Nhng cng trnh xy dng cn bo v theo cp III sau y khng cn phi
chng st nh thng:
a. Nhng cng trnh khi b st nh thng, cng khng gy ra nhng thit hi g
ng k v ngi v ca.
b. Nhng cng trnh nm trong phm vi bo v ca cc cng trnh cao (k c cc
cy cao) xung quanh.
c. Nhng cng trnh c chiu cao di 8m (k t mt t n nh cao nht ca cc
cng trnh) c s ngi tp trung cng mt lc khng qu 50 ngi hoc khng c nhiu
gia sc ln (tru b, nga, d, cu...) khng c cc b phn kt cu ln hoc cc my
mc ln bng kim loi v xy dng ti nhng vng t st (t 5 nm tr ln khng thy
st nh trong vng ).
1.8. Khi chng st cho cng trnh xy dng thuc cc cp, nn ch y n nh
hng ca b phn thu st t cng trnh bn cnh, chng st nh thng ch thc hin
cho phn cn li ca cng trnh nm ngoi phm vi bo v ca cng trnh bn cnh ni
trn. Trong trng hp ny vic chng cm ng tnh in, cm ng in t v in p cao
ca st lan truyn phi p dng cc bin php tng ng vi cp chng st ca cng
trnh .
Khi chng st nh thng cho cc cng trnh xy dng khng ln lm ng ring l
cng nh mt nhm cc cng trnh tng t cn bo v theo cp II, III, nn li dng
cc cng trnh cao c sn lm b phn thu st nh: cc ng khi, ng thi kh, i
nc,... hoc cc cng trnh cao tng t.
1.9. Vic thi cng lp t b phn chng st ni t cho cng trnh xy dng
thuc cc cp (k c cng trnh ci to hay m rng) phi lm ng theo thit k v
ph hp vi tin thi cng chng hon thnh cng mt lc vi cc cng vic
chnh.
1.10. Khi thi cng cc cng trnh cao gp vo ma ng st, lc xy n cao t
15m tr ln nn t cc kim hoc dy thu st tm m bo an ton v mt chng st cho
ngi v cng trnh trong qu trnh xy dng.
- Cc kim thu st tm t theo mt trn ca cng trnh. Dy xung t t do dc
theo tng ct v phi ni vi b phn ni t chng st nh thng. Khi cng trnh c
xy cao dn, cc kim v dy thu st, dy xung cng chuyn ln theo. Cc ch ni
ca b phn thu st, ni t, c dng bulng bt ni - xem iu 3.28
Khi thi cng cc cng trnh cao bng kim loi ngay t u phi ni mng cng
trnh vi b phn ni t chng st nh thng.
1.11. Cc b phn chng st nh thng, chng cm ng tnh in v cm ng in t
ca cc cng trnh xy dng cn bo v theo cp II v III phi c a vo s dng sau
khi cng trnh xy dng xong. Ring i vi cng trnh cn bo v theo cp I cc b
phn chng st ni trn phi a vo s dng khi bt u lp t cc thit b my mc c
bn trong cng trnh.
Chng II
QUY NH I VI BO V CHNG ST2.1. Cc cng trnh xy dng cn phi s dng cc
phng thc chng st nh sau:
a) i vi cng trnh cp I v II nht thit phi s dng phng thc bo v ton
b.
b) i vi cng trnh cp III. Nu l nhng cng trnh c mt vi phng c nguy
c n chy, hoc nhng cng trnh thng xuyn tp trung ng ngi cn phi s dng
phng thc bo v ton b. Nu l nhng cng trnh khng c cc phng c nguy c n
chy, v khng tp trung ng ngi th s dng phng thc bo v trng im - xem iu
2.24.
2.2. B phn thu st - C th s dng hnh thc kim, dy, ai hoc li thu
st. Phi cn c vo c im c th ca mi cng trnh thit k ph hp vi yu cu v mt
bo v, cng nh cc yu cu v kinh t, k thut.
