Estimating Cable Lengths Required

Since a measuring wheel can only give an estimate distance (and cable lengths required for an installation) by walking in straight paths; what would be the best formula for estimating wire runs in ceillings and hidden walls with conduits ?? I've heard some very exotic formulas used by some engineers like "Length x Width squared, then add 25 - 50% extra feets"


Length x Width squared, then add 25 - 50% extra feet.

What does Width here refer to?

In a perfect square: the shortest side, or shortest "length" for that matter would be the width. Not sure what is the correct term for that.

This is probably a better formula for carpeting than cabling.

I don't think he actually means squared, as in resulting in square feet. I think the intent is as in a squared (90 degree angles) cable run.

Got it.

So the formula is like

Beeline distance from punch to plate x 1.4 + Fudge = Cable distance

Yes?

I walk it off or count tiles, floor or ceiling, and add 25%. Of course, Google Earth makes outside jobs much easier now.

measuring wheels would be about the most precise way of measuring off distances for cable runs... cabling runs will (should) always be parrallel and perpendicular in a building, add your service loop lengths for DTR and station location if it is communications cabling or any other extra necessary for the system you are installing...

In cases where I don't know the actual cable path, I guesstimated right angle runs, added 10 feet at the far end and 20 feet at the near end. That was to account for the drop down the wall plus a small service loop at the far end, and service loops and rack routing at the head end.

Then when I had runs totalled up I'd add a box or two of cable to the whole thing, depending on size.

Crazy question: In cases where you are replacing existing category cable, can any of those fancy reflectometers tell you the length of the run?

U2, yes a TDR could measure the cable length for you or you could also use a certifier or verifier.

I did the same thing but added 10%-20% or so at the end to count for waste in lieu of adding a box or two. When a spool gets down to the last 70 feet rarely does it find a use. Granted, these were large cabling projects with more cable than the surveillance portion usually (school intercom or nurse call) so YMMV.

Not sure what your purpose is....

In the hundreds of jobs I've done over the years, I generally have just plugged a round number formula or a $ amount per camera for the pricing. Only exception would be if a site visit unusually long runs like to a detached school gym. When it's time to pull the cable, I'd generally eyeball to see where we could match different runs maximize the boxed cable. Totally agree about the 70' mark. If it's there I chunk it. That's after years of not doing that and having a corner of the shop full of cable boxes that just weren't usuable.

Wholesale cost on Cat5 is under $65 for 1000'. I'll usually estimate 3 runs from it so really no need to wheel measure every run. You're not going to gain much money for the effort.

Additional trip: always plan for 20-25% "extra" runs - example, in a bundle of 4-5 cables, add one spare... 9-10 cables, add two spares, etc. This practice has saved me a lot of work and headache when a customer wants to add cameras later, or if a run gets damaged along the way.

Also makes you look like a hero if the customer decides to add a network drop, IP phone, WAP, etc. in the middle of things. Like U3Int says, standard FT-4 Cat5e is cheap like borscht now, the cost of pulling an extra 100' run in a bundle is minimal compared to the labour of doing it after.

We do a lot of structured cabling. Typically I wheel off 5-10 drops per sheet "eyeballing" where the majority of pulls are, take the average of those, multiply by total drops, and add 10%. It's worked well so far and hasn't gotten me into trouble yet (not saying it won't, but I've been using this method for the past two years). Fiber I add 30-40 feet of what I wheel off.

I've tried to find distances of each single cable in a print before and ended a few thousand short on cat6 plenum (we're a panduit dealer so I use General cable) and it was a costly mistake.