You're right to be concerned about potential issues. Switching from a simple mechanical timer to an electronic one, especially an astro timer that switches based on calculated sunrise/sunset, introduces new possibilities for problems, especially with that existing network of underground wiring and history of storm-related issues. Here's a breakdown of concerns and potential solutions, with a focus on surge protection and isolation

Understanding the Potential Problems:
Ground Loops

The multiple buildings and long wire runs, combined with the ground connections in each building's electrical panel, likely create ground loops. These loops can carry circulating currents, which can induce voltage spikes and noise on the control circuit. This is especially problematic with sensitive electronic timers.

Transient Voltage Surges (TVSS)

Lightning strikes, utility switching, or even internal building events can induce voltage surges onto the wiring. The underground copper acts as an antenna, potentially amplifying these surges.

Voltage Drop

Over that length of cable, you could experience a significant voltage drop, especially during the initial surge when all 28 contactors pull in simultaneously. This could cause the contactors to chatter or not engage reliably, shortening their lifespan.

Electromagnetic Interference (EMI)

The electronic timer itself, and the switching of the contactors, can generate EMI, which can interfere with other devices or even create false alarms.

Solutions and Mitigation Strategies


Surge Protection (Key Focus)



Option 1: High-Capacity TVSS at the Timer Location Install a robust Transient Voltage Surge Suppressor (TVSS) immediately before the Honeywell timer. This should be a dedicated device, not just a standard surge protector for sensitive electronics. Look for a TVSS with: High Surge Current Capacity

You need something substantial. Aim for at least 100kA per mode (L-N, L-G, N-G). More is better.

Low Voltage Protection Rating (VPR)

This is the clamping voltage. Lower is better, but make sure it's above the normal operating voltage. Ideally, under 500 volts for a 120V system.

Sine Wave Tracking

This is a more advanced surge protection that protects against a wider range of surges.

Status Indication

You want an indicator (LED, audible alarm) that tells you if the TVSS has sacrificed itself to protect the system.

Option 2: Cascaded Surge Protection This is a more robust approach. Use a service-entrance-rated TVSS at the main electrical panel feeding the timer circuit. Then, add a second TVSS immediately before the timer itself, as described in Option 1. The service entrance TVSS takes the brunt of large surges, and the second one provides more granular protection. Important Considerations for TVSS



Proper Grounding

The TVSS must be properly grounded to work effectively. Use a short, direct grounding conductor to the building's grounding electrode system.

Series vs. Parallel

TVSS devices are typically wired in parallel. Do not wire them in series.

UL 1449 Listing

Ensure the TVSS is UL 1449 listed (3rd edition or later). This is a safety standard.

Replaceable Modules

Consider a TVSS with replaceable surge protection modules, so you don't have to replace the entire unit if it takes a hit.2.

Isolation (Important)



Isolation Relays/Optocouplers

This is where you can truly isolate the new timer from the existing wiring. Use isolation relays or optocouplers to drive the existing contactors. The timer switches a low-voltage, isolated circuit, which then activates the relays/optocouplers to switch the 120V contactor circuit. This physically separates the timer's electronics from the potentially noisy and surge-prone existing wiring.

Example

The Honeywell timer's output could trigger a low-voltage relay. The contacts of this relay then switch a 120V circuit that energizes the 28 contactors.

Benefits

Completely isolates the timer from the existing 120V wiring. Protects the timer from surges and ground loop currents. Minimizes the risk of damage to the timer. Consider solid state relays for longer life and no audible click.3.

Grounding Improvements



Verify Grounding

Ensure all grounding connections throughout the system are tight, corrosion-free, and meet code requirements. This includes the grounding electrode system at the main service and the grounding conductors in each building.

Consider Supplemental Grounding

Depending on the severity of the ground loop issues, you might consider adding supplemental grounding electrodes at strategic locations within the complex. Consult with a qualified electrician experienced in grounding and bonding to determine if this is necessary and how to implement it properly.4.

Wiring Considerations



Inspect Existing Wiring

Carefully inspect the underground wiring for damage, corrosion, or splices. Replace any damaged sections.

Shielded Cable (Control Circuit)

Consider using shielded cable for the control circuit between the timer and the contactors. The shield should be grounded at one end (preferably at the timer location) to provide a path for induced noise currents to flow to ground.5.

Consider a Different Control System



Wireless Control

If the cost is justifiable, consider a completely different control system that uses wireless communication between the timer/controller and the contactors. This eliminates the need for physical wiring and greatly reduces the risk of surges and ground loops.

Low-Voltage Power Line Carrier (PLC)

These systems use a modulated signal that is immune to voltage drops on the power wires.6.

Timer Choice



Industrial-Grade Timer

Instead of a wall timer, consider an industrial-grade astronomical timer designed for outdoor use and switching larger loads. These are built to be more robust and handle voltage fluctuations better.

Steps to Take


Consult with a Licensed Electrician

This project requires a qualified electrician with experience in surge protection, grounding, and electrical systems for multi-building complexes. They can properly assess the situation and recommend the best solutions.2.

Load Calculation

Calculate the total inrush current of all 28 contactors pulling in simultaneously. This is crucial for sizing the TVSS, relays, and wiring.3.

Grounding Inspection

Have the electrician thoroughly inspect the grounding system for proper installation and effectiveness.4.

Implement in Stages (Optional)

If possible, implement the changes in stages. For example, start with the TVSS and see if that resolves the issues. If not, add the isolation relays, etc.

Important Cautions



Don't Cut Corners

Surge protection and grounding are critical for safety and reliability. Don't try to save money by using inadequate components or skipping steps.

Local Codes

All electrical work must comply with local electrical codes.

Documentation: Keep detailed records of all work performed, including wiring diagrams, component specifications, and test results.By taking a proactive approach and implementing these solutions, you can significantly reduce the risk of problems and ensure a reliable and safe lighting control system for your customer. Remember to prioritize safety and consult with a qualified electrician. Flag for review