--- title: "Devices in Another Building — Fiber, LAN and Modbus" description: "Connect energy meters and devices in another building to TapHome Core: LAN over fiber with media converters, Modbus to LAN converter PE11, a second Core, or RS-485 over fiber." url: "https://taphome.com/en/docs/wiring/remote-buildings/" language: en lastmod: 2026-11-08 generator: hugo ai: topics: ["remote-buildings","fiber-optic","media-converter","modbus-tcp","modbus-rtu","energy-metering","multiple-cores"] questions: ["How do I connect energy meters in another building to TapHome?","Can the TapHome bus run over fiber or over the LAN?","Is there a fiber optic module for the TapHome Core?","What do I need to connect two buildings over fiber?","How do I connect Modbus RTU energy meters over the network?","How do I connect TapHome modules in another building?","How do two Cores share devices?","Can I send RS-485 directly over fiber?"] --- # Devices in Another Building — Fiber, LAN and Modbus How to connect energy meters, Modbus devices and TapHome modules in another building of a site: LAN over fiber with a Modbus to LAN converter, a second Core, or RS-485 over fiber. Last updated: 2026-11-08 The TapHome bus does not run over a network or fiber. To reach devices in another building of the same site, run an ordinary LAN between the buildings — over fiber when it is already there — and connect the devices over Modbus. TapHome has no fiber module for the Core, because a standard network does the same job. ## Which Option to Choose | What is in the other building | Option | |---|---| | Energy meters or other devices on RS-485 (Modbus RTU) | [A — LAN over fiber](https://taphome.com/en/docs/wiring/remote-buildings/#lan-over-fiber) with a Modbus to LAN converter | | Devices with Modbus TCP (LAN port) | [A — LAN over fiber](https://taphome.com/en/docs/wiring/remote-buildings/#lan-over-fiber), no converter needed | | TapHome modules (switches, relays, inputs) | [B — second Core](https://taphome.com/en/docs/wiring/remote-buildings/#second-core) | | RS-485 devices only, and the site does not want a LAN between buildings | [C — RS-485 over fiber](https://taphome.com/en/docs/wiring/remote-buildings/#rs485-over-fiber) | ## A — LAN over Fiber (Recommended) ![Building B connected over fiber: LAN, Modbus to LAN converter and RS-485 energy meters](https://taphome.com/documentation/wiring/remote-buildings-lan-fiber.svg) Two media converters, or switches with an SFP slot, carry the LAN over the fiber. Fiber also isolates the buildings galvanically, so a lightning surge or a ground difference between them does not travel along the cable. - **Media converters or switches with an SFP slot** — 100 Mbit is enough. The SFP module must match the fiber that is in the ground: multimode reaches a few hundred meters, single-mode several kilometers; the connector (LC, SC) must fit, and a single fiber needs a matched pair of modules (A and B side). A DIN-rail model powered from 12–48 V DC runs from the TapHome 24 V supply; in an unheated building choose a model rated for frost. - **Modbus to LAN converter** for RS-485 devices, for example the Protoss PE11. One converter serves one RS-485 line of up to 32 devices and 1200 m of cable. All meters on the line share its baud rate, parity and stop bits, and each needs a unique Slave ID. The setup steps are on the product page. **In the TapHome app:** add a **Modbus TCP** interface in **Hardware**, a module with the IP address of the converter and each meter's Slave ID, and the meters from their templates or by registers ([Modbus](https://taphome.com/en/docs/integration/modbus/)). Give the converter a fixed IP address, either a DHCP reservation in the router or a static address in the converter. The PE11 in the Modbus protocol mode is a Modbus TCP gateway, so keep **Modbus RTU over TCP** off; turn it on only for a transparent converter that passes RS-485 through unchanged (TapHome 2026.1 and newer, [release notes 2026.1](https://taphome.com/en/docs/release-notes/2026-1/)). ### Example Products | | Product | Use | |---|---|---| | ![Moxa IMC-21GA media converter](https://taphome.com/documentation/wiring/products/moxa-imc-21ga.jpg) | [Moxa IMC-21GA](https://www.moxa.com/en/products/industrial-network-infrastructure/ethernet-media-converters/ethernet-to-fiber-media-converters/imc-21ga-series) | Media converter with an SFP slot, DIN rail, 12–48 V DC; the -T version for −40 °C | | ![Protoss PE11 Modbus to LAN converter](https://taphome.com/documentation/wiring/products/protoss-pe11.png) | [Protoss PE11](https://taphome.com/shop/PROTOSS-PE11) | Modbus to LAN converter for one RS-485 line, sold in the TapHome shop | ## B — Second Core in the Other Building ![Second Core in building B connected over fiber, with TapHome modules on its bus](https://taphome.com/documentation/wiring/remote-buildings-second-core.svg) When building B needs TapHome modules, give it its own Core with the modules on its bus, connected to the main Core over LAN on fiber as in option A. Core B exposes the devices the main Core needs in **Expose Devices** → Modbus TCP ([TapHome to Modbus](https://taphome.com/en/docs/expose-devices/modbus/)), and Core A reads them through a **Modbus TCP** interface with the IP address of Core B; each device is set up on Core A by the registers that Core B lists for it. Core A can also read the [TapHome API](https://taphome.com/en/docs/expose-devices/taphome-api/) of Core B over the local network with a Packet Parser HTTP script. When the fiber is down, Core B keeps running its own modules and smart rules; Core A only loses the shared devices. ## C — RS-485 over Fiber ![RS-485 over fiber: a pair of fiber modems between the Core and Modbus RTU energy meters](https://taphome.com/documentation/wiring/remote-buildings-rs485-fiber.svg) A pair of RS-485 fiber modems carries the two RS-485 wires over fiber without a network; in the app, the meters are ordinary Modbus RTU devices on the Core's bus port. Each pair is one point-to-point line and takes one bus port of the Core, and it offers no diagnostics beyond its LEDs. Choose modems with automatic data direction control and 12–48 V DC power, for an unheated building a model rated for frost. Each copper section needs 100 Ω termination at both ends: the Core has it built in, the modem usually has a switchable one ([Modbus RTU wiring](https://taphome.com/en/docs/wiring/modbus-wiring/)). ### Example Product | | Product | Use | |---|---|---| | ![Moxa TCF-142 RS-485 fiber modem](https://taphome.com/documentation/wiring/products/moxa-tcf-142.jpg) | [Moxa TCF-142](https://www.moxa.com/en/products/industrial-edge-connectivity/serial-converters/serial-to-fiber-converters/tcf-142-series) | RS-485 fiber modem with automatic data direction control, 12–48 V DC; DIN-rail kit sold separately, the -T version for −40 °C | ## TapHome Modules in Another Building TapHome modules cannot be connected over the LAN, Wi-Fi or a converter: the Core runs the TapHome bus only on its own bus terminals and on the [Bus Extender](https://taphome.com/en/docs/wiring/bus-extender/). For modules in another building, use [option B](https://taphome.com/en/docs/wiring/remote-buildings/#second-core), or a copper cable from an isolated Bus Extender port (below). ## Copper Cable Between Buildings When there is no fiber and a bus cable has to leave the building, use an isolated port of the [Bus Extender](https://taphome.com/en/docs/wiring/bus-extender/) with a separate power supply in the other building, and [surge protection](https://taphome.com/en/docs/wiring/surge-protection/) at both ends. An [optical bus isolator](https://taphome.com/en/docs/wiring/optical-isolation/) adds galvanic separation but does not replace surge protection. An RS-485 line for Modbus RTU can be up to 1200 m long.