Instantaneous adjustments to circuit breakers are approved arc flash mitigation methods according to the National Electrical Code (NEC) Section 240.87. There are two types of instantaneous adjustment methods:

• An instantaneous trip setting. Temporary adjustment of the instantaneous trip setting to achieve arc energy reduction shall not be permitted.
• An instantaneous override 

Methods related to instantaneous were first added to the approved list of mitigation methods in NEC Section 240.87 in 2017 but have been revised in 2020. Understanding the advantages and limitations of these methods (and the rest of the methods approved by NEC Section 240.87) is integral to choosing the right safety plan. 

Instantaneous trip setting

During an arc flash study, the available arcing current for the equipment downstream from the protective device being considered must be determined. Then, the instantaneous trip setting of the device must be set to trip below the calculated arcing current. 

The advantage to choosing instantaneous trip setting as your arc flash mitigation method is that it requires no additional equipment beyond a relay unit with a programmable instantaneous trip. For some facilities, this can be a cost-effective choice. 

However, there are two important caveats:

• If the instantaneous trip setting is too low, selective coordination may not be achieved with some electrical systems. 
• And, the 2020 update to NEC Section 240.87 stipulates that it is not permitted to dial down an instantaneous setting in the field. 

Instantaneous override setting

The instantaneous override method, often found in molded case circuit breakers, protects against fault currents above the withstand capability of the breaker. It will override any adjustment made to the electronic trip unit when fault current reaches a preset level. 

However, there is one important caveat:

• Since the instantaneous override setting in the circuit breaker is fixed and not adjustable, it is imperative to verify that the maximum instantaneous override current is below the minimum possible arcing fault current. Otherwise, this method cannot be used.

Power Defense MCCBs

Eaton's Power Defense molded case circuit breakers provide communicating electronic trip units and the ability to generate the data to help you optimize your facilities' performance,  and to help keep your employees, customers and end-users safe by reducing the risk of arc flash events.

Magnum with Power Xpert Release trip units

Eaton’s Magnum with Power Xpert Release trip units offer the highest ANSI interrupting and withstand ratings in the industry in the smallest physical size and are the most easily maintained ANSI circuit breakers on the market.

Distribution relays

Eaton’s distribution relays offer complete metering, protection and control for all voltages in a single compact case to reduce panel space, wiring and overall costs. All relays meet or exceed instantaneous and time overcurrent requirements.

Bus differential relays

Eaton's bus differential relay is a digital protection relay designed for high impedance differential protection schemes. The intuitive operating system with validation checks and extensive commissioning functions, such as the built-in fault simulator, allow safe and time-optimized maintenance and commissioning.