Double click from transfer switch before engaging generator

[TuroPaldea]

Tonight’s outage gave me a small surprise when my generator transfer switch didn’t behave exactly like it usually does. Instead of the normal single click, it clicked twice before engaging the load. Everything powered up fine and there were no alarms, but it stood out enough that I made a mental note.

It’s one of the colder evenings we’ve had this December, so temperature is the main variable that’s different. I’m trying to figure out if this is a normal cold related delay or a sign that something is starting to wear or stick.

have you worked with transfer switches? like during winter conditions... have you noticed extra clicks or delays before engagement and how did you handle it?

 

[GotouTensei]

That would catch my attention too, even if everything powered up fine. In winter, I usually watch for patterns more than one off behavior. If it only shows up during cold starts and not during warmer tests, it might be temperature related. If it starts clicking multiple times or delaying longer, that’s when I’d dig deeper.

 

[PGB1]

I don't have a lot of experience with small, residential units Large units from 150 kW to in the multi-megawatt & high voltage, I have much, much experience. Perhaps the below doesn't apply to small units, but is worth considering:

What you experienced is called "Engagement Hesitation". It is common.

Causes:
Sometimes in cold, moisture condenses on the sliding surfaces of contactors and freezes. Often the magnetic force of the coil has trouble overcoming this hoar frost. You will then hear the contactor make a sound (click in your case, clunk on larger ones), then it finally completes its movement by breaking through the hoar frost.

Another cause is that during the preventative maintenance cycle the contactor does not move. (On purpose). The slides get a bit dirty or stiff. Sometimes insects build nests in the slides. This may cause some hesitation & a double or triple or more click the next time it's needed.

If this happened once and the load was small, nothing bad happened. Check if your voltage on the load side is good.
If it happens often or if the load is large, (or if there was buzzing between clicks) some arcing might occur and pit or burn the contact points. You will have low voltage.

Try This: Have someone simulate a power failure by opening the disconnect on the utility side while you listen at the generator for a good, solid single click.
It is also good to force the contactor to move every few months by doing the above.

Also, if you hear it trying to engage but failing (buzzing sound usually), a tap with a rubber mallet often frees it & lets the contactor complete its cycle.

Hope This Helps,
Paul

 

[Alan]

If it powered cleanly with no alarms, I’d treat it as “watch it, don’t panic.” Next outage, see if it repeats and note the timing. If you can, listen for whether it’s the contactor pulling in twice or the switch doing a brief “test” pull then the real transfer. Cold can also make a relay a little sluggish.