HNG DN LA CHN DY CP IN TRONG XY DNG NH Tnh ton la chn dy dn in cho nh l mt vic cn thit v quan trng, th nht l vn an tan cho ngi v ti sn, th hai l tit kim (v c th trnh c vic phi tho ra lm li khi thy khng ph hp). Hng dn ny trnh by mt cch ngn gn v vn ny, ng hu gip cho ngi dng t tin v d dng hn trong vic la chn dy dn in cho nh . Trong hng dn ny, cu trc v tn gi ca cc loi dy lp t trong nh (xem 3.3) c tham kho theo tiu chun TCVN 2103; cc loi cp ngoi tri v cp in k (xem 3.1 v 3.2) c tham kho theo tiu chun ca ngnh in lc cng nh cc nh sn xut cp uy tn Vit nam hin nay. Hng dn gm cc mc nh sau: - Cc ngun in s dng cho nh - Mt s cch i dy v loi dy tng ng, thng dng - Cc loi dy dn thch hp cho nh - Cng sut chu ti ca cc loi dy cp in thng s dng cho nh - Cch tnh ton v la chn dy dn - Cc lu cho h thng in nh - Nhng tc hi khi dng dy & cp in km cht lng - Nhng kinh nghim la chn dy in cho nh 1. Cc ngun in s dng cho nh 1.1 Ngun in 1pha 2dy (thng dng nht) Ngun 1pha 2dy gm c 1 dy pha v 1 dy trung tnh (cn c gi l 1 dy nng v 1 dy ngui). y l ngun in cho nh thng dng nht ti Vit Nam hin nay. 1.2 Ngun in 1pha 3dy Ngun in 1pha 3dy gm c 1 dy pha 1 dy trung tnh v 1 dy ni t (cn c gi l 1 dy nng, 1 dy ngui v 1 dy bo v). Vit Nam hin nay ngun in ny bt u p dng cc ta nh cao tng, bit th, building, khch sn, cc ni c s dng cc my mc thit b quan trng hoc cc nh cao cp hn. 1.3 Ngun in 3pha 4dy (t gp) Ngun in 3pha 4dy gm c 3 dy pha v 1 dy trung tnh (cn c gi l 3 dy nng, 1 dy ngui). Vit Nam hin nay ngun in ny t gp trong nh , tr khi ch nh c nh s dng thit b in 3pha. 1.4 Ngun in 3pha 5dy (rt t gp) Ngun in 3pha 5dy gm c 3 dy pha 1 dy trung tnh v 1 dy ni t bo v (cn c gi l 3 dy nng, 1 dy ngui v 1 dy bo v). Vit Nam hin nay ngun in

