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EV.4.9 Housings and Enclosures
EV.4.9.1 Every housing or enclosure containing parts of the Tractive System other than Motor housings, must be labelled with the:
a. Symbol specified in ISO 7010-W012 (triangle with black lightning bolt on yellow background)
b. Text “High Voltage” if the voltage meets T.9.1.1
Graphic - HV Symbol
Graphic - HV Symbol
Aside from the Motor Controller Enclosure and Motor Enclosure, 4.9.1.a requires that the "High Voltage Triangle" (pictured left) be visible on every housing or enclosure. EV.4.9.1.b references T.9.1.1, and requires that if its conditions are met, each enclosure or housing aside from those mentioned above is properly labeled "High Voltage".
T.9.1 Definitions
T.9.1.1 High Voltage – HV
Any voltage more than 60 V DC or 25 V AC RMS
EV.4.9.2 If the material of the housing containing parts of the Tractive System is electrically conductive, it must have a low resistance connection to GLV System Ground, see EV.6.7
This rule is further elaborated on in EV.6.7, though at the basic level, specifies that electrical grounding is required of components that are in close proximity to the High Voltage System. Furthermore, electrically conductive parts and parts that may be electrically conductive are required to have specific resistances. Note that at Technical Inspection, the electrical conductivity of any component on the vehicle can be tested!
Rules Reference - EV.6.7
Rules Reference - EV.6.7
EV.6.7 Grounding
EV.6.7.1 Grounding is required for:
a. Parts of the vehicle which are 100 mm or less from any Tractive System component
b. The Tractive System Firewall T.1.9
EV.6.7.2 Grounded parts of the vehicle must have a resistance to GLV System Ground less than the values specified below.
a. Electrically conductive parts 300 mOhms (measured with a current of 1 A)
Examples: parts made of steel, (anodized) aluminum, any other metal parts
b. Parts which may become electrically conductive 5 Ohm
Example: carbon fiber parts
Carbon fiber parts may need special measures such as using copper mesh or similar to keep the ground resistance below 5 Ohms.
EV.6.7.3 Electrical conductivity of any part may be tested by checking any point which is likely to be conductive.
Where no convenient conductive point is available, an area of coating may be removed.
Graphic - Sea of Electrons
Graphic - Sea of Electrons
We define electrical conductivity as a property of materials which quantifies a potential flow of electric charge. High levels of conductivity typically occur within a material when the valence shells of its atoms are loosely bound, forming what's called a sea of electrons.
Now, why might we choose to ground electrically conductive components to the chassis using low resistance?
Well, resistance grounding is normally used to reduce the probability of a line-to-ground arc flash, making systems much safer.
Low resistance grounding, though, is used on medium-to-high-voltage systems to keep the return current at a high level, typically 100A or more. This allows protective fault clearing relays to quickly clear the fault, typically within a few seconds. The fast response time helps to limit damage to equipment, prevent additional faults, localize the fault, and prevent overheating and mechanical stress on conductors.
Graphic - Low Resistance Grounding
Graphic - Low Resistance Grounding
In our case, most components of the Tractive System were enclosed in non-conductive housings. The only component of ours that was relevant in this consideration was our Orion 2 BMS, in that it was metallic. The housing, though, was anodized with internally galvanic isolation. Still, it had to be grounded to the chassis for full compliance! For more information on how to ground to the chassis, see EV.6.7.
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