EV.6.3 Wiring

EV.6.3.1 All wires and terminals and other conductors used in the Tractive System must be sized for the continuous current they will conduct

Continuous current, also known as Direct Current (DC), refers to the flow of electric charge in a single, constant direction. Wires, terminals, or conductors that are too small may cause excessive voltage drop, so it is important to ensure that the voltage drop is within acceptable limits for your system. The undersized connections can also potentially overheat due to excessive current flow, increasing the risk of electrical fires or damage to the insulation. Proper sizing helps prevent overheating and ensures safe operation.

Graphic - Wire Sizes

EV.6.3.2 All Tractive System wiring must:

a. Be marked with wire gauge, temperature rating and insulation voltage rating.

A serial number or a norm printed on the wire is sufficient if this serial number or norm is clearly bound to the wire characteristics for example by a data sheet.

b. Have temperature rating more than or equal to 90°C

Photo - Marked Cable

Shown to the left are two of wires with the same type and markings. Due to the way that these wires are fastened, though, it is difficult to see all of the criteria met from just one exposed wire. As you can see, though, the wire gauge (2/0), temperature rating (-50ºC - 105ºC), and insulation voltage rating (600V) are all properly marked. EV.6.3.2.a also allows that the wire's serial number tied to a datasheet would be an acceptable alternative.

In the case of our EXRAD-HVX1/0X cables, we ordered the product with the expectation that it would have markings as shown on the storefront, but unfortunately this was not the case. After submitting a rules inquiry, we were able to confirm that a paper trail inclusive of the order receipt and datasheet for the cable was sufficient.

Additionally, the peak temperature rating of the Tractive cables must be at least 90ºC as per EV.6.3.2.b. Our depicted range of -50ºC - 105ºC is allowable because our 105ºC ceiling is beyond the 90ºC minimum.

EV.6.3.3 Tractive System wiring must be:

a. Done to professional standards with sufficient strain relief

b. Protected from loosening due to vibration

c. Protected against damage by rotating and / or moving parts

d. Located out of the way of possible snagging or damage

This rule stipulates that the Tractive wiring rated for High Voltage be properly protected on account of safety and reliability, which is essential in preventing system failure and potential electrical faults.

Starting with EV.6.3.3.a, the wiring must be professional and orderly. Though this sounds subjective, there are a few avenues which can be used to ensure compliances, such as adherence the National Electrical Code (NEC). A few key fundamentals are considering appropriate wire sizes and rates for intended loads, securely mounting and routing components, using insulation to shield conduits and wires, properly terminating connections, as well as documenting and labeling wiring layout and connections.

In terms of strain relief, it is important to ensure that your component uses flexible materials such as copper and aluminum to prevent breaking. Another option is to utilize devices like strain relief connectors, cable sleeves, or cable glands where wires connect to other components. These mechanisms help to absorb and distribute mechanical stress, reducing the risk of damage at the connection points.

Photo - Professional Wiring

EV.6.3.3.b requires protection from loosening due to vibration which can be done by encasing cables in flexible conduits, using anti-vibration mounts or pads to isolate equipment and cables from sources of vibration, employing connectors with locking mechanisms that prevent them from loosening due to vibrations, or otherwise implementing a comprehensive cable management system.

There are a few ways to tackle EV.6.6.3.c in order to prevent damage from moving parts, one being to use cable guards, sleeves, or conduits to shield wires from abrasion. Another solution for cases of significant movement would be drag chains, an option which protect and guide cables while allowing for movement without significant stress. Finally, an option which follows in suit with EV.6.6.3.d is using brackets or mounting hardware to position the cables outside of the range of motion of moving parts. Intentionally placing components wath a far-enough proximity to moving parts works to prevent snagging or damage to the system.

EV.6.3.4 Any Tractive System wiring that runs outside of electrical enclosures:

a. Must meet one of:

Enclosed in separate orange nonconductive conduit
Use an orange shielded cable.

b. Must meet one of:

Run in a fully enclosed container. Bodywork is not an enclosure.
The conduit or shielded cable is securely anchored at each end to allow it to withstand a force of 200 N without straining the cable end crimp

c. Any shielded cable must have the shield grounded.

