Q: If you were working inside of a panel with high and low voltage, would it be allowable to have a shield installed to separate the two so that you could work on the low voltage equipment without needing to put on all of the arc flash and shock PPE?
A: Electrical hazards are made up of electrical shock and electrical arc flash.
Temporarily covering up with a dielectric material in such a way that no exposed energized parts are present does indeed reduce the risk of shock to a tolerable level IF the insulating material (and equipment that it is being installed on) is adequately rated, regularly maintained, and properly installed. This negates the need for electrical gloves (either HV or LV). It may further allow persons with either LV or HV qualifications to work on the installation and influence barricading (boundary) distances.
However, temporarily covering up may not necessarily reduce the risk of arc flash since this risk is influenced by both exposed parts and interaction with equipment. So although covering up will reduce the electrical shock exposure, a formal risk assessment is required to determine whether the arc flash hazard is removed.
The arc flash hazard is largely dependent on the short circuit current and over current protective device (OCPD) clearing time, as well as other factors. This means that a lower voltage doesn’t necessarily imply a lower arc flash energy. So where does the higher arc flash hazard reside – the HV or LV side of the panel? You wouldn’t know unless an arc flash engineering study (arc flash hazard analysis) has been performed.
Covering up one voltage in a multiple voltage panel reduces the risk of shock against one voltage, but does not necessarily reduce arc flash hazard. Also, voltages above 50V can cause electrocution. There is no clear cut answer, and each application should be uniquely assessed to determine the risk.
Ken Sellars CESCP (our NEC expert) adds that as per the NEC, a permanent cover/shield may be considered altering equipment and may violate the listing and labeling of the equipment. This is illegal, unless the installation of the cover/shield is done by the manufacturer (or similar) and adequately tested afterwards. Certain modifications (that do not iinfluence current density, heat transmission, dielectric insulation, etc.) may not alter the design and may not warrant retesting. Be aware, however, that only the manufacturer or a testing/certifying body will be able to confirm.
The risk assessments around each of these are covered in our Low and High Voltage qualified electrical safety training classes based on NFPA 70E® 2018 and OHSA Subpart R and Subpart S as applicable.
You can also read more about Risk Assessments here.