20A Pro Shore-Power Cart — L5-20P Inlet, Rack PDU, DIN Meter + E-STOP
Locking feed, metal rack PDU, real-time power metering (CT), and an emergency mushroom that trips the main.
What You’re Building
NEMA L5-20P lock-in inlet
20A rack PDU (UL 1363)
DIN meter + 5A CT
E-STOP → shunt-trip main
Mobile, listed-parts-only AC distro for PCs, lights, chargers, and networking — not for heaters/AC/fridges.
Rules of Engagement (Safety)
- Use UL-listed strips/RPDUs (UL 1363). Don’t daisy-chain power strips or run cords through walls.
- 20A branch math: continuous loads (≥3 h) → plan for ≤ 16 A (~80%).
- Use 12 AWG copper conductors for 20 A circuits; keep grounds continuous.
Follow local code. If unsure, get a licensed electrician.
Parts (Spec-First)
- Locking inlet: NEMA L5-20P flanged inlet (panel-mount, UL 498). Use a short adapter pigtail 5-20P → L5-20R for standard wall circuits.
- Main disconnect: 20 A UL 489 shunt-trip breaker (120 V shunt coil) in a small enclosure.
- E-STOP: 22 mm red mushroom, latching, NO contact driving the shunt-trip coil (listed to IEC/UL 60947-5-5/-5-1).
- Meter: DIN rail multifunction meter (e.g., Socomec DIRIS A-10) + 100 A/5 A CT.
- PDU: 1U metal rack PDU, 120 V/20 A, L5-20P input, 5-15/20R outlets.
- Cabling: 12 AWG THHN/MTW inside enclosure; 12 AWG SJTW for cord sets; ring/fork lugs, ferrules, labels.
Staged Banks (Behavior)
- Bank A — HEAVY: PCs, LED fixtures with inrush (turn on first).
- Bank B — MEDIUM: monitors, chargers.
- Bank C — LIGHT: router, USB power (can be “always-on”).
Sequence: A → B → C. Keep total ≤ 16 A continuous.
One-Line Wiring (Simplified)
[ L5-20P Locking INLET ] --strain relief--> [ 20A Shunt-Trip MAIN (UL 489) ] --HOT--> [ DIN Meter (V/A/W) ]
| |
| (coil) |--CT around HOT-->
[ E-STOP 22mm ] v
| [ Rack PDU (UL 1363) ]
NEUTRAL ---------------------------------------------> Meter N/through ---------------------> PDU N
GROUND ---------------------------------------------> Bond/through -------------------------> PDU G
E-STOP energizes the shunt-trip coil to open the main instantly. Reset = twist-release E-STOP → re-close breaker.
Build Steps
- Mount: Flanged L5-20 inlet near the cart handle; fit cord grip; install breaker enclosure, DIN meter, CT, and PDU.
- Main line: Inlet HOT → shunt-trip breaker LINE; breaker LOAD → meter LINE; meter LOAD → PDU feed. Neutral/ground pass as per manuals.
- Meter CT: Loop the PDU HOT through the CT in the arrow direction; land CT to the meter’s 5 A inputs.
- E-STOP: Wire E-STOP NO → shunt-trip coil (with a small inline fuse per maker). Test trip.
- Dress & label: A/B/C bank stickers, total 20 A/16 A continuous note, emergency-off label at mushroom.
Commissioning
- Continuity & polarity check; ground verified.
- Power up with a 5-20R wall circuit using a short 5-20P→L5-20R pigtail or an L5-20R receptacle if available.
- Trip-test E-STOP; confirm breaker opens and power drops to PDU.
- Add loads bank-by-bank; verify volts/amps/watts.
Don’t
- No daisy-chained strips or cords through walls/ceilings.
- No space heaters, ACs, or fridges on the cart. Plug those directly to a dedicated circuit.
- No unlisted meters or mystery modules on mains.
Sources & Standards
- UL 1363 (Relocatable Power Taps / rack PDUs): UL overview and Intertek summary.
- OSHA interpretation—power strips: low-power loads, no daisy-chain.
- NEMA L5-20 locking devices & flanged inlets (UL 498 listings): Hubbell / Leviton datasheets.
- Rack PDU (L5-20P input) example datasheets.
- DIN meter (CT) example: Socomec DIRIS A-10 (UL/CSA variants available).
- E-STOP standards (IEC/UL 60947-5-5 / -5-1) and UL note on certifying emergency-stop devices.
- Shunt-trip breaker examples (UL 489): Square D QO shunt-trip, Eaton BR-ST series.
- NEC continuous-load 125% rule (→ 80% on standard breakers), branch circuits & OCPD.
- Ampacity tables for 12 AWG on 20 A circuits.
Always follow your exact product manuals and local code.
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