In our previous blog on arc flash mitigation, we discussed the mechanics of an arc flash and why it is important to reduce the risk of these dangerous, destructive incidents. Fortunately, the manufacturing industry has successfully created more awareness of arc flash risks, providing education and guidance about safe work practices and the installation and maintenance of electrical equipment. Manufacturers have coalesced around the standards in the National Fire Protection Association® (NFPA) 70E and the National Electrical Code® (NEC).
Many have embraced the concept of safety by design as the best way to reduce, avoid, prevent, and contain arc flashes. Collectively, our industry’s efforts have made working on or near electrical equipment safer. We’ve also elevated the attention each arc flash gets at every level from the front-line to the back office.
Many benefits of arc flash mitigation are obvious: worker safety, reduced injuries and equipment damage, and more business continuity, to name a few. Reduced arc flash incidents also improve profitability and demonstrate compliance with NFPA 70E, thus helping to protect business’ reputations for safety. These are basic reasons why investing in safety today provides downstream advantages that carry forward for years. They begin with understanding different types of arc flash risks.
For manufacturing sites and facility teams who are engaged with Motor Control Centers (MCCs), it’s no secret that they present a high opportunity for arc flash risk. While a large motor control center is typically more dangerous, arc flashes can also occur with smaller motor controls, such as a 10-hp motor starter disconnect switch that is commonplace in many facilities. The benefits to reducing these risks are both humanitarian and financial, but not all arc flash risks are as well known.
Another area of concern is UL 891 switchboards. Here are some examples of the benefits related to addressing these risks.
More arc flash control on the line-side
Consider this scenario: A transformer between 750 and 2,000 kVA feeds a UL 891 switchboard. The switchboard, which consists of a bus, overcurrent protective devices, and ancillary components in an enclosure, is of open internal construction per the UL 891 standard. Due to the open construction, there is the possibility of an arcing fault propagating from the load side of the main overcurrent protective device to the line side of that device.
If the switchboard is fed by a large enough transformer, the result is an extremely high arc flash incident energy (AFIE) that can reach hundreds of calories per cm2, especially if upstream devices are protected by fuses with longer fault-clearing times. The switchboard arc-flash label must show the higher AFIE and have a correspondingly large arc flash boundary.
ArcBlok™ 2500 by Schneider Electric™ was recently developed to provide energy-reducing line side isolation. ArcBlok 2500 is a passive solution for arc flash protection that is compatible with most UL 891 switchboards from any manufacturer. It isolates the line side connectors in a cable vault equipped with barriers between phases that cause an arcing fault to elongate and self-extinguish in less than one cycle (<16.67 ms).
Even if an arc occurs, the maximum AFIE on the line side is reduced to 1.2 cal/cm2. Because the line side is fully isolated, ArcBlok makes it impossible for an arc to propagate from the load side to the line side so the switchboard can be labeled at the lower load-side AFIE level. Energy-reducing maintenance switches (ERMS) and other load-side protective measures remain necessary, but ArcBlok eliminates the exacerbated risk on the line side.
Reduced PPE for switchboard maintenance and first-time energization
When energizing UL 891 Switchboards for the first time, manufacturers face a unique set of conditions and considerations, as the available AFIE can easily exceed 200 cal/cm2. NFPA 70E requires that workers wear personal protective equipment (PPE) to protect against the available incident energy. In practice, there are no viable options for PPE above 140 cal/cm2 (and even then, many project stakeholder safety policies prohibit exposure to such high levels regardless of PPE) which means that first-time energization must be performed from a great distance.
One way to do this is by energizing from the primary side of the transformer with the switchboard main closed. In most cases, however, the electric utility controls the primary side, so the owner does not have access. An alternative is to put the main overcurrent protective device in a separate switchboard from the feeder devices. But this adds layers to the installation, including cabling and bussing between the two, a second pad, and a larger footprint, all of which add expense and complexity. It also leaves the separate switchboard housing the main at a high AFIE level.
The solution is ArcBlok 2500. When properly installed, ArcBlok allows switchboard equipment to be energized on the line-side with the switchboard main open, and then use the switchboard main to energize the remainder of the switchboard. And it can typically be done while wearing 40-calorie PPE, standing at the switchboard instead of the transformer.
The same PPE levels apply for tasks such as absence of voltage confirmation, infrared scans, or accessing meters and programmable logic controllers during commissioning and maintenance. ArcBlok 2500, in combination with an alternative clearing-time-reduction method such as an Energy Reduction Maintenance Settings (ERMS), as stipulated for circuit breakers above 1,200 A in section 240.87 of the NEC, may even further reduce PPE requirements for maintenance and troubleshooting.
Game-changing arc flash mitigation and risk reduction
Until now, line-side protection for UL 891 switchboards has been difficult to provide. ArcBlok 2500 changes the landscape for commercial and light industrial environments by eliminating line-side arc propagation. It simplifies the process of energizing and deenergizing equipment, makes compliance with NFPA 70E easy, and provides a cost-effective solution that protects workers.
In addition to new and existing switchboard integration, each ArcBlok can also be specified for, and installed into, new MCC orders or retrofitted as new main sections as part of a modernization project to add protection to existing Model 6 MCC equipment.
And as we noted in a previous blog, ArcBlok protects workers by extinguishing arcs before they can propagate. Barriers keep foreign objects, such as a hand, a dropped nut, or a screwdriver from entering the energized line side.
Don’t be left unprepared. Learn more about ArcBlok and how to enhance workplace safety.
Add a comment