Your questions answered: Electrical distribution equipment
It is useful for both electrical and nonelectrical engineers to understand basic features when selecting, specifying, and applying electrical distribution systems. To narrow the broad scope of electrical distribution, this discussion focuses on practical considerations for specifying electrical distribution systems. The discussion focuses on common low-voltage 480/120 V electrical distribution equipment encountered in most facilities and touches on medium-voltage equipment. Also, basic considerations for rooms housing these pieces of electrical equipment are highlighted.
Presenters Brian Rener, PE, LEED AP, SmithGroupJJR, Chicago; and Freddy Padilla, PE, ATD, Page, Austin, Texas, respond to questions not answered during the live “Electrical: Distribution equipment” on June 21, 2018.
Question: Referring to codes and standards, first, what are the code requirements governing the layout of electrical rooms and spaces? Second, what provisions of other building or energy codes affect the layout of electrical rooms and spaces? For example, this might include fire ratings of room envelope versus NFPA 70-2017: National Electrical Code (NEC), Article 700.
Freddy Padilla: The place that you will find most of the requirements for a typical electrical room is NEC Article 110.26. Also, other codes, such as NFPA 110-2016: Standard for Emergency and Standby Power Systems is a good source for room requirements.
Q: What is the biggest challenge in coordination of mechanical systems with electrical?
Brian Rener: Who provides starters or variable frequency drives (VFDs) and whether certain larger equipment requires multiple services.
Q: If we need to refurbish an existing switchgear, does that have to be done by the contractor with supervision by original manufacturer to not void the UL listing? What happens if the original manufacturer is not available or may be out of business?
Padilla: You can always bring the UL or ETL inspector onsite to inspect and provide the listing. But using the original manufacturer is always a good choice to keep the UL listing.
Q: Please explain when to use switchgear and when to use switchboards.
Rener: Ideal applications for switchgear include hospitals, factories, data centers, or other facilities where interruptions can present loss or risk. Switchboards do come in several flavors with higher end switchboards having some features similar to switchgear, but in general, switchboards are the norm for standard commercial facilities.
Q: What is meant by “cycles?”
Padilla: The graphic refers to a one wave cycle.
Q: In an industrial area where electrical gear is not within an electrical room, what would the egress requirements be for paths away from the gear? For example, if storage is placed around the gear or other equipment.
Rener: Storage should not be placed around or on electrical gear; this is a violation of code. Egress for equipment 1,200 amp and 6-feet wide still must comply with the NEC regardless of location or what the space is called.
Q: Can electrical switchgear or electrical switchboard, such as motor control center be located within the chiller room or pump room with chilled and condenser water piping running overhead?
Padilla: Yes, they can as long as you follow NEC Article 110.26 rules and the equipment requirements.
Q: Regarding working space above electrical systems, are you required to renovate if there are older installations that have not reserved the space, or installed electrical equipment without the working space above?
Rener: It would depend on the local authority having jurisdiction but if it was permitted this way (and not modified later), then usually it is grandfathered. The latest NEC edition does address existing insulation exceptions.
Q: Regarding temperature ratings on lugs, the panel is still rated at 75°C, but the switchboard is now rated 90°C, NEC still requires the cabling be 75°C rated, correct?
Padilla: Panels are rated for 40°C, but the connections and wires can be 75°C or 90°C. Typically, compression connections are rated 90°C and mechanical connections are rated 75°C.
Q: What was meant by arc flash zone versus working space in electrical rooms? It was mentioned that it must be considered when figuring room clearances.
Padilla: Arc flash zones shall be considered an interruption of an egress path. The idea is that if you perform maintenance on a panel that is located in an egress path because you are not allowed to walk inside the arc flash zone. Basically, you could block the egress path during the maintenance window by not allowing people to escape in case of emergency.
Q: How long can switchgear last with excellent maintenance?
Padilla: Typically, 25 to 30 years like we mention in the presentation, but keep in mind that regular testing should be performed to breakers and the breakers have limitations of how many times they can be operated. It is very important to understand the uses of the equipment to make a good determination if the equipment needs to be replace or not.