What is the difference between ERMS and MMS?

Product Line:

Circuit Breakers

Answer:

Both are methods to meet NEC article 240.87 requiring arc flash mitigation. However, the way each does it is different.

ERMS (Energy Reduction Maintenance Setting): This system works differently depending on what breakers it is used with.

Powerpact P/R frame; Masterpact NT/NW: The ERMS works by using an IO module to communicate with the trip unit and change the instantaneous setting to a preset value (default is 2x) when the switch is on, regardless of what the instantaneous is set to (it will revert to its setting when the switch is turned off). This requires a P or H trip unit with the blue ERMS label in the top right corner.

Masterpact MTZ: The ERMS works through a control unit digital module that, when the switch is turned on, changes all settings on the breaker to preset ERMS values.

MMS (Maintenance Mode Switch): This system utilizes the built in ZSI capabilities of A, P, and H trip units (only available on Powerpact P/R frame and Masterpact NT/NW) to eliminate the short time delay when the switch is on. This essentially resets the instantaneous setting to the short time setting. The short time delay is activated again when the switch is turned off.

Released for: Schneider Electric Canada