Ideas for Improving Hipot Safety
Cirris hipot testers are designed to be as safe as practically possible. Injuries from hipot test equipment are very rare. Still, not every hipot test situation is safe. There are always things you can do to increase the safety and reduce the risk a hipot test might present. This page outlines some ideas you can use to design a safe hipot test environment.
Learn about OSHA
The "Occupational Safety and Health Act of 1970" makes it clear: workplace safety is the responsibility of an employer. Ultimately, employers are held accountable for the safety of their employees. Learn more at: http://www.oshatrain.org/
High voltage is just one of the hazards you might find in your work environment. To reduce the risk from most hazards consider:
Training is important. Employers should make sure everyone knows how to safely do their job. Supervisors should make sure operators are trained to safely use equipment. Operators should only use equipment when they have the proper training. Learn more at: http://www.oshatrain.org/
Processes are Important. Design your production processes to be safe. Change the design as needed to eliminate every hazard possible. Create designs that "fall back" to a safe state when something fails or breaks down.
Preparation is Important. Have safety and emergency response equipment placed in the best possible locations. Make sure people are trained and prepared to respond to emergencies.
How Risk Varies with Current and Voltage:
The National Fire Protection Association's "NFPA 70E Standard for Electrical Safety in the Workplace 2009 Edition" states: "Employer and employees shall be aware of the following hazards:"
For AC Voltages
At 5mA, current is perceptible,
At 10mA person may not be able to let go,
At about 40mA, the shock, if lasting 1 second or longer, may be fatal.
For DC Voltages
At 2mA, current is perceptible,
At 10mA person my not be able to let go.
Voltage in General
Voltages less than 30 Vrms or 42 Vdc are considered safe (except when skin is broken).
Intrinsically Safe Testers
IEC's "EN61010-1, Safety requirements for electrical equipment for measurement, control and laboratory use, April 1993" sets guidelines for safety. If your tester doesn't meet these guidelines then you need to implement a process to keep people way from the high voltage during a test:
- The total charge you can receive in a shock should not exceed 45 uC.
- The total hipot energy should not exceed 350 mJ.
- The total current should not exceed 5 mA peak (3.5 mA rms)
- The fault current should not stay on longer than 10 mS.
Cirris Tester Safety
|1000H, 2000H, 1000H+, Touch 1, 1100H+, CH+||Intrinsically Safe|
|CH2, (w/o xHVSupply)||Intrinsically Safe|
|CH2, (with xHVSupply)||Requires safety interlock|
Georgia State University's Electric Shock Page shows physiological effects of a shock.
Bussman's Safety Basics Book is geared toward power electrical hazards but it is an excellent source of electrical safety information.
High Voltage Safety Issues
For high voltage testing here are some specific ideas to consider:
Know your test equipment. Testers that are "intrinsically safe" have been designed to eliminate the risk of serious harm by carefully limiting the current and energy an operator might be exposed to. In many cases the risk these testers present is small enough you'll find that simply training operators to keep their hands off the cable being tested is all you need to do.
Still, even with intrinsically safe testers you may want to use additional safety measures. People should be aware that the "zap" they receive during a test will almost certainly startle them. They may jump a bit, drop what they are holding, or bump nearby things. You will want to plan your work area to cut down the hazards that might arise from being startled. People with electronic implants (or any medical condition with which they should not be startled) should avoid high voltage testing.
There are high voltage testers that are not intrinsically safe. Those testers are often designed to turn off the high voltage at the first sign of trouble. Injuries with these higher current testers are rare but they can deliver enough current or energy that they might cause harm. If you have a higher current (or higher energy) tester, or you use a mix of high voltage equipment where some are not intrinsically safe you should develop processes that increase operator safety while using the test equipment. You may want to simplify your training by standardizing on using the same safety processes for all your test stations.
Keep away from high voltage. Keeping people away from high voltage is the best way to keep them safe. To keep people away from high voltage consider:
Test in a dedicated area. Clearly designate an area for high voltage testing. Use safety tape and signs to draw attention to the area and warn untrained people to keep out.