ny rt t gp trong nh , tr khi ch nh c nh s dng thit b in 3pha v c yu cu thm v dy bo v. 2. Mt s cch i dy v loi dy tng ng, thng dng 2.1 i dy ni: Dy & cp in c lun trong cc ng nha hoc np nha v c c nh trn tng, trn nh. S lng dy trong ng cn xem xt sao cho ng qu cht c th rt dy, lun dy khi cn thit sa cha thay th. Cc loi dy nh VCm, VCmd, VC l thch hp cho cch i dy ni. 2.2 i dy m tng, m trn, m sn: Dy & cp in c lun trong cc ng nha (ng trn khi i thng, ng rut g khi chuyn hng) t m trong tng, trn hoc sn nh. S lng dy trong ng cn xem xt sao cho ng qu cht c th rt dy, lun dy khi cn thit sa cha thay th. Cc loi dy nh VC, CV, CVV l thch hp cho cch i dy m. 2.3 i dy ngm: i vi cc cng trnh ngoi vi, khng dnh lin vi nh, dy & cp in c lun trong cc ng nha cng hoc ng thp chu lc, khng thm nc v chn ngm di t su khang 0,7mt. Cc loi cp c o gip thp hoc c bc kim loi th c th chn trc tip trong t m khng cn lun trong ng. Cn thit phi chn cc loi dy/ cp c kh nng chng thm nc, chng cn trng cho ng dy i ngm. 3. Cc loi dy dn thch hp cho nh Theo thng l ca ngnh in lc cng nh thc t hin nay Vit Nam, hng dn ny chn ngun in 1 pha 2 dy trnh by cho mc ch nh . Hng dn ny chia h thng dy cho nh ra lm 3 phn v tng ng vi mi phn hng dn ny a ra cc ngh v cc loi dy dn c th c dng nh sau: 3.1 on dy ngoi ng vo u nh (on dy ngoi tri) on dy ny l dy ni t li in a phng vo n nh, thng thng on dy ny nm han tan ngoi tri (ngoi tr mt s rt t nh s dng cp ngm th on dy ny c chn di t). on dy ngoi tri ny c ngh s dng mt trong cc loi dy/cp sau y: Cp Duplex rut ng, cch in PVC (Duplex Du-CV) Cp Duplex Du-CV c 2 rut dn bng ng, rut dn l 1 si ng c hoc 7 si ng c xon li vi nhau, mi rut dn c bc cch in PVC sau xon vi nhau. Cp in p ca cp l 450/750V hoc 0,6/1kV. Cp Duplex rut ng, cch in XLPE (Duplex Du-CX) Cp Duplex Du-CX c 2 rut dn bng ng, rut dn l 1 si ng c hoc 7 si ng c xon li vi nhau, mi rut dn c bc cch in XLPE mu en sau xon vi nhau, mt trong hai li c gn ni phn bit pha. Cp in p ca cp l 0,6/1kV.

3.2 on dy t u nh vo in k (on cp in k) on dy ny l dy ni t u cui on dy ngoi tri (c ni mc 3.1) n in k (ng h o in nng tiu th). Thng thng on dy ny nm mt na dc theo tng, mt na trong nh (v thng thng in k c t trong nh). on dy ny c ngh s dng mt trong cc loi dy/cp sau y: Cp in k rut ng, cch in PVC (K-CVV) Cp in k rut ng cch in PVC cn gi l cp Muller rut ng cch in PVC, cp c 2 hoc nhiu hn 2 rut dn, rut dn l 1 si ng c hoc 7 si c xon li vi nhau, mi rut dn c bc cch in bng vt liu PVC, mt lp bc lt PVC, mt lp bng nhm ( chng trm in) v lp v bc PVC bo v bn ngoi, cp in p ca cp l 450/750V hoc 0,6/1kV. Cp in k rut ng, cch in XLPE (K-CXV) Cp in k rut ng cch in XLPE cn gi l cp Muller rut ng cch in XLPE, cp c 2 hoc nhiu hn 2 rut dn, rut dn l 1 si ng c hoc 7 si c xon li vi nhau, mi rut dn c bc cch in bng vt liu XLPE mu trng-trong (mu t nhin), mt trong hai li c bng mu hoc sc mu phn bit pha, mt lp bc lt PVC, mt lp bng nhm ( chng trm in) v lp v bc PVC bo v bn ngoi, cp in p ca cp l 0,6/1kV.

3.3 Dy dn t in k n cc thit b tiu th in (dy dn trong nh)

Vit Nam, hu nh 2 on dy cp mc 3.1 v 3.2 u do ngnh in lc t la chn v lp t nu ch nh khng c yu cu g ring. Cn cc dy dn t in k n cc thit b tiu th in, hu ht l do ch nh t quyt nh lo liu, y l cng vic m hng dn ny cho l ch nh cn thit phi quan tm. Cc dy dn ny c ngh s dng mt trong cc loi sau y. 3.3.1 Dy n cng (VC) Dy n cng (VC) l dy c rut dn l 1 si ng, bc cch in PVC. Cp in p ca dy l 600V. Ngoi ra, cn c Dy n cng khng ch (LF-VC), khng tc hi cho con ngi v mi trng bng cch s dng vt liu PVC khng ch (LF-PVC), ph hp quy nh RoHS (Restriction of Hazardous Substances) ca chu u.

