Electrical safety testing has been one of the most misunderstood, and misapplied functions performed by manufacturing companies. Manufacturers in the know are very aware that such testing, while required to meet safety standards, can also yield information that leads to important product improvements.
Hipot safety testing is the most important type of electrical test. What type of Hipot testing is a manufacturer required to do? The correct answer is: whatever your customer requires. There is no federal law requiring electrical safety compliance. But, even without any specific customer requirement, a manufacturer will definitely want to do safety checks for their own well-being and peace of mind.
Types of Hipot Tests
There are two types of hipot tests: type testing (design verification) and production/customer qualification testing. There are a number of standards delineating how the tests should be performed, but two stand out as preferred – and these two cover just about all of what the other standards require.
A key standard for electrical household appliances is UL/IEC 60335, which defines safety standards at a system level. IEC 60730, referenced by 60335, addresses the electronic controls in appliances. 60335 includes tests for leakage current at operating temperature, electric strength, and AC ground bond.
One of the main standards is IEC60950-1. It applies to ac-dc power supplies found in information technology (IT) and industrial equipment and requires products to pass an input-to-output isolation test of 3 kV ac.
Production hipot testing of a product should not exceed 1,500 V ac, or its DC-rectified equivalent of 2,121 V dc, from input to output or input to ground. Generally, a product that operates at voltages of 120-240 V ac is tested at 1,000 V plus two times the operating voltage. Using this rule, a 120 V ac powered unit would be tested at 1,240 V ac.
It would be wise to have a versatile hipot test system, with both ac and dc test voltages, to be able to meet varying customer requirements.
Hipot Testing Overview
A dielectric voltage-withstand test, usually referred to as a hipot test, stresses the insulation of a product beyond what it would encounter during normal operation to be certain of the unit’s safety, even under uncommon circumstances. High voltage is applied from the mains input lines to the chassis of the product. The hipot test is usually a 100% production line test and can be performed using either an AC or a DC voltage.
A ground continuity test assures the ground wire of a product is intact. A low voltage is applied from the chassis of the product to the ground pin to determine if the appropriate amount of current flows.
The insulation resistance test is used to verify the product’s insulation by applying an AC or DC voltage and measuring the resulting leakage current.
Electrical products have been broken down into two categories for safety testing: Class I and Class II. A Class I product is terminated in a 3-pronged line cord with an earth ground connection to chassis. Class II products, also known as double-insulated products, have no earth ground connection to chassis since the chassis itself is usually made of some insulating material such as plastic.
A Test Setup That Covers All the Bases
Having a great test setup will save time and frustration, especially in production testing, and provide consistent, documented measurements. The recently introduced Hypot Series 3805, 3865, 3870, 3880 instruments from Associated Research are examples of test systems that offer just about all the features you could ask for and come in a small and easy-to-operate unit.
All versions of Hypot have full step-by-step programmability that is made easy to configure with the help of a large touch screen. The series also provides easy measurement traceability with on-board data storage and a front panel USB port for loading or off-loading data or setups. This port can also be used for remote program design. A second USB port allows operators to use a barcode reader to scan any product and automatically bring in its test setup for more time savings.
These new instruments are 30% smaller and now weigh in at just 12 lbs. (except the 3880), about half the weight of the previous versions.
Measurements have a programmable maximum current and the operator will see an error if this setting is exceeded. The units feature automatic operator shock protection. SmartGFIA hardware interlock is included on the PLC Remote - a relay on the high voltage output opens when the interlock signal is disabled ensuring safer operation of the instrument. The units also have a dual palm remote switch option for extended operator safety. The model 3870 includes insulation resistance check capability with readings to 50 GΩ.
AC and DC outputs are ramped up at a programmable rate to avoid stresses on the unit under test. The operator touch panel instructions can be shown in any of eight languages – English, Traditional Chinese, Simplified Chinese, Spanish, German, French, Portuguese, and Turkish. In addition, a custom ID and password ensure security.
Also available to compliment hipot testing is the Hyamp 3240A 40 AAC/DC Ground Bond Tester. The ground bond test verifies that the ground conductor of a product has a high enough current capacity to handle any fault current to ground. The 3240 has a voltage output from 3.00 to 8.00 VAC or VDC, giving the user the flexibility to establish a high limit with either resistance or voltage settings as called out by various safety standards.
It also has an Auto-Detect function. When a Hyamp instrument is connected to a Hypot instrument it automatically detects this and sets the PLC Remote output to on. The user is then prompted to set sequential or simultaneous operation for easy system setup.