Hybrid safety

Jan. 1, 2020
The world around us is changing fast, and the automotive world is changing with it. The greater part of this dynamic is due to tougher government regulations regarding safety, emissions, and fuel economy. Customer expectations play a role as well; wh

There are certain precautions you must take when working on today's hybrids.

underhood hybrid hybrid service hybrid safety repair shop training technician training automotive aftermarket
The world around us is changing fast, and the automotive world is changing with it. The greater part of this dynamic is because of tougher government regulations regarding safety, emissions and fuel economy. Also, society is demanding more from its automobiles, and these escalating demands are creating a shift in the technologies that appear in our service bays.

Vehicle electrification is a technology trend that sputtered in its infancy but now is growing unabated. Most independent repair shops already have some experience with this as hybrid-electric vehicles (HEVs) have been around for more than a decade. While the number of available HEV models is increasing steadily, we are on the cusp of seeing pure electric vehicles (EVs) as well. There are common threads between these cars and their gasoline-powered cousins, but some profound differences exist.

For decades, technicians have had to deal only with low voltages (less than 30 volts) when servicing most automotive electrical systems. These systems only required minimal precautions on the part of the technician, and their threat to personal safety was relatively low. However, the introduction of the HEV (and the upcoming EVs) has added a new dimension to our daily practice as they have electrical systems that operate at anywhere from 42 to 650 volts.

Starting With Attitude

Before we go any further, we need to make something abundantly clear. When servicing high-voltage (HV) automotive systems, be absolutely certain to follow the manufacturer's recommended service procedures. It should be said, however, that safe and effective HEV service also is going to require an attitude adjustment. We all get into a rush sometimes and bypass steps we shouldn't when working on cars. Maybe you've paid the price once or twice for taking this path.

In the case of HV system service, the price is too high to justify skipping steps. Use the correct equipment and follow the recommended procedures at all times. We have a saying here in Alaska: "There are old pilots, and there are bold pilots, but there are no old bold pilots." You can live to be an old technician if you decide that you won't compromise on the safety issue.


If one is to take this safety stuff seriously, it is helpful to understand the impact that electricity has on the human body. What is most interesting here is that it is the current, not the voltage that actually does the damage. Keep in mind that voltage is electrical pressure; it is what pushes electrons through a conductor. Without sufficient voltage, very little current will flow. However, the potential for higher current to flow becomes greater as voltage increases.

The human body is not a good conductor, but it is a conductor nonetheless. If voltage is applied to flesh, damage will be done in proportion to the amount of current that flows through it and for how long. While as little as 1 mA (milliamp or 1/1,000th ampere) will cause a faint tingle, a mere 9 mA can cause a painful shock and a loss of muscle control. As current increases, the consequences also escalate:

  • 50 mA can cause severe muscle contractions, and may stop breathing as well as preventing the victim from letting go.
  • 1 to 5 amperes will cause nerve damage and abnormal heart rhythm.
  • 10 amperes will cause severe burns, cardiac arrest and probable death.

Depending on the individual, death can occur when as little as 100 mA passes through the body for as little as two seconds. Based on this information, we need to do whatever is necessary to prevent electric current from flowing through our bodies. This will start with wearing the correct personal protective equipment or PPE.

Become an Insulator

When working on high-voltage (HV) automotive electrical systems, it is critical to examine everything you are wearing and ask yourself a basic question: Is this item helping to make me a conductor or an insulator? Start your personal audit by removing all jewelry such as rings, watch bands and necklaces. You should also consider items that are less obvious. How about a metal belt buckle? Think carefully and remove any other clothing items that could compromise your safety in a high-voltage environment.