3.3.2 Dy n mm (VCm) Dy n mm (VCm) l dy c rut dn gm nhiu si ng c xon vi nhau, bc cch in bng vt liu PVC. Cp in p ca dy l 250V. Ngoi ra, cn c Dy n mm khng ch (LF-VCm), khng tc hi cho con ngi v mi trng bng cch s dng vt liu PVC khng ch (LF-PVC).

3.3.3 Dy i mm dt (VCmd) Dy i mm dt (VCmd) l dy c 2 rut dn, mi rut dn gm nhiu si ng xon li vi nhau, 2 rut dn ny c bc cch in PVC v phn cch in ca 2 rut dn dnh vi nhau to ra mt dy dt c 2 rut dn cch in song song vi nhau. Cp in p ca dy l 250V. Ngoi ra, cn c Dy i mm dt khng ch (LF-VCmd), khng tc hi cho con ngi

v mi trng bng cch s dng vt liu PVC khng ch (LF-PVC).

3.3.4 Dy i mm xon (VCmx) Dy i mm xon (VCmx) l dy c xon li t 2 dy n mm (VCm) ring bit. Cp in p ca dy l 250V. Ngoi ra, cn c Dy i mm xon khng ch (LF-VCmx), khng tc hi cho con ngi v mi trng bng cch s dng vt liu PVC khng ch (LF-PVC).

3.3.5 Dy i mm trn (VCmt) Dy i mm xon trn (VCmt) l dy gm 2 dy n mm (VCm) ring bit c xon li hoc t song song ri bc bn ngoi mt lp v bo v bng PVC. Dy ny cng c gi l cp CVVm. Cp in p ca dy l 250V. Ngoi ra, cn c Dy i mm trn khng ch (LF-VCmt), khng tc hi cho con ngi v mi trng bng cch s dng vt liu PVC khng ch (LF-PVC).

3.3.6 Dy i mm van (VCmo) Dy i mm van (VCmo) l dy gm 2 dy n mm (VCm) ring bit c xon li hoc t song song ri bc bn ngoi mt lp v bo v bng PVC. Dy ny cng c gi l cp CVVm van. Cp in p ca dy l 250V. Ngoi ra, cn c Dy i mm van khng ch (LF-VCmo), khng tc hi cho con ngi

v mi trng bng cch s dng vt liu PVC khng ch (LF-PVC).

3.3.7 Dy n cng, rut nhm (VA) Dy n cng, rut nhm (VA) l dy c rut dn l 1 si nhm, bc cch in PVC. Cp in p ca dy l 600V. Ngoi ra, cn c Dy n cng rut nhm khng ch (LF-VA), khng tc hi cho con ngi v mi trng bng cch s dng vt liu PVC khng ch (LF-PVC).

3.3.8 Dy in lc rut ng, cch in PVC (CV) Dy in lc rut ng, cch in PVC (CV) l dy c rut dn gm 7 (hoc 19) si ng xon ng tm, bc mt lp cch in PVC. Cp in p ca dy l 450/750V hoc 0,6/1kV. Ngoi ra, cn c Dy in lc rut ng, cch in PVC khng ch (LF-CV), khng tc hi cho con ngi v mi trng bng cch s dng vt liu PVC khng ch (LF-PVC).

3.3.9 Cp in lc rut ng, cch in PVC, v bo v PVC (CVV) Cp in lc rut ng, cch in PVC, v bo v PVC (CVV) l cp c 1 hoc nhiu li cp, mi li cp c rut dn gm 7 (hoc 19) si ng xon ng tm v bc mt lp cch in PVC. Cp CVV c mt lp v bo v PVC bn ngoi. Cp in p ca cp l 450/750V hoc 0,6/1kV. Ngoi ra, cn c Cp in lc rut ng, cch in PVC khng ch, v bo v PVC khng ch (LF-CVV), khng tc hi cho con ngi v mi trng bng cch s dng vt

liu

PVC

khng

ch

(LF-PVC)

cho

cch

in

v

v

bc.

