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  • For Safety’s Sake: reliable healthcare power systems design

Selective coordination (SC) in healthcare facilities keeps power running during an emergency. Remember that SC is the design of an electrical system in which a downstream protective device (like a fuse or circuit breaker) nearest to a system fault clears the fault without affecting upstream overcurrent protective devices (OCPDs). This prevents wide-spread power outages throughout a facility. The healthcare industry, by and large, has pursued methods that do not consider fault current, and I believe more needs to be done to implement SC in power distribution systems to increase reliability and help assure patient and staff safety. 

Current SC requirements do not address the evaluation of power system performance for fault conditions in healthcare facilities. Instead, these organizations are only required to consider overload currents per National Fire Protection Association (NFPA) 99 and Article 517 of the National Electrical Code (NEC). Other types of power systems that are concerned with life safety employ SC as mandated by the NEC: Articles 620 for elevators; 645 for IT equipment; 695 for fire pumps; 700 for emergency systems; 701 for legally required standby systems; and 708 for critical operation power systems — each considers all levels of fault current for these life-safety systems.


SC debates in healthcare

I’m concerned with requirements in the healthcare industry that ignore important safety fundamentals for power-system performance when life-safety systems in other industries, like data centers and tall buildings, must adhere to more stringent requirements. Many professionals are also genuinely concerned by healthcare facility system safety and look to broaden SC requirements to eliminate fault-current failure possibilities. Others resist diving deeper into these requirements with arguments that range from higher costs of implementation to increased incident energy.

Ultimately, everyone has the best intentions for safety. Having been part of many spirited debates, I’ve found that the majority of those involved in the discussions fall into one of two camps:

All currents at all times

Supporters of this SC approach aim to leave nothing to chance when ensuring reliable life-safety systems. This group insists that engineers calculate the maximum available fault current and ensure that OCPDs are selectively coordinated at that current. Further, they believe engineers should evaluate OCPD and equipment ratings to this fault current, including interrupting ratings and short-circuit current ratings (SCCR).

0.1 seconds

This camp feels that reviewing OCPD performance only for overload currents is sufficient. The approach of 0.1 seconds established by the healthcare industry as part of the requirements of NFPA 99 and NEC Article 517 foregoes fault-current levels, whether they be maximum- or minimum-available fault-current values. 0.1 seconds is the line drawn across the Time Current Characteristic (TCC) curve below which all trip curves are hidden to conceal overlap and disregard fault currents. This group may ignore fault currents for coordination purposes, but still evaluates OCPD and equipment ratings to the maximum available fault current, including interrupting ratings and SCCR.

More needs to be done to implement SC in power distribution systems to increase reliability and help assure patient and staff safety.

Thomas Domitrovich, vice president, technical sales

Healthcare facilities must account for all currents

I tend to align with the “All currents at all times” position — not because of NEC requirements, but for engineering and safety reasons. The second approach ignores fault current and, in my opinion, should be revisited. The industry should not ignore overlaps of OCPD TCC curves below 0.1 seconds and fault currents within the instantaneous region of multiple OCPDs.

One argument that I feel has merit is an increase of incident energy for circuit breaker solutions. Incident energy must be addressed no matter the design and level of coordination achieved in the power system. Many cost-effective technologies exist to mitigate these concerns.

 

Look to improved solutions now and in the future

Innovative design changes and product advancements are currently available on the market and should be leveraged no matter the preferred coordination method. Examples include SC software tools that have expanded to help the engineer select the right OCPDs and circuit breaker tables that select the smallest upstream OCPD possible to reduce the footprint and cost of upstream equipment.

I believe we’ll see more solutions as competition in the industry increases. Competition drives improvement, and it’s probably only matter of time before the market drives increased safety for healthcare facilities on the whole.

 

We can increase safety in healthcare environments via SC

It’s been my experience that healthy discussions and disagreements lead to compromise. And through those discussions, engineers can take steps to approach the design of reliable healthcare power systems by understanding how OCPDs respond to current. A good recipe for success may include the following:

  • Establish a performance level for healthcare that everyone in your firm can adhere to, whether it’s selective coordination to the maximum available fault current or an agreed-upon lower level. Just remember — if the fault current selected is below the maximum available fault current you are accepting some level of cascading-event risk, which could impact lives. 
  • Communicate expectations to suppliers, contractors and code officials in your design specifications. Details and clarity are important; be specific as suppliers always quote the lowest-cost solution. You may not get what’s expected if specifications are unclear.
  • Some jurisdictions permit a lower level of SC in varied systems and falsely maintain that if it’s good for healthcare emergency systems, it’s right for high-rise buildings and data centers. Remember that the requirements for healthcare are not the same as other life-safety systems. While healthcare requirements offer design flexibility, systems under NEC Articles 620, 645, 695, 700, 701, and 708 do not. Separate requirements make 0.1 seconds a lesser safety option and fixing selective coordination issues “after the fact” an expensive problem.

The electrical industry has a responsibility to provide reliable power for life safety, and I strongly believe that engineers and system designers can selectively coordinate systems in a way that strikes the balance we all seek between reliability, system damage and cost.  

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