When you start planning a Modular Power Distribution Center (PDC), it makes sense that much of the initial focus is on the equipment. What needs to be powered and controlled? How many motors are involved? What switchgear, MCCs, drives, and control systems need to go inside?
Those are important questions, and they are really just the start of the decision-making process. That’s because once you put all of that equipment inside a modular building, there are many other things to think about in terms of how cables will enter and exit the building, how much heat will be generated, whether there is enough clearance around switchgear, and how a large piece of equipment may be extracted and replaced someday.
All of these decisions can affect cost, schedule, installation, long-term maintenance, and ultimately how smoothly things go when it is time for startup. The key is thinking about them early.
Key Takeaways
- Good PDC design goes beyond making the equipment fit. Clearances, equipment access, cable entry, heat, weight and other building considerations can affect how the PDC is installed, operated, and maintained.
- Small design decisions can have a significant impact on the overall project. Choices around controls architecture, wiring, equipment, and even building dimensions can influence labor, lead times, transportation costs, and schedule.
- Bring your PDC provider into the planning process early. Working through equipment requirements, site standards, availability, and potential trade-offs before specifications are locked in can help control costs, address schedule risks, and avoid problems later in the project.
Start with why you’re going modular.
One of the first questions we ask customers is: Why modular?
For many projects, the answer comes down to space or schedule. But understanding what’s driving the decision helps guide a much broader conversation about what the PDC needs to accomplish. We’ll explore:
- What process will it support?
- What equipment does the PDC need to house?
- How will the equipment be controlled?
- How much space is available onsite?
There are also your manufacturing operations’ standards to consider. You may have standardized on a particular drive, PLC, or other equipment because you want consistency through the plant. That makes sense. But we also need to understand how those choices affect the rest of the PDC design, including footprint, wiring, controls architecture, parts availability, and lead time.
Everything fits. But does it work?
You can put all of the specified equipment on a drawing and confirm that everything technically fits inside the building. That’s great! But does the building actually work?
Take medium-voltage switchgear. It requires minimum clearance, so it isn’t enough to allocate space for the equipment itself. You need the appropriate space around it, including walkways. Move the switchgear and you may affect something else. Make the walkway larger and you may change the dimensions of the building.
Then think about how the equipment got there in the first place. It has to get into the PDC during fabrication, of course. But what happens five or ten years from now if that same piece of equipment has to come out? Can it be removed from the building? Does access need to come from the side or the roof?
Equipment weight creates another consideration. Something that could easily be mounted on a wall in a traditional plant environment may be too heavy to mount the same way inside a modular structure. Moving it to the floor may be a better solution.
Even cable entry matters. Where possible, bringing cables through the bottom of the building instead of penetrating an exterior wall can eliminate a potential point for water intrusion.
These aren’t necessarily the things you may be thinking about when you compile your needs and equipment list. You’re focused on your process and outcomes. Our job is to think about what has to happen around the process to make the PDC work and deliver the results you’re after.
Small Decisions Can Have a Surprisingly Big Impact
Each minor decision presents an opportunity to simplify the project. Here are just a couple of examples.
Consider the variable frequency drives (VFDs) that may be required for the building. Depending on the control scheme, the traditional approach can require multiple individual wires for every drive. Multiply that by the number of drives in the PDC and suddenly there is a lot of wire to pull, terminate, and test.
If the application allows those drives to communicate over Ethernet instead, the wiring picture can change dramatically. We’re not just making a decision here about how a drive communicates. We’re potentially affecting the amount of wiring, panel design, network architecture, fabrication labor, and work that needs to happen in the field. Instead of running individual control wires, many signals can travel over the network, leading to fewer wires, fewer physical connection points, and significantly reducing the I/O card burden. Across multiple devices, those reductions can add up quickly. Of course, the industrial network and device configuration become more important in this scenario, which is another reason decisions need to be considered as part of the complete PDC design.
