Yes, based on the excerpt you provided from 700.3, if your emergency generator is the single alternate source of power, you should provide a means to connect a portable or alternate source of power during maintenance or repair of that generator. This typically involves a second transfer switch.Here's a breakdown of why and how: The Intent

The code aims to ensure continuous emergency power, even when the primary alternate source (your generator) is unavailable. This ensures critical loads remain powered during generator downtime.

Single Point of Failure

Since your generator is the only alternate power source, its failure (even for routine maintenance) creates a single point of failure, leaving the emergency system without backup.

Permanent Switching Means

The code requires a "permanent switching means," meaning a proper transfer switch or connector, not just a plug and cord. This ensures a safe and reliable connection for the portable generator.

Practical Implementation



Two Transfer Switches

The most common approach is to install two transfer switches:

Main Transfer Switch

This switches between normal power and the emergency generator.

Bypass/Maintenance Transfer Switch (MTS)

This MTS is connected downstream of the main transfer switch. In normal operation, it simply allows power from the main transfer switch to pass through to the emergency loads. However, when the generator needs maintenance, the MTS can switch the emergency loads to a connection point for a portable generator.

Location

The connection point for the portable generator should be readily accessible and clearly labeled.

Interlocks

Interlocks are crucial to prevent backfeeding the utility or the generator simultaneously. The transfer switches must be designed to ensure only one source (normal power, generator, or portable generator) can be connected to the emergency loads at any given time.

Code Considerations



700.3 (F)

This section specifically talks about the alternate source (Generator or Battery).

700.4 (E)

It also has specific requirements if your emergency generator is under 150kW, and you want to supply other loads than emergency system loads when the normal power is available. It might not be your case, but it is useful to consider.

Alternatives (Rare, but Possible)

While a second transfer switch is the most common solution, other approaches might be considered, but are less common and require careful evaluation and approval by the authority having jurisdiction (AHJ):

Dual Generators

If you had two permanently installed generators, and each could independently handle the entire emergency load, you might not need a separate portable generator connection. However, this is generally more expensive. The design must also ensure that the generators are regularly tested and maintained to ensure their reliability.*

UPS System

A UPS system sized to carry the emergency load for a significant period (e.g., several hours) could potentially provide enough runtime to allow for generator maintenance. However, this would depend on the specific load requirements and the desired level of redundancy. This is also a generally more expensive solution.

Recommendation: Consult with the AHJ (Authority Having Jurisdiction) and a qualified electrical engineer or contractor familiar with emergency power systems. They can help determine the most appropriate and cost-effective solution for your specific situation, ensuring compliance with all applicable codes and standards. They can also help with the selection of the right transfer switch (or switches) and ensure proper installation and interlocks. Flag for review