What This Comparison Is About
I coordinate emergency parts for industrial plants. In the last eight years, I have handled more than 120 rush orders, including same-day turnarounds for a food processing plant and an automotive supplier. When a 24 VDC power supply dies, the clock is measured in hours, not days. The part that gets the line running again is often a terminal block on a TS35 rail.
Today I am going to compare two ways to land power supply wiring: the classic Weidmuller WDU 35 screw-clamp terminal block and Weidmuller push-in terminal blocks. I will compare them the way I actually look at them when triaging a breakdown—speed, reliability, repairability, space, and cost.
First, the Names: What Is What?
What Is Weidmuller Holdings?
Weidmuller Holdings is the corporate parent behind the Weidmuller brand. You don't order from the holding entity; you order a terminal block from a distributor. But it matters because the holding company decides which product lines stay in the catalogue, how spares are stocked, and which technologies get development money.
What Is a TS35 Rail?
TS35 is the DIN rail profile. Per IEC 60715, a TS35 rail is a top-hat rail with a 35 mm width. It is the standard rail in almost every control cabinet I touch. Terminal blocks clip onto it. Power supplies mount on it or sit right next to it.
What Is a WDU 35?
WDU 35 is a feed-through terminal block from Weidmuller. The WDU family uses screw-clamp termination. Per Weidmuller's published product information (as of early 2025), the 35 in the name refers to the rated conductor cross-section in square millimeters. It is not a current rating. This is a block for real power wiring—230 VAC feeds into a power supply, larger DC outputs, motor leads, that kind of thing.
What About Power Supplies?
The power supplies I am referring to here are the switch-mode 24 VDC units used in modern panels. Whether it is a single 5 A unit or a 40 A redundant setup, the input and output circuits usually go through terminal blocks on the rail. That makes the terminal block the point where an emergency repair lives or dies.
The Comparison Framework
Here is what I care about when a line is down: time, feasibility, and worst-case risk. I will go through five dimensions, and I will give a verdict after each one.
1. Wiring Speed
On a fresh panel, push-in wins. Strip the wire, push it in, done. A prepared wire connects in seconds. I have wired control circuits this way, and the time savings are real. Last quarter alone, we processed 47 rush orders, and three of those were for panels using push-in blocks. The electricians finished clearly faster than with screw clamps.
But an emergency is not a fresh panel. In March 2024, a packaging plant called at 2:30 PM with a dead 24 VDC power supply. The replacement supply was in our van. The problem was the existing wire: 2.5 mm² stranded, no ferrules, already cut to length. The new push-in block on the drawing required a ferrule. The old WDU 35 did not. We sent the WDU 35 instead.
Wait, no ferrules? Let me explain why that matters. Fine stranded wire without a ferrule can splay inside a push-in termination. The spring may grip part of the strands, making the connection look seated when it is not. A screw clamp compresses the bundle and lets you tighten it down. In that moment, the WDU 35 was the only safe call.
That is not entirely fair to push-in technology. If the wire had been ferruled, push-in would have done the job quickly. But that is the point: in an emergency, you don't get to choose what the last electrician did.
Verdict: Push-in is faster in a planned installation with prepared wires. The WDU 35 is faster in an unplanned emergency with as-found wire.
2. Long-Term Reliability and Vibration
I used to think any terminal block was fine as long as it was tight. Then I found a loose connection in a cabinet next to a cooling fan. The wire looked seated. It was not. The screw had backed off because someone had not used a torque screwdriver.
Push-in spring contacts have an advantage here. The spring applies constant pressure. It does not depend on someone getting the exact torque, and it resists loosening from vibration. In a cabinet with fans, that is a strong point.
Does that mean WDU 35 is risky? No. A correctly torqued screw clamp is reliable. But correct torque is a condition, not a guarantee. I have seen electricians overtighten and strip threads. I have also seen them undertighten because the wire felt snug.
Verdict: Push-in wins for vibration resistance. The WDU 35 is dependable if installed with discipline, but it is less forgiving of human error.