4. Cng sut chu ti ca cc loi dy cp in thng s dng cho nh Mi c dy/ cp (tit din rut dn) v mi loi dy/cp c mc chu ti khc nhau. i vi mc ch nh , hng dn ny a ra cc bng m t cng sut chu ti ca cc loi dy/cp nh di y. Cng sut chu ti nu trong cc bng ny l ph hp vi nhit mi trng n 40 C v cng xem xt n vn st p nhm m bo cht lng in sinh hot cho nh . Bng 1: Cng sut chu ti ca cp Duplex Du-CV, Duplex Du-CX Tit din rut Cng sut dn chu ti 2 3 mm 5,5 kW 2 4 mm 6,8 kW 2 5 mm 7,8 kW 2 5.5 mm 8,3 kW 2 6 mm 8,7 kW 2 7 mm 9,5 kW 2 8 mm 10,6 kW Chiu di Tit din rut ng dy dn 30 m 10 mm2 30 m 11 mm2 35 m 14 mm2 35 m 16 mm2 35 m 22 mm2 40 m 25 mm2 40 m 35 mm2 Cng sut chu ti 12,1 kW 12,9 kW 15,0 kW 16,2 kW 20,0 kW 21,2 kW 26,2 kW Chiu di ng dy 45 m 45 m 50 m 50 m 60 m 60 m 70 m

Chiu di ng dy ngh s dng bng ny c tnh tan theo st p khng qu 5% iu kin y ti.

i vi ngun 1pha 2dy, 220V, sau khi chn c tit din rut dn ph hp vi cng sut nhng cha ph hp vi chiu di ng dy mong mun th ch vic tng tit din ln mt cp (v d tng t 3mm2 ln 4mm2) v kim tra li theo cng thc di y, nu tha mn th tit din dy va tng ln l ph hp, nu cha tha mn th tng tit din rut dn ln mt cp na v kim tra li nh trn cho n khi tha mn.

Trong P = Cng sut tnh tan chn dy, kW L = Chiu di ng dy mong mun, m S = Tit din rut dn ca dy, mm2 Bng 2: Cng sut chu ti ca cp in k K-CVV, K-CXV Cng sut chu ti Cch in Cch in PVC XLPE (K-CVV) 6,4 kW 7,6 kW 8,8 kW 9,4 kW 9,8 kW 10,8 kW 11,8 kW (K-CXV) 8,2 kW 9,8 kW 11,2 kW 11,9 kW 12,4 kW 13,8 kW 15,0 kW Cng sut chu ti Cch in Cch in PVC XLPE (K-CVV) 13,4 kW 14,2 kW 16,6 kW 17,8 kW 22,0 kW 23,6 kW 29,0 kW (K-CXV) 17,0 kW 18,1 kW 20,7 kW 22,0 kW 27,2 kW 29,2 kW 36,0 kW

Tit din rut dn 3 mm 4 mm2 5 mm2 5,5 mm2 6 mm2 7 mm2 8 mm22

Tit din rut dn 10 mm 11 mm2 14 mm2 16 mm2 22 mm2 25 mm2 35 mm22

Thng thng chiu di s dng Cp in k kh ngn nn khng cn quan tm n st p.

Bng 3: Cng sut chu ti ca dy VC, CV, CVV Tit din rut dn 0,5 mm2 0,75 mm2 1,0 mm2 1,25 mm2 1,5 mm2 2,0 mm2 2,5 mm2 Cng sut chu ti 0,8 kW 1,3 kW 1,8 kW 2,1 kW 2,6 kW 3,6 kW 4,4 kW Tit din rut dn 3 mm2 4 mm2 5 mm2 6 mm2 7 mm2 8 mm2 10 mm2 Cng sut chu ti 5,6 kW 7,3 kW 8,7 kW 10,3 kW 11,4 kW 12,5 kW 14,3 kW

