Understanding FT Style Test Switches

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Understanding FT Style Test Switches

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Before we isolate the relay from the system and connect our test-set to the relay, we should take a closer look at Westinghouse/ABB/States FT test switches to make sure everyone understands how they work, and what they are supposed to do. This video will look at the different styles of FT switches along with some installation problems that I’ve spotted in the past and recreated in our hands-on relay classes. We have all skill levels in our hands-on classes. Guess how many students found the problems on their own? Guess how many spotted the problem after they were told that there was a problem?

No student has spotted the problems we discuss here. Maybe you’ll be the first in a future hands-on class after watching this video?

 

Don’t use FT Switches? Describe the switches you use in the comments below and we’ll see if we can make a video about the style you use.

 

Click “Mark Complete” below after watching the video so you can keep track of your progress.

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hi it work till I got to this section it stopped working, I will restart my pc and log back in to see if it change.

thanks

It is important to always wire the top of a test switch to a relay. The corresponding test plugs that are made for those switches are designed to only hit the odd number poles. If you inject 208/120V into your Doble 6150 Voltage outputs you are going to have a very bad day.

Chris Werstiuk (Administrator) October 19, 2017 at 1:11 pm

Thanks for the comment, but you should ALWAY CHECK FIRST! The CTs must always come in the bottom because that’s where the shorting happens. The PT’s can be wired to the top or bottom depending on the owner’s standards. It actually considered to be “safer” if the PTs are connected to the top because the blades will be dead. If you always wire to the top of the test switch automatically, you are going to have a bad day someday when you blow up your test-set.

Outstanding explanation. Much appreciated!

Chris Werstiuk (Administrator) December 30, 2020 at 7:59 am

Thanks!

Chris, ABB has it in their manual https://library.e.abb.com/public/237bcda3f2b7eb14c1257b130056ca70/FT1%20DB41-077April2010_2.pdf on page 5 in bold wording that all PT’s and CT’s should be connected to bottom (even) terminals.

Chris Werstiuk (Administrator) April 2, 2021 at 8:27 am

As I mention in the video, I agree that everyone should follow those instructions. However, some sites think that the “safety” of PTs and DC voltages on the top is more important and will connect the PTs to the top terminals. Assuming everyone makes their connections the same way can blow up you test-set, which happened several times to customers when I worked at Manta.

The CTs must ALWAYS be connected to the bottom terminals, otherwise the internal shorting connections are useless and the CTs will open-circuit when they are supposed to be shorted.

Chris, it was mentioned in the video above that if you’re using a test paddle to connect to currents coming in bottom and voltages in the top that there would be problems. In this scenario, how do you recommend mitigating this if one is used to only using a test paddle?
Can you use alligator clips to clip onto the bottom side of knife blade switches for your voltages and just use currents on the test paddle or do you recommend some other solution? Thank you

Chris Werstiuk (Administrator) August 25, 2021 at 10:38 am

The solution you describe is pretty much your only option if you want to use a test paddle and the voltages come in the top.

Thanks for the question!

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