You're correct in your assessment regarding the Life Safety Branch and Article 700. A 90-minute runtime is the standard requirement for Life Safety loads as outlined in Article 700.12(A).The key to the Equipment Branch runtime lies in understanding its purpose and Article 517.
35. Unlike the Life Safety Branch, which has a mandated runtime due to its critical safety role, the Equipment Branch's runtime is performance-based.Here's a breakdown of how to approach this:1. Define Critical Equipment

The first and most important step is to clearly define what equipment is connected to the Equipment Branch. This should be a collaborative effort with the clinic staff (doctors, nurses, administrators) and based on a risk assessment. Ask: What equipment must continue to operate during a power outage to allow for safe patient care? Examples include: Refrigerators/Freezers for medication storage. Medical gas alarm panels Certain critical medical equipment (e.g., IV pumps, vital sign monitors, suction devices). This is where you'll need input from the medical staff on which equipment is critical. Essential communications equipment (phones, network equipment). HVAC for critical areas. (Especially important if you have a server room.) IT Equipment used for patient care.2.

Determine Acceptable Interruption Time

For each piece of critical equipment on the Equipment Branch, ask: "What is the maximum acceptable interruption time before the equipment must be powered up?" This is critical. For medication refrigerators, an interruption of longer than 30 minutes could be unacceptable, requiring immediate generator startup. For communication equipment, a short interruption of a few minutes might be acceptable while the generator starts. For HVAC systems serving critical areas, the tolerable interruption time will depend on the severity of the climate, the occupancy, and insulation values of the clinic building.3.

Performance-Based Design

Now you can design the backup power system to meet those interruption requirements. Here's how the answers to the above questions impact your Equipment Branch backup:

No Mandatory Runtime

Unlike the Life Safety Branch, Article 517.35 does not specify a mandatory runtime for the Equipment Branch.

Acceptable Delay

Article 517.35 says "The equipment system shall automatically restore operation to equipment required for health care functions and shall be arranged for delayed automatic or manual connection to the alternate power source." This implies that there can be a delay in the equipment branch receiving power.

Generator Sizing

Your generator's capacity must be sufficient to power all the equipment you've identified as critical on the Equipment Branch simultaneously. Don't underestimate this.

Generator Startup Time

Account for the generator's startup time. If some equipment needs immediate power, consider UPS (Uninterruptible Power Supply) systems for those specific loads as a bridge until the generator comes online. This is common for critical IT equipment.

Runtime Calculation

The runtime for the generator is determined by the operational needs of the clinic during a power outage.. If a planned generator system outage is needed, and you want to keep the clinic running, then your run time will depend on the clinic's outage plan. If you plan to shut down and evacuate the clinic in the event of a power outage, the run time will be shorter. This is a business and risk based decision to be made with the client.4.

Documentation is Key

Thoroughly document your design decisions, including: The list of equipment on the Equipment Branch. The rationale for why each piece of equipment is considered critical. The acceptable interruption time for each piece of equipment. Calculations showing the generator's capacity is adequate. The generator's startup time. The chosen generator runtime and the justification for that runtime. The location and ampacity of each piece of equipment connected to the equipment branch.5.

Coordination with Authorities Having Jurisdiction (AHJ)

Discuss your design with your local AHJ early in the process. They may have specific interpretations or requirements that you need to address. This is especially important in healthcare facilities.

Example Scenario

Let's say you have: A medication refrigerator that must not lose power for more than 30 minutes. Essential network equipment. Medical gas alarm panel.You might choose: A generator with a startup time of 10 seconds. A UPS system for the network equipment to bridge the 10-second gap and provide a clean power source. A generator with enough capacity to power all of the above loads simultaneously. A generator runtime of 4 hours.

In summary, the Equipment Branch runtime is not explicitly defined in the NEC. It's determined by a risk assessment, the acceptable interruption times of the critical equipment, and a performance-based design that ensures continuous operation to maintain essential patient care during a power outage.

Remember to consult with qualified electrical engineers, the clinic staff, and the AHJ to ensure a safe and compliant design.Good luck with your project! Flag for review