Bo v cc cng trnh cp I
2.3. Chng st nh thng cho cc cng trnh cp I nht thit phi b tr kim,
dy thu st t c lp hoc cc b phn thu st khc t trc tip, nhng phi cch li
vi cng trnh qua cc loi vt liu khng dn in. Cc b phn thu st ni trn
phi m bo c phm vi bo v nh c trnh by trong chng 4.
2.4. Khong cch an ton t thit b chng st t c lp hoc cch li vi cng
trnh nh sau:
a) Khong cch khng kh (Skk), khng c nh hn 5m.
b) Khong cch trong t (S) khng c nh hn 5m i vi cng trnh c nguy c
n hoc thng xuyn tp trung ng ngi, khng c nh hn 3m i vi cc cng trnh
khc v vi dy thu st.
c) Khong cch qua cc loi vt liu khng dn in xc nh theo cng cch in
ca vt liu.
d) i vi cng trnh chn nui gia sc phi theo quy nh iu 2.27.
2.5. in tr xung kch ca b phn ni t khng c ln hn 10 m nu in tr sut
tnh ton ca t (8.tt) nh hn 5 x 104 m.cm, hoc khng c ln hn 40 m nu in
tr sut tnh ton ca t ln hn 5 x 104 m.cm.
2.6. Khi trn cng trnh c ng khi hoc cc loi ng k thut khc nh cao
ln khi mi, dng thi cc cht kh c nguy c gy n th khong khng gian trn
ming ng cn phi nm trong phm vi bo v ca b phn thu st. Khong khng
gian ny c gii hn bng mt hnh bn cu c bn knh bng 5m.
i vi cc ng thi khc, khong khng gian ni trn c gii hn trong phm vi
mt hnh tr c kch thc nh sau:
+ H =1m; R=2m, khi loi kh cho thot ra nng hn khng kh, c p lc d
nh hn 0,05at - d (a-ti).
+ H=2,5m; R =5m, khi loi kh cho thot ra nng hn khng kh. C p lc d
nh hn 0,05 n 0,25at - d hoc nh hn khng kh, c p lc d n 0,25 at
d.
+ (H v R l chiu cao v bn knh ca hnh tr).
Khng cn a vo phm vi bo v ca cc b phn thu st khong khng gian trn
ming cc loi ng sau:
+ ng thi cc cht kh c nguy c gy n.
+ ng thi kh nit.
+ ng thng xuyn thi kh v kh thi thot ra t ming ng thng xuyn chy
thnh ngn la, hoc ch chy thnh ngn la khi thi.
ng hoc van an ton dung thi cc cht kh c nguy c gy n, nhng cc loi
kh ny ch cho thi ra trong cc trng hp ht sc hn ch nh lc c s c.
2.7. chng cm ng tnh in, tt c cc b phn kt cu kim loi v cc my mc
ln c trong cng trnh phi ni vi mt b phn ni t chng cm ng st hay ni vi
b phn ni t bo v thit b in.
B phn ni t chng cm ng st phi c tr s in tr tn dng in tn s cng
nghip khng ln hn 10 m v phi t cch xa b phn ni t chng st nh thng mt
khong cch S nh nu iu 2.4.
2.8. chng cm ng in t, phi ni tt c cc ng ng kim loi, cc kt cu kim
loi di, ai v v kim loi ca cc cp ti nhng ch chng i gn nhau nht
(trong phm vi 100mm). Nu chng song song vi nhau, dc theo chiu di c
cch nhau 15 n 20m phi ni lin h vi nhau. Nu cc on song song khng di
qu 20m th phi ni ti hai u ng.
Cc mi ni, mt bch hay mng-sng ni ca cc ng ng phi m bo in tr tip
xc 0,03 m, nu khng bo m tip xc tt phi hn vt thm cc cu ni bng thp
trn hay thp dt.
2.9. chng in p cao ca st lan truyn trong cng trnh nu c h ng ng
ngm bng kim loi dn vo, v tr u vo cng trnh phi ni h ng ng vi b phn
ni t chng cm ng st hay ni vi b phn ni t bo v thit b in.
B phn ni t chng st nh thng phi t cch xa h ng ng ngm v cc b phn
ni t khc mt khong cch S nh nu iu 2.4.
