Introduction

In many regions such as Asia and Europe, ATS control power is typically taken from phase + neutral (L + N).

However, in the United States, the power system is different.

The standard system is 120/240V split-phase (sometimes referred to as 110/220V), and many users are not familiar with neutral wiring or may not use it at all.

Because of this, incorrect wiring of ATS control power is very common.

This guide explains a simple and reliable way to connect ATS control power, especially for split-phase systems.

Understanding Split-Phase Power (USA)

A typical US power system includes:

• L1 (Line 1)

• L2 (Line 2)

• N (Neutral)

Voltage characteristics:

• 120V between L1 and N

• 120V between L2 and N

• 240V between L1 and L2

Recommended ATS Control Wiring (Key Point)

For ATS units requiring 220–240V AC control power:

Use L1 + L2 (two live wires)

This method provides:

• Stable 240V control voltage

• No need for neutral

• Easier and safer installation

Wiring Diagram Explanation

1. 220/380V Three-Phase Four-Wire System

Control Power Method:

• Use one phase (L1 / L2 / L3)

• 
  

• Neutral (N)

This provides 220V AC control power

Diagram Notes:

• Source 1 → terminals 302 & 303

• 302 = Phase (L)

• 303 = Neutral (N)

• Source 2 → terminals 304 & 305

• 304 = Phase (L)

• 305 = Neutral (N)

• The terminals shown in the diagram are green control terminals (not busbars)

2. 120/240V Split-Phase System (USA)

Control Power Method:

Use two live wires (L1 + L2)

Do NOT rely on neutral if the user is unsure

Diagram Notes:

• Source 1 → terminals 302 & 303

• 302 = L1

• 303 = L2

• Source 2 → terminals 304 & 305

• 304 = L1

• 305 = L2

• Neutral (N) is not used in this configuration

• Terminals are green control wiring terminals

Why L1 + L2 is Recommended in the US

• Avoids confusion with neutral wiring

• Reduces installation errors

• Matches actual field conditions

• Provides correct 240V control power

Important Notes

• Always confirm the rated control voltage of the ATS (e.g., 220–240V AC)

• Ensure wiring matches the diagram

• Disconnect power before installation

• Tighten all terminals securely

Summary

Practical Advice

For US projects:

• If neutral is clearly available → L + N can be used

• If unsure → always use L1 + L2

This is the safest and most practical solution in real installations.