We’ve seen the same thing happen with something as basic as building dimensions. On a PDC we’re currently engineering, we identified some relatively small changes that allowed us to reduce the overall size of the building. The smaller structure itself costs less, but that wasn’t the biggest impact. Changing the dimensions will also significantly reduce the projected freight cost to get it to the customer’s site.
That’s why we look at the project from beginning to end during the planning and engineering phases, because sometimes the best opportunity to remove cost or time from a project isn’t initially where you might expect to find it.
Think About the Schedule Now
Equipment availability has to be part of early conversations, particularly in a market where lead times for some electrical equipment can be significant.
If a customer has already specified and purchased everything going inside the PDC, our options may be fairly limited. On the flip side, if we’re involved early in the process, we have more room to look to alternatives when a particular component or engineered solution threatens the schedule.
And there is one other big advantage we can deliver if we are involved early in the process. Tri Tech’s ability to engineer and modify components in-house can provide additional options when lead times threaten the project schedule. Motor Control Centers (MCCs) are just one example where we can modify an available solution to meet project requirements rather than waiting for a longer-lead engineered solution.
Ask Questions While There Is Still Time to Arrive at the Best Answers
There are many decisions that go into a modular PDC, and you shouldn’t be expected to arrive knowing all of the questions you need to ask. You know your process and what you need to power and control, as well as the space available for the PDC and when you need it up and running.
It’s our job to take that information and start asking what comes next. Where does everything need to go? How will people work in and around it? How can we get all of the components needed to meet the timeline? What happens when something needs to be replaced? Are we creating unnecessary wiring? What does a design decision for one aspect of the project do to the cost or complexity in another area?
It’s much easier to work through those questions while the PDC is still in design. Discovering the answers after all the parts and pieces are secured or after the building has been fabricated is a very different conversation.
Tri Tech brings extensive experience in controls engineering and panel building to the PDC design and fabrication process. Learn how we can bring that expertise to your next PDC project to meet your requirements and timeline while reducing risk at startup. Reach out to get the conversation started today.
Frequently Asked Questions
What should I consider when designing a modular PDC?
Be sure to consider more than the equipment that needs to go inside when designing your modular PDC. Things like equipment clearances, access for maintenance and replacement, cable entry and routing, cooling requirements, equipment weight, site standards, transportation and project schedule can all influence the final selection of components and the design itself. Evaluating these factors together helps ensure the PDC works for the complete project, not just the equipment list.
How early should the modular PDC provider be involved in a project?
Your modular PDC provider should be involved as early as possible, while equipment, layout and other requirements are being defined. Ideally, your PDC provider should be involved in development of specifications whenever possible. This provides the opportunity to evaluate equipment availability, lead times, wiring and controls architecture, building size and other tradeoffs before specifications are locked in and changes become more difficult.
How do equipment choices affect modular PDC design?
Equipment choices can affect many aspects of the PDC, including its footprint, wiring requirements, controls and network architecture, fabrication labor, materials availability and ultimately the overall project schedule. For example, using Ethernet-enabled VFDs where appropriate may reduce point-to-point control wiring, while selecting equipment with long lead times may require the project team to evaluate alternate solutions or risk not delivering on schedule.
How do I determine the right size for my modular PDC?
The right size for your modular PDC depends on more than whether the specified equipment physically fits inside the building. Required electrical clearances, walkways, cable routing, HVAC, maintenance access and the ability to remove and replace equipment all require space. Building dimensions should also be evaluated in the context of transportation because a relatively small change in building size can have a significant impact on freight requirements and cost.
What building considerations are important when designing a modular PDC?
The modular PDC design needs to account for how equipment, people, power and cables will move into, out of, and through the building throughout its useful life. Important considerations can include equipment weight and mounting, cooling requirements, cable penetrations and water-intrusion risk, required clearances and walkways, equipment removal, state and local regulations, and applicable requirements for the location where the PDC will be installed.
