Last edit: 16/05/2023
THE QUESTION
Manufacturers of industrial control panels to be installed in North America often don’t know which electrical tests to submit their products to.
What are the mandatory electrical tests for Industrial Control Panels to be installed in USA or Canada ?
WHAT TESTS ARE REQUIRED?
Effective ground continuity of exposed conductive parts of the assembly: this verification must be performed using a resistance measuring instrument able to provide at least 10 A (AC or DC). A current flows among each ground and the outer protective conductor (PE) terminal: the measured resistance must not exceed 0.1 Ω. The continuity test ensures that the cabinet's bonding system is properly designed.
Dielectric voltage withstand test: a test voltage of 1000 V ac + 2 Vi must be applied for 60 seconds, without interruption, between each phase and the ground bar, to industrial control panels, typically operating at 480 V in North America, where Vi is the nominal input voltage. With Vi = 480 V the test voltage is 1960 V for 60 seconds. The dielectric voltage withstand test can be performed applying a DC voltage instead of an AC voltage, as long as the voltage used is 1.414 times the values just above.
The dielectric voltage withstand test ensures the minimum insulation level and might reveal defects in the insulation (mechanical damage) or the presence of a foreign material (such as water) that can fill the insulation.
CONSIDERATIONS
Are Control Panel Manufacturers obliged to perform these tests in order to sell to North America?
The answer is that these tests are not mandatory for industrial control panels to be installed in the USA and that, on the other hand, only the dielectric voltage withstand test is required for industrial control panels to be installed in Canada.
As a mattter of fact, UL 508A, the U.S. Standard for Industrial Control Panels, does not require any of these tests.
NFPA 79, the U.S. Electrical Standard for Industrial Machinery, mentions the effective ground continuity of exposed conductive parts (0.1 Ω limit) and the Voltage Test, but it does not consider them as mandatory.
C22.2 N° 14, the Canadian Standard equivalent to UL 508A, on the other hand, requires the industrial control panel manufacturer to submit his product to the the dielectric voltage withstand test only.
Moreover, from 6th January 2022, C22.2 N° 14 will not be anymore the Canadian reference for the Panel Shop program and it will be replaced by C22.2 N° 286. In the latter, Article E.1.2 (Clause 1.2) allows the manufacturer to test the industrial control panel at a voltage 20% higher (than the one previously specified) for 1 second, instead of 60 seconds. Given a nominal voltage of 480 V, instead of a 1960 V test for 60 seconds, it will be possible to test at 1960 + 0.2 x 1960 Vac, corresponding to 2352 Vac for 1 second.