Thermostats destroyed by outage in several homes

Several airplanes had big problems because all their engines were the same model and serviced at the same time. ETOPS rules help with the servicing problem.

This is a 24 volt thermostat. Most 24 volt thermostats run off a transformer. Transformers have some amount of ability to damp surges, but they will also pass through the voltage they receive. So if your 240V spiked to 2000V, your 24V spiked to 200V. It sounds like their electronics section was not up to the task, and they all had the same problem for the same reason.

And that just happened to be the point of failure. I'm sure your planned community has all the same microwaves, all the same refrigerators, all the same dishwashers, all the same bathroom fans - it could have been any of those instead.

Yes, whole-house surge protectors are a thing. They come in a variety of form factors.

- Some slip under the electric meter.
- Some are built into new panels (not least, whole house surges are now Code).
- Some hang off a knockout in your main panel.
- Some have the form-factor of a circuit breaker and snap into 2 breaker spaces.

Which one is right for you depends on your situation - a flush-mount panel won't favor a knockout approach, a full panel won't favor a 2 breaker spaces approach, an existing panel you don't want to replace will cross off a "part of new panel" approach.


They don't "operate like" a circuit breaker. They just sit there and absorb surges.

kimnjerry said:

Greetings.
Two days ago, a power surge from an electrical storm destroyed at least 5 thermostats in our planned community neighborhood of 60 homes. In each instance, the thermostat was a Nexia/Trane model 624 (or similar), which was installed with the furnace by the same HVAC contractor (since fired by the builder) when the homes were built 6-7 years ago. No other electrical devices were affected by this power surge. I had the unit replaced yesterday by a Trane tech with the upgraded model.

I would appreciate answers the following (which the HVAC tech was not able to provide):
1. Why was the power surge damage limited to thermostats and no other devices?
2. Could this brand/model of thermostat be more susceptible to power surge than others? Is six years the expected life of this unit?
3. Is there a device/strategy (e.g., whole house surge protector) which will prevent the recurrence of this event in the future? Does a surge protector operate like a master circuit breaker? What should we look for in such a device and its cost?

We greatly appreciate your assistance.

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1. Why was the power surge damage limited to thermostats and no other devices?

Thermostats are low voltage devices. They rely on being protected by the transformer/power filter of the device sourcing the power and therefore typically have less protection than a device that plugs into the wall.

2. Could this brand/model of thermostat be more susceptible to power surge than others? Is six years the expected life of this unit?

Of course it could...or it could be average. Without doing a teardown of a bunch of thermostats and analyzing their power protection circuits no one would know. You'd also have to know how they actually failed to make an accurate assessment of their durability.

Most electronics are designed for a 10 year life. But most can live much longer as long as they are in a controlled environment. Lifespan doesn't take into account catastrophic damage like a power surge beyond what the unit was designed to handle. That will fail a unit at 1 day of use just as likely as 10 years of use.


3. Is there a device/strategy (e.g., whole house surge protector) which will prevent the recurrence of this event in the future? Does a surge protector operate like a master circuit breaker? What should we look for in such a device and its cost?[/I

Yes a whole home surge protector will help prevent this. However, if you are only looking at preventing your thermostat from failing...the ROI is not going to be very good.