Day Thu Cap Thu Hai cua May Bien Ap va Sut Ap
Mach thu cap cua may bien ap de bi hieu nham vi aptomat trong tu dien co ve nhu da cho du thong tin. Thuc te, can xem khoang cach tu dau cuc thu cap den thiet bi bao ve dau tien, dong dien thu cap thuc te va muc sut ap co the lam dong co, VFD, may han, HVAC hay mach o cam yeu di bao nhieu.
Voi du an theo NEC, can kiem tra NEC 240.21(C) cho day thu cap, NEC 450.3 cho bao ve may bien ap, NEC 310.16 cho ampacity va muc tieu 3% / 5% trong ghi chu cua NEC 215.2(A)(1) va 210.19(A)(1). Theo IEC, IEC 60364-5-52 va bang G.52.1 la tai lieu thuc dung nhat. NEC IEC
“When a transformer secondary run is long, code legality is only step one. The equipment still needs healthy voltage at the far end.”
— Hommer Zhao, Technical Director
Vi Sao Thu Cap Can Duoc Kiem Tra Rieng
- May bien ap co the gan nguon nhung xa tu dien, khien day thu cap tro thanh diem sut ap yeu nhat.
- Khi ha ap, dong dien tang len. Mot may bien ap 45 kVA o 208Y/120V co dong thu cap lon hon nhieu so voi phia 480V.
- Quy tac day thu cap phu thuoc vao vi tri thiet bi bao ve dau tien. Cau hinh hop le van co the cho hieu nang kem neu chi chon day theo ampacity toi thieu.
- Ngoai hien truong, dau hieu dau tien thuong la den mo, dong co kho khoi dong va mini-split hay may nen nghe co ve qua tai.
Cac Moc Tieu Chuan Nen Ghi Tren Ban Ve
- NEC 240.21(C): day thu cap cua may bien ap chi duoc phep khi dap ung dieu kien ve chieu dai, bao ve va diem ket thuc tai OCP dau tien.
- NEC 450.3: bao ve qua dong cua may bien ap can duoc phoi hop giua phia so cap va thu cap.
- NEC 310.16: truoc tien day dan phai hop le ve nhiet, sau do moi toi uu sut ap.
- NEC 215.2(A)(1) va 210.19(A)(1): muc tieu pho bien van la khoang 3% o doan cuoi va 5% tong cong.
- IEC 60364-5-52 / bang G.52.1: gioi han thong dung la 3% cho chieu sang va 5% cho tai khac, co xet den group va cach lap dat.
Vi Du Co So Cu The
May bien ap 25 kVA, 480-240V 1 pha, 104A thu cap, 60 ft den tu dien
Dong 1 AWG cho sut ap khoang 3,0 V, tuc 1,25% o 240V. 2/0 nhom vao khoang 4,8 V, tuc 2,0%. Ca hai deu co the dung, nhung dong de lai bien an toan tot hon cho o cam va dong co nho.
May bien ap 45 kVA, 480-208Y/120V, 125A thu cap, 110 ft den panelboard
1/0 dong cho khoang 6,0 V line-to-line, tuc 2,9% o 208V. Tang len 3/0 dong thi giam con 3,8 V, tuc 1,8%, tot hon cho VFD va dieu khien HVAC.
May bien ap 75 kVA, 480-240V 1 pha, 312A thu cap, 180 ft den MCC
4/0 nhom co the ra khoang 8,9 V, tuc 3,7% o 240V. 250 kcmil nhom giam xuong khoang 6,0 V, tuc 2,5%, su khac biet thuong thay ro tren dong co.
Danh Sach Kiem Tra Truoc Khi Chot Co Day
- Tinh dong thu cap day tai tu kVA va dien ap truoc khi nhin vao aptomat.
- Do dung khoang cach mot chieu tu dau cuc thu cap den OCP dau tien hoac CB tong cua tu.
- Xac nhan cau hinh dap ung NEC 240.21(C) hoac phuong phap dia phuong / IEC.
- Xem dung tai thuc te: dong co, HVAC, may han, bo sac va dieu khien dien tu nhay cam hon tai tro.
- Dua cac lua chon cuoi vao calculator va so sanh voi dung sai dien ap cua thiet bi, khong chi voi ampacity toi thieu.
Kiem Tra Thu Cap Truoc Khi Keo Cap
Nhap dien ap thu cap, dong tai, co day va chieu dai mot chieu de so sanh cac phuong an truoc khi thi cong.
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