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04.9 EV HV isolation

How do you isolate high voltage systems on an EV?

There are five ways in which high voltage systems on an EV can be shut down:

  1. When airbags deploy* - automatic

  2. Cut loop 

  3. Pull plug 

  4. Pull fuse 

  5. Manual Service Disconnect 

*As discussed on the Electrocution Risks page, when airbags deploy in an electric vehicle following a collision, the high voltage systems should automatically isolate.

It's important to note that some EVs don't have a low voltage method to isolate high voltage systems, instead relying on airbag deployment alone.

While automatic HV isolation following airbag deployment should occur, there is no way for emergency responders to test or measure this; ie. we cannot test for current in DC power circuits.

What does HV isolation do?

The high voltage battery pack, components & cables are all contained within an EV, & can pose a risk of electrocution in some circumstances.

When we isolate high voltage systems, all the electricity is drained to the high voltage battery pack underneath the vehicle; this is not an area responders would usually be touching or cutting into for passenger extrication, so isolating HV makes responders safer to work around the EV.

How do EV HV isolation methods work?

To compare each side by side, we've created the following table; click on each heading to read more, see images & a video.

HV isolation following airbags deployment

  • Isolation should occur automatically, with no action required by emergency responders

  • Responders cannot detect or measure whether isolation has occurred in an electric vehicle's DC circuits

  • Follow the manufacturer emergency response guide (ERG) & your agency SOPs on appropriate PPC / PPE 

    • PPC would include full structure gear & self-contained breathing apparatus at a minimum

    • PPE would include (at a minimum):

      • Insulated cutting tools

HV Isolation airbags.png

Watch: How to isolate an EV battery for emergency responders

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