Grounding Ethernet Cable on a Ship? 58
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?"
hmmm (Score:3, Funny)
I thought the general idea was to not run aground on a ship.
Re:hmmm (Score:1)
Ground one end (Score:5, Informative)
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)
quick question (Score:1)
Re:Ground one end (Score:3, Informative)
Probably to reduce emissions.. Most boats have a lot of sensitive electronics.. and when you're under EMCON, you don't want anything avoidable to emit. Also, consider you'd want to make at least a minimal attempt to harden the equipment against any kind of EMP.
Had a friend that worked at a naval shipyard.. spent weeks trying to locate, identify, and eliminate undesired emissions from various (uncertified and certified) electronics.
Re:Ground one end (Score:2)
The more likely concern is picking up other frequencies on the cable itself on the shield!
So - the guy is likely really asking about how to ground the shield - not the transmission lines themselves. At least I hope so - grounding the transmission system itself isn't to good an idea.
Re:Ground one end (Score:2)
Re:Ground one end (Score:2)
On an ocean going ship, shielded cable & grounding is a must. Static discharge from bulkheads is more than capable of corrupting data or even zapping a NIC. Other sources of interference include active radars or even shortwave transmitters in certain circumstances.
Depending on the type of vessel, there may be other things going on to interfere with things. Fishing vessels has powerful motors and machinery. Naval vessels have fire control radar and ECM. Cruise liners have everything from big speakers in the disco to large electric ovens and water heaters.
Re:Ground one end (Score:1)
Re:Ground one end (Score:3, Informative)
One of the reasons for the 100 meter spec for distance of Ethernet runs is potential voltage. If you are on a ship with long runs of Ethernet, you should definately ground the shields using good straps to the hull or to studs that aren't covered in paint. I would ground both ends and perhaps along the middle. I'd also use something akin an APC ProtectNet [apcc.com] or Tripp Lite DNET1 [tripplite.com]. The longer the run, the higher the potential voltage on the line and ground these to the hull as well.
The shield, while it could carry a charge, is mostly about radiation -- into or out of the shielded cable. If you are running your Ethernet along power like the fool on the houseboat (inducting 60Hz into his Ethernet) you are asking for collisions, power spikes, etc. The potential charge on Ethernet conductors itself over longer runs probably will spell trouble all by itself without assistance from 60 cycle.
Re:Ground one end (Score:2)
Big problems. (Score:4, Informative)
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.
Re:Big problems. (Score:1)
Good advice. (Score:3, Informative)
Good advice. Run heavy ground wires between the points. Then use shielded Cat-5 with the shield grounded at one end. You don't want the shield to carry current; it is only to prevent common mode pickup.
"Common mode" is capacitive or inductive coupling to both wires of a pair at the same time. Common mode voltages can overload the Ethernet common mode voltage range. The common mode range is a few volts, so you also need the ground wires to insure that the range is not exceeded.
Re: Big problems. (Score:2)
What happens if the actual computer and network equipment at each location is grounded there? You've just run 90 volts into an Ethernet port.
Definitely make sure all equipment grounds are connected.
Sounds like a nightmare.
Trade one for another (Score:2)
What kind of vessel is it? (Score:1)
Re:What kind of vessel is it? (Score:2)
Shielding could be required for many reasons, depending on the layout of the ship and how the cables are run. Things like flourescent lighting, electric motors, pumps and generators are more than capable of producing enough interference to disrupt the signal.
Re:What kind of vessel is it? (Score:2)
Re:What kind of vessel is it? (Score:2)
Ground at the switch. (Score:4, Informative)
Allen-Bradley's Web site has a handy little pdf document [ab.com] 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.
Re:Ground at the switch. (Score:2)
Grounding and Ethernet at sea (Score:2)
I presume you are talking of how to ground the shields of your shielded cable. To be effective as shields for EMC purposes, you will want the shields grounded to something. Normally, we'd connect any shield at one end to case-ground and leave it open at the other, to avoid ground loops. However, in the rest of the world we are required to bond our RF and Power grounds. Your power ground is floating. For EMC purposes, I'd think it would be the RF ground not the floating AC ground. In which case, you'd want it isolated from computer AC ground / case ground at both ends. How to ensure the AC ground stays floating from the RF ground must be covered in your shipboard electrical codes, good luck.
I'd recommend discussing this with a qualified marine radio installer. They'd be aware of the grounding practices for digital cables in shipboard installations.
Bill N1VUX (licensed for AMATEUR radio only)
Re:Grounding and Ethernet at sea (Score:2)
Each NIC transformer-couples Tx and Rx data. The transformers often have a non 1:1 ratio so they are usually impedance matching as well as isolation. There's usually a 1Kv-rated ceramic capacitor from the transformer center tap to chassis ground to bypass static charges.
