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Shop building racks vs. onsite onstruction
Al Clayton:
The good new is business is growing, and we are doing larger installs. The bad news is, we do a lot of public work and must pay prevailing wage when my guys are on site. Obviously the less time they spend on-site, the more profitable the job will be.
So I'm thinking I would like to be doing more pre-construction/wiring of racks in the shop.
Since the racks interface with field wiring, I wonder how practical it really is to wire in the shop. Certainly there is a savings to be realized on the internal wiring. But are there ways to increase the speed/efficiency of terminating the field wiring in the rack?
It seems like a field termination would need to be made either way.
Does anyone have a good resource for best practices when it comes to this kind of thing? What do you do? Comments,suggestions,welcome. Pictures?
Al Clayton:
Musings part II
There also are the issues transporting the racks themselves. A 77" rack, loaded with amplifiers and other electronics can easily exceed 600 lbs. So even if the rack is pre-wired, we often have to remove equipment just to transport the rack.
Especially if the amplifier room is on the second floor and the on access is a stairwell.
Inevitably the Electrical contractor wants the racks ahead of time so he can "Pipe" into the and pull cables. How do those of you who build racks in your shop handle those issues?
Just brainstorming a little here...
Tom Young:
Lots of issues with building racks in a shop versus at a job site.
Regarding terminations, I think that most contracting firms utilize screw terminals mounted on rack panels on the rear of each rack. These and the wires are labeled and correspond to shop drawings. Rack-to-rack wiring is sometimes done with multipin connectors whch are disconnected for transport. I prefer to not do this as it adds another connection point which can fail.
In some cases we connect directly to the equipment connectors.
Most of the racks I oversee are transported with equipment in them but in some cases we remove all, or the heaviest, gear and reinstall (plus re-terminate) them on site.
But trucking empty racks along with boxed equipment plus installation tools and equipment requires more truck space or additional runs.
It has been mostly my own smaller projects where the racks get built and wired on site. Seldom is it as easy due to lack of room and no easy means to elevate the rack (if it is less than full size) to make it easier to see and work on. It is also often a huge PITA to deal with boxes and other rubbish removal at the job site. Testing and signal tracing is much easier in the shop.
Running wire and bundling, supporting bundles, creating service loops and terminations (including teflon tube over shields and heat shrink, plus wire numbers) is easier in the shop where you have access to all tools and parts and no other-trade distractions or interference.
Although it perhaps would be easier to have the electrical tie-ins done with an empty rack, we always leave plenty of room for AC power and oversee where they knockout or create holes for connection of conduit. Perhaps half the time we do all inter-rack AC wiring and they work with our stub outs (at the top, usually) with a J-box and then make their terminations/splices.
There are other issues I cannot think of right now. I will be curious to read what others have to say.
Charlie Zureki:
Hello,
For my past installs, I've always considered the final location and the transportation of the racks, although the only real concern has been wall mounted racks. I would never expect anyone to try and hang a rack that's fully loaded.
In most cases, I've installed the equipment and prewired and terminated all interconnects....then, the only tasks left are to terminate signal runs and connect the power feed to the rack.
(I use rack power rails of different lengths)
If the racks are full heigth amp racks, I only install the bottom half of the rack and wheel in...the remaining amps to be installed on site.
With two Techs and a refrigerator dolly it's pretty painless to get any rack where you need it.
The racks today are so much lighter than the racks of 20+ years ago... ever try to move a 30 year old Cabtron rack? Even an empty Cabtron rack? They weigh as much as a Buick!
So...to sum up my answer...it depends on where the rack is going to live and how hard it is to get there.
Cheers,
Hammer
Joseph Macry:
My habit: Attached (wall mounted) racks with hard-wired terminations get built on site. Portable racks meant to plug into, say, wall plates are built in shop then delivered. Portable racks destined to be hard wired, I build in the shop unless the electrician needs to install flex conduit or install an outlet inside the rack.
Here, it doesn't make a big difference because our guys get the same wage on site or in the shop. But building in the shop usually saves a few trips to the job site.
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