Proper wiring of Test Switches for Protection Devices

[DTR2011]

Can someone please explain to me why some designers continue to wire relay test switches "backwards"?

Example...

I am reviewing a DC schematic, where the +DC goes to the top (odd number ) of an FT type switch, then out the blade, then to the LOR contacts. This appears to only function as an isolation device and provides no convenient means of actually testing the contact operation, without getting into terminal blocks in the panel.

I am specifically griping about ABB/Westinghouse type FT test switches, which in my experience have a correct and incorrect way of applying. (Top of switch (odd numbers) goes to relay, bottom (Even numbers) goes to system).

I have heard from some designers that there is concern about a live blade. Any other valid concerns?

 

[davidbeach]

Odd numbers to the relay. End of story.

 

[rasevskii]

Concerns about "live blades" on test switches must be for those who not ever have actually worked on equipment in the field...Must everything be made so supersafe that even the most incompetent clod cannot get hurt. Or is this some new Arc Flash concern...

Only competent technicians and engineers should ever be allowed anyways near hands-on work in the power environment.

rasevskii

 

[dpc]

I think it is done based on the power wiring maxim of not having the open blade energized combined with a lack of understanding of the way the test switch is used.

I have always found test switch wiring to be confusing - especially the current switches, because I'm not a testing guy. There is one drawing from ABB I have found that shows how things are connected to a typical relay, but in general the documentation from test switch vendors is terrible, IMO. Without some prior examples to work from or an experience hand to consult, it's pretty difficult to figure out test switch wiring based solely on the manufacturer's information. Test switches always make me feel stupid for some reason (and no, that is not my drawing!).







David Castor

http://www.cvoes.com