Key Technical Specifications
- Rated Load Current: 40 A
- Nominal Voltage: 24 V DC
- Operating Voltage Range: 22 V DC to 29 V DC
- Power Dissipation: Typically 12 W at 40 A (keep airflow in mind!)
- Mounting Type: DIN Rail (NS 35/7.5 or NS 35/15)
- Degree of Protection: IP20 (Needs a proper enclosure)
- Operating Temperature: -20 °C to +60 °C (Derate above 40 °C)
- Connection Method: Spring-cage / Push-in (Tool required)
- Dimensions (W x H x D): 45 mm x 90 mm x 82 mm
- Standards: UL Listed, CE, cULus
Product Introduction
You lose a power supply in a redundant setup, and the remaining unit takes the full load plus the dead unit’s short circuit. That’s where this module earns its keep. The PHOENIX CONTACT QUINT-DIODE/40 (2938963) acts as a high-current traffic cop, isolating your 24V DC power sources so a catastrophic failure on one side doesn’t cascade to the other. I’ve used these in water treatment plants where a single pump drive shorted out its PSU; without this diode module, the PLC would have browned out and tripped the whole line.Engineers stick with this specific 40A diode block because it handles the massive inrush currents without welding its internal contacts shut. It keeps the voltage drop under 0.3V at full load, which matters when your field devices are already starving for power at the end of a long cable run. Just remember, this thing gets hot. If you pack it in a sealed NEMA 4X box next to a VFD, it will cook itself. Give it breathing room or add a fan.
Quality SOP & Tech Pitfalls
The Lab Report:
We don’t just pull these off a shelf and ship them. Every 2938963 goes through a visual inspection for bent pins or cracked housing. We bench-test them on a Phoenix QUINT test rack, pushing 40A through both channels while monitoring the forward voltage drop with a Fluke 115. If it runs hot or drops more than 0.4V, it fails. We log the batch code, pack it in anti-static shielding, and seal it.The Engineer’s Warning:
Here is where guys mess up: they assume “redundancy module” means they can wire two power supplies in parallel to get 80A. Wrong. This is for decoupling, not current sharing. If you wire two 40A supplies into this without proper load balancing, one supply will do all the work and burn out. Also, never ignore the heat. I saw a panel in a steel mill where a tech shoved three of these flush against each other with zero ventilation. The ambient temp hit 55°C, the diodes went into thermal runaway, and the whole redundant system melted into a plastic brick. Always derate by 20% if your panel runs hot.
Installation & Configuration Guide
- Pre-Installation: ⚠️ LOCKOUT/TAGOUT. Verify 24V is dead with a meter. Take a clear photo of the existing wiring and DIP switches (if any) before touching a single wire.
- Removal: Label every wire with a sharpie or tag gun. Press the DIN rail release tab with a flathead screwdriver and pull the module straight out. Don’t pry it.
- Installation: Copy the old DIP switch settings exactly. This is where 90% of startup headaches come from. Push the new QUINT-DIODE/40 onto the DIN rail until you hear a solid click.
- Wiring & Power-On: Connect your two power supplies to the inputs and the load to the output. Double-check polarity. Energize the system. Watch the green “DC OK” LED. If it’s red or off, check your input voltage immediately. Download your program and verify the redundancy monitoring signal is reading correctly in the PLC.
Compatible Replacement Models
| Compatibility Tier | Model | Notes |
|---|---|---|
| ✅ Drop-in Replacement | QUINT-DIODE/40 (2938963) | Exact match. Same footprint, same specs. |
| ✅ Drop-in Replacement | QUINT4-DIODE/12-24DC/2X20/1X40 (2907719) | Newer QUINT4 generation. Same 40A rating, but verify your DIN rail space as dimensions differ slightly. |
| ⚠️ Software Compatible | QUINT-DIODE/20 (2938955) | Same form factor, but only 20A. Only use if your actual load is under 15A. |
| ❌ Hardware Mod Required | QUINT-ORING/2X20/2X20 | Active MOSFET redundancy. Better performance, but requires rewiring and different DIN rail space. |
Frequently Asked Questions (FAQ)
Can I hot-swap this module while the system is live?
Technically, yes, the design allows it. Practically, I wouldn’t risk it unless the system is absolutely critical and cannot tolerate a 2-second power loss. If you must, wear your PPE and use an insulated screwdriver. One slip and you’ll arc out the 24V bus.Why is my module getting hot to the touch?
Diodes aren’t perfectly efficient. At 40A, a 0.3V drop means 12 watts of heat. That’s normal. But if you can’t hold your hand on it for more than 3 seconds, you’re either overloading it, running in a high-ambient environment, or one of your power supplies is fighting the other. Check your load current with a clamp meter.Will this fix my power supply that keeps tripping its breaker?
No. This module isolates faults, it doesn’t create power. If your PSU is tripping, you have a short circuit or an overload downstream. Use a clamp meter to find the dead short before swapping parts.Is the 2938963 the same as QUINT-DIODE/40?
Yes. 2938963 is just the Phoenix Contact ordering code. They are the exact same physical module.Do I need to configure anything in my PLC?
The diode block itself is dumb hardware. But your PLC needs to know when redundancy is lost. Wire the “Signal” or “Monitor” contact on the module to a discrete PLC input. Write a simple rung to alarm if that contact opens. Don’t skip this; flying blind defeats the purpose of redundancy.What happens if one input voltage sags?
The diode block isolates the sagging supply. The healthy supply will instantly pick up the full load without a glitch. The module’s monitor contact will open, telling your PLC that one source has failed. This is exactly what it’s designed to do.
