Vi_TCVN46_1984

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