In a blog posted a few months back, when discussing test procedures, we mentioned multiple tests that power cords must undergo before being approved by safety agencies. To refresh your memory, some of the tests we talked about were:
- Grounding test
- Continuity test
- Hi-pot test
- Polarity test
- Insulation test
Today we will be discussing another important test to be done – flame rating (or flame resistance) test. Fire safety is a huge concern when working with all different types of wires, cables, and cords. All safety measures should be taken to make sure your power cord meets fire prevention requirements for the device. Underwriters Laboratories (UL) focus specifically on product safety. In order for your power cord to be approved by UL Standards, it must first go through multiple flame tests.
First, we’ll start with an FT2 horizontal flame test for flexible cords. This test includes a series of cycles. In the course of each cycle, a burner flame burns a horizontal sample for 15 seconds then is turned off for an additional 15 seconds. Or it will burn until the sample stops smoking before 15 seconds have passed and must not go beyond 100mm from end to end. This process is repeated 5 times.
Second, there is FT1 vertical flame test. The vertical flame test is performed similarly to the horizontal flame test. The sample must still endure five 15 second burning repetitions. However, the burner flame is at a vertical angle. You will know your sample passed the FT1 vertical test when it doesn’t smoke longer than 60 seconds and with no more than 25% of the paper indicator is burnt.
Lastly, we have the UL VW-1 vertical wire flame test. This test is only performed on the finished cable and also the insulated single conductors within the cable. The VW-1 test is to screen out flammable wires. Once the wire sample is mounted, the ignition source (Bunsen burner) is applied for 15 seconds and then removed. The flame is then reapplied and repeated in the same procedure as the above tests. Once the sample passes this test, it must not burn for more than one minute and must not burn more than 25% of the paper indicator. In addition to passing this test, the cotton at the base of the burner most not catch flame.