Limit access to the test area. Use "crowd control" stanchions with ropes, ribbons, or chains to block access to large assemblies being tested. Place the barriers so you have a four to five foot space around the high voltage area.
Use safety covers to block access to small assemblies being tested.
If you have a mobile test cart for your hipot tester you can design the cart to carry the stanchions, ropes, and signs needed to limit access to a test area.
Alert/inform people nearby. Use signs and lights to indicate when a hipot test is in process. You may be able to automate the high voltage indicators using output signals from your high voltage tester.
Test only when everyone is ready. Many high voltage testers provide for safety switches to let nearby operators control or abort a hipot test. Some of the uses for these switches include:
- Emergency-Stop "E-Stop" Switch. This switch quickly aborts any hipot test and puts the tester into a safe state. Often times just pressing the switch causes it to pop to a locked state that disables the hipot test. To enable the hipot again you have to rotate or pull the switch. You should locate E-Stop switches in easy-to-reach spots nearby high voltage test areas.
- Key "Enable" Switch. To allow a hipot test you insert a key and turn the key to the "Ready to Hipot" state. If you need to work in an test area you can turn the key to the "Disable Hipot" state, pull the key, and carry the key with you. Key switches are a good way to limit testing to only trained personnel.
- Palm Switches. To allow a hipot test an operator must use each hand to hold down a button. The buttons are positioned a safe distance away from the high voltage. As long as the buttons are held down the hipot test will happen. If either switch is released, the hipot test aborts. This type of system works for fast hipot tests but can be impractical for long duration hipot tests.
- Safety Mats. Mats can detect the presence of a person in the test area. The mat can be used to automatically disable or abort the hipot test if someone is near the high voltage (there are OSHA guidelines for mat placement based on speed of travel and distance from high voltage). Mats are most useful when sensing the area right next to the high voltage. Be careful not do design a system where someone can be near high voltage but not detected by the mat.
- Light Curtains. A light current can sense the presence of a person in the test area. The light curtain can automatically disable or abort the hipot test if someone is near high voltage. (There are OSHA guidelines for light curtain placement based on speed of travel and distance from high voltage). Light curtains are most useful when sensing the area right next to the high voltage. Be careful not to design a system where someone can be near high voltage but not be seen by the light curtain.
- Controllers. If you use light curtains or safety mats you will likely need a controller. The controller reads the state of the mat or light curtain and signals when it's safe or unsafe to hipot.
Plan for breakdowns. With any safety switches, mats, and controllers you need to make sure that a common failure leaves the system in the safest possible state. This means if a safety switch wire becomes disconnected, the tester should not allow hipot testing.
Maintenance is Important. When equipment is calibrated or serviced you should verify the correct operation of the safety systems.
An Example Hipot Safety System.
Here is an example of hipot safety system. This system relies on an area being clearly marked and labeled as the "High Voltage Test Area." The test area uses a warning sign, a key switch, and an e-stop switch. An operator must be trained to follow this process:
Nothing is Perfect
This example process is far from perfect. It relies on an operator to carefully follow each step of the process every time. "Remember to put the sign up. Remember to take it down. Watch the test area." There is a lot for an operator to do. Still, the main problem you'll experience with any safety system isn't that an operator forgets something, it is that people judge the risk and take short-cuts when they think the risk is small and the reward is worth it.
Modern hipot test systems are fairly safe so it's easy for people to misjudge the risk in some situations. Make sure everyone knows the risk of each test system. Most test systems will just give you an annoying "zap" but some systems might cause real harm. Reward people who work safely. Don't reward unsafe behavior.
Plan for Trouble
Encourage people to take emergency response training. "ABC's" training (Airway, Breathing, Circulation) can be very helpful should someone receive a shock. Basic "First Aid" training is useful should someone become injured after being startled by high voltage.
Consider getting a "Home Defibrillator" along with a good First Aid kit to help with your emergency response.
Hipot testing is fairly safe but it can present some risk to operators. With training, careful process design, and proper preparation, employers can reduce the risk of harm from high voltage testing.