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|I am preparing a statement of work for a cabling project. Part of the design is calculating exact cable lengths and quantities of connectors, wall boxes, wall box modules, etc. From those quantities I will prepare a Bill of Materials (BOM). My company wants to who ever wins the bid to purchase material according to the BOM. How much sluff should I add to my exact quantities?|
John Kendra RCDD
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|Our experience says (now we are supervising and commisioning cable projects) as contractors, that it can varies depending on installers training, and of course designing issues|
under raised flooring?
above ceiling (modular or plenum?)
Jhooks? or cable tray?
But in any case labour is the key; so for proffesional crew a 5% is more than enough, if you have designed accordingly on building pathways characteristics.
No slag is necesary then.
I hope this help you. in any case a you can pay the cable (as far as 90mts) as the scaaner mesearuments give the proof of installed cable, for other components (panel, connectors, face plate, and so) no trouble they sholud be in theri place.
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John Kendra (9/23/2010)
I am preparing a statement of work for a cabling project. Part of the design is calculating exact cable lengths and quantities of connectors, wall boxes, wall box modules, etc. From those quantities I will prepare a Bill of Materials (BOM). My company wants to who ever wins the bid to purchase material according to the BOM. How much sluff should I add to my exact quantities?
You are going to get as many various answers to this as can be imagined and then may be a few more.
I normally allow different percentages for various materials, cabling being the hardest since the number of runs out of a reel will depend on avg lengths and the efficency of the foreman.
Why not have your exact quanties be the "finished quanties" and state that the winning contractor is responsible for any waste, overage, etc.? This will put the waste factors on his back and he should know his crews history.
That being said my copper cable formula is as follows assuming 1000' reels of cable round down 1000/avg run x 1000. Avg run is the rough pull number including all ups and downs for termination at each end plus a 5% waste factor.
example point to point average via cable path is 150' + 15' at station + 20' at closet = 185' + 10' (5% waste) =195'. then
round down of 1000/195= 5 runs per reel. Total runs / 5 = rounded up is the number of reels required.
Wall boxes and face plates actual + 1% rounded up to the next quantity by package example if the faceplates are 25 to a box and you have 190 locations then it is 190+2 waste =192 then round up for boxes of 25, total 200. If you have differnt faceplate style of faceplates (surface vs. furniture, etc, figure each style separately).
Jacks use the same formula as faceplates but use a 3% waste factor (don't forget to figure it for each color of jack that is required).
Patch panels, blocks, wire management panels, racks or any large item, use the exact quantity. smaller items like 110C clips allow some waste (2-5%)
Cable ladder, figure each room for the number of full lengths required, you should not have more then 10' waste per room for a standard closet but it will be higher for medium to large room/datacenter.
Backbone fiber and copper cabling should have proper allowences for termination on your racks/wallfield including some relocaation slack.
Last, recheck your numbers, there is nothing more embarressing then being wrong due to a math error and it may jepordize your completion date if additional materials must be ordered at the last minute.
Again my opinion, is to put the responsibility in the hands of the contractor (Yes I worked for a cabling contractor for over 25 yrs) and ask them to list their material quantities as part of the RFP response so you have a warm and fuzzy feeling that they understand the scope of work.
Joseph Golan, RCDD (Retired)
Palm Coast, FL