2.10. chng in p cao ca st lan truyn trong cng trnh nu c h ng ng
bng kim loi t ni bn ngoi dn vo cn phi:
a) Nu h ng ng t trn cc tr , v tr u vo cng trnh - ni ng vi b phn
ni t chng cm ng st. Ti tr th nht (gn cng trnh) ni t vi tr s in tr
tn dng in tn s cng nghip 10 m v tr th hai l 20 m.
Dc theo ng ng khong 20 n 30m ni t lp li vi in tr tn dng in tn s
cng nghip 30 m.
b) Nu h ng ng t mt t, ti v tr u vo cng trnh, ni ng vi b phn ni t
chng cm ng st. cc im dc theo chiu di ng , cch v tr u vo cng trnh 10
v 20m, ni t vi in tr tn dng in tn s cng nghip tng ng bng 10 m v 20
m. Sau c tip nhau tng khong 20 n 30m ni t lp li vi in tr tn dng in
tn s cng nghip 30 m.
2.11. Cc ng dy dn vo cng trnh c in p di 1000V (ngoi ra, cc ng dy
khc u khng c dn vo) nht thit phi t cp ngm sut t trm bin p cung cp
ti cng trnh, ng thi phi p dng thm cc bin php sau:
a) Ti trm bin p cung cp in, pha in p thp v ti hp u cp ca cng
trnh, trn cc li cp phi t b chng st h p.
b) V hp u cp, ai v v kim loi ca cp u vo cng trnh phi ni vi b phn
ni t ca cc b chng st h p.
Bo v cng trnh cp II
2.12. i vi cc cng trnh cp II c th b tr thit b chng st c lp, cch
li hoc t trc tip ln cng trnh. Cn phi tnh ton v so snh v kinh t k
thut chn phng n hp l nht.
- Nu b tr thit b chng st c lp hoc cch li vi cng trnh qua cc vt
liu khng dn in, cn phi thc hin theo iu 2.3 ; 2.4.
- Nu b tr thit b chng st trc tip trn cng trnh cn phi tha mn cc
yu cu sau:
a) i vi kim loi hay dy thu st - t mi kim loi hoc dy thu st phi c
t nht l hai dy xung.
b) i vi li thu st - lm bng thp trn, kch thc mi li khng c ln hn 5
x 5m. Cc mt li phi c hn ni vi nhau.
Trng hp cng trnh c mi bng kim loi, nu b dy mi ln hn 4mm, c th s
dng mi thu v dn st. Trong mi trng hp phi m bo s dn in lin tc gia cc
b phn ring r ca mi vi nhau.
c) Trn mi ca cng trnh nu c t cc b phn nh cao bng kim loi (nh ng
thng hi, thang cha chy ...) th mi b phn ny phi m bo dn in lin tc v
phi c hn ni vi li thu st hay mi kim loi nu cc b phn nh cao ni trn
khng phi bng kim loi (nu nh ng khi, ng thng hi xy bng gch..), phi t
thm ln trn cc b phn thu st ph (kim hoc ai thu st) v hn ni b phn thu
st ph ny vi li thu st hay mi kim loi.
d) i vi cc cng trnh cao qu 15m cn phi thc hin ng p tng tng. Ti
cc tng ca cng trnh, phi t cc ai san bng in p bao quanh cng trnh, cc
dy xung phi ni vi cc ai san bng in p v tt c cc b phn bng kim loi, k
c cc b phn kim loi khng mang in ca cc thit b, my mc c cc tng cng
phi c ni vi cc ai san bng in p bng dy ni. Trng hp ny phi thc hin ni
t mch vng bao quanh cng trnh.
e) Khi s dng b phn ni t cc hay cm cc chn thng ng, cc dy xung phi
t pha ngoi trn cc mt tng ca cng trnh. Khi s dng b phn ni t ko di
hay mch vng th dy xung phi t cch nhau khng qu 15 n 20m dc theo chu
vi mi cng trnh.
g) C th s dng cc b phn kt cu kim loi ca cng trnh (nh: ct thp, v
ko thp...) cng nh ct thp trong cc cu kin b tng ct thp (tr ct thp c
ng lc trc v ct thp ca cu kin b tng nh) lm dy xung, vi iu kin k thut
thi cng phi m bo c s dn in lin tc ca cc b phn kim loi c s dng lm dy
xung ni trn (bng phng php hn in).
