Power equipment considerations
This month's panel discusses the ideal projects and facilities for both stick-built and pre-integrated power equipment, in addition to industry and specification issues. CSE: What are the considerations for stick-built power equipment? What types of projects and facilities are ideal for this system? AHUJA: Stick-built power equipment is suitable for customers who want easy shipment, minimum fi...
This month's panel discusses the ideal projects and facilities for both stick-built and pre-integrated power equipment, in addition to industry and specification issues.
CSE: What are the considerations for stick-built power equipment? What types of projects and facilities are ideal for this system?
AHUJA : Stick-built power equipment is suitable for customers who want easy shipment, minimum field work, the equipment to be factory assembled and tested for immediate hookup at field, meeting facility space requirements, weather enclosures where required and to meet electrical characteristics of facility, such as short circuit ratings, amps, volts and phases.
FLICKINGER : The traditional panelboard and switchboards afford more flexibility for expansion and modification should a facility be expanded. In design-build scenarios where one would expect significant tenant build out, the cost of traditional stick-built power distribution can be directly charged to the tenants to accommodate their special needs. Stick-built power distribution has inherently higher installation labor costs due to the individual components and feeder requirements. However, the individual components are less costly than the integrated equipment. Our experience with respect to total installed cost for stick-built systems vs. integrated systems has determined that the stick-built is approximately 5% to 7% less than the integrated systems. This installed cost does not take into consideration the physical building space cost.
For institutional applications, specifically hospitals and justice facilities, it is easier to segregate emergency power from normal power via stick-built vs. modular equipment. Additionally with the advent of arc flash considerations, one can only presume that the PPE level will be significantly higher for integrated equipment vs. individual panelboards, which typically are located a distance from the main switchboard.
AMANN : By selecting each component individually, a system can incorporate features that may not be available from an integrated system vendor. So for instance, if an owner has lots of experience with a particular line of PLC (programmable logic controls), it may be important for them to use that controller on their power system. Not all manufacturers have the flexibility to work with various PLCs. Another example might be a system that requires an interrupt rating of 200,000 amps, which might exceed the UL-listing capability of a certain vendor's switchboard, even though their generator might be perfectly suited to the project.
CSE: Some manufacturers of pre-assembled, integrated systems acknowledge that they only make sense on certain project types. What types of projects and facilities are ideal for this system?
AHUJA : Integrated equipment is suited for industrial, high-energy usage facilities such as data centers; mission critical facilities; areas where there is extended temporary power usage during long construction or disaster recovery; institutions; and hospitals.
FLICKINGER : The use of integrated equipment is not limited by the project type as much as the need for space optimization. We have used integrated systems for retail, industrial, commercial and some institutional installations. The ideal installation for integrated switchboards is when space is at a premium, such as a retail environment, where the prime consideration is to minimize “back-of-house” space requirements while maximizing available sales floor area. For retail installations, one also can readily incorporate lighting controls—similar to Powerlink—directly into the switchboard. Institutional, industrial and commercial applications for integrated systems can be best served when an existing building is expanded or renovated and the equipment space must be optimized. Again, there is a cautionary note with respect to emergency segregation requirements.
AMANN : It depends somewhat on the particular project requirements and objectives. There are some clear benefits to having one source provide several of these very interdependent components. However, there also are limits on the capabilities and features that are available from most of these manufacturers. But where one manufacturer can meet all the project requirements, there can be several advantages to all stakeholders. On the right project, pre-integrated systems have the potential to deliver quicker, have shorter and easier commissioning schedules, and save costs.
One of the most outstanding benefits of a pre-integrated approach is the ability to monitor all of the system components through a single control interface. Because each component operates on an integral and proprietary controller, it is difficult and/or expensive to have a complete user interface to each component when they are stick-built. With the pre-integrated approach, all of the components can communicate over one bus with integrated monitoring on one user interface.
CSE: Do you think that a pre-integrated system requires a certain amount of customization? Please describe your experiences.
FLICKINGER : Generally speaking, the answer is no. The integrated equipment is comprised of standard parts and pieces, which are individually listed. The primary consideration is the actual listing of the specific integrated equipment, and the approval of the AHJ (authority having jurisdiction).
AMANN : Some projects are somewhat cookie-cutter, i.e. a single generator with a single transfer switch picking up the entire load. This type of system generally can be provisioned with pretty standard configurations and features. However, more sophisticated systems will generally require at least some customization. We have many of the straightforward projects. But for clients that require a higher degree of reliability, we often design configurations and system requirements that some vendors cannot fabricate.
AHUJA : Yes, to meet facility space constraints, equipment movement constraints and for integration with existing electrical distribution or maintenance issues.
CSE: It seems that pre-integrated power would be the perfect fit. Is this not the case?
FLICKINGER : An integrated power system would indeed be optimal solution for cogeneration applications if the resulting system is categorized as “optional standby” under NEC Articles 702 and 705. Ideally, the integrated equipment would incorporate the automatic transfer switch or paralleling equipment and be provided through a utility program.
