Moxa IMC-21A-M-SC Ethernet-to-Fiber Media Converter

Copper-to-fibre conversion for long runs and noisy plants

The Moxa IMC-21A-M-SC is an entry-level media converter that links a 10/100BaseT(X) RJ45 port to a 100BaseFX multi-mode fibre port with SC connector. It is used to extend an Ethernet segment beyond the 100 m copper limit, to isolate equipment from electrical noise or earth potential differences, and to bring field devices onto a fibre backbone. DIP switches set full or half duplex, 10 or 100 Mbit/s, or auto and forced modes, and Link Fault Pass-Through (LFPT) passes a fibre or copper link loss to the other side so that the connected equipment can detect it. The RJ45 port has 1.5 kV built-in magnetic isolation.

Technical specifications

Models in the IMC-21A series

Using converters correctly

Converters work in pairs, so both ends must use the same fibre type, wavelength family and connector; two multi-mode SC units are matched to each other, not to a single-mode unit. Before ordering, confirm that the link budget exceeds total fibre loss plus the dispersion penalty. On short single-mode runs Moxa recommends an attenuator to avoid damaging the receiver. A converter does not manage traffic; where you need multiple fibre ports or ring redundancy, a switch such as the Moxa EDS-316-MM-SC-T is more appropriate. For serial equipment over fibre, see the Moxa TCF-142-S-SC-T. Seven Star LLC, an independent supplier in Muscat, quotes the exact order code. The datasheet (version 1.6) is attached, and related products are in Industrial Communications. Installation is straightforward: clip the 30 mm wide unit onto a DIN rail, connect 12 to 48 VDC to the terminal block, plug in the copper and fibre cables and set the DIP switches to match the connected equipment. Use auto mode unless the other device cannot negotiate; forcing speed and duplex on one end while the other end auto-negotiates causes a duplex mismatch. Keep fibre connectors capped when not in use and clean them before connecting, since dirt is a common cause of marginal links. Note that the 1.5 kV figure is port magnetic isolation, not a lightning surge rating. As a rule of thumb from the datasheet formula, a multi-mode link has a 12 dB budget and 3 dB dispersion penalty, so the fibre and connector losses must stay well below 9 dB; a single-mode link has a 29 dB budget and 1 dB penalty, leaving about 28 dB for losses. Always measure the installed link rather than relying on typical distance figures.