Lý thuyết điện & an toànElectrical theory & safety · BàiLesson 4/6
DC Cables and Connectors
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Solar Knowledge HubDây cáp và đầu nối một chiềuDC cable and connectors
Phần một chiều dùng dây một chiều, phần điện trong nhà dùng dây xoay chiều, tuyệt đối không kéo dây trong nhà lên mái cho chuỗi pin.DC side uses DC cable, indoor wiring uses AC cable: never run household cable up to the roof for a PV string.
| Tiêu chíCriterion | Dây một chiều (PV1-F, H1Z2Z2-K)DC cable (PV1-F, H1Z2Z2-K) | Dây xoay chiều dân dụngHousehold AC cable |
|---|---|---|
| Loại điệnCurrent type | Một chiềuDirect current | Xoay chiềuAlternating current |
| Điện áp làm việcWorking voltage | Cao · 1000–1500VHigh · 1000–1500V | Thường tới 450/750VUsually to 450/750V |
| Chịu tia cực tímUV resistance | Rất tốtExcellent | Trung bình / kémFair / poor |
| Chịu nhiệtHeat rating | Tới 120°CUp to 120°C | Tiêu chuẩn dân dụngHousehold standard |
| Chống cháyFire resistance | Tốt hơnBetter | Bình thườngOrdinary |
| Ứng dụngUse | Tấm pin, pin lưu trữ, chuỗi DCPV, battery, DC strings | Lưới, tải AC trong nhàGrid, indoor AC loads |
| GiáPrice | Cao hơnHigher | Rẻ hơnLower |
- Hồ quang: hồ quang DC khó dập, nhiệt cao → dây DC cần cách điện & chịu nhiệt tốt hơn.Arcing: DC arcs are hard to quench and hotter → DC cable needs better insulation and heat rating.
- Điện áp: chuỗi pin tới ~1000–1500V; điện áp DC cao làm cách điện PVC dân dụng (450/750V) xuống cấp nhanh.Voltage: strings reach ~1000–1500V; high DC voltage ages household PVC insulation (450/750V) fast.
- Môi trường: dây DC chạy ngoài mái nóng; dây dân dụng không chịu UV, nứt vỡ sau vài năm (dây chuyên dụng > 25 năm).Environment: DC cable runs on hot roofs; household cable fails under UV in a few years (purpose cable > 25 years).
Chuỗi pin dùng đầu nối MC4 chuyên dụng, bấm đúng đầu MC4 bằng kìm chuyên dụng. Trộn đầu nối khác hãng hoặc bấm sai → tiếp xúc kém, nóng giắc, hồ quang.Strings use proper MC4 connectors, crimped with the right tool. Mixing brands or bad crimps → poor contact, hot joints, arcing.
Dây chuyên dụng đắt hơn vì phải chịu nắng mưa 25 năm + điện áp DC cao mà dây thường không kham nổi. Tiết kiệm tiền dây = đánh đổi bằng rủi ro cháy.DC cable costs more because it must survive 25 years outdoors and high DC voltage. Saving on cable trades for fire risk.
A question that seems simple but leads to serious failures is whether household electrical cable can substitute for purpose-made cable in a solar string. The short answer is: it should not, and in many cases it must not. This document explains why DC and AC cables differ and why using the wrong cable is a foreseeable fire risk.
For: installation technicians and procurement staff, newcomers who need to distinguish between the two cable types, and sales staff who need to explain why purpose-made cable is more expensive but necessary.
Quick summary
DC cable is used on everything before the inverter: from the panels to the inverter and from the battery storage to the inverter. AC cable is used on everything after the inverter: from the inverter to the distribution board, household loads, and the grid connection.
Purpose-made DC cable is rated for high voltages up to approximately 1000 to 1500 V, withstands UV radiation and high outdoor temperatures, and has thicker insulation. Household AC cable is rated only to 450/750 V and is not durable outdoors.
Using AC cable for a DC string is incorrect: high DC voltage degrades the insulation quickly, the jacket of household cable cracks under sunlight, and the risk of a DC arc fault increases significantly.
Two cable types for two sections of the system
A solar power system has a clear boundary at the inverter. Everything before the inverter carries direct current: the runs from the panels to the string combiner box, from the combiner box to the inverter, and from battery storage to the inverter. Everything after the inverter carries alternating current: the runs from the inverter to the distribution board, to household loads, and to the grid connection. Each section requires its own cable type.
Purpose-made DC cable is designed for harsh outdoor environments and high DC voltages. The two common types are PV1-F and H1Z2Z2-K, with H1Z2Z2-K being the newer standard. They feature multi-strand fine-wire copper conductors, thick insulation rated to 120 °C, and an outer jacket that is UV-resistant and flame-retardant, with an outdoor service life of 25 years or more. Cross-sections commonly used for residential strings are 4 or 6 mm².
Household AC cable is optimised for indoor wiring. It has copper conductors, conventional PVC insulation and sheath, is rated to 450/750 V, is easy to install, and is less expensive. Its weaknesses are poor UV resistance and no design provision for high DC voltage.
Why the two types cannot substitute for each other
There are three technical reasons why AC cable should not be used in a DC string. The first is arc fault behaviour. As discussed in document 01-03, a DC arc is difficult to extinguish and generates more heat, so DC cable must have superior insulation and thermal resistance.
The second reason is voltage. A solar string can reach several hundred volts, and on modern systems up to approximately 1000 V (and up to 1500 V on commercial systems). Household cable is rated only to 450/750 V AC; high DC voltage causes charge accumulation in the PVC insulation layer, accelerating its degradation.
The third reason is the environment. DC cable typically runs outdoors on a hot roof, where household cable cannot withstand UV radiation, cracks and ages rapidly. A household cable used on a rooftop can fail in its insulation after just a few years, while purpose-made cable is durable for more than twenty-five years.
| Criterion | DC cable (PV1-F, H1Z2Z2-K) | Household AC cable |
|---|---|---|
| Current type | Direct current | Alternating current |
| Working voltage | High, 1000 to 1500 V | Typically up to 450/750 V |
| UV resistance | Excellent | Moderate or poor |
| Thermal rating | Up to 120 °C | Standard residential |
| Flame retardancy | Superior | Standard |
| Application | Panels, battery storage, DC strings | Grid, household AC loads |
| Price | Higher | Lower |
Connectors matter as much as cable. Strings use purpose-made MC4 connectors, which must be crimped with a dedicated MC4 crimping tool to ensure a secure contact. Mixing connectors from different manufacturers or improper crimping is a common cause of poor contact, overheating at the connector, and arc faults.
Sales takeaway
When a customer asks why solar cable costs more than standard cable, the concise answer is that purpose-made cable must withstand sun, rain, and outdoor conditions for twenty-five years while handling high DC voltages that standard cable simply cannot tolerate. Saving money on cable here means trading it for a fire risk, a trade-off that is not worth making.
An easy message for customers to remember: the DC section uses DC cable, the household wiring section uses AC cable, and under no circumstances should indoor cable be run up to the roof for a solar string.