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benji_ee•2mo
Electrical Engineering for Buildings & Infrastructure

Neutral conductor overheating in hospital panelboards during EVSE rollout

We’re retrofitting a 20-year-old hospital with EVSE (Level 2) charging infrastructure tied to spare panel capacity in the existing emergency garage. Despite balanced loading across phases, we’re seeing significant neutral conductor heating under full draw, even though harmonics were assumed negligible. The loads are modern and non-linear, but well within rated capacity. Preliminary THD readings showed neutral current at 130% of expected under multi-unit charging sessions. Is this a case of underestimated triplen harmonics from charger PSU design? Anyone had to retrofit neutral capacity or filtering after EVSE installs?
2

Comments (10)

DE
deeptank.pm2 months ago
From a construction oversight standpoint, we forced our EC to run all neutrals in dedicated conduit with labeled color coding. If you need to retrofit filters, tracing wiring becomes easier — don’t overlook basic access.
JO
joe.bridges2 months ago
Interesting crossover: our transportation team noted the same spike in EV charger neutrals in a train depot. They swapped the charger bank for units with active PFC correction — problem vanished. Worth testing a unit swap before major retro.
RA
raquel_mepcoord2 months ago
Also check for shared neutrals. A lot of older hospitals still run shared neutrals across circuits, especially if there was an upgrade to LED lighting earlier. The cumulative harmonic return could be overloading what looks balanced on paper.
SI
sitaspecs2 months ago
Did you model this in SKM or ETAP with real charger profiles? We had a spec sheet show <5% THD, but field readings hit 18%. Always test the actual waveform, not the catalog promise.
EM
emma.builds2 months ago
From a safety lens, I’d push for thermal IR scanning during peak hours. We had two cases where neutral lugs cooked inside live panels even though current stayed under nameplate. Harmonic heat build-up is sneaky.
MK
mkale.codes2 months ago
You’re likely dealing with 3rd and 9th harmonic stacking on the neutral. EV chargers with poor PSU isolation tend to dump balanced-phase nonlinear loads that spike neutral current beyond design. We ran FFTs and confirmed the spike wasn’t load-driven, but waveform distortion.
IM
imani.amlo2 months ago
Suggest checking IEEE 519 compliance clauses in your project agreement. We negotiated a waiver for post-retrofit THD levels on a public bus depot since compliance would’ve required major neutral upgrade.
BU
buildpulse_fm2 months ago
We now add clamp-on harmonics loggers during commissioning of any panel tied to EV loads. Keeps a baseline for comparison and helps defend against claims that your neutral design was flawed.
TA
tasha.qs2 months ago
If your insurer or FM team ever audits this, they may insist on capacity derating based on real-world harmonics, not just nameplate load. We’ve had to cost in neutral rerouting as a change order post-turnover.
PO
powerraul2 months ago
We saw neutral overheating in a retirement home garage upgrade. Solved it by installing a line reactor at the subpanel feeding the chargers — dropped harmonic content by 40% and let us avoid replacing the neutral altogether.

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