Electric Vehicles: HV Tools & Equipment

Electric Vehicles: HV Tools & Equipment

Having the right tools is the first step when working with high-voltage systems; knowing how to properly use them is the next one.

This article is the third in a series on battery electric vehicles (BEVs) and hybrid electric vehicles (HEVs). Find the first article here and the second article here.

In previous installments of this series on electric vehicles (EVs), we covered topics such as the importance of battery precautions and welding safety. Working safely with high-voltage (HV) systems is of the utmost importance. As such, we will continue to lightly touch on that in this installment, but the focus this time will be on the tools and equipment needed to properly work on HV systems.

Electrical Systems

Although modern EVs vastly differ from one another, they all have one thing in common: an HV electrical system. HV is defined as having greater than 30 volts AC current or 60 volts DC current. Whenever high-voltage is discussed, it should be mentioned that special protective gear and equipment is required to disable/isolate the battery or to perform work on these systems.

Specialized Hand Tools

In addition to special safety gear, working on HV systems requires specific and specialized tools as well. Grabbing any off-the-shelf screwdriver or wrench is not going to cut it when performing work on an HV system. Specialized tools that are insulated for high-voltage are necessary. These specialized tools are typically rated for up to 1,000 volts and are either made out of a non-conductive material, such as plastic, or may be coated to insulate it from electricity. Care must be taken with these tools to ensure that their insulative properties are not compromised. Tossing them in with the rest of the tools in the toolbox can cause abrasions or cuts to the insulation, allowing electricity to flow through them and into the technician.

Other Tools

In addition to common hand tools, HV systems also require specialty tools for reading the power of the battery and the system in volts and amps. These tools are not only designed to be insulated from high-voltage, they’re designed to safely have high-voltage and amperage run through them. Just like the hand tools, these electrical testers and meters need to be handled with care – not only to ensure proper functionality but to minimize the risk of compromising the tool’s insulative properties and increasing the risk of deadly electric shock.

Attempting to use a standard DVOM on an HV system will almost undoubtedly have disastrous results.

An HV digital volt ohm meter (DVOM) is likely the most common tool that will be used with an HV system. As the name implies, this meter is designed for HV applications and typically can handle up to 1,000 volts. Attempting to use a standard DVOM on an HV system will almost undoubtedly have disastrous results. In addition to the risk of deadly electrocution, the DVOM will almost assuredly be destroyed.

Electrical measurement tools are categorized at different levels, from CAT I to IV. The following are brief explanations of each level:

CAT I. Category I is for measurements performed on circuits not directly connected to mains. Examples are measurements on circuits not derived from mains and specially protected (internal) mains-derived circuits. In the latter case, transient stresses are variable; for that reason, IEC 61010-1-5.4.1(g) requires that the “transient withstand capability” of the equipment is made known to the user.

CAT II. Measurement category II is for measurements performed on circuits directly connected to the low-voltage installation. Examples are measurements on household appliances, portable tools and similar equipment

CAT III. Measurement category III is for measurements performed in the building installation. Examples are measurements on distribution boards, circuit-breakers, wiring (including cables), busbars, junction boxes, switches, socket-outlets in the fixed installation, and equipment for industries.

CAT IV. Measurement category IV is for measurements performed at the source of the low-voltage installation. Examples are electricity meters and measurements on primary overcurrent protection devices and ripple control units

For HV measurement purposes, a minimum of a CAT III meter is required. However, the use of CAT IV is preferred as it adds a better layer of protection when working on a high-voltage system.

Proper Usage

Having the right tool and using it correctly are two different things. Other than the safety factor of using the HV-DVOM correctly, it is necessary to know how to obtain proper readings. Testing the meter on a known low-voltage source, such as the vehicle’s 12-volt battery, is the first step. This allows the technician to verify not only the proper use of the tool but tool accuracy as well.

Faulty meters or leads can produce a false “zero voltage” reading. You’re better off discovering an issue with low-voltage than with high-voltage. Because the HV system circuits are isolated from the vehicle chassis ground, the leads must take readings directly from the HV connections. OEMs will typically provide information on where to measure. Depending on the work that is being performed, the locations to measure may be HV cable ends, connectors or the battery itself.


