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Updated · 17 Sep 2026 · Sheet checked · 17 Sep 2026
It depends
Which path hardwires a portable generator without backfeeding the utility — and which fits how you run loads in an ice storm.
| Generator interlock kit | Manual loadside transfer switch (Pro/Tran 2 class) | |
|---|---|---|
| What it is | Mechanical plate on the panel cover; main and generator breakers cannot both be ON | Separate indoor transfer cabinet; selected branch circuits move onto generator |
| Panel use | Existing panel stays the load center | Kit cabinet wired for chosen circuits only |
| Circuits | All breakers in that panel (you shed load by hand) | Only circuits landed in the kit (often 6–10 single-pole class) |
| Amp / inlet | Dedicated generator breaker + outdoor inlet (30 A / 50 A common) | Kit-rated — 310-class 30 A L14-30 (~7,500 W max gen); 510-class = 50 A |
| Listing (mfr) | Eaton: UL Listed + NEC Art. 702; GenInterlock: MET/UL + Art. 702 | Reliance Pro/Tran 2: UL 1008; suitable per NEC Art. 702 |
| Isolation | Break-before-make via interlocked breakers | Break-before-make in the transfer cabinet |
| Outdoor inlet | Usually separate | Often in CRK kits (PB30 + cord with 310CRK) |
| Fit | Whole-panel access; simpler hardware | Fixed essentials; clearer kit wiring; more kit + labor |
Two code-oriented ways to hardwire a portable generator so utility and generator cannot feed the house at once.
Interlock kit: A panel-cover accessory matched to a specific load-center family. Eaton frames its mechanical interlock kits as UL Listed for its load centers and as meeting NEC Article 702 — utility main and generator breakers cannot both be ON. GenInterlock and peers sell panel-specific plates and cite MET/UL listing plus the same Article 702 rule. Wrong plate for the catalog number is unsafe, not "close enough."
Manual transfer switch kit: A listed loadside cabinet an electrician wires for a fixed circuit set. Reliance Pro/Tran 2 sheets: UL Listed to UL 1008, suitable for use per Article 702. A complete 310CRK pairs indoor 310C (10 single-pole / 5 double-pole class, 30 A combined @ 250 V) with outdoor PB30 L14-30 inlet and cord. Not a phantom "Reliance 3100" — live coverage is 310CRK. Same family steps to 510-class for 50 A / ~12,500 W generator framing.
Interlock — will run / manage yourself: Any circuit already in the panel, limited by generator continuous output and shedding. Fridge, furnace, well (if start current fits), tools — available if you kill non-essentials first.
Transfer kit — will run: Only landed circuits. Typical kits: fridge, selected lighting, furnace, one 240 V slot — not every branch in a full panel. Watt meters help balance legs; they do not raise amp rating.
Skip or measure first (both): Shopping for a power source. Automatic standby. Unlisted "universal" plates your AHJ rejects. Pairing a 50 A portable to a 30 A kit. DIY panel work without permit where required. Continuous-watt claims for transfer gear — amp rating and circuit count are the limits.
Skip both if… a couple of extension-cord loads are enough — still never backfeed a dryer outlet.
It depends. Prefer a listed, panel-matched interlock when the AHJ accepts that path, you want whole-panel access, and you will manage load by hand. Prefer a UL 1008 loadside transfer kit (310CRK class for 30 A L14-30 portables; step up in-family for 50 A) when you want fixed essentials and clear kit wiring. Both need a licensed electrician and local approval. Neither replaces a generator sized to continuous watts you actually need.