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Become intimately familiar with project.
Review project specifications
Review job book
Review mechanical design or begin
Integrate, check, and correct (if necessary) electrical elementary and piping.
Calculate area needed
Rough overall estimate
Add reasonable "Future" area
Divide into logical, manageable units (roughly)
Do actual layout
Compare layout to piping, electrical and mechanical (panel front layout)
All devices shown in electrical and piping should be on mechanical (front or subpanel)
Workable design
Wiring aids
Spare area
Become intimately familiar with project.
Scan specs to see not only how they are written but to catch those items someone might have forgotten to document: e.g. "14-gauge wiring throughout". some things are done in our shop that are different than the particular specs but are in the spirit of the specs and need someone's written approval.
Scan job book not only to see what has already been done but to become more and more familiar with the job and what has not been done. The job book should contain the Bill of Material and transmittal data, both of which are details necessary to layout of supanels.
Review mechanical design or begin
Look over the drawings of the mechanical details necessary to build the panel or begin the mechanical details as necessary. Include a first pass guess at subpanel size and location in order for the structural details can be designed as soon as possible.
Integrate, check, and point out corrections (if necessary) of the electrical elementary and piping diagrams
Begin a data take-off, sheet by sheet of the electrical elementary, counting relays as a whole and by type, counting terminals to give a total for that sheet. Check off devices that appear on the electrical elementary that are not mounted on subpanels but are front panel mounted or mounted somewhere other than the immediate area of concern. The process of take-off is a different way of viewing the elementaries performing a check on the prints, insuring a more accurate drawing. Although it takes a little extra effort to do this, the rewards are worth the effort. Keep on thought in mind, "If it is on the electrical (or pneumatic or ...) it has to be on the front layout or the subpanel layout (watch out for those instruments on the front layout that have additional components that have to be supanel mounted that have not been drawn completely. Furthermore, sometimes some components are forgotten on the electrical that need to be there, as well as on the mechanical; e.g. supply voltage terminals and main power circuit breaker.
Calculate area needed
This operation may be required before the electrical drawings are made, but it can be done because the operation is in essence a lot of guessing. Some good, proven rules-of-thumb are necessary to do some intelligent guessing. So a general file of information will become available after this procedure is written.
By using the rule-of-thumb that one relay needs fifteen (15) square inches of subpanel, it must be understood that there are constraints involved in that formula. So to make sure that enough area is reserved, fudge in some more relays and/or higher figures. For other components use appropriate formulas or actual dimensions with an eye toward ease of assembly and wiring.
Above and beyond whatever area is calculated previously, remember that these particular drawings are still in a state of flux; they can and probably will be changed up until the sob has been shipped from our shop. So, keep something in your back pocket to take care of these annoyances. After thinking about the possible changes, you should think about the "real" future, that period of time when the customer wants to add another filter or clarifier or something, or maybe he suddenly comes into some money.
So, build in spare space with an eye to two (2) futures and make a lot of people happy. Remember, a lot of our business is repeat and add-on.
Divide into logical, manageable units (roughly)
Subpanels should not be so small that only five (5) relays, or some such, will fit on them, nor should they be so large that the assembled weight exceeds 125 lbs., (11-gauge steel weighs 5 lbs. per square foot without paint - 15 square feet weighs 75 lbs. (3' x 5'); so extremes should be avoided, if possible). All subpanels should be of the same size, where possible.
Logical division of groups of components will make assembly, wiring, and testing easier on everyone. This guiding thought should be considered, along with the design of the whole unit.
Do actual layout while considering the aforementioned thoughts. Build a file. Add to your general file. Change rules-of-thumb as experience dictates.
Compare layout to piping, electrical and mechanical (panel front layout)
You have to keep checking at each step - one thing forgotten, overlooked, or not there can and does affect the following step. This procedure is details and more details.
All devices shown in electrical and piping should be on mechanical (front or subpanel layout)
Now that the stage has been reached where everything should be accounted for, check it to make sure that everything has been accounted for.
You must make sure that the panels can be removed, installed, and are manageable. After all the changes of the previous steps, review again.
When and where possible, consider building-in wiring troughs (steel) and/or angle to facilitate wiring ease. Always any time saved in shop labor will be well spent in engineering time, if only to reduce errors and document what was left out.
The final step in the process is sort of a repeat of ("Future" and future). By this stage you should have some 10% spare space or at least know of where to get some, if the need arises.