Proper Test Switch Wiring 1

[Tyler F]

We are looking to install test switches at one of our facilities, and I thought that we would need to install the test switches in such a way to avoid tripping anything downstream while testing. After doing some digging into drawings from our other plants, it looks like all test switches are used to create an open in the relay contact circuits. Which is correct, and is there a standard used for installing test switches?

 

[9wearSuave]

We wire test switches on both positive and negative side of the relay output contacts only. You don't want to wire a test switch directly inline to the breaker trip coils for obvious reasons. Any testing of the breaker trip circuit needs to be done when the breaker is isolated from the system.

 

[thermionic1]

IN North America, the ABB/Westinghouse FT test switch is very popular for a variety of reasons, including that it's the same mechanism that was used on the electrotechnical relays of the past. The FT switch has a companion test paddle (separate source) that many relay techs carry several at all times. The FT switch can be used without a paddle, which is also a benefit. For CT circuits, many consider this a superior design, as one can see the shorting mechanism operate.

(ABB FT) Test switches must be wired so that the odd numbered terminals go to the relay and the even numbered to the 'system'. Failure to wire the switch this way defeats many of the benefits of having a switch. Wiring the switch with the even terminals to the relay may be seen as a safety precaution from a design standpoint, but actually makes things much more dangerous for the relay tech.

On output contacts, it's desirable to have both sides of the contact accessible at the test switch. The more positive side should be on the left. Inputs to the relay should also come through a test switch. Having the relay control power through switches also allows access to the battery for relay inputs. Most relay techs use the ABB test paddle when testing the relay, but this also provides isolation for the live blades.

I've seen modern installations with the GE XLA test switch and shake my head. These devices require insertion of 'tuning fork' shorting devices for CT circuits. There is one correct way to make these connections and multiple incorrect ways.

 

[System Protection]

SecuControl Test Switches are gaining popularity. Similar to the FT but with no exposed metal. You can test with just banana jacks or use an optional test jack.