Ground loop isolation in data networks and interconnections

Isolating serial data lines

When you have two computers in different rooms connected together using long RS-232 wiring you can face ground loop problems. Isolating RS-232 line communications is harder than those audio or antenna connections. The best solution to solve those ground loop problem is to buy a commercial equipment which is designed for this kind of purposes. There are RS-232 isolators, current loop converters and short distance modems which can do the job. B&B Electronics has a very good data sheet collection (including schematics of many products) availabla on thei web site. They have also very good RS-422/485 and Current Loop application notes available on their technical library.

Ethernet networks and ground loops

Ground loops in Ethernet networks can cause network not to operate properly and other annoying ground loop problems.

Thick Ethernet

The thick coaxial media system was the first media system specified in the original Ethernet standard of 1980. Today most sites use twisted-pair media for connections to the desktop. Thick coaxial segments are still sometimes installed as a backbone segment for interconnecting Ethernet hubs, since thick coaxial media provides a low-cost cable with good electrical shielding that can carry signals relatively long distances between hubs.

An Ethernet interface is attached to a thick Ethernet segment with an external MAU. The MAU provides an electrical connection to the thick Ethernet coax and transfers signals between the Ethernet interface and the network segment. The MAU is powered from the Ethernet interface, but all signal lines coming to the MAU are electrically isolated in the ethernet card.

The standard notes that the thick coax segment should be grounded at one point for electrical safety reasons. There must only be one grounding point, to avoid disrupting the Ethernet signals carried by the cable. All other metal parts on the cable should be insulated or carefully routed and fastened in place with plastic cable ties to avoid accidentally touching an electrical ground. If the components and cables conencted to MAY are properly isolated from nearly grounded metal parts, the system is ground loop problem free.

Thin Ethernet

Thin Ethernet (10Base-2) uses coaxial cable which goes from computer to another. That cable should be grounded from one end for safety resons. That cable is electrically isolated from the computers at the ethernet card. The cable shield be accidentally and easily get in contact with the matal case of the computer if the metal connectors in the cable touch the matal case of the computer.

To avoid this kind of problems it is a good idea to use connectors which have plastick isolation over them or install a platic isolation around them. Make sure that the you don't have any metal connectors or broken cable shields connectors touching the metal wiring conduit.

Twisted Pair Ethernet

10Baset-T Ethernet used twisted pair wiring and RJ-45 connectors. The wiring is completely transformer isolated in network card and HUB end. 10Base-T network using unshielded twisted pair wiring does not cause any ground loop problems. If you are

If you are working in enviroment where ground loops are very problematic then 10Base-T network using unshielded twisted pair cables is one of the the safest choises. It can cost a little bit more but is very flexible and you will save very much in long run in network trouble shooting costs.

The same which applies to 10Base-T applies also to 100 Mbit/s Ethernet which used unshielded twisted pair wiring (100Base-TX).

Fiber optic links

If you use Ethernet cabling with fiber optics, those fiber optics links are free of ground loop problems, because the systems on the ends of the cables are optically isolated from each other by the long optical fiber between them.

MIDI

MIDI interface is designed for controlling musical equipments and the possible ground loop problems in audioo systens are taken to acount. MID interface is designed so that the interface is isolated in the receiving end so that it does not make ground loops if wired correctly.


Tomi Engdahl <Tomi.Engdahl@iki.fi>