2.13. nhng vng t c tr s in tr sut nh hn hoc bng 3 x 104 m.cm,c
php s dng ct thp trong cc loi mng bng b tng ct thp lm b phn ni t,
vi iu kin k thut thi cng phi m bo c s dn in lin tc ca cc ct thp
trong cc loi mng ni trn.
2.14. Tr s in tr xung kch ca b phn ni t chng st nh thng p dng iu
2.5.
2.15. Khong cch gia cc b phn ca thit b chng st v cc b phn kim
loi ca cng trnh, cc ng ng, ng dy in lc, in yu (in thoi, truyn
thanh...) dn vo cng trnh:
a) Pha trn mt t khng c nh hn 1,5m; pha di mt t khng c nh hn
3m.
b) Trng hp thc hin khong cch quy nh trn gp nhiu kh khn v khng hp
l v kinh t - k thut th c php ni chng v c cc b phn kim loi khng mang
in ca cc thit b in vi thit b chng st, tr cc phng c nguy c gy ra chy
n, v phi thc hin thm cc bin php sau:
- Cc ng dy in lc, in nh phi lun trong cc ng thp, hoc s dng cc
loi cp c v bng kim loi v ni cc ng thp, hoc v kim loi ca cp vi ai
san bng in p ti ch chng gn nhau nht.
- Phi t ai san bng in p bn trong cng trnh.
ai san bng in p l mt mng cc li nm ngang, chn su khng nh hn 0,5m
so vi mt sn, lm bng thp trn hoc thp dt tit din khng c nh hn 100mm2
v b dy thp dt khng nh hn 4mm.
Kch thc mi li khng c ln hn 5 x 5m.
- Nht thit phi s dng hnh thc ni t mch vng bao quanh cng trnh v
dc theo mch vng ni t, c cch nhau tng khong 10 n 15m phi hn ni lin h
vi ai san bng in p trong cng trnh: in tr xung kch ca mch vng ni t
khng vt qu tr s nu iu 2.5.
- Khi s dng ct thp trong cc mng bng b tng ct thp ca cng trnh lm
b phn ni t th khng yu cu t ai san bng in p bn trong cng trnh.
2.16. Chng st cho cc b cha kn t ngoi tri.
a) Trng hp b cha bng kim loi, nu thnh b c b dy t 5mm tr ln, c s
dng thnh b thu v dn st, nu b dy thnh b nh hn 5mm th phi t b phn thu
st ring, thnh b ch c s dng dn st.
b) Trng hp cc b cha bng b tng ct thp, c th b tr thit b chng st c
lp, cch li hay t trc tip trn b cha .
c) Nu c ng thng hi hoc thot kh trn b th khong khng gian trn cc
ng cng phi c bo v nh nu iu 2.6.
d) in tr ni t xung kch ca b phn ni t khng c ln hn 20 m v phi c t
nht l hai dy xung ni thnh b hay b phn thu st vi b phn ni t.
2.17. chng cm ng tnh in, p dng iu 2.7. Trng hp s dng mi kim loi
chng st nh thng, hoc t li chng st nh thng trn mi cng trnh th khng
phi chng cm ng st, nhng phi thc hin ng p tng tng v ni cc kt cu kim
loi hoc my mc bn trong cng trnh vi ai san bng in p.
2.18. chng cm ng in t, p dng iu 2.8.
2.19. chng in p cao ca st lan truyn trong cng trnh, nu c h ng
dy, ng ng ngm bng kim loi dn vo, p dng iu 2.9.
Ring khong cch trong t S t b phn ni t bo v chng st nh thng n cc
ng dy, ng ng v b phn kim loi khc p dng iu 2.15.
2.20. chng in p cao ca st lan truyn trong cng trnh nu c h ng
dy,ng ng bng kim loi t ni bn ngoi dn vo, p dng iu 2.10.
