Richard, I believe the MOV, or any type of protection, may offer some level of surge protection; however, factors such as lead length will limit its effectiveness, particularly concerning other parts of the mains connection within the larger building. The primary goal is to have the surge protection as close as possible to the equipment it is meant to protect. In larger facilities, the line impedances and other parasitics will significantly influence the protection results. From a standards perspective, quantifying these factors is extremely challenging.
~Doug Douglas E Powell Founder & Principal Consultant Vertex Compliance Consulting <https://bit.ly/45BXk3Y> (VertexCC) Laporte, Colorado, USA LinkedIn <https://www.linkedin.com/in/realdougpowell/> Colorado Registered Business | Entity ID: 20191778678 (UTC-06:00, US-MDT) On Fri, Mar 13, 2026 at 2:44 PM Richard Nute <[email protected]> wrote: > Hi Derek: > > I guess I am wrong about the MOV subjected to the hi-pot test. Thanks for > correcting me. > > However… the MOV is there to protect the equipment from overvoltage. > Doesn’t it protect all equipment that is connected to that branch circuit > and ALL of the 120-volt premises system? I think we only think of the > immediate load. The MOV must protect ALL of the distributed circuit, not > just the load. > > True? > > Thanks, and best regards, > Rich > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > [email protected] > > All emc-pstc postings are archived and searchable on the web at: > https://www.mail-archive.com/[email protected]/ > > Website: https://ewh.ieee.org/soc/pses/ > Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to > unsubscribe) > List rules: > https://pses.ieee.org/wp-content/uploads/2024/12/EM-PSTC-List-Rules.pdf > > For help, send mail to the list administrators: > Mike Sherman at: [email protected] > Rick Linford at: [email protected] > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > _________________________________________________ > To unsubscribe from the EMC-PSTC list, click the following link: > https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1 > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to [email protected] All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://pses.ieee.org/wp-content/uploads/2024/12/EM-PSTC-List-Rules.pdf For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher: <[email protected]> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
