Hank_Thompson
Member
- Location
- Chicago
- Occupation
- Electrical Engineer
I’m looking for safety and industry-practice perspectives on voltage sensing for 480 V metering using an SEL-735.
In practices I’ve seen this implemented both ways:
• Voltage inputs taken directly from 480 V line-to-line with appropriately sized inline fusing
• Voltage inputs taken through PTs to step down voltage and limit available energy at the meter
There’s an appeal to eliminating PTs (fewer components, less complexity, fewer failure points), but I don’t want to remove something that is electrically important for limiting fault energy or personnel hazard.
SEL has indicated that direct 480 V connection (within the meter’s voltage rating and with proper fusing) is a valid configuration. My question is really about the safety nuance behind that:
• From a personnel safety / incident-energy standpoint, does eliminating PTs meaningfully increase hazard exposure at the meter or during maintenance?
• Do PTs in this application materially limit fault current or energy into the voltage circuit in a way that inline fusing or miniature breakers alone does not?
• In what situations would one consider PTs essential even when the meter is rated for direct 480 V connection?
I’ve been researching this topic in manufacturer documentation and application notes and am trying to understand the practical risk consideration. I also understand this forum provides professional opinion and experience rather than formal design or liability guidance.
My background is primarily low-voltage control systems, so I’m trying to make sure I’m not overlooking protection or hazard-limiting functions that PTs may be providing in typical 480 V metering schemesk. Interested in both NEC considerations and field experience.
Thanks for any and all insights, cheers.
In practices I’ve seen this implemented both ways:
• Voltage inputs taken directly from 480 V line-to-line with appropriately sized inline fusing
• Voltage inputs taken through PTs to step down voltage and limit available energy at the meter
There’s an appeal to eliminating PTs (fewer components, less complexity, fewer failure points), but I don’t want to remove something that is electrically important for limiting fault energy or personnel hazard.
SEL has indicated that direct 480 V connection (within the meter’s voltage rating and with proper fusing) is a valid configuration. My question is really about the safety nuance behind that:
• From a personnel safety / incident-energy standpoint, does eliminating PTs meaningfully increase hazard exposure at the meter or during maintenance?
• Do PTs in this application materially limit fault current or energy into the voltage circuit in a way that inline fusing or miniature breakers alone does not?
• In what situations would one consider PTs essential even when the meter is rated for direct 480 V connection?
I’ve been researching this topic in manufacturer documentation and application notes and am trying to understand the practical risk consideration. I also understand this forum provides professional opinion and experience rather than formal design or liability guidance.
My background is primarily low-voltage control systems, so I’m trying to make sure I’m not overlooking protection or hazard-limiting functions that PTs may be providing in typical 480 V metering schemesk. Interested in both NEC considerations and field experience.
Thanks for any and all insights, cheers.