2.21. Cc li in c in p di 1000V, li in yu (in thoi, truyn
thanh...) ch c a vo cng trnh bng cp ngm. Hp u cp, ai v v cp bng kim
loi phi ni vi b phn ni t chng cm ng st. Nu cc li in trn l ng dy trn
khng, mun a vo cng trnh phi chuyn sang dng cp ngm, chiu di on cp ny
t nht l 50m.
Vi li in in p di 1000V, ct c s chuyn i t ng dy trn khng sang ng
dy cp, hp u cp, ai v v cp bng kim loi cng nh x, chn s bng kim loi
trn ct phi ni vi mt b phn ni t c in tr tn dng in tn s cng nghip
khng ln hn 10 m, ngoi ra gia mi ng dy vi cc b phn kim loi c lin h
vi b phn ni t phi t cc b phn chng st h p hay khe h phng in vi khong
cch phng in bng 2 n 3 mm.X v chn x bng kim loi trn ct ng dy k tip
vi ct c s chuyn i ni trn phi ni vi mt b phn ni t c in tr tn dng in
tn s cng nghip khng ln hn 20 m.
Bo v cc cng trnh cp III
2.22. i vi cc cng trnh cp III cn phi t thit b chng st ngay trn
cng trnh, ch c php t thit b chng st c lp vi cng trnh trong nhng
trng hp c bit thun li v k thut v kinh t.
B phn thu st c th s dng hnh thc kim, dy, ai hoc li thu st ty tng
trng hp c th. Khi bo v bng li thu st, kch thc mi li khng c ln hn 12
x 12m v phi b tr thm cc kim hoc ai thu st bo v cho cc kt cu nh cao
ln khi mi. Cc dy xung phi t men theo tng pha ngoi cng trnh (tr trng
hp thit b chng st t c lp vi cng trnh).
Khi bo v bng li thu st, dc theo chu vi mi c cch nhau 20 n 25m,
phi t mt dy xung. Ngoi ra dy xung v b phn ni t cng c p dng iu 2.12g
v 2.13.
in tr xung kch Rxk ca b phn ni t ng vi cc tr s in tr sut t tnh
ton (Udtt) v cc cch b tr thit b chng st khng vt qu cc tr s nu trong
bng 1.
Bng 1
Thit b chng st t c lp vi cng trnhThit b chng st t ngay trn cng
trnh khng thng xuyn c ngi hoc lm vicThit b chng st t ngay trn cng
trnh c ngi v lm vic thng xuyn
(dtt < 5 x104m.cm(dtt 5 x104m.cm(dtt < 5 x104m.cm(dtt 5
x104m.cm(dtt < 5 x104m.cm(dtt 5 x104m.cm
Rxk
205020501030
2.23. Cc b phn kim loi ca thit b chng st phi t cch xa cc vt bng
kim loi ca cng trnh mt khong cch khng c nh hn 1,5m nu vt kim loi
cao di 20m so vi mt t, v khng c nh hn 1:10 chiu di ca on dy xung nu
vt kim loi cao t 20m tr ln (S t 0,1L), trong L l chiu di ca on dy
xung o dc theo ng dy t mt t n im kho st.
Trng hp c mt vch ngn bng vt liu khng dn in gia vt kim loi v thit
b chng st, c th gim khong cch trn mt on bng 3 ln chiu dy ca vch
ngn.i vi cc ng dy in lc, in nh cng phi bo m khong cch quy nh trn
(1,5 hoc 1:10 chiu di ca on dy xung).
Khong cch t cc b phn kim loi ca thit b chng st n cc ng ng kim
loi ngm hoc cc ng cp ngm dn vo cng trnh khng c nh hn 3m nu khng s
dng chng lm vt ni t t nhin.
Trng hp thc hin cc khong cch quy nh trn gp nhiu kh khn v khng hp
l v kinh t - k thut th c php ni chng v c b phn kim loi khng mang in
ca thit b in vi thit b chng st, tr cc phng c nguy c gy ra chy n,
nhng phi s dng hnh thc ni t mch vng bao quanh cng trnh. Dc theo chu
vi mi, c cch nhau t 15 n 20m t mt dy xung v hn dy xung vi mch vng
ni t ni trn.
