So what do you know about how High Voltage systems work? Are you scared you will get shocked by a hybrid or EV? Like everything in the fire service, every firefighter should have a basic understanding on a high voltage system works. Toyota put together a comprehensive hybrid safety training presentation that was developed as a resource to train emergency responders on the safe operation of hybrid vehicles. The presentation is available for download below. The first link provides the ability to view the presentation, while the second link is a zip file that contains the presentation that can be played from a local system, along with Instructor Notes and a Student Handout.
Insulated cables and connectors
All high voltage power cables and connectors are color coded bright orange. The power cables and connectors are insulated to prevent contact with the bare wire conductor.
Low voltage wiring connected to vehicle body ground. The 12 Volt low voltage circuit uses the vehicle metal body as a ground (see picture below illustration). The presentation shows an animation of the low voltage circuit electrical flow through the vehicle metal body ground. A responder contacting the vehicle metal body ground and a bare positive/hot wire completes the low voltage circuit.
High voltage wiring insulated from vehicle body ground. The high voltage circuit does not use the vehicle metal body as ground (see picture below illustration). Instead, a separate ground high voltage power cable is routed from the battery to the component. The battery and component are insulated from the vehicle metal body ground. The presentation shows an animation of the high voltage circuit electrical flow though the high voltage power cables. A responder contacting the vehicle metal body and a bare high voltage positive/hot wire does not complete the high voltage circuit because the high voltage ground is insulated from the metal vehicle body.
When the ignition switch/power button is Off, no 12 Volt battery power (red dotted lines) is supplied to the hybrid computer which keeps the high voltage battery pack positive and negative relays open (green boxes). The high voltage circuit is Off, and no electricity flows from the high voltage battery pack to the power cables (orange dotted lines).
When the ignition switch/power button is turned On, 12 Volt battery power (red solid lines) is supplied to the hybrid computer. The hybrid computer powers the high voltage battery pack positive and negative relays (green boxes) which allows them to close (orange contacts). Once the relays close, the high voltage circuit is On and electricity flows from the high voltage battery pack to the power cables (orange solid lines).
To manually disable the high voltage system, turn the ignition switch/power button Off. This stops electrical flow from the high voltage battery pack to the power cables.
The hybrid computer provides automatic disabling of the high voltage system. SRS collision sensors (yellow shaded boxes) and high voltage current/voltage sensors (black dashed callouts) are monitored by the hybrid computer. When airbags deploy or when a current/voltage imbalance is detected, the hybrid computer automatically opens the positive and negative relays to stop electrical flow from the high voltage battery pack to the power cables. A fuse located in the high voltage battery pack also provides automatic high voltage disabling during an overload condition.