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DrKlahn
DrKlahn, Computer Engineer
Category: Networking
Satisfied Customers: 1967
Experience:  BSci: Electrical Engr., Industrial Engr, and Computer Sci.
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Topic: Outdoor network infrastructure for residential application. Situation:

Customer Question

Topic: Outdoor network infrastructure for residential application.

Situation: Comcast cable is unable to provide residential cable internet to my home because its a good 250 feet away from the cable "pedestal," and most of its juice is already occupied powering a 300 foot coax run up to my neighbor's house across the street. To solve this problem, I am going to site a cable modem (in a NEMA outdoor-rated enclosure) right next to the cable tap, then bring the signal to my home with ordinary LAN equipment. I've extensively researched all the options and considered their cost-effectiveness; now I simply need a once-over from an expert to determine if I missed anything.

Question: I've settled on a 250 foot run of direct-bury rated Cat6 cable to the road, using Power over Ethernet injectors/splitters to power the cable modem. I have two concerns here:

1. 250 feet is "within spec" for both PoE and Ethernet data; but its pushing close to the 100 meter limit. How likely is my signal reliability to suffer, pushing the limits like this?

2. Without running a separate 110v power line to the enclosure, I'll have to rely on passive radiators on the enclosures exterior (and a few 12v computer case fans split from the PoE device) for cooling. (Location is SE Michigan; summer highs of 80 degrees F. must be accounted for.) Do you think this will be adequate?
Submitted: 1 year ago.
Category: Networking
Expert:  DrKlahn replied 1 year ago.

DrKlahn :

Thanks for using JustAnswer, the internet's independent site for Q&A consulting. I'm "DrKlahn," and I'd like to help you with this question.

DrKlahn :

Notice / disclosure: JustAnswer is a commercial Q&A site not associated with any computer hardware or software manufacturer. The "9 second" banner ad does not mean questions are answered in 9 seconds - it means about 400 questions are answered per hour.

DrKlahn :

Please send me a short message when you're online and ready to begin.

DrKlahn :

Thanks for using JustAnswer, the internet's independent site for Q&A consulting. I'm "DrKlahn," and I'd like to help you with this question.

DrKlahn :

Please send me a short message when you're online and ready to begin.

DrKlahn :

Notice / disclosure: JustAnswer is a commercial Q&A site not associated with any computer hardware or software manufacturer. The "9 second" banner ad does not mean questions are answered in 9 seconds - it means about 400 questions are answered per hour.

DrKlahn :

The system indicates that you're a new user of our site, so do not hesitate to ask any questions you may have about how things work.

DrKlahn :

Before starting, I would like to confirm that you know that JustAnswer is a Q&A service business, and not the official customer support site for Comcast, or any computer hardware company?

Customer:

Completely understood.

DrKlahn :

Thank you. Are you the customer who asked me this same question yesterday? If so, you should return to the original question and there won't be an additional charge for a new question.

Customer:

No, I am not. First time using this service.

DrKlahn :

OK. We will take a look at the situation then and see if the result is the same.

DrKlahn :

What voltage is the PoE hardware injecting onto the cable? It is usually 12V DC or 24V DC.

Customer:

12 volt DC, to power a 12 volt cable modem.

DrKlahn :

Thank you. Is the wire the usual 26 AWG copper wire?

Customer:

Cat 6 direct-bury wire is what I'll be using.

DrKlahn :

That is usually 26 or 28 AWG, so we will use 26 as the wire gauge which is slightly larger than 28 AWG.

Customer:

Okay.

DrKlahn :

250 feet is far outside the capacity of PoE power in this situation. One moment and I'll bring in an image of the power calculator.

Customer:

Okay.

DrKlahn :

Full Size Image

DrKlahn :

(click anywhere on the above image to view it at full scale)

DrKlahn :

The remote access point will pull at least 1 amp of current, so PoE won't do the job in this case.

Customer:

Thank you. In that case I will have to run a 110v power cable to the road.

DrKlahn :

Would you like me to calculate the wire gauge necessary to run DC power on a separate cable for the remote AP?

DrKlahn :

(My guess is that it's going to be around 12 AWG to 14 AWG, which is the diameter used for normal house wiring)

DrKlahn :

Yes, you could just barely do it with 14 AWG cable. The voltage drop would still be 10%, but it would probablywork.

DrKlahn :

Full Size Image

Customer:

No need. I may as well commit to running a 110v direct-bury cable so I can also power environmental controls in the enclosure itself.

DrKlahn :

However, if you're going to be burying 12 or 14 AWG cable, it makes more sense to run 110 on it as the resistive losses will be far less.

Customer:

Yes. Is there a minimum distance between the 110v cable and the data cable to avoid excessive interference? Obviously they will both need their own trench.

DrKlahn :

Other than this issue, the solution you've proposed is workable.

Customer:

Excellent. Thank you for your time.

DrKlahn :

There won't be any significant interference between the AC cable and the data cable, though I recomment putting gas arc suppressors on both ends of each to prevent induction voltage spikes from any nearby strikes.

Customer:

Ah, noted, thank you.

DrKlahn :

I would recommend enclosed flat-panel antennas at both ends, which should give you about a 12 to 14 dBi gain over omnidirectional antennas. These are readily available on ebay and on most internet networking suppliers. Figure $40 to $60 each.

Customer:

Okay. And 802.11n would be preferred for this application if I go with a wireless network bridge?

DrKlahn :

The reason I've recommended gas arc suppressors is because there is very little effect on the signal quality until they arc over. The more common MOV surge arrestors act like capacitors, which is not an issue on the AC side but is definitely an issue on the network side.

DrKlahn :

... I need to look up the frequency allocations for a/b/g/n to give you a correct answer for that one. Please bear with me a moment.

Customer:

Thank you.

DrKlahn :

I would recommend staying with b or g. The reason for this is that b and g run in the 2.4 GHz spectrum while a and n run in the 5 GHz spectrum. The shorter the microwave, the more chance that there will be a problem in rain, snow or damp conditions.

DrKlahn :

802.11n is allocated both 2.4 GHz and 5 GHz spectrum, but I don't know how it is handled in the case of transmission problems.

Customer:

Ah, okay. With flat-panel antennas it won't be an issue anyways.

Customer:

I'm satisfied with these answers. I feel you've provided more detail then was originally requested; I will up compensation accordingly.

DrKlahn, Computer Engineer
Category: Networking
Satisfied Customers: 1967
Experience: BSci: Electrical Engr., Industrial Engr, and Computer Sci.
DrKlahn and 4 other Networking Specialists are ready to help you
Expert:  DrKlahn replied 1 year ago.
I hope that I answered your questions satisfactorily. Don't hesitate to follow up if you have any further questions, or would like to discuss possible approaches to the problem. Closing a question does not mean that our support has ended.

There is one thing I forgot to mention. Even with the cable buried, and with arc suppressors at both ends, there is a chance that a nearby strike may destroy the transceivers in the network equipment. I recommend buying spares for the equipment at each end, and configuring them before they go on the shelf. Then, if the spares should ever be needed, they can be swapped in immediately.

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DrKlahn
DrKlahn
Network Technician
1967 Satisfied Customers
BSci: Electrical Engr., Industrial Engr, and Computer Sci.