AHUJA : I think this is not the case due to multiple variables involved with facilities on co-generation. A few issues include: requirement for balancing heat usage and heat recovery; power system integration with local utility company; local utility protective relaying requirements; metering requirement for revenue and monitoring; and remote utility-controlled transfer requirement.
AMANN : Pre-integrated power depends a great deal on the system loads and control scheme. If the gensets are controlled just to meet the power load, and the waste heat is used incidentally, then a pre-integrated system will probably work fine. But in more complicated systems where the engines need to meet a thermal load as well, a custom approach is required.
CSE: What are some of the pre-integrated emergency power systems familiar to you?
AHUJA : Cummins/Onan, Russelectric, GE, Cutler Hammer and Siemens.
AMANN : Several of the major generator manufacturers are now offering pre-integrated emergency and standby power systems. These include systems that they provision complete with enclosures, switchboards, transfer equipment and controls. They range from simple, single-generator systems, to more sophisticated paralleled arrangements that may connect to the utility grid or co-generate. In some cases, the system also includes a UPS System, with rotating UPS (uniterruptible power supply) systems the most prevalent.
FLICKINGER : We have utilized Square D, General Electric, Siemens and Val-Tec (VTI). We have had some challenges with AHJs accepting integrated emergency power systems primarily due the equipment listing for a given installation. The AHJs usually don't question the individual component listing, but rather the entire system AIC (available interupt current) rating for the equipment. Additionally, when utilizing integrated equipment for emergency systems, consideration should be given to NFPA 110-7.2.2 for Level 1 EPSS (emergency power supply system) equipment, which must be in a separate room from the normal equipment if rated over 150 volts to ground and equal or greater than 1,000 amps.
CSE:What are some of the problems encountered when attempting to evaluate the merits of competing systems?
AHUJA : Customers should consider labor costs vs. first costs, local union markup on pre-integrated systems and concern on support due to dependence on one manufacturer for various components of system.
FLICKINGER : We have not experienced many challenges with respect to the various manufacturers. Their equipment must reflect all the components on our one-line, comply with the specifications, physically fit within the space requirements, and be UL listed.
AMANN : We encourage many of our clients to pre-order or pre-purchase their generators, switchgear and transfer equipment. In this instance, we can evaluate the relative merits and features available from each vendor. This works fine with the pre-integrated systems as well. But if the job is a traditional plan-and-spec bid, it is very difficult to evaluate substitutions that a contractor may submit in a time frame that works effectively for the project.
CSE: Do you perceive a growing reliance on pre-assembled systems by consulting engineers?
AHUJA : Right now it is case-by-case by consulting engineers. Design-build contractors will promote pre-assembled systems to save labor cost and coordination of deliveries on all vendors to build the system at the site. Acceptance with consulting engineers will grow if contractors can show economical advantage and local unions do not discourage use in the field.
AMANN : On projects where they fit the bill, certainly engineers will gravitate to pre-integrated systems. It relieves the engineer of some responsibility in assuring the components are compatible, and that the controls match up between the various components.
FLICKINGER : Not really. If space considerations and time constraints require an integrated system, then that is what we specify. The majority of our designs incorporate traditional stick-built distribution systems primarily due to lower first costs, flexibility, segregation issues and AHJ acceptance.
CSE: Some engineers use breakers and transfer pairs as opposed to transfer switches, when specifying mission critical work that uses multiple buses and typically saves money. However, this lends itself to confusion regarding UL listing and ANSI requirements. Do you think this keeps other engineers away from stick-built gear?
FLICKINGER : Quite the contrary, it is due to the UL listing issues for a specific application that tends to promote traditional stick-built installations. The real question is what is appropriate for the application? For mission critical applications similar to data centers, we utilize multiple automatic transfer switches that are individually mounted. This allows truly independent and redundant power distribution systems utilizing segregated bussing serving a common load. Further, the UL listing is not in question and it allows for modification and flexibility as the load increases.
AMANN : While almost every paralleling system employs operable breakers to connect generators to the output bus, or for a main-tie-main, very few engineers seem to use the same approach to connecting the loads to the bus. In certain emergency power systems, i.e. healthcare facilities, a listed transfer switch (UL 1008) is required by NEC for emergency loads. But for other loads, we find that by using operable breakers (in accordance with UL 489 and ANSI/IEEE 241) we can diversify loads and maintain reliability without incurring the costs and space required when using transfer switches. This approach also allows for superior fault isolation and load-shedding schemes.
Anil Ahuja , P.E., LEED AP, RCDD
Senior VP, CCJM Engineers, Chicago
Thomas Flickinger , P.E., CSI
Vice President & Director of Electrical Engineering, Durrant, Madison, Wis.
William Amann , P.E., LEED AP
President, M & E Engineers, Somerville, N.J.