in January 2009
Back To The ‘Drawing’ Board
By Jerrold Stevens
Are shop drawings a necessary evil…or profit saver?
So, you got that job and it’s time to install the system. If it was a consultant-designed project, the specs probably call for submittals, including shop drawings, to be submitted for approval before you order the equipment. You might be thinking to yourself, “Why on Earth does a consultant ask for this stuff? This is going to cost me a lot of money in engineering time and I just don’t have room in the project budget for this!”
Those pesky shop drawings can actually save you money in the long run. Think about some of your recent installs. Have you ever had a crew of three or four stop work to come and ask, “How many of what type cables are we pulling from here to there?” or say “This XYZ unit has BNC connectors and all we have are F connectors!”
Think About It
Think about how much you are paying these installers per hour, times how many of them are standing around either waiting for someone to pull out the drawings to figure out how many wires you want in that pipe or waiting for someone to find some BNC connectors. How many times have you had to send a crew out an extra trip because some critical piece of the system was not available?
I suspect that successful integrators will tell you that shop drawings are essential to the profitability of a project, whether it’s a consultant spec job or their own design/build job. Why? Because field time is more expensive than shop time. And, missing a deadline for substantial completion can cost you money and reputation.
Consider all the expenses of putting a crew in the field. First, there’s non-productive travel time to and from the job site for each employee. Then there are hotel rooms, meals, transportation and other travel expenses. Add in time hunting for materials and parts that didn’t make it on the truck and additional overnight shipping expenses for last-minute orders for those pieces you forgot.
Then there’s the additional time the crew might have to spend going back to change the taps on a few hundred loudspeakers because calculations were not done beforehand and noted on the drawings. It’s easy to see how inefficient field time can quickly cut into your profit on the job.
Office Time Is Efficient
By comparison, engineering labor in the office is very efficient, especially if you are exchanging engineering and drafting time for field time. The process of creating shop drawings can reveal “gotchas” in the system, such as unexpected termination types and incompatibilities. It’s much cheaper to work out a solution here and now than it would be in the field. A few hours creating shop drawings in the office can shave many hours of expensive installation time on the job site. It only makes sense to try to minimize field time and maximize shop time.
So what are shop drawings? They are the “installation manual” for the project. These drawings should contain any information the installer will need in an easy-to-read, quickly accessible format. These drawings, in combination with the installation and owner’s manuals for the equipment, will keep your field crew productive. They will also help ensure that your crew will have all the parts and materials they will need on the job site.
The drawings and specs issued by the consultant are not shop drawings; they are bid documents, so don’t expect to send a copy of the consultant’s drawings back in your submittal package and get an approval. Bid documents don’t incorporate a lot of the little details your crew will need to install the system. Although they do show how the system is to be wired and the design intent, they do not tell the installer what type of connector is required and how that connector should be terminated. And, they probably won’t tell the installer anything about what to expect when he starts performing tests and measurements so he knows if the measurement is up to spec.
So what do we want to put on our shop drawings? First, we will need detail sheets with diagrams for how each type of connector and signal type should be terminated. These should include details for how much the jacket and conductor insulation should be trimmed, any heat shrink that should be added, what color conductor connects to which pin, etc. These should also include grounding schemes and loudspeaker installation details for each different type of loudspeaker used on the job.
Details for each type of mounting (wall mounts, pole mounts, etc.) for flat-panel displays and projection screens should be included. You will also need a legend sheet showing all the symbols, with their descriptions, that will be used in your drawings, and a sheet index with a description of each sheet. These detail sheets can be created one time and just duplicated for each project.
These drawings should also include plans showing all conduit provided for your work. I suggest showing wire fills for each pipe on these plans to make it easy for your crew to know what to pull in each pipe. You will also want a chart listing every cable that will be used on the job, with its origin, destination, cable type and cable number identified.
RCPs should be included showing the location of each ceiling loudspeaker. These plans should also indicate which circuit number (and cable number) is to be connected to each loudspeaker. If it’s a constant-voltage system, then include the tap value to be terminated for each loudspeaker, as well.
Next, you will need block diagrams for all systems. These drawings should show the signal flow from one device to the next. They should also include the type and ID number for every cable, as well as the termination and connector type for every termination with a reference to the appropriate wiring detail. I would also suggest noting appropriate levels and impedances on these drawings.
For example, noting the anticipated impedance for each loudspeaker circuit where it connects to the amplifier quickly tells the installer if the value he measures is correct, speeding up the testing and troubleshooting process. You will also want to include block diagrams of the internal configurations of any DSPs in the system.
Your shop drawings should include page layouts for control system panels and explanations of the functions of each control. Rack elevations with the mounting location of each piece of equipment should be included with details for electrical connections, wire ways, lacing bars, blank and vent panels, rack-grounding instructions and conduit penetration details.
You will also want detailed rigging drawings of any large suspended equipment, such as loudspeaker arrays.
Finally, you will want details for any remaining equipment and parts. This could include plate and panel construction details, patch bay layouts…basically anything your installers might need to know to complete the job.
I think you can see how useful all this information can be. Complete and accurate parts lists can be taken from a set of detailed shop drawings including all the connectors and wire types…even the number of rack screws your purchasing department will need to order and your installation crew will need to load on the truck. In fact, some drafting programs allow blocks to be created for each device in your system, with attributes such as associated connectors. Then you can generate a parts list from your drawing automatically!
All this information at the installer’s fingertips means minimal field time is wasted looking for answers or making runs to the local electrical/electronics supply house. Crews will be more organized and better able to plan their work.
Do you still think you can’t afford to do shop drawings? I say, you can’t afford not to!
Jerrold Stevens, a Principal Consultant with PMK International in Dubai, UAE, has more than 20 years of experience in the audio industry. He is a member of the NSCA’s Consultant Executive Council and InfoComm International’s Professional Education and Training Committee (PETC). He has been an InfoComm Academy Adjunct Instructor since 2007.