2.24. i vi cc cng trnh cp III khng cao hn 16m, khng rng hn 20m,
khng c cc phng c nguy c n chy, khng tp trung ng ngi v xy dng ti
nhng vng c mt st nh thng khng cao, c th p dng phng thc bo v trng im
nh sau:
a) i vi cng trnh mi bng, ch cn bo v cho cc gc nh v dc theo chu
vi ca ng vin tng chn mi.
b) i vi cng trnh mi dc, mi rng ca, mi chng dim, ch cn bo v cho
cc gc nh, gc dim mi, dc theo b nc v dim mi. Nhng nu chiu di ca cng
trnh khng qu 30m th khng cn bo v b nc, v nu dc mi ln hn 280 th cng
khng cn bo v dim mi.
c) Bo v cho nhng b phn kt cu nh cao ln khi mt mi phi b tr cc kim
hoc ai thu st.
Nhng kim hoc ai ny phi c b ni vi b phn thu st ca cng trnh.
2.25. i vi nhng cng trnh c mi kim loi c php s dng mi lm b phn
thu v dn st nu b dy ca mi:
- Ln hn 4mm, i vi nhng cng trnh c mt s phng c nguy c n, chy.
- Ln hn 3,5mm, i vi nhng cng trnh khng c nguy c n, chy.
- Khi s dng mi lm b phn thu v dn st phi m bo c s dn in lin tc ca
mi. Nu khng, phi hn ni cc b phn ring r ca mi vi nhau, mi b phn t
nht phi c hai mi ni.
Dc theo chu vi mi c cch nhau 20 n 30m phi t mt dy xung, nu cng
trnh nh t nht cng phi c hai dy xung.
Trng hp b dy mi kim loi nh hn cc tr s quy nh trn, phi t b phn
thu st ring bo v, ch c s dng mi dn st v cng phi bo m yu cu dn in
lin tc nh trn.
2.26. i vi cc cng trnh bng tranh, tre, na, l phi b tr thit b
chng st c lp vi cng trnh. Nu xung quanh cng trnh c cc cy xanh, tt
nht l s dng cy xanh t thit b chng st, nhng cng phi bo m cc khong
cch an ton nh quy nh trong iu 2.4 ; 3.30 v 3.31.
Trng hp c li nhiu v kinh t - k thut th c php t thit b chng st
ngay trn cng trnh, nhng cn phi tha mn cc yu cu sau:
a) Phi s dng kim thu st lp trn ct cch in (g, tre...) khong cch t
cc phn dn in ca kim n mi cng trnh khng c nh hn 400mm.
b) Dy xung phi b tr trn cc chn khng dn in v cch mi t 150mm tr
ln.
c) Dy xung khng c xuyn qua mi. Trng hp c bit phi xuyn qua mi th
phi lun trong ng snh hoc s.
2.27. i vi cng trnh chn nui gia sc (loi gia sc ln) phi b tr thit
b chng st c lp. B phn thu st v b phn ni t phi t cch xa mng cng trnh
v ca ra vo mt khong cch t nht l 10m.
Trng hp c li v kinh t th c php t b phn thu st ngay trn cng trnh,
nhng b phn ni t phi t cch mng cng trnh v ca ra vo mt khong cch t
nht l 5m. Nu khng bo m c nhng khong cch ni trn, khi t xong b phn ni
t th phi ph lp ln trn mt lp dm (hoc si) nha ng c chiu dy t 100mm tr
ln, km theo nn t mt bin bo phng nga.
2.28. Chng st nh thng cho nhng ng khi cao:
a) Nu ng khi lm bng kim loi, b dy thnh ng ln hn 4mm, s dng ng
khi thu v dn st, trng hp ny ch cn tin hnh ni t cho ng khi. Nu b dy
thnh ng nh hn 4mm, phi t b phn thu st ring, ch s dng thnh ng dn st.
Khi s dng thnh ng thu st v dn st, cn phi hn ni cc b phn ring bit ca
ng vi nhau.
b) Nu ng khi bng b tng ct thp hay xy bng gch, , c th bo v bng
kim hoc ai thu st vin quanh ming ng khi.
