Reducing electrical system costs

It occurs on projects far too frequently. While putting in a lot of effort on a project, the customer chooses to review a cost estimate. The project goes over budget, and the next thing you know, the design is completely scrapped. The customer is looking for suggestions on how to lower construction costs without sacrificing the functionality of the building. Basic components start to be removed from the project. Curved walls, angular chambers, and ornate architectural finishes are swapped out for more affordable options. More sensible light fixtures take the place of opulent ones. Given the high cost of procuring and installing the components, attention naturally shifts to the electrical distribution system as a means of further decreasing costs. It is your responsibility to engineer novel ideas for the electrical system. This article offers suggestions for reducing costs throughout the new-building engineering process as well as cost-saving strategies for adapting current equipment.

Go underground

Install as many feeders and branch circuits in the concrete floor slab or below grade as you can. This strategy lowers expenses in a number of ways. Using less expensive PVC conduit rather of more expensive electrical metallic tubing, intermediate metal conduit, or rigid conduit lowers material costs. Further cutting labor and material expenses is achieved by doing away with the overhead support systems for the conduit lines. Rigid conduit is more difficult to install than PVC conduit. Although it is possible that in subterranean or slab installations, feeders and branch circuits may need to be derated, the additional cost of the derated conductors will usually be less than the cost of placing the conductors overhead (see Figure 1). One other advantage of putting the feeders and branch circuits in slab or underground is that the building schedule could be shortened. This method necessitates precise conduit stub-up site coordination, despite the potential for significant cost reductions. This might be challenging if the equipment hasn’t been chosen or bought yet. This strategy could also limit future flexibility and make cable inspection and maintenance more difficult.

Three-wire setup

Even if there are loads that need a neutral, design the system to employ a 3-phase, 3-wire electrical distribution system (three phases plus a ground). Since the designer finds it difficult to obtain all the load data required to compute a reduced neutral size, the neutral conductor is usually the same size as the phase conductors. Furthermore, a smaller neutral size may prevent future load adjustments. As a result, the distribution system’s designer offers a full-size neutral and is often conservative. This results in a roughly 25% increase in feeder conductor prices. Since the neutral wire carries current and the National Electrical Code (NEC) mandates that all four current-carrying conductors in a conduit be derated by 20%, the actual cost increase is actually greater. There is a 30% to 40% cost increase, or more, for each four-conductor feeder.

A more economical approach would be to restrict the number of four-conductor feeds. Designing a three-phase, three-wire system does this. Install a delta-wye transformer in cases where single-phase loads require a neutral conductor. The distribution voltage does not always need to be altered using this transformer. To handle 277 V lighting, for instance, construct a 3-phase, 3-wire system instead of a 4-phase, 3-wire system. If necessary, supply a 480 V delta to 480 V/277 V wye transformer for the 277 V lighting.

Examine aluminum once again.

Have an open mind towards other kinds of conductors and think about utilizing aluminum conductors. This might be a reasonably priced option. Although certain states or municipalities may prohibit their usage, aluminum conductors are NEC compliant and UL approved. The alloys of aluminum used in conductors nowadays are far superior to those in the past. The old alloy, which so many people are afraid of, does not have the same expansion and contraction problems as the electrical-grade aluminum alloy conductor material AA-8000. The majority of equipment terminations are normally dual rated for conductors made of copper or aluminum. Although bigger parallel feeders should be taken into account owing to the possibility of landing more conductors than the equipment is designed to terminate, terminations can be either compression type or mechanical set screw. Additionally, because aluminum has a higher resistance per foot than copper, the voltage drop on aluminum conductors will be larger than that on copper conductors. Aluminum conductors are suitable for branch circuit wiring, feeders, and service entries in all UL-listed raceway systems. Aluminum conductor insulation types that withstand sunlight can be installed in both dry and moist environments.

Using a mix of copper and aluminum conductors for the project is an additional choice. Take into account using copper when building branch circuits and feeders with ratings lower than 250 A. Feeders rated more than 250 A should only be made of aluminum. This method results in a 15% price difference between a 400 A, 3-phase, 3-wire subterranean aluminum feeder and a similar copper feeder. Additionally, instead of using copper in panelboards and switchboards, think about selecting aluminum windings for transformers and tinned aluminum bus bars.

Performance vs. detailed design

Rules-based specifications for circuits and conduits should provide the electrical contractor the freedom to decide where to route conduits and combine circuits. Although the engineer is able to provide project documentation that details routing and circuiting, this is usually not required. Give the electrical contractor carte blanche to choose the optimal routing alternatives based on building types, source/load locations, construction sequencing, and conduit support sharing. To prevent routing conflicts between disciplines, the designer might still need to create routing zones.

Permit the electrical contractor to share neutral conductors when necessary and combine circuits in a conduit. The design documentation should include information on situations when conduits need to be routed in an extremely exact place or where circuits need to be put in a certain way. The contractor can deliver the optimal route with the least amount of work and materials by using rule-based circuit and conduit layout. Moreover, this offers the advantage of freeing up design team members’ time to concentrate on pressing conduit and circuit coordination problems rather than unimportant ones.