By default, safety glasses should be at the top of your list for high-voltage Personal Protective Equipment (PPE). It doesn't matter what type of automotive work you are doing, you should be wearing your safety glasses. The complaints and arguments against them are well-known: I can't see with these on, they don't stay on the bridge of my nose, they make me look like a geek, etc. Just buy a pair of approved safety glasses that fit you and get over it! If necessary, get a prescription set if you don't like the kind that goes over regular eye glasses. If you wear them long enough in the work environment, it will get to the point that you feel naked without them. Besides, there are plenty of stylish designs available that may even improve your image.

Footwear is another critical PPE item. Just like safety glasses, you should be wearing safety shoes whenever you are working in the automotive environment. Beyond protecting your toes, you need to examine your footwear for its electrical qualities. Remember, we are doing everything we can to make ourselves an insulator. Check to be sure your shoes have rubber soles that prevent you from becoming a path to ground.

HV Glove Care, Feeding

Let's talk about gloves. This may be the most important aspect of your personal protective equipment plan. Certified Class 0 linesman gloves must be worn whenever doing work on HV automotive electrical systems. While these might seem expensive, keep in mind that the correct gloves are specially constructed and certified by a lab to protect the wearer at up to 1,000 volts AC. While this is more than enough protection for work on HEVs, it will be compromised if the glove gets damaged.
To prevent damage, rubber linesman gloves should be used with leather outers. They also should be carefully inspected before each use, including lightly inflating the glove to look for perforations. Recent designs have made inspection easier by coloring the glove orange on the outside and blue on the inside. If a glove is damaged, discard it and replace it with a new set.

Electrical Measurement

Another aspect of HV system service is the ability to make safe and accurate voltage measurements. Now is not the time to be using a multimeter of questionable pedigree; look for appropriate certifications and capabilities. A meter should be approved by both the UL (Underwriters Laboratories) and CSA (Canadian Standards Association). The meter also should be certified to a minimum of CAT III at 1,000 volts. Test leads should have ratings similar to the meter and be in good condition.
When you are ready to make a measurement, start by confirming that the meter is working correctly. Take a DC volts measurement at the vehicle's auxiliary (12 volt) battery first, and then continue your work once you know for sure that the meter is OK. Nothing like reading 0 volts at an HV voltage source because the meter has a blown fuse! This brings up another key point: NEVER assume that a high-voltage system is discharged. Always double-check the system with a functioning multimeter before concluding that it is safe to service.


Automotive electrical systems are classified by voltage level. This would include:

  • Low voltage – less than 30 volts DC
  • Intermediate voltage – 30 to 60 volts DC
  • High voltage – over 60 volts DC.
Low voltage would cover most conventional electrical systems. Any wiring in this category likely would be in black conduit and requires limited precautions on the part of the technician. The next classification is intermediate voltage, which covers mild hybrids and the electric power assist steering system on some strong hybrids.
Intermediate voltage wiring generally is blue, but can be yellow in some applications. An orange conduit is an indication of high voltage, usually found on medium and strong hybrids or pure EVs. Take extra care when working around this wiring, especially underneath the car where it is possible for misplaced lift arms to damage them.

Editors note: Be absolutely sure to follow the manufacturer's recommended service procedures whenever servicing high-voltage automotive electrical systems.

The blanket rule when working with any HV automotive electrical system is to turn the vehicle off and take the key out of the ignition. Then, take the key and secure it so it won't be put into the ignition without others being notified. Once the car has been shut off and the key is secured, OEM-recommended procedures then can be followed to further disable the system before service work commences.

Wrapping Up

Respect is a key word when servicing HV automotive electrical systems. You know that the system is capable of causing severe injury or death, but you need to prepare yourself with the correct equipment, knowledge and, most of all, attitude. Never work alone, never assume the system is discharged, never skip steps and you can go home safe at the end of the day to those who care most about you.

Tony Martin is an associate professor of automotive technology at the University of Alaska Southeast in Juneau, Alaska. He holds Canadian Interprovincial status as a Journeyman Heavy Duty Equipment Mechanic. He also has 19 ASE certifications, including CMAT, CMTT, L1 and L2.

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