The advice to pre-install conduit is very good, but be sure that you do it right. Specify a LARGE diameter (perhaps 4-inch or more) in order that you can easily install a MESSENGER LINE too if the runs are more than about 15 feet. A Messinger Line is a length of nylon cord from one end of the entire run to the other in the form of a loop, and one attaches the end of a cable to the line and with the ends of the loop around a pully or smooth post, one pulls one side of the loop to cause the cable to be dragged through. This remains in the filled conduit, and if future cable changes are necessary, the line allows another cable to be pulled in (IF the conduit was carefully deburred!). If all goes well, this line can be installed as the lengths of conduit are pieced together, and there will then never be the need to install a cable by means of the slow and difficult fishing method. The additional cost of larger conduit will be much less than electricians' fees for hours needed to fish a long run.
If the conduit must pass underground or exposed to weather, consider encasing it in plastic plumbers' pipe as it is installed, with the plastic joints sealed (glued shut as for plumbing) to forestall water penetration. Even a little water inside the conduit may penetrate any connectors and that could degrade the signal -- or block it completely. It may be tempting to use only plastic plumbers' pipe, but part of the value of steel (or, better yet: aluminum) conduit is that it can be grounded to act as a shield to any Radio Frequency waves (broadcast, airplaines, microwave phones, etc, etc.!) that might penetrate your cables and garble your sound and pictures.
Be sure that the contractor is bound by contract to make drawings of the layout of the conduit(s) by the actual contract he signs so that future installers will have confidence in the layout and materials, else they may insist upon installing their own known layout at considerably greater cost to you, --and much larger profit to them! Conduits should be capped off on each end at least with removable foam or silicone sealant to prevent entry of vermin as well as water (contractors often neglect this, so you may have to do it). Note that you cannot run any form of signal in a conduit carrying mains power, so plan on separate conduit runs, if need be.
If the street-side entry of your utilities is to be underground according to local ordinance, then you may have to install a small underground VALVE PIT like chamber to receive present and future conduits and cables. If cables are to be attached aerially to your building, you would do well to plan a large closet at or near the point of entry to receive your conduits.
It would also be good planning to bring a LARGE copper earth ground wire (1/8th-inch diameter or greater) to such an entry and leave a coil of it upon the floor for any future need of interference suppression, but this only works well if the other end of the ground wire goes outside to soil that is usually moist at least five feet down into which a groung rod has been sunk. (Such sold at Radio Shack and TV antenna dealers.) This is a cheap provision that could save you many headaches due to interference now -- and that which is likely to develop later! Any electronics technician trained in RFI will be grateful for such a High Quality Earth Ground, and will know how to use it to your advantage to create a Star-Point ground. Note that the larger the diameter of the ground wire, the better, since it will then be more receptive to carrying a greater range of interfering frequencies to earth ground, all other factors being equal. Your electrician may be the one to ask for this building ground wire, since, while its high current carrying capacity is not needed, its low inductance, capacitance and resistance is needed. This is the province of an electronics tech trained in RFI suppression, so your electrician may not understand why you need such large twisted strand copper grounding cable. Such grounding cable may be jacketed if you prefer and that will protect it from moisture and rapid corrosion. Best Wishes, Jim
[This message has been edited by jimor (edited September 21, 2006).]
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