3. Emergency Repairability
Here is where my emergency bias comes in. In a repair, I need to change a connection without replacing the whole block, without waiting for a special tool, and without removing the wire if I don't have to.
The WDU 35 is brilliant at that. Loosen the screw, move the wire, tighten it back. You can reuse the same block many times. You can release a wire with a standard screwdriver. Every electrician on the floor knows how to work with it.
Push-in blocks are fast to install, but they are less forgiving in repair situations. To release a conductor, you need to insert a release tool while pulling the wire. If the wire is damaged, you cannot simply re-strip a few millimeters and push it back in—you might need to replace the conductor or add a ferrule. That is easy in a workshop. It is annoying at 3 AM on a live cabinet.
Had 20 minutes to decide whether to airfreight a WDU 35 or reroute the circuit to a spare push-in slot. Normally I would run a full calculation. Not then. I chose the block I could install quickly, test with a meter, and walk away from. That was the WDU 35.
Verdict: WDU 35 wins for repairs and retrofits. Push-in rewards planning; screw-clamp rewards flexibility.
4. Space and Panel Density
On a TS35 rail, terminal blocks are measured by width. In small control circuits, push-in blocks can be narrower than equivalent screw blocks, which lets you pack more into the same cabinet. That is a real advantage when adding function to an existing panel.
But for power supply feeds, I am not looking for maximum density. I am looking for safe wire bending radius, clearance for big lugs, and room to work with a screwdriver. The WDU 35's larger body actually makes it easier to land a fat 35 mm² conductor than a compact push-in block. You get more finger space, a bigger cable entry, and fewer geometry problems.
The surprise was not density. It was access. I assumed 'same TS35 rail' meant every terminal block would fit into the same envelope. I did not verify. It turned out the push-in version was a few millimeters taller and blocked the cable duct above the panel. That mistake cost us two hours and a lot of colorful language.
Verdict: Push-in wins for signal-level density. WDU 35 wins for power-level access.
5. Total Cost, Not Just Unit Price
The WDU 35 tends to have a lower list price than a comparable push-in block. That is a good reason to use it in maintenance spares. But total cost is more than the part. If push-in wiring cuts installation time on a 200-point panel by 30 percent, the labor savings can exceed the material cost difference.
For an emergency, the cost calculation changes completely. Downtime is the real cost. In one case, a client paid an $800 air-freight bill to get a terminal block overnight. It saved a $12,000 line-start delay. The terminal block itself cost $20. That is the only cost that mattered.
I will not quote exact list prices here because they vary by distributor and region (as of early 2025, at least). The pattern is consistent: screw-clamp tends to be cheaper upfront; push-in can be cheaper to install; and neither matters when a plant is down.
Verdict: For new production panels, push-in often wins on installed cost. For one-off emergency replacements, WDU 35 is the lower-risk choice.
So Which One Should You Use?
Here is the practical answer, not a brand-preference answer.
- If you are building a new cabinet from a clean drawing, with controlled wire preparation and exposure to vibration: go push-in. It will save time and stay reliable.
- If you are maintaining existing machines, supporting plants with mixed wire types, or stocking emergency spares: keep WDU 35 in stock. It is the block that still works when the situation is messy.
- If you are a panel builder who also does field service: standardize on both, but label zones clearly—push-in for new builds, WDU 35 for repair-friendly spares. Forcing one technology into every scenario is how you get a cabinet that nobody enjoys working on.
Call it old-school, but the WDU 35 is what I pull from the stock drawer when a line is down. Push-in is the future. WDU 35 is the insurance.
Looking back, I should have standardized on push-in sooner for new panel builds. At the time, changing the BOM meant retraining contractors and rechecking approvals (UL 1059 in North America, IEC 60947-7-1 in Europe). It seemed simpler to keep screw clamps. In hindsight, the transition was worth doing earlier. But given what I knew then—especially about repair work—my hesitation was not unreasonable.
There is something satisfying about a perfectly executed emergency swap. After all the stress and coordination, seeing the power supply come back online with the WDU 35 holding a clean 24 VDC output—that is the payoff. If you choose the right block for the situation, you get that payoff too.
