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Read MoreThe UKK series is Naihang Electric’s line of single-phase distribution blocks, rated from 80 A up to 500 A. They look similar at a glance, but each model accepts a different input conductor range and offers a different number of output positions, so choosing the wrong one means either an undersized block that overheats or an oversized block that wastes panel space. Size a UKK distribution block by matching three things: the total load current, the input conductor range, and the number of output circuits you need to feed. This guide walks through each step with the full UKK series specifications.
Quick Answer: How to Pick the Right UKK Model
Follow this three-step logic, then confirm against the table below:
- Calculate the total load current. Add the full-load current of every branch circuit, then apply a safety margin of about 20% for startup surges and ambient temperature.
- Match the input conductor. Your feeder wire size must fall inside the model’s input conductor range (for example, 10 to 70 mm² for the UKK 160 A).
- Count the outputs. Choose a model with at least as many output positions as the branch circuits you need, and make sure each branch conductor fits the output ranges.
In practice, the UKK 80 A suits small panels and light loads, the 125 A and 160 A models cover common distribution duties, the 250 A handles heavier feeders, and the 400 A and 500 A models are for large single-phase distribution points.
UKK Series at a Glance
All UKK models share the same construction: nickel-plated brass conductors, nickel-plated steel screws, PA66/UL94 V-2 housing, a transparent PC cover, 35 mm DIN-rail or screw mounting, 690 V rated voltage, and compliance with IEC 60947-7-1 with CE and RoHS certification. They differ in size, current rating, input capacity, and output layout.
| Model | Rated Current | Dimensions (L×W×H) | Input Range | Output Positions | Impulse Withstand (IPk) |
|---|---|---|---|---|---|
| UKK 80 A | 80 A | 69 × 31 × 46 mm | 6–16 mm² | 2.5–6 mm² × 4 + 6–16 mm² × 2 | 22 kA |
| UKK 125 A | 125 A | 75.5 × 31 × 46 mm | 10–35 mm² | 4–25 mm² × 1 + 2.5–16 mm² × 6 | 30 kA |
| UKK 160 A | 160 A | 75.5 × 31 × 46 mm | 10–70 mm² | 4–25 mm² × 1 + 2.5–16 mm² × 6 | 30 kA |
| UKK 250 A | 250 A | 97 × 50 × 50 mm | 35–120 mm² | 6–35 mm² × 2 + 2.5–16 mm² × 5 + 2.5–10 mm² × 4 | 51 kA |
| UKK 400 A | 400 A | 97 × 50 × 50 mm | 95–185 mm² | 6–35 mm² × 2 + 2.5–16 mm² × 5 + 2.5–10 mm² × 4 | 51 kA |
| UKK 500 A | 500 A | 97 × 50 × 50 mm | 8 × 24 mm² (busbar style) | 6–35 mm² × 2 + 2.5–16 mm² × 5 + 2.5–10 mm² × 4 | 51 kA |
Step 1: Calculate Your Load Current
The distribution block must carry the combined current of every branch it feeds, so start by adding the full-load current of all connected loads. If the loads are motors or other equipment with startup surges, add a margin of about 20%, and check the ambient temperature of the enclosure, since high ambient heat reduces the effective capacity of any electrical component.
Example: three branch circuits drawing 30 A, 45 A, and 60 A give a total of 135 A. With a 20% margin, the design target is about 162 A, which points to the UKK 160 A or higher rather than the UKK 125 A.
Never pick a block rated below the sum of the branch currents. The first terminal and the internal conductor carry the full combined current, and an undersized block runs hot and fails early.
Step 2: Match the Input Conductor Size
Every UKK model specifies an input conductor range. The feeder cable must fit inside that range; forcing a conductor into a smaller terminal, or leaving a large lug only partially filled, creates a poor connection that runs hot.
- UKK 80 A accepts 6–16 mm² input, roughly AWG 16–4.
- UKK 125 A and UKK 160 A accept 10–35 mm² and 10–70 mm² respectively.
