Photocells themselves (also known as photoresistors or light-dependent resistors - LDRs) aren't generally "5V DC". They are variable resistors. The circuit around them determines the voltage output. What you're describing sounds like a complete photocell sensor module or assembly designed specifically for a 5V system, outputting a voltage that indicates light level.Given the specific voltage readings and the connection configuration (2-conductor plus shield), it's highly unlikely you'll find an exact replacement off-the-shelf. The Square D 5C lighting manager is an older system, and manufacturers often used proprietary sensors.Here's a breakdown of why and what your options are: Proprietary Design

The Square D sensor was likely designed to work specifically with their system. They likely specified an LDR with a particular resistance curve and then incorporated it into a voltage divider circuit to achieve the desired output range (0.56V to 4.99V).

Aging Components

Even if you could find a compatible module, any NOS (new old stock) components are likely to be affected by age. LDRs drift in characteristics over time.

Your best options, from most ideal to most challenging, are


Contact Square D/Schneider Electric (Less Likely)

It's a long shot, but try contacting Schneider Electric (who acquired Square D). They may have a replacement part number or even a modern equivalent (unlikely, but worth the effort). If you have part numbers, try searching on line or asking your electrical supply house2.

Search for Used Replacements (Riskier)

Search online auction sites (eBay, etc.) and used equipment suppliers. Search for things like "Square D 5C photocell" or "Square D lighting manager sensor." Be prepared for the risk that the used part may also be failing or close to failing.3.

Reverse Engineer & Rebuild/Replace the LDR

This is the most likely path to success, but requires some electronics knowledge:

Open up the existing sensor (Carefully!)

If possible, carefully disassemble the existing sensor to identify the LDR used. Note its physical size, resistance range (if marked - often not), and any other identifying characteristics.

Identify the LDR Type (Difficult)

Unfortunately, determining the exact LDR used in the original is tough. However, you can use a multimeter to measure its resistance in full light and full darkness to get an idea of its range.

Rebuild the Circuit

With some research you can determine the specific part number LDR that is in the unit. Find one on line. Remove the existing failed LDR and replace with the new LDR. If this does not work, then:Determine the resistance of the LDR in the sensor module. Then measure the resistance of the resistor in the sensor module.Using the full voltage 5 volts, and your voltage readings in full sun and dark, determine the resistance necessary of the LDR to output this voltage given the load of the resistor in the sensor module.Replace the LDR with an LDR that fits this curve

Test and Calibrate

Connect the modified sensor to the Square D 5C unit and test its operation. You may need to adjust the resistor values in the circuit to fine-tune the output voltage range to match the original sensor.4.

Replace the Entire Lighting Manager System (Last Resort)

If all else fails, you might need to replace the entire Square D 5C system with a modern lighting control system. This would be the most expensive option but would give you access to current technology and readily available replacement parts.

Important Considerations



Safety

When working with electrical systems, always disconnect power and take appropriate safety precautions.*

Calibration: After replacing or modifying the sensor, you'll need to recalibrate the lighting manager unit to ensure it's responding correctly to light levels. Consult the Square D 5C documentation for calibration procedures.Let me know if you have any questions. Good luck! Flag for review