The exterior sump holding capacity above the high level alarm is required when installed on which type of system?

• A. Complex system
• B. Simplex system
• C. Duplex system
• D. Triplex system

Answer: (B)

In a pump system, the need for exterior sump holding capacity above the high level alarm shows up when there’s only a single pump—a simplex setup. With just one pump, there isn’t a backup to move wastewater if the pump stops, loses power, or the switch is tripped. The high level alarm serves as a warning, but you still want somewhere for sewage to go without immediately overflowing or backing up into the building. The exterior sump above the alarm provides that extra storage buffer so the system can continue to hold wastewater until the pump issue is fixed or service is performed.

When multiple pumps are used (duplex or triplex), there’s redundancy, so the risk of a total failure is lower, and the requirement for that extra exterior storage is not imposed in the same way.