The global demand for construction driven by the energy transition, the rollout of digital infrastructure, and the need for buildings and civil works is nothing short of mind-boggling. This demand, coupled with an ever-shrinking pool of skilled labor, is pushing owners and contractors to look at prefabrication work traditionally done on construction sites.
But what exactly does prefabrication even mean? To some, it means moving work traditionally done on site to a controlled shop environment. For others, it means fabricating and assembling complete three-dimensional modules off site and then erecting them on site. Some see it as using sophisticated high-volume production tooling, including robotics, while others focus on a kit-of-parts approach. If this is the case, why is it so difficult?
Challenges with moving electrical work off site
Regardless of its definition, moving work — especially electrical work — off site is not that simple. Existing construction industry processes and practices are not designed for prefabrication and assembly off site. The very nature of electrical work does not lend itself easily to prefabrication, as it’s typically one of many components embedded within sub-assemblies. Furthermore, 3D models that are now commonplace are not created at the level of detail that will provide the detail required to fabricate off site without field measurement/verification. The exception is units like motor control centers (MCCs) that are primarily made up of electrical equipment components.
Electrical work for many industries is still field-measured and fabricated on site, as the precise dimensions and routes may differ based on what is already installed. Therefore, embedded electrical in work assembled off site must be carefully designed and thought through to a much more precise degree than typical on-site work. Space, tolerances, preassembled subassemblies, and methods to make interconnections between assemblies must all be given close attention.
In addition, there are many other considerations as a part of the greater strategy – logistics challenges, including temporary structural support for transport and rigging, and limitations associated with over-the-road equipment size and weight, which often call for larger hoisting equipment. Consideration must also be given to materials traditionally designed for on-site assemblies such as wallboard, switches and plugs, insulation, paint, etc., that will need to be assembled off site and transported to the site without damage or creating additional work in the preassembly approach.
Several energy companies report that off-site assembly has not and does not reduce duration and cost, but rather is used to address skilled labor challenges in remote locations.
Differentiating making parts vs. assembling those parts
An effective framework for prefabrication begins by separating the term “prefabricate” into two elements:
- The process of making parts.
- The assembly of these parts into sub-assemblies and final assemblies.
We also need to translate what the term “assembly” as a noun means in construction. In construction, an assembly can be a kit of parts, a conduit run, or an entire MCC (known in the construction industry as 3D volumetric).
We then need to ask where each element (make and assemble) is best performed, keeping in mind that there could be multiple “makes” and “assembles” depending on the complexity of the “assembly.” For the most part, the actual making is best done in a shop environment where mechanization or even robotics can be used. But assembly and its associated logistics challenges are far more complex.
To answer this question effectively, we must look across the end-to-end process or value stream. We must also apply fundamental operations science to understand the process flows, where to locate inventory (whether inbound raw materials, work-in-process, or finished goods ready to ship to the next process center), how best to allocate capacity and its contributors (equipment, labor, and space), and how to determine when (which can be defined in terms of amounts of work-in-process or dates) to perform each process across the elements and assemblies within and throughout the operations, especially when there are multiple “makes” or “assembles” with varying lead and process times.
The nature of electrical work with home-run cabling, interconnected control wiring, and power distribution requires extremely thoughtful design and planning for prefabrication to be of any value. Despite the best intentions, it is quite easy to make things worse.
A real-world case study
For example, a recent remote giga oil and gas project seeking to improve efficiency and move labor hours from the field to industrial shops adopted a modularization strategy. The scope of the work included a significant amount of high-voltage cabling to be installed.
To improve efficiency and move hours out of the field, power cable lengths were predetermined based on engineering drawings and then spooled on large reels for delivery to the site. Unfortunately, the spools were wound for optimizing cable/spool capacity and not wound so the cables coming off the reels would be in the order needed by the construction crews. So, you guessed it. Spools had to be unwound in a laydown area so the right cables could be rewound on spools for installation by the crews. This resulted in a significant increase in overall labor costs and time to do the work.
An after-action analysis determined that a lower-cost approach would have been to have large spools of uncut cable delivered to the site and a near-site shop set up to cut the cable on demand to the lengths needed by the crews a week in advance. This would have resulted in some cable waste, but that cost would have been far less than what was done.
Five considerations for off-site electrical work
What should those looking to prefabricate electrical do?
- Determine the actual or real cost of moving work off site using an end-to-end production system or value stream perspective (e.g., logistics, temporary bracing, facility rent, tooling, labor, etc.). Remember, the price is not the cost.
- Model, simulate, analyze, and optimize the end-to-end production system using operations science to determine what, where, and when to make and assemble parts.
- Use computer-aided production engineering (CAPE) to design, visualize, and optimize product and process design, including critical tolerances in space, time, and sequence of the work.
- Synchronize production by replacing conventional project controls, including the use of forecasts and schedules to plan production, with operations science-based production control, including the use of push, pull, and constant work in progress (CONWIP) protocols to meet the production objectives while avoiding work in place (WIP) explosion.
- Ensure all parties perform their work per the overall objectives by aligning commercial incentives and agreements.
While these are general guidelines, a deeper dive into how each of these points can be accomplished should be undertaken to ensure improvement and overall success for off-site prefabrication of electrical facilities.
To learn more, visit Project Production Institute at www.projectproduction.org.
