I asked MS Copilot AI chatbot about this general scenario and here’s what it
suggested:
=====================
A reasonable plan could look like:
1. Define segments:
* Segment A: Genset output to main distribution (excluding genset
windings).
* Segment B: Each 480 V motor feeder (cable from panel to motor, motor
isolated).
* Segment C: Control power circuits and control wiring (electronics
removed/bypassed).
2. Choose DC hipot for large segments:
* Use DC hipot at an agreed voltage (e.g., DC equivalent of the AC
requirement) to keep current manageable.
* Ramp up slowly, hold for 1 minute, monitor leakage current.
3. Use insulation resistance tests where appropriate:
* For long runs or sensitive circuits, use 500 V DC IR tests with a
defined minimum MΩ value, referencing IEC 60204‑1 as supporting practice.
4. Document everything:
* Test plan with rationale (size, capacitance, outdoor use).
* Drawings showing segmentation and isolation points.
* Records of test results for each segment.
5. Review with your certifier/AHJ early:
* Send them the plan before you build your test setup.
* Adjust voltages or segmentation based on their feedback rather than
after the fact.
That seems a solid approach and likely a good stating point for you.
Ralph
_____
If you want, tell me roughly how many motors, approximate cable lengths, and
whether you have any electronics in the control panels (PLCs, HMIs, VFDs,
etc.). I can sketch a more specific test sequence and example acceptance
criteria that would be realistic for your exact machine.
From: Chester Summers <[email protected]>
Sent: February 27, 2026 12:27 PM
To: [email protected]
Subject: [PSES] hipot considerations for large electric machinery?
Hello, colleagues—
I’m looking at hipot testing a physically large electric machine and trying to
determine the best approach to complete the task. NFPA 79 & C22.2 No. 301 say
hipot is required, IEC 60204-1 leaves it to the manufacturer’s consideration.
The machine supports outdoor construction work, contains several 3-phase 480V
motors and is powered by on-board genset, all mounted on semi truck trailer.
Process control is done through simple pushbutton switchgear panels. There are
no programmed electronics or PCBs.
This is by far the largest product I’ve considered for hipot. Isolation of the
product isn’t feasible (won’t fit on test table :) and disassembly is strictly
limited. I’m looking for practical guidance from those that routinely test and
inspect physically large equipment. IR and ground bond testing are already
planned. Risk assessment thus far tells me hipot may not be essential,
however, the standards say…
How should I address this elephant?
Thanks in advance & best regards,
Chet Summers
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