Cng sut nu trong bng trn ph hp cho chiu di dy n 30m, vi st p khng qu 5% iu kin y ti

Bng 4: Cng sut chu ti ca dy i mm VCm, VCmd, VCmx, VCmt, VCmo Tit din rut dn 0,5 mm2 0,75 mm2 1,0 mm2 1,25 mm2 1,5 mm2 2,0 mm2 Cng sut chu ti 0,8 kW 1,2 kW 1,7 kW 2,1 kW 2,4 kW 3,3 kW Tit din rut dn 2,5 mm2 3,5 mm2 4 mm2 5,5 mm2 6 mm2 Cng sut chu ti 4,0 kW 5,7 kW 6,2 kW 8,8 kW 9,6 kW -

Cng sut nu trong bng trn ph hp cho chiu di dy n 30m, vi st p khng qu 5% iu kin y ti

Bng 5: Cng sut chu ti ca dy VA Tit din rut dn 1,0 mm2 1,5 mm2 2,0 mm2 2,5 mm2 3 mm2 4 mm2 Cng sut chu ti 1,0 kW 1,5 kW 2,1 kW 2,6 kW 3,4 kW 4,2 kW Tit din rut dn 5 mm2 6 mm2 7 mm2 8 mm2 10 mm2 12 mm2 Cng sut chu ti 5,5 kW 6,2 kW 7,3 kW 8,5 kW 11,4 kW 13,2 kW

Cng sut nu trong bng trn ph hp cho chiu di dy n 30m, vi st p khng qu 5% iu kin y ti

5. Cch tnh ton v la chn dy dn Tnh ton v la chn dy dn cn phi thc hin theo cc bc sau y. - Xc nh ngun in s dng - Tnh tng cng sut thit b tiu th in - La chn dy dn cho tng phn ca nh , bao gm ba bc nh: + La chn an dy ngoi tri + La chn an cp in k + La chn dy cho tng nhnh v dy n tng thit b tiu th in. 5.1 Xc nh ngun in s dng Cn c vo thit b in trong nh m ngi dng s dng l thit b 1 pha hay 3 pha, ng thi cng phi cn c vo ngun cung cp ca in lc a phng mnh c nhng loi ngun in no. Hu ht ngun in dng cho nh hin nay Vit Nam l ngun 1 pha 2dy. Bc ny thng b ph thuc vo ngun cung cp tng a phng, nu ngi dng

ch xi thit b in 1 pha v ngun a phng ca in lc ch c 2 dy (1 nng, 1 ngui) hoc 4 dy (3 nng, 1 ngui) th ch c ngun 1pha 2dy (nh nu mc 1.1) l p dng c. Trong trng hp ny vn c th chn ngun 1pha 3dy (nh nu mc 1.2) dng, nhng phi thit k thm h thng ni t cho h thng in trong nh, pha sau ng h o in. 5.2 Tnh tng cng sut thit b tiu th in Thit b tiu th in l nhng thit b hat ng bng nng lng in. Cc thit b tiu th in trong nh c th k ra nh: n in, qut in, ni cm in, bn i, t lnh, my git, l nng vi sng, my iu ha nhit , my bm nc Trn mi thit b tiu th in, hu ht u c ghi tr s cng sut, c n v l W (Woat) hoc kW (KilWoat) hoc HP (Horse Power- Sc nga). Mt cch gn ng, c th xem tt c cc tr s cng sut ghi trn cc thit b l cng sut tiu th in. Tnh tng cng sut thit b tiu th in l lit k v cng li tt c tr s cng sut ca cc thit b tiu th in trong nh nhm xc nh cng sut tiu th in tng ca c ngi nh. Khi gp cc n v cng sut khc nhau th quy i sang cng mt n v nh sau: 1kW = 1.000W 1HP = 750W 5.3 La chn dy dn cho tng phn ca nh y l buc cui cng tm ra cc c dy cn phi dng. Ty theo cng sut chu ti ca tng nhnh trong s in, ngi dng c th chn nhiu loi dy, c dy khc nhau. * V d: Tnh tan la chn dy dn cho mt nh c th. bi: Cn tnh tan chn la dy dn cho h thng in ca mt ngi nh 1 trt 1 lu, i dy m tng, khang cch t nh n li in a phng l 30m, tt c thit b in trong nh s dng in 1pha 220V, v c cng sut c nu trong bng sau.

