Electrical Installation

💡 Understanding LED Loads

Modern LED lights are very efficient and draw minimal current during normal operation. A typical 15-watt LED light on 240V AC draws only about 60 milliamps (0.06 amps) during normal running.

This low current means you don't need large, expensive relays for switching lights and fans. Small relays work perfectly for these loads.

⚡ The Inrush Current Problem

Here's where it gets tricky. When an LED light is off, there's a discharged capacitor in the LED driver circuit. When you switch the light on, this capacitor tries to charge up instantly, creating a massive current spike - sometimes up to 100 times the normal running current.

This huge inrush current can weld relay contacts together, destroying the relay. Think of it like a dam bursting - all that energy hits at once instead of flowing steadily.

🌡️ The Simple Fix: NTC Thermistors

A typical NTC (Negative Temperature Coefficient) thermistor is a simple device that changes resistance based on temperature.

I wanted to install some 40W LED lights and so the normal current flowing would be 40/240A = 0.167 and inrush would be 16.7A. I needed to a NTC thermistor which at room temperature is 40 ohms of resistance. When current flows through it, the thermistor heats up and its resistance drops dramatically. The NTC thermistor must be sized for the desired application but for the above situation the Ametherm MS15 40004 was used..

How It Works

During startup, the thermistor's high resistance limits the inrush current to safe levels. Once current starts flowing and the thermistor warms up, its resistance drops to almost nothing, allowing normal operation with minimal power loss.

🗄️ Electrical Cabinet Setup

The small relays perfect for home automation are typically 5mm wide. This compact size means you can fit a lot of them in a standard electrical cabinet.

For this many relays, you'll need either an ultra-wide cabinet or two separate enclosures. These should be located as centrally as possible to minimize cable runs.

Essential Cabinet Components

Your electrical cabinet needs space for miniature circuit breakers for protection, earth bus bar for safety grounding, neutral bus bar for neutral connections, DIN rail for mounting relays and automation boards, and cable ducting to keep wires organized and accessible.

🔌 Cable Runs & Ducting Strategy

Home automation requires a significant amount of cable - both low voltage control cables and mains voltage power cables. Proper ducting makes installation much easier and keeps everything organized.

Separate High and Low Voltage Ducting

Create two separate cable ducting systems: one for low voltage (ethernet, control signals) and another for mains voltage (240V power to lights and fans). This separation prevents interference and meets electrical safety requirements.

Due to the very low currents in both lighting cables and ethernet cables, heating is not an issue. You can use plinth boards to create two major duct runs efficiently.

⚠️ Safety & Legal Requirements

While you can install the low voltage automation components and prepare the ducting yourself, any work involving mains electricity requires professional installation to ensure safety and compliance with local electrical codes.