  • Hybrid Vehicle Identification and Damage Analysis
  • Hybrid, Electric and Alternative Fuel Vehicle Service
  • Introduction to Electric Vehicles
  • Understanding High Voltage Safety
  • Electric Vehicle Inspection and Handling
  • Electric Vehicle Damage Analysis
  • Electric Vehicle Service Considerations

Another HV tool is a two-pole voltage meter. As the name implies, this tool measures only voltage. Unlike a DVOM, this tool is not dependent on an internal battery to perform its functions. This means that there is no failure to read or reading inaccuracy that can occur due to a low or dead internal battery. In addition, unlike the DVOM, there are no settings to adjust or select. This eliminates the potential of having the meter on the wrong setting. Just as with the HV-DVOM, it is a good idea to test the two-pole voltage meter on a known low-voltage source. These meters will often have a function that will allow the technician to simply press a button or buttons on the tester to place a slight load on the circuit, allowing any residual or “ghost” voltage remaining in the circuit after isolation or disconnection to be dissipated. It is important to note that this feature is not designed to discharge a capacitor.

Testing for Voltage

When testing for voltage on an HV system, a good practice is to not only test for voltage between HV+ and HV- but to also test for HV+ to vehicle ground and HV- to vehicle ground (chassis). This helps to identify any potential faults in the HV system that have allowed the high-voltage to break containment and now be flowing through the vehicle chassis. This is important as the possibility of this voltage breach is heightened in the event of a collision but can also occur due to chaffing, chemical deterioration or cuts that compromise the HV wiring insulation.

Once you’ve confirmed your voltage with the three-step process, there is still one more step. Take your DVOM or two-pole voltage meter and go back to the same low-voltage source you tested on and take another reading. This is another safety step that helps ensure that there was not an error with the function of the tool when testing the HV system.

Milliohm Meter

Another tool that is needed for HV systems is a milliohm meter, which will measure very small amounts of electrical resistance. A milliohm is 1/1000th of an ohm.

Measuring such a small amount of electrical resistance is accomplished by two probes that each have two terminals. One of the terminals on each probe provides an electrical charge of typically one amp. The other terminal on each probe reads voltage. This allows the tool to determine the resistance in ohms by applying ohms law, which has an exact and constant relationship between volts, amps and ohms. The tool calculates this quickly and accurately.

With an HV system, due to the high amount of volts and amps, even the smallest resistance in the wiring or components of the system is going to cause issues. Being able to accurately identify and read these small amounts of resistance is imperative and is something a standard ohm meter or DVOM simply cannot do. Accurate measurement in milliohms is important to measure bonding of an HV component to the chassis. Only a good bonding allows the insulation guard in the CU to detect insulation arrows.


Having the proper tools for testing and repairing HV systems is important not only for safety but for accurate electrical measurements as well. Having the right tools is the first step when working with HV systems; knowing how to properly use them is the next one.

You May Also Like

Pre-Repair Scans and Post-Repair Scans: Timing is Everything

Without a scan being done before repairs begin and after repairs are complete, the time and energy you’ll need to spend on diagnostics will multiply.

With the ever-increasing amount of electronics being added to vehicles, the importance of pre-repair scans and post-repair scans cannot be stressed enough. 

The number of systems that are networked together in current vehicles is amazing to all of us in the collision repair industry — and this trend does not show any signs of letting up. This has spawned an entirely new breed of technician and launched an industry within an industry. No facet of the repair industry has escaped the changes to the processes required to repair vehicles today. Collision, mechanical, glass and even paintless dent repair have all seen changes — and I could name more. 

Lucid Group Debuts New EV with 516-mile Range

Lucid claims the 2024 Air Grand Touring starting at $109,900 is the longest-range EV available today.

Electric Vehicles and ADAS

Jason Stahl and Jason Wong discuss the similarities and differences in calibrating ADAS systems in EVs vs. ICE vehicles.

Autel Releases the AC Elite G2 Charging Series 

The charger can be used in various settings, such as public commercial parking areas, residential areas, hospitals and service areas.

Tesla Model 3 TPMS Service

Resetting and programming TPMS sensors for a Tesla is a lot like any other vehicle, and the challenge is still the same: keeping the light off.

Other Posts

California Governor Passes on Zero-Emission Aftermarket Conversion Project

Senate Bill 301 aimed at incentivizing the conversion of gas and diesel-powered cars into zero-emission vehicles was vetoed by California Governor Gavin Newsom.

Honda Starts Production on 2025 Honda CR-V Fuel Cell EV

The all-new CR-V e:FCEV is the first production hydrogen FCEV in the U.S. to combine an all-new U.S.-made fuel cell system with plug-in EV charging capability.

Report: Decrease in Used EV Prices Coincides with Increase in Total Loss Claims

Mitchell trends report indicates EV total loss rates were 9.93% and 7.48% in the U.S. and Canada, an increase of approximately 8% from Q4 2023 and 30% from Q3 2023 in both regions.

Crash Champions Expands Luxury and EV Certified Repair Line

Crash Champions has expanded its LUXE | EV Certified repair center network with the acquisition of Mitchell Collision Repair and its two locations in Land O’ Lakes and Belleview, Fla.