Tng trt Tng lu Tn thit b/ S Tng cng sut Tn thit b/ S lng lng Cng sut Cng sut Bng n hynh 8 40 x 8 = 320W Bng n hynh 5 quang 1,2m/ 40W quang 1,2m/ 40W n trang tr/ 20W 5 20 x 5 = 100W n trang tr/ 20W 3 Qut in/ 100W 4 100 x 4 = 400W Qut in/ 100W 3 Ni cm in/ 1 600 x 1 = 600W My iu ha/ 1 600W 1,5HP

Tng cng sut

40 x5 = 200W 20 x 3 = 60W 100 x 3 = 300W 1,5 x 750 x 1 = 1125W

Tivi/ 150W 1 u my + ampli/ 150W L nng vi sng/ 1 1000W Bn i/ 1000W 1 My iu ha/ 1,5HP My git 7kg/ 750W M-t bm nc/ 750W Bi gii: 2 1 1

150 x 1 = 150W Tivi/ 150W 150 x 1 = 150W B my vi tnh/ 500W 1000 x 1 = My sy tc/ 1000W 1000W 1000 x 1 = 1000W 1,5 x 750 x 2 = 2250W 750 x 2 = 1500W 750 x 1 = 750W -

1 1 1 -

150 x 1 = 150W 500 x 1 = 500W 1000 x 1 = 1000W -

Bc 1: Xc nh loi ngun in s dng: V tt c thit b in trong nh s dng in 1pha, 220V nn ta chn ngun in thng dng nht l ngun 1pha 2 dy. Bc 2: Tnh tng cng sut thit b tiu th in: Cng tt c cng sut ca cc thit b ca tng trt, tng lu v cng sut tng ca c nh ta c s liu sau. Tng cng sut tng trt: 7.470W Tng cng sut tng lu: 3.335W Tng cng sut c nh: 10.805W Bc 3: La chn dy dn cho tng phn ca nh La chn an dy ngoi tri on dy ngoi tri l an dy dn in vo nh nn n phi chu c tng cng sut c nh l 10.805W. Tuy nhin, hu nh khng c thi im no m tt c cc thit b in trong nh hat ng ng thi cng mt lc, cho nn ngi ta c th gim cng sut tnh tan xung cn khang 80% cng sut tnh tan ri mi chn la dy dn theo cng sut c gim. Khi gim xung 80% nh vy ngi ta c cch gi khc l chn h s ng thi (kt) = 0,8. Trong v d ny hng dn ny cng chn kt = 0,8 v cng sut sau khi gim l: P = 10.805 x 0,8 = 8644W = 8,644kW on dy ngoi tri thng thng c s dng l loi dy Duplex rut ng, cch in PVC (Du-CV). Cn c vo cng sut 8,644kW ta tra bng tm c (tit din rut dn) cp cho thch hp. Tra bng 1 (cp Du-CV v Du-CX), chn gi tr ln hn gn nht ta thy cp tit din rut dn 6mm2 c cng sut chu ti ph hp. Chiu di lp t ca cp c tit din rut dn 6mm2 cho trong bng 1 cng tha mn vi chiu di lp t m u