- UKK 250 A accepts 35–120 mm² input (up to 250 kcmil).
- UKK 400 A accepts 95–185 mm² input (up to 400 kcmil).
Check the tightening torque for your chosen model and use a torque wrench or screwdriver with a calibrated setting. The UKK datasheets publish the torque values for each interface group.
Step 3: Count the Output Circuits
Then count how many branch circuits the block must feed and check the output layout. The UKK series offers different output combinations per model:
- UKK 80 A: 2.5–6 mm² × 4 plus 6–16 mm² × 2.
- UKK 125 A and 160 A: 4–25 mm² × 1 plus 2.5–16 mm² × 6.
- UKK 250 A, 400 A, and 500 A: 6–35 mm² × 2 plus 2.5–16 mm² × 5 plus 2.5–10 mm² × 4.
Each output position is sized for a specific conductor range, so verify that every branch wire fits its assigned position. If you need more outputs than one block provides, you can use a second block or a busbar arrangement; the distribution block vs busbar comparison explains that choice.
How Many Poles Do You Need?
The UKK series is single-phase: each block distributes one phase. For a three-phase panel, install one UKK block per phase, with phase separation in the panel layout. When you order, specify the quantity per phase, and keep the phases clearly labeled for maintenance.
If your distribution point must handle more than one phase in a single packaged unit, Naihang’s four-phase distribution block range is the better fit; the power distribution block selection guide covers that decision in more detail.
Voltage, Standards, and Environment
All UKK models are rated 690 V and comply with IEC 60947-7-1, with CE and RoHS certification. For export panels, confirm that these certifications match the requirements of your target market, and note that the transparent PC cover allows visual inspection of the terminations without de-energizing the panel.
The PA66 housing carries a UL94 V-2 flammability rating, suitable for standard industrial enclosures. If your panel operates in high ambient temperatures, derate the block’s current rating accordingly and check the manufacturer’s guidance.
Common Sizing Mistakes to Avoid
- Choosing by current rating alone. The input conductor range and output layout are just as important; a block rated high enough for the amps may still reject your feeder wire.
- Forgetting the margin. A block sized exactly at the calculated load runs at its limit with no room for surges or temperature.
- Mixing up single-phase and three-phase. UKK blocks are single-phase; install one per phase for three-phase systems.
- Over-tightening terminals. Use the published torque values to avoid damaging the conductor or the block.
- Skipping overcurrent protection. A distribution block distributes power but does not protect circuits; install the correct upstream protective device.
FAQ
How do I choose the right UKK distribution block size?
Add the full-load current of all branches with a safety margin, match the feeder conductor to the model’s input range, and confirm the output positions cover your branch circuits.
What is the difference between the UKK 125 A and UKK 160 A?
They share the same footprint (75.5 × 31 × 46 mm) and output layout, but the 160 A model accepts a larger input conductor (10–70 mm² versus 10–35 mm²) and is rated for higher current.
Can a UKK block be used for three-phase distribution?
UKK blocks are single-phase. For three-phase systems, install one block per phase or use a purpose-built multi-phase distribution block.
What wire sizes do UKK blocks accept?
Input ranges span 6–16 mm² on the UKK 80 A up to 95–185 mm² on the UKK 400 A; output positions range from 2.5 mm² up to 35 mm² depending on the model.
What certifications do UKK distribution blocks carry?
All UKK models comply with IEC 60947-7-1 and carry CE and RoHS certification, with PA66/UL94 V-2 housing and 690 V rated voltage.
Conclusion
Sizing a UKK distribution block is a three-step exercise: calculate the total load current with margin, match the input conductor to the model’s range, and confirm the output layout covers your branch circuits. The UKK 80 A to 500 A range covers everything from light single-phase distribution to heavy feeders, all with the same PA66 housing, transparent cover, and 690 V / IEC 60947-7-1 compliance. Browse the single-phase distribution block range or contact the manufacturer with your load currents and conductor sizes to confirm the right model for your panel.
