New Fuses Address Arc-Flash Risks Posed by Medium-Voltage Connections

Despite the volumes that have been written regarding the dangers of 
arc-flash to electrical workers, many facilities are still working to 
address the risks in their own facilities. It can be a complicated 
issue, with what can often be multiple layers of hazards. <br><br>Of 
course, the first line of defense is personal protective equipment 
(PPE), and tremendous advances have been made in this area over the last
 decade. Mersen

Chuck Ross

Despite the volumes that have been written regarding the dangers of arc-flash to electrical workers, many facilities are still working to address the risks in their own facilities. It can be a complicated issue, with what can often be multiple layers of hazards.

Of course, the first line of defense is personal protective equipment (PPE), and tremendous advances have been made in this area over the last decade. While one might initially envision cumbersome jump suits, today’s PPE includes jeans, work shirts and other apparel that just happens to feature arc-rated protection.

The Occupational Safety and Health Administration requires employers to analyze the arc-flash hazards to which their employees might be exposed and provide PPE adequate to those risks. However, if potential arc-flash energy is found to exceed 40 cal/cm2, not even the hardiest PPE will provide enough protection. Employers are required to prevent access to equipment areas where this is the case unless power to that equipment is disconnected, which can be a difficult requirement to maintain.

Even an industrial plant’s main breaker panel could pose such risks. In many cases, the 480V panel serving such a facility is supplied from a local 15.5kV transformer. That transformer will, itself, be protected by upstream fuses, but the only protection between the transformer’s load-side and the facility panel’s line-side is the medium-voltage (MV) fuse or circuit breaker on the line-side of the transformer. This leaves the line side of the plant’s main breaker exposed to arc-flash energies much stronger than anything PPE is designed to handle.

Now, controllable MV fuses are coming to market designed as plug-in retrofits for use in existing switchgear. The devices are designed to address arc-flash hazards on the low-voltage side of a medium-voltage transformer and operate like a normal MV fuse under short-circuit and overload situations. They also, however, can be connected to an arc-flash detection system to open a circuit quickly enough to limit hazards to those addressable with Category 2 PPE.


Photo courtesy of Mersen