Phm vi bo v ca kim thu st phi bao trm ton b ming ng khi. S lng v
kch thc kim phi xc nh theo tnh ton, nhng chiu di mi kim khng nn qu
3m.
Dc theo chiu cao ca ng khi, nu c dy bc thang dn in lin tc th c s
dng lm dy xung.
i vi ng khi cao t 40m tr ln phi c t nht l hai kim thu st v hai
dy xung, tr s in tr ni t xung kch khng ln hn 10 m.
2.29. Chng st nh thng cho nhng cng trnh khc nh i cha nc, thp
khoan, my ng cc, cn trc quy nh nh sau:
a) Nu chng bng kim loi, dn in lin tc t trn xung th s dng lm b
phn thu v dn st. Trng hp ny ch cn ni t cho cng trnh vi tr s in tr
ni t xung kch 10 m. Nu cng trnh nh cng phi c t nht l hai dy ni
t.
Trng hp cng trnh bng kim loi khng dn in lin tc, phi hn cc b phn
ring bit li vi nhau hoc t cc cu ni nhng khng c lm nh hng n hot ng
bnh thng ca thit b.
b) Nu chng khng phi lm bng kim loi, cn t b phn thu st ring bo v.
Dy xung b tr gn bc thang. Nu bc thang dn in lin tc th c s dng lm dy
xung. Nu cng trnh cao t 40m tr ln phi c t nht l hai kim thu st v
hai dy xung. Tr s in tr ni t xung kch khng c ln hn 10 m.
2.30. bo v chng st nh thng cho cc tng, i k nim khng phi bng kim
loi (gch, b tng ct thp, , p bng ...) nh tng i cn phi t kim hoc ai
thu st, khong cch t nh kim, hoc ai n nh tng, i khng quy nh. Dy xung
c th s dng ct thp chu lc trong thn tng i, nhng phi bo m dn in lin
tc. in tr ni t xung kch khng vt qu 10 m.
Trng hp tng, i bng kim loi phi m bo dn in lin tc v ch cn ni t
cho cc tng i vi in tr ni t xung kch khng vt qu 30 m.
2.31. Chng st nh thng cho cc b cha kn t ngoi tri p dng iu
2.16.
2.32. chng in p cao ca st lan truyn t ng dy trn khng dn vo cng
trnh phi p dng cc bin php bo v sau:
a) i vi ng dy in p di 1000V, ti u vo cng trnh phi t b chng st h
p, hoc khe h phng in. B phn ni t c in tr tn dng in tn s cng nghip
khng ln hn 20 m, ti ct th nht v th hai gn cng trnh phi ni t x v chn
s trn ct vi in tr tn dng in tn s cng nghip tng ng bng 20 v 30
m.
Ring i vi cc cng trnh xy dng dn dng c th khng cn t b chng st h p
hoc khe h phng in u vo cng trnh.
Nu in p ln hn 1000V, cn bo v theo cc quy nh ca Ngnh in lc.
b) i vi cc ng dy in yu cn bo v theo quy nh ca cc Ngnh ch
qun.
2.33. chng in p cao ca st lan truyn t cc ng ng bng kim loi, t ni
dn vo cng trnh phi p dng cc bin php bo v sau:
a) Ti u vo cng trnh, ng phi c ni t vi in tr tn dng in tn s cng
nghip khng ln hn 20 m.
b) Ti hai ct u tin gn cng trnh, mi ct phi c ni t vi in tr tn dng
in tn s cng nghip bng 40 m.
c) Ti cc ct tip theo thuc khu vc xy dng cng trnh, c cch nhau 250
n 300m phi ni t lp li vi tr s in tr tn dng in tn s cng nghip ca mi
b phn ni t bng 50 m.
Nu ng t nm mt t cng tin hnh ni t theo trnh t nh trn.
Chng III THIT B CHNG STKim thu st
3.1. Kim thu st c th bng thp trn, thp dt, thp ng hoc thp gc vi
tit din phn kim loi ca nh kim khng c nh hn 100 mm2 (nu thp dt, b dy
khng c nh hn 3,5mm; nu thp ng, b dy thnh ng khng c nh hn 3mm) v
chi
