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Grounding Ethernet Cable on a Ship?
wrschaeffer asks: "On a ship (a vessel at sea) where a floating ground exists, we are running shielded Ethernet cable to connect between 5 and 10 PC in our LAN. We are unsure on the grounding requirement. ABS (American Bureau of Shipping) has no requirements concerning grounding of Ethernet cable (just smoke and waterproof standards). We have many possibilities: ground one end; ground every end; ground every end and install a isolation transformer at the punch-down block; or don't ground any end. What should we do?"
I would only ground one end, and the end at the hub, since that would be the most common point of the network.
But this raises the question: Why are you using shielded ethernet? Ethernet is differential, and thus pretty immune to common mode noise.
I've had 25m ethernet cables draped across running engines (test equipment) with HEI ignition, and not experienced any problems (I can't say that I checked the error counters very often, but in high speed data collections, I wasn't seeing any unexpected decreased throughput).
In addition, I live on a houstboat, and I have ethernet run in the same conduits as AC power carring 5 to 15 amps on 4 different circuits, and don't experience any problems (max cable length is probably 20 meteres)
I've heard of ground differentials as large as 90 volts on ships -- a serious problem, and one you wouldn't expect on a metal vessel surrounded by nice conductive salt water.
I would recommend you run some fairly heavy -- 12 gauge should do -- ground wires in between the points you will be running the ethernet, and use the cables to interconnect the equipment ground points. Once you've done this, there shouldn't be any dangerous potentials on your ethernet lines. While you're at it, I'd also suggest you occasionally check for currents running on those ground wires; if you hook an ammeter around the wire and see more than a few dozen milliamps, you've got a bigger problem than ethernet grounding.
Allen-Bradley's Web site has a handy little pdf document describing a bunch of industrial Ethernet wiring practices, which would likely work well on a ship. Page 3-5 looks like the definitive spot for grounding shielded Ethernet cable -- connect the shield at the switch end, disconnect the shield at the remote end, and give the switch a good ground.
Hope this helps.
You shouldn't be asking us this. The high schoolers that lurk here are going to make jokes or give their 'best guesses', the rest are going to give you anecdotal evidence (ie, 'what I've heard'), and those that really know what's going on will be ignored. This is something for an electrician, someone that does this stuff for a living. That sure isn't me, and it sure isn't 99% of the slashdot population.
On our boat we use Fiber. =) Problem solved. (Military vessel)
Personally, I wouldn't ground the cables, to reduce the chance of them being hit during a lightning strike (on a small civilian boat)
It realy depends on what sort of vessel.
I would suggest to go fiber, it's immune to this kind of problems and I have seen fiber optic cards for decent prices in stores. Or use fiber for long distance connections and regular wired ethernet for LANs.
If you must do copper, ask someone who has done a copper-based university or large building WAN. They will likely have had to solve the same problems, as the same grounding issues can appear between equipment powered from AC sourced different phase lines. I don't recall exactly but grounding at only one end and leaving the other in the air might have been the solution.
The applicable US DoD standard is MIL-STD-1310G - "Shipboard Bonding, Grounding, and Other Techniques for Electromagnetic Compatibility and Safety". I'm not sure if that document specifically addresses Ethernet, but one of the illustrations should describe how to ground some differential twisted-pair data network. You can get MIL-STD documents from DAPS.
First things first... lots of people are saying that ethernet doesn't require a ground. That's WRONG... a ground is always required, especially on transmission lines like ethernet cables. However, CAT5 is a balanced transmission line and shielding isn't all that important unless you're running the cable through an environment likely to disrupt this balance.
Second, the type of boat you're on makes a big difference. If you're on a metal hulled boat (or a boat with a metal mast or other convenient absolute ground), you're ground doesn't float... the water is ground. Salt water is especially good as a ground reference.
If you're in a fiberglass boat, the whole vessel is floating above ground. See if you can find a metal object (preferably brass or other non-oxidizing metal) always submerged and use it as your ship's ground.
Either way, the easy answer is don't worry about grounding the shield.
If you run into problems with data corruption (or want to prevent such problems), you should ground BOTH sides of the shield. On long cable runs (longer than a half-wave at your operating frequency) you should ground only ONE side. The hub-side is the best to ground as it is already the central network point... so making it the central grounding point makes sense as well.
The BEST solution is to use something called telescoping grounds. In a telescoping ground, both ends are grounded, but to different shields. Both shields are independent and isolated from one another and overlap for the length of the cable. This prevents common-mode currents on both components and avoids ground-loops at the same time. Professional audio cables use this technique often.
Another option you may not have considered is wireless. With a wireless network, the only ground that's important is that of the base station (for efficiency's sake). The client devices have their own ground reference and its relationship to the base station isn't important.
At any rate, good luck!
All opinions presented here aren't mine.
You've had a lot of input here, some of which seems good to me. But I think you're looking for input on something that isn't YOUR problem.
Grounding the network cables would be your problem if you were fighting noise. Then grounding one end would be the place to start.
But if you're worried about a difference in ground potential causing you problems, anything to do with network cable is NOT the solution. That is something that had better be dealt with by a marine electrician. Not any electrician, one who knows ships and knows them well.
Here's why: Network cable is small signal, low current stuff. If you have a difference in ground potentials you could be talking about high voltage and/or current. You don't want this on your network, it will fry everything. Have those problems solved first by an electrician and know that the enviroment you'll be working in is friendly for your network.....AND FOR YOU!
As an AC pointed out, you can do harm to the ship by changing the electrical properties of it. When those changes start to happen it will likely also do damage to your network.
If it were me I would:
1) Consult the marine electrician most familiar with the ship. Once you have his ok for safety and blessing with your project then...
2) Check with the radio operator/technician if you have one. He's got equipment that works much like your network. There are things he may know which will save you heartache and speed up your progress.
3) Install the network, tie all shields to the hub. Then "ground" the hub to whatever the electrician tells you to. Remember that you're only doing this to prevent noise on the network, it has NOTHING to do with ships ground...and you don't want it to.
4) Ask the electrician and radio op to check your work when you are done. Log this. Then if there is ever a problem you can show the captain the log and he'll know you did your homework. Cover your ass always.
5) Have a nice day.
. Quit playing Monopoly with Bill. Switch to one of many non-Microsoft products today.