Insulation is usually made from a non-metallic material. The majority of electrical insulation is made of PVC, plastic, or rubber. An example is the insulation coating on a busbar.
Isolation resistance is required between parts of a battery pack or the surrounding systems to prevent current flow.
Isolation Resistance of a Pack
The isolation resistance of the complete HV system to ground with the contactors closed should be >500Ω/V and hence for a battery pack its resistance target must be specified by the HV System designer, typically >1,500kΩ.
Creepage and Clearance
High voltage circuits can discharge across a gap, the gap can be through the air or across a surface.
- Creepage: distance between two conductors on the surface.
- Clearance: the distance between two conductors through the air.
EN IEC 60529 gives the following definitions [1]:
- Equipment marked IPXXB is protected against access with the finger, or rather the jointed test finger of 12 mm diameter, 80 mm length has adequate clearance from hazardous parts.
- A marking of IP2X shows equipment is protected against solid foreign object with diameter ≥ 12,5 mm, or rather the object probe, sphere of 12,5 mm diameter does not fully penetrate. Moreover, the mark IP2X also ensures protection against access to danger parts. In particular an equipment marked IP2X is protected against access to hazardous parts with the finger, or rather the jointed test finger of 12 mm diameter, 80 mm length has adequate clearance from hazardous parts.
HV Isolation & Ground Fault Monitoring
An HV battery pack’s isolation from the vehicle chassis is normally maintained by design, but a monitoring circuit still has to watch for it failing in service: a chafed wire, a component drifting out of spec, or moisture ingress can all drop the barrier low enough to become a shock hazard. That is the job of the Insulation Monitoring Device (IMD): a circuit permanently connected between the HV bus and chassis ground that continuously estimates insulation resistance rather than waiting for a periodic test.
References:
- Protection from direct contacts: IPXXB or IP2X?, GT Engineering
Isolation resistance is commonly verified in production and validation testing via a HiPot test, which applies a high voltage across the isolation barrier to confirm it can withstand the required dielectric stress without breakdown.