Within our vehicle, we have a multitude of subsystems within the Electrical System which interact with one another. With each subsystem having its own enclosure, there must be connections that run between housings and subsystems. Shown to the right is an example of wiring that runs outside of defined electrical enclosures. If this wiring happens to be electrically connected to the motor or accumulator(s), then there are very specific rules which apply as discussed below.

Schematic - Master View of Enclosures

EV.6.3.4.a imposes that the wiring should be colored orange as per The National Highway Traffic Safety Administration's (NHTSA's) rule, FMVSS 305. In section E, this rule states that cables for high voltage sources that are not located within electrical protection barriers must be identified by an orange colored outer covering. Now, for our purposes, these cables should either be contained in a nonconductive conduit or be of the shielded-cable type. Now, an electrical conduit is a protective tube or channel through which electrical wires or cables are run with the purpose of safeguarding the wiring from physical damage and providing a structured path for travel. Shielded cables, alternatively, are electrical cables which includes a layer of conductive material surrounding the internal wires and safeguarding against electromagnetic interference and radio frequency interference. A photo of each application avenue is shown below.

Photo - Orange Nonconductive Conduit

Photo - Orange Shielded Cables

As for EV.6.3.4.b, the Tractive Wiring outside of electrical enclosures must have safeguards against disconnection through use of an additional fully closed container or otherwise anchoring the connection to withstand a significant amount of pulling force without strain. The best way to ensure compliance here would be to either get a rated strain relief and bring the datasheet to competition, or build a model and test how much force your solution can take before failure. From there, you can document your test data, and prove that your model matches the mounting on the car.

Photo - GND Clamps

Finally, EV.6.3.4.c regulates that any shielded cable used must be grounded to the chassis. HV cables are mainly composed of four parts: conductor, insulation, shielding and sheath. The shield of the cable is responsible for blocking electromagnetic interference (EMI) and radio frequency interference (RFI). It also prevents leakage currents from being generated between adjacent cables. Therefore, it plays a very important role in cable design. To prevent external interference, which increases the reliability of the HV connector and reduces the failure rate. To improve the performance of the connectors in harsh environments. To withstand strong electromagnetic fields and ensure reliable power transmission between an electric vehicle and its charging station.

The intent of the rule is that the shield of these wires has a low impedance (less than 300 mOhms) to Grounded Low Voltage (GLV) ground (GND) so that your Insulation Monitoring Device (IMD) is guaranteed to activate and turn off your car if the insulation barrier between the High Voltage (HV) conductor and shield is broken. That prevents the shield of these wires from becoming a hazardous exposed live part. The reason that the shielding for High Voltage cables can be connected to the chassis is because the induced electromotive force (EMF) is quite low (according to the Biot-Savart Law). For our cases, our 2023 team had peeled back the first layer of insulation to reach the braided shield, and then clamped around it. Then, a wire was sent from the clamp and bolted to the chassis.

Biot-Savart's law is a fundamental principle in electromagnetism that describes the magnetic field produced by a current-carrying conductor, where B represents the magnetic field intensity, µ represents the permeability of free space (which is a constant), N represents the number of turns in the solenoid, I represents the current intensity through the wire, and R represents the perpendicular distance from the wire to the point where the field is being measured.

Formula - Biot Savart's Law

EV.6.3.5 Wiring that is not part of the Tractive System must not use orange wiring or conduit.

The orange coloring for Tractive System wiring is imposed upon by The National Highway Traffic Safety Administration's (NHTSA's) rule, FMVSS 305. In section E, this rule states that cables for high voltage sources that are not located within electrical protection barriers must be identified by an orange colored outer covering.The voltage taps are orange because the BMS is partially tractive system and not tractive system. So don't use any orange where there is not high voltage. Because some connectors can be so small that the markings on these connectors would be not easily read and that high voltage cables going into the connectors are required to have orange outer covers, which should signal that the cables and their connectors are high voltage.

That said, if there are other wires or conduits which are not part of the Tractive System who are colored orange, they would be indistinguishable from the Tractive wires and therefore a safety hazard. The intent of this rule is to visually differentiate between high and low voltage connections.

It is important to note that because the AMS (Accumulator Management System) is connected to battery cells which are Tractive Components, the Voltage Taps fit within the category of Tractive Wiring and therefore are allowed to be connected using orange cables.

Shown below are examples of the orange connections.

Photo - Orange Cables in ORION BMS 2

Photo - Orange Cables in Accumulator

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