bi yu cu l 30m, v vy ta c th chn on cp ngoi tri l cp Du-CV 26mm2 hoc Du-CX 26mm2 La chn an cp in k on cp in k ni t an dy ngoi tri vo n nh nn n cng phi c cng sut chu ti ln hn hoc bng 8,644kW. Tra bng 2 ta thy cp K-CVV tit din rut dn 5mm2 hoc cp K-CXV tit din rut dn 4mm2 l ph hp. on cp in k thng kh ngn (< 10m) nn khng cn quan tm n in p ri theo chiu di. Nh vy, ngi dng c th s dng K-CVV 2 x 5mm2 hoc K-CXV 2 x 4mm2. La chn dy cho tng nhnh v dy dn n tng thit b in Ngi nh c tng trt v 1 tng lu, hai tng c cng sut tiu th khc nhau nhiu, do tit kim ngi dng c th phn lm 2 nhnh. ng dy cho 2 nhnh ny ngi dng nn chn loi dy n cng (VC). Nhnh 1 cho tng trt: Tng trt c cng sut tng l 7.470W = 7,47kW. Tng t nh cp trn, hu nh cc thit b khng hat ng ng thi nn c th chn h s ng thi kt = 0,8, lc cng sut chn dy dn l 7,47 x 0,8 = 5,976kW. Tra bng 3 ta thy dy VC tit din rut dn 4mm2 l ph hp, nh vy ngi dng c th chn dy VC 4mm2 cho nhnh 1 (tng trt). Nhnh 2 cho tng lu: Tng lu c cng sut tng l 3.335W = 3,335kW. Tng t nh cp trn, hu nh cc thit b khng hat ng ng thi nn c th chn h s ng thi kt = 0,8, lc cng sut chn dy dn l 3,335 x 0,8 = 2,668kW. Tra bng 3 ta thy dy VC tit din rut dn 2mm2 l ph hp, nh vy ngi dng c th chn dy VC 2mm2 cho nhnh 2 (tng lu). Dy cho tng thit b: Theo l thuyt th mi thit b c cng sut khc nhau s cn mt c dy khc nhau. Vic chn tng c dy ring cho tng thit b nh vy c u im l tit kim c chi ph dy dn, nhng li rt phc tp cho vic mua dy cng nh i dy, s phc tp ny nhiu khi cng rt tn km. V vy, khi trong nh khng c thit b no c cng sut ln c bit th ngi dng c th chn mt c dy v dng chung cho tt c cc thit b. Cng sut s dng cc cm thng khng c nh, khng bit trc chc chn, v i khi c hai hay nhiu thit b s dng chung mt cm, do , bm bo, ngi dng nn chn dy cho cm hn mt cp so vi c dy d nh dng chung cho tt c cc thit b. Ty theo cch lp t, ngi dng c th chn loi dy n cng hoc dy i mm, ngi nh trong v d ny c yu cu i dy m tng nn ta chn dy n VC cho tt c cc thit b. Nhn vo bng cng sut ta thy cng sut ca my iu ha nhit 1,5HP (1,125kW) l ln nht, tra bng 3 ta thy cp VC tit din rut dn 0,75mm2 l ph hp,