Only for coax (IMHO) (Score:2, Interesting)
Always, always ground one end (Score:2, Informative)
don't ask slashdot this (Score:4, Interesting)
Re:don't ask slashdot this (Score:1)
Re:don't ask slashdot this (Score:3, Insightful)
Re:don't ask slashdot this (Score:1)
Err, wrong. Try electrical/computer engineer, as many of the
Eletricians don't wire Cat5 for a living and the few that do rarely understand its electrical characteristics.
Good point, sort-of (Score:2)
What you really need here is an experienced telco person.
Bad grounding is a killer - literally. (Score:3, Informative)
First of all, ethernet doesn't need a ground.
If you're already dedicated to it, however, you do need to look into it, because an ungrounded shield can be dangerous as well.
For ideas, do a web search on grounding rs-485 network cables. rs-485 is a differential signalling system similar to ethernet that is meant for long serial runs (kilometer or more) where grounding is a an issue.
In most cases, you need to find out what the voltage differential is, possible current flow, and run a suitable grounding wire along with the cable since the shield may not be adequate to the job, and may still leave quite a voltage differential. Sometimes, however, it's appropiate to allow a voltage differential and ground through a capacitor and/or resistor.
In other words, there's no single way to do it, and the way you do it will depend on many things, not the least of which is what you're doing with the network and where it's being used.
Good luck! Don't suck on the wires, especially when you know for sure that they aren't live (they are always 'live').
-Adam
Re:Bad grounding is a killer - literally. (Score:4, Informative)
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.
Grounding theory? (Score:1)
Ground one end: YES
Ground every end: no, unless you want noise
Ground every end and install isolation transformer (on the ethernet TX/RX ckt I assume): No, unless you want an expensive solution to produce noise.
Don't ground any end: this is the safest if you don't know what you're doing.
IANAEE, but common sense tells me that you should be running your computer equipment on isolated ground circuits. If you're also using shielded ethernet, either ground the shield at the nics or at the hub, and be consistent. If you're using isolation transformers ON the ethernet TX/RX circuit itself, grounding should definitely be at the hub, bonded to the isolation transformer's neutral or ground.
I know..... (Score:1)
use fiber optic (Score:4, Informative)
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.
DoD grounding recommendations (Score:5, Informative)
Grounding, ethernet, etc. (Score:5, Interesting)
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!
go optical and/or don't do ethernet (Score:2, Informative)
first: if you can, put in optical fiber. that way you will avoid the ground loop problems entirely.
indeed, first time most folks saw optical fiber was in the raised floor computer room, separating the mainframe chassis and peripherals.
second: electric grounding on boats gets really complicated really quickly. you have several conflicting requirements for "grounding": HF radio counterpoise, electrical noise reduction, shore-side AC ground, perhaps onboard generator AC ground, onboard DC ground, lightning strike diversion, metal conductor bonding (hand rails and engines etc.)
go to a marine book store like red tide or armchair sailor or west marine and get some books on marine electrics. or hire a real marine electrician, it's money well spent.
Don't ground aboard a ship. (Score:2, Informative)
YOU COULD SINK THE SHIP IN HOURS.
Sorry to shout, but current flowing through the hull is about as bad as sailing over reefs or bumping into mines. Check with experts before connecting anything.
Noise vs. Electrical (Score:4, Informative)
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.
Re:CONTACT A PROFESSIONAL NOW (Score:2)
Oh... (Score:2)
So, why would you run grounded ethernet? What's wrong with a normal Cat-5? What kind of ship is it? How far is it between the pc's? Have you considered fiber? Unless you can say a bit more about why you worry, it's impossible for anyone to give a qualified answer.
Re:Oh... (Score:2)
Aha, so that's how it is. When you have experience on ships everything becomes clear. Because anyone that has ever worked offshore, will obviously understand ethernet cabling much better than everyone else.
For your information, I actually do have some experience on ships. I make software that is used on ships, and occasionally travel out to them. And I can assure you that whatever works in your office with regards to cabling, works there too.
But as other posters have pointed out, it might not be the ship itself that is worrying. It could be the radar, the engine, or a number of other factors. But a large ship is nothing special.
Now, can you please explain to me how someone with experience on ships should be able to guess what kind of environment he is speaking of?
"floating" (Score:1)
haha... Very funny...
I've designed ethernet... (Score:2)
In a situation where you're not sure if you're running the two ends off of a common ground, I definitely would not recommend using shielded cable. You could end up sending that cable up in smoke if your grounds shift.