# Placement and cabling

> Where to place the IO modules and how to cable them; the number of modules follows the physical layout of the installation.

Source: https://voltmasters.io/en/docs/dso-rtu/io-module/placement-and-cabling/

The IO modules provide the digital outputs and inputs that DSO RTU uses, for example the [hardware emergency stop](https://voltmasters.io/en/docs/dso-rtu/io-module/emergency-stop/). **How many modules you need, and where they go, depends on the physical layout of your installation**, because every relay has to be wired to the asset or switchgear it controls.

For the module's dimensions, mounting options, terminal sizes and electrical limits, see [Technical specifications](https://voltmasters.io/en/docs/dso-rtu/io-module/technical-specifications/).

### How many modules do I need?

There is no fixed number; it follows the **physical setup**:

-   A single module can serve every relay and input that is **near it** (in the same cabinet).
-   If outputs or inputs are needed in **physically separate cabinets**, each of those cabinets needs its **own** module, because the wiring to the relays stays local to the cabinet.

So a compact, single-cabinet installation may need just one module, while an installation spread over several cabinets needs one module per cabinet that has to be controlled.

### Placement and cabling

**Single cabinet**

Place the module in the cabinet, close to the assets and the relay(s) it drives.

**Separate cabinets**

For each additional cabinet:

1.  Run a **network (Ethernet) cable** from the installation network to the cabinet.
2.  Place an **IO module** inside that cabinet.
3.  Wire the cabinet's relays and inputs to that local module.

This keeps the safety wiring short and local, while every module stays reachable by the controller over the network.

### Layout

```
                  ┌───────────────────────────┐
                  │    Voltmasters controller  │
                  └───────────────┬────────────┘
                                  │
                  installation network (Modbus TCP)
                                  │
        ┌─────────────────────────┼─────────────────────────┐
        │                         │                         │
   network cable             network cable             network cable
        │                         │                         │
┌───────▼────────┐        ┌───────▼────────┐        ┌───────▼────────┐
│   Cabinet A    │        │   Cabinet B    │        │   Cabinet C    │
│  ┌──────────┐  │        │  ┌──────────┐  │        │  ┌──────────┐  │
│  │ IO module│  │        │  │ IO module│  │        │  │ IO module│  │
│  └────┬─────┘  │        │  └────┬─────┘  │        │  └────┬─────┘  │
│  relays/inputs │        │  relays/inputs │        │  relays/inputs │
│  (local assets)│        │  (local assets)│        │  (local assets)│
└────────────────┘        └────────────────┘        └────────────────┘

   One module per cabinet; the number of modules follows the layout.
```

### Network and power

-   Connect each module to the **installation network** (the same network the controller uses for Modbus TCP).
-   Give each module a **fixed IP address**, and power it from the cabinet's 24 VDC supply (12–36 VDC, ≈ 4.5 W per module).
-   Note each module's **IP address, port and Modbus slave ID**, since you need them when adding the device on the platform.

> **Note**
>
> Each module has **two Ethernet ports** that act as a small switch, so modules can be **daisy-chained** instead of each taking up a port on a switch. Remember that a daisy chain is a single path: a module that loses power also cuts off the modules behind it. For a module that carries an emergency stop, prefer a direct link to the switch.

For converting RS-485 devices to Modbus TCP elsewhere in the installation, see [RS485 to Modbus TCP adapters](https://voltmasters.io/en/docs/getting-started/adding-and-verifying-devices/rs485-to-modbus-tcp-adapters/).

### Next steps

Once the modules are installed and reachable on the network, add each one on the platform and assign its outputs. See [IO module](https://voltmasters.io/en/docs/dso-rtu/io-module/) for adding the device and configuring its ports, and [Emergency stop](https://voltmasters.io/en/docs/dso-rtu/io-module/emergency-stop/) for the emergency-stop configuration.