Lesson 2.3 — Stabilise & Verify Zero: Test Before Touch

PC 2.3: stabilise the vehicle and ensure zero residual voltage. Inverter and charger capacitors store real, lethal energy after disconnection — manufacturers specify a discharge wait, typically five to ten minutes. Waiting is not verification. The only proof of a dead bus is measurement, and the measurement is only proof if the meter is proven: PROVE the meter on a known live source, TEST the HV bus (HV+ to HV−, HV+ to chassis, HV− to chassis — all below 5 V DC), then PROVE the meter again. Wear your gloves and face shield throughout the verification: until the second prove, the bus is still officially live. Only after prove–test–prove may HV PPE be relaxed for the service work itself, per the workshop procedure.

Key points

Capacitors can bite minutes after shutdown — respect the OEM discharge time, then still verify
Measure at the manufacturer-specified verification point with insulated CAT III leads
< 5 V DC on every combination = de-energised; any higher reading means STOP and re-isolate
Log the readings — time, meter serial, values — on the depower record

Evidence task

Upload a photo of your multimeter reading at the HV verification point together with your completed depower checklist (with the three prove–test–prove readings recorded).

📖 Case Study — The Capacitor That Waited

A European workshop, documented in an industry safety alert: a technician depowered a BEV correctly — key away, 12 V off, service plug out — then went straight to unbolting the inverter, skipping the discharge wait and the zero-volt test because 'the plug was in his pocket, so it was safe'. The inverter DC-link capacitors were holding 280 V. His insulated ratchet slipped, his bare forearm bridged the terminals, and the discharge threw him off the vehicle. He survived with burns and a damaged shoulder — because the current path was arm-to-arm across muscle, not across his chest, and because a colleague reached him with the rescue hook in seconds. The plug removes the source; it does not remove stored energy. Prove. Test. Prove.

List the two barriers this technician skipped, and for each, name the PC in Element 2 that mandates it.