How to Select a DT Copper Lug When All You Know Is the Load Power
Choosing a DT copper lug is complicated only if you make it complicated. It is complicated because it involves converting voltage, current and power, plus the various demands of the installation environment. It is simple because it comes down to one sentence: look at the cable first, then at the current, and finally leave yourself some margin.
🔌 Voltage, current, power — which one drives the selection?
Many people worry: “Mine is 380 V or 220 V — does a higher voltage mean a bigger lug?” In fact, DT lug selection depends on current alone. The voltage class mainly affects insulation and creepage distances; for a purely conductive bare terminal like a copper lug, as long as the voltage stays within the insulation rating of your equipment, the same cable can use the same lug at any of these voltages.
Power and current, on the other hand, do require a calculation. For a 10 kW three-phase 380 V motor the rated current is around 20 A (a rough rule of thumb: power × 2); a single-phase 220 V 10 kW load, by contrast, pulls about 45 A. So the first step is to establish the rated current of your equipment.
📊 Quick selection table (just look it up)
Below are the common DT sizes and their reference ampacity ratings. Note that these current values are safe reference ranges — they vary between standards and installation conditions — but they are enough for a first-pass selection.
| Cable cross-section (mm²) | DT model | Reference ampacity (A) | Typical use | Stud hole reference |
|---|---|---|---|---|
| 10 | DT-10 | 50–80 | Low-power equipment, control panel wiring | M6/M8 |
| 16 | DT-16 | 60–106 | Lighting feeders, small motors | M6/M8 |
| 25 | DT-25 | 80–143 | Distribution box feeders, medium motors | M8/M10 |
| 35 | DT-35 | 100–175 | Workshop power lines, service drops | M8/M10 |
| 50 | DT-50 | 125–223 | Power supply for larger equipment | M10/M12 |
| 70 | DT-70 | 160–265 | Switchgear main circuits | M10/M12 |
| 95 | DT-95 | 180–329 | High-power equipment, main incomer | M12/M16 |
| 120 | DT-120 | 250–382 | Transformer outgoing, main runs | M12/M16 |
| 150 | DT-150 | ~445 | Large distribution systems | M12/M16 |
| 185 | DT-185 | 315–519 | Main distribution, high-current circuits | M16 |
| 240 | DT-240 | 400–609 | Main incomer, transformer side | M16/M20 |
| 300 | DT-300 | ~705 | High-capacity distribution | M16/M20 |
| 400 | DT-400 | ~832 | Substations, heavy industrial equipment | M16/M20 |
| 500 | DT-500 | ~965 | Heavy industry, large transformers | M16/M20 |
| 630 | DT-630 | ~1134 | Main transformers, very large equipment | M20 |
Note: the ampacity figures reference recommended values from several sources; allow 15–20% margin in real applications.
📝 Selection in practice: three steps
Step one: pick the model from the cable. The number in the DT model corresponds directly to the cable cross-section. If you are holding 35 mm², choose DT-35 — this is a hard rule. The internal diameter of the lug has to match the cable’s outer diameter, and it should normally be 0.2–0.5 mm larger than the cable; too loose and it will not crimp tight, too tight and the cable will not go in.
Step two: pick the size from the current. Say you have calculated a rated current of 150 A. Looking at the table, DT-50 covers 125–223 A, so DT-50 is sufficient. But if the equipment runs at full load continuously, step up one size to DT-70 for extra margin.
Step three: leave margin. Manufacturer ratings are normally measured at an ambient temperature of 40 °C with a temperature rise of no more than 50 K. Your actual installation may be hotter, or several conductors may be bundled together with poor heat dissipation. In that case use the terminal at 80% of its rated current — in other words, apply a 20% derate. For 150 A, choose a size rated to carry 180 A or more.
⚠️ Two common pitfalls
Do not get the stud hole wrong. The number after DT is the wire size, but the stud hole in front of it has to match as well. If your busbar stud is M10, choose a lug with a hole of about 10.5 mm — a hole 0.2–0.5 mm larger than the stud is just right. Too small and it will not fit; too large and the contact area is insufficient, which leads to heating.
Match the material and plating to the environment. For ordinary environments, T2 copper with tin plating is sufficient — the tin prevents oxidation and keeps the contact resistance stable. But if your equipment is damp, oily or near the coast, the oil-block structure of the DT series (with a sealing ring on the inner wall) is the better choice, because it stops moisture and oil from tracking down the conductor into the barrel.