tuy nhin cn chn dy cho cm hn mt cp cho nn ngi dng c th chn dy VC 1,0mm2 cho tt c cc thit b v cm. Tm li: Cc loi dy, c dy c tnh ton la chn cho ngi nh trn nh sau: - on dy ngoi tri: cp Duplex Du-CV 26mm2 hoc Duplex Du-CX 26mm2 - on cp in k: cp K-CVV 2 x 5mm2 hoc K-CXV 2 x 4mm2 - Dy cho nhnh tng trt: dy VC 4mm2 - Dy cho nhnh tng lu: dy VC 2mm2 - Dy cho cc thit b in v cm: dy VC 1,0mm2 Ghi ch: Ngi dng c th la chn lp t cc loi dy & cp khng ch vi tit din rut dn ging nh la chn trn. 6. Cc lu cho h thng in nh - Nn chia ng in phn phi trong nh thnh nhiu nhnh thun tin cho vic ngt in khi cn sa cha, thay th. - Cc dy pha (dy nng) c cng mu v tt nht l mu , mu cam hoc mu vng. Khi c nhiu nhnh i chung mt tuyn m kch c ging nhau th mu ca tng nhnh nn khc nhau d phn bit. - Dy cho h thng ni t nn c mu ring bit vi tt c cc dy khc v nn chn dy mu xanhscvng hoc vngscxanh. - Khi lun dy trong ng hoc trong np, phi chn kch thc ng, np rng sao cho d lun, d rt m khng h hi n dy dn. - Khng nn i dy ni m thp hoc qu gn cc ngun nhit, ha cht. - Mi ni dy phi cht, tip xc tt khng gy ra m-ve nc la khi mang ti. - Khng c ni trc tip rut dn ng v nhm vi nhau. on dy i trong ng khng nn c mi ni. - Khng nn i dy m trong nn ca tng trt nu nn khng m bo c nh vi tng khi nn b ln. - Khng nn s dng dy c tit din nh hn 0.5mm2. 7. Nhng tc hi khi dng dy & cp in km cht lng Khi rut ng km cht lng hoc khng tit din c th gy ra cc tc hi sau - Dn in km, gy st p trn ng dy lm cho thit b hat ng khng hiu qu, tui th thit b gim nhanh. - Pht nng qu mc trn ng dy, gy h hi lp cch in, gy chm chm chy n. - Rut ng km cht lng rt d gy, kh ni, kh lp vo cc ph kin in khc. Khi lp cch in km cht lng c th gy ra cc tc hi sau Nt cch in, h rut dn, gy in git cho ngi. - Rn nt cch in sau mt thi gian ngn, gy r in, tn tht in nng, chm chp

chy n. - Khng chu c nhit cho php ca rut dn, chy nho gy ra chm chp chy n. - Khng t tt khi b pht chy bi tc nhn bn ngoi. - Mt mu sau mt thi gian ngn, gy nhm ln cc dy vi nhau khi sa cha, thay th. 8. Nhng kinh nghim la chn dy din cho nh Nhng kinh nghim c nu y ch yu hng ti cc loi dy dng trong nh (nh mc 3.1 cp). Vi rt nhiu cc loi dy in trn th trng hin nay, tt c, xu c, tht c, gi c, thm ch c khi gp dy chng c nhn mc, tn nh sn xut g c. V vy, mt ngi khng chuyn th vic la chn dy no, nhn hiu no m c th tin cy c l mt vic khng d dng g. Bng mt vi kinh nghim ca ngi bin son, hng dn ny a ra mt s khuyn ngh v nhng ch du hy vng rng ngi dng c th trnh c cc sn phm dy/ cp in km cht lng. - Khng nn chn dy khng c nhn mc trn bao b, khng c tn nh sn xut, khng a ch r rng. - Khng nn chn dy m trn dy khng c cc thng tin c bn nh: nhn hiu, tn loi dy, tit din, cu trc rut dn (s si v ng knh mi si), tiu chun sn xut. - Dy tt thng c b ngoi ca v nha bng, lng. - Lp nha cch in ca dy tt rt do, khi tut ra khi rut dn, c th ko gin gp i, gp ba chiu di ban u m cha b t. Dy c th b gp nhiu ln hoc xon gt nhng b mt cch in khng b rng nt. - C th kim tra rut dn, bng cch m s si nh bn trong so vi s si c ghi bn ngoi. ng knh ca cc si nh bn trong rt kh kim tra, v phi c thc chuyn dng mi o c. Tuy nhin, vi mt thng hiu uy tn, trn dy c ghi c th cu trc rut dn (s si v ng knh mi si) th c th tin tng c. - Dy tt th c rut dn sng, bng, nu l dy ng th rut dn rt mm do. i vi dy rut dn ng c nhiu si nh th c th dng hai ngn tay xon rut dn d dng m cc si nh khng bung, khng gy, khng m vo tay. i vi dy rut dn c mt si th c th b gp rut ng n vi chc ln m khng gy. - Thng thng, dy tt c gi cao hn dy dm vi cng c loi. TP.HCM, thng 3/2009 Ng Hu on- Cng ty Cp in Thnh Pht