Industrial data cable wiring practice 4

[bentov]

I'm installing a data conduit for my new place (4 buildings on 5 acres, wiring infrastructure spans about 600 feet), going to put (8) Cat 6 UTP cables plus (1) RG6 coax in a 1 1/4" conduit with J-boxes big enough for patch blocks at various locations - won't use much of that capacity initially but trying to allow for all future phone/security video/TV/ethernet traffic while we're pulling wire.

That data conduit arrives at my main repair shop 6" away from the power conduit (200a 240V 3 phase) - both will be metal (rigid or EMT) everywhere above ground. The best place for my data J-box is right next to the breaker distribution panel, which is also within a couple feet of a custom power supply we use to test run motors (pair of 75kva 3ph dry type 2:1 transformers with a bunch of interlocked contactors, so we can step down to 60V 800A when necessary to start large motors, then step up to 480V for no load full voltage testing - big inductive current surges when we energize those transformers). Right next to that is an old slip ring motor rewound as an autotransformer, 0-480V output over a 1/4 turn gearmotor driven arc with 240V input. Should I worry about the surging/fluctating magnetic fields from those power supplies affecting my data signals in the nearby conduit & J-box, or will the metallic conduit & enclosure provide adequate shielding? Or is that kind of EMI even a problem for these kinds of signals over twisted pairs?

 

[VEBill]

Sounds like it's close enough that interference is a risk. It depends on a million variables, so the best initial guess is 50/50 odds.

Personally, if it was me, I'd add some distance. Or at least arrange things so that you can move it further away if the worse comes to pass. If that's not possible, then you could always button down the shielding later.

PS: I hope you're not running many hundreds of feet of RG-6 coax in one run. Depending on the frequency (Ch 4 vice 2.2 GHz satellite IF), the loss can become serious after about 100 to 200 feet.

PS2: There's never enough cables no matter what you do. Many modern satellite dishes often require four cables.

 

[robertjo24]

A couple of thoughts…

The conduit and metallic enclosures should provide adequate shielding for the scenario you describe, if all the junction boxes and equipment are properly bonded to the common building ground. If the boxes are not grounded properly, there I think there is a potential for a lot of interference. I wouldn’t rule out the noise that will be fed back from the power systems as well if they are all tied to the same grid if there isn’t adequate filtering.

Also, by running copper between the buildings you open yourself up to possible problems with power/lightning surges. I would terminate all copper in each building on a protection block.

If running Ethernet to each of the buildings, the proper way would be to have one main distribution switch where you main network interface resides, then have smaller switches in each building (hub & spoke). It would be ideal if these switches could be interconnected via fiber. Of course, I too live and work in the real world and budgets do not always allow for doing things 100% up front, particularly when planning for future use. So at a min, I would install the protection blocks. Next step up is having small switches in each building connected back to the main switch. And if you can put the money out up front, fun fiber to all the buildings.

 

[amurray]

To help minimize your magnetic interference keep your data conduits parallel to the power circuits if possible & as far away as mentioned by others. Also be careful of the grounding in the shields of any long distance cable runs. I have seen +70V on shielded CAT5 cable runs. Only ground only 1 end of the shield, but that other end can have a high votage to ground on it.

I would second the suggestion of running fiber. I am not sure what uses you have for all the cables but typically there are fiber optic - X (Ethernets, RS-485, etc) converters you could use at each end. This would also allow for just 1 cable to run route & then subdivide the fibers at each end for all the different uses.

Another issue to consider is the potential damage/wear on the electronics & power supplies that the surges & harmonics that your large test sets may introduce to your whole electric distribution system. Good surge protectors & UPS should be used.

My 2 cents.

Andy

 

[bentov]

Thanks for your thoughts and replies. I did consider optic for it's noise immunity, finally veered off given the cost of termination (will touch down in 4-5 locations, really adds up with the multiple uses). None of my data stuff is what you'd call "mission critical", but I'd certainly rather not build in any long term headaches.

My best physical relocation option heads in the direction of the welding shop, probably not a good idea though I don't really have a feel for that either. I guess it's all radiation on amplitude and wavelength spectrums - big, low frequency main & harmonic magnetic fields from the test sets, plus unknown blasts from the contactor arcs at make & break, vs. something different from each kind of welding process, right? Some reflects directly onto the supply grid, some travels the air inducing currents in vulnerable conductors and parallel ground loops?

Guess I'll put the J-boxes in the original planned locations, pay special attention to bonding, check out those protection blocks per robertjo24, hope for the best! VE1BLL, the RG-6 is just in case some future outside service provider prefers it, nothing to hook to at the moment - I presume I can amplify/repeat if necessary when the time comes? I will be stuck with satellite ISP's for a while at least, usually drop that coax straight through the roof down to the modem in a very short run, lan cable from a router after that.

Thanks again for the replies, I appreciate the time taken.