by , on May 11, 2015
red background with burning question

Q:  When a qualified worker opens a control panel to reset a fault condition on a motor drive or observe PLC status lights AND is within the ARC FLASH BOUNDARY, is the worker considered to be performing live work which requires Arc Rated PPE?

No other interface with equipment and/or interaction that would change equipment status is being performed. And in particular when accessing [the] motor drive, controls have the drive and other starters in a standby or lockout condition. Shock hazard has been addressed by insulating gloves.  Thanks.

A: This is a situation that can get very delicate and is dependent on multiple factors.

First of all, resetting a fault condition on a modern motor drive requires power to be on the drive, unlike an older-style motor heater overload, which requires a manual reset of the heater and can be performed with power removed from the motor circuit. The issue with older solder pot-style heaters is that IF the motor circuit is still in a “run” state and the overloads are manually pushed in to reset, the motor could very well start back up when the contactor is pulling in, surprising the individual performing the reset. This could possibly create a shock and/or arc flash hazard if the employee is performing this action with the motor controller door open, exposing energized conductors. By definition this is an arc flash hazard and the boundary applies.

Modern motor drives are mostly electronic, and are computer-driven, and a manual reset of an electronic overload is sending a “clear” signal to the processing unit. The shock hazard is reduced often because many modern drives utilize finger-safe terminals, and incorporate low-voltage wiring (24 VAC, for example). As you mention, the use of voltage-rated gloves ensures that the qualified electrical worker is properly protected against inadvertent contact with an energized conductor.

Is energized work occurring as defined in NFPA 70E, and does an Energized Electrical Work Permit need to be completed?  NFPA 70E 130.2 discusses electrical work conditions in detail. The ultimate goal is simple – if possible, turn off the power and create an electrical safe work condition. However, in this situation, 130.2(A)(2) allows using the power as it is “infeasible” to reset an electronic overload without having power applied to the motor controller. Continuing to 130.2(B)(3), we come across EEWP exemptions – testing, troubleshooting, and voltage measurement. Performing a motor reset is a common electrical task and typically would be considered part of troubleshooting, although it is not specifically addressed in the NFPA 70E standard, once the reason for the overload situation has been addressed, the action of performing such a reset should fall under the EEWP exemption. However, even though an EEWP is not required, the wearing of arc rated PPE is required because the worker is within the arc flash boundary, exposed to energized parts and interacting with the equipment.

So in this case, (1) the worker is not starting up the motor, (2) the worker has on the correct shock and arc flash PPE, (3) the worker has recognized and applied control measures for the proper arc flash and/or limited approach boundary, and (4) the worker has a full understanding of the motor controller’s operation and all manufacturer-required safety precautions when performing testing and/or troubleshooting.

Note: Some motor controllers and MCCs allow the operator to remove the main motor terminal power and leave the control circuit power on. This greatly reduces the chance of an arc flash. When purchasing new equipment, it is always a good idea to consider newer designs that incorporate electrical worker safety by the design.

Have a question about electrical safety and standards? Ask us here!


Ken Sellars
About author:
Ken Sellars is an instructor of electrical safety, NEC, Grounding/Bonding and Arc Flash Safety courses nationwide. Read more about Ken.

Leave a Reply