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My home was built in 2014; California code requires hardwired smoke detectors. I also have a 10kW Generac whole-house standby generator. Whenever I lose power, every smoke alarm in the house gets activated...I contacted Kidde to find out why, and the technician responded that hardwired detectors CANNOT be used with a standby generator, because the generator produces voltage spikes that can damage detectors. He said I either need to have the detectors on a circuit not connected to the generator, or use non-hardwired detectors that utilize wi-fi for interconnection. Problem is the 1st solution means the detectors wouldn't operate in a power outage (NOT good!), and the 2nd solution won't meet code, which requires detectors be hardwired. My electrician says he's never heard of hardwired detectors not being able to be used if one has a backup generator, and I haven't been able to find anything about that on the 'Net either. Can anyone shed any light on this or offer suggestions?

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    Do your smoke detectors have battery backup? If not, then I'd replace them with ones that do have battery backup since you apparently live in an area prone to power failures, and even if your generator can power the smoke alarms, you probably don't want to count on it. – Johnny Sep 1 '17 at 20:45
  • Are the smoke alarms actually going off, or are they chirping (low battery/trouble)? – ThreePhaseEel Sep 1 '17 at 22:16
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This is certainly a new one for me also. I'm not sure this is a problem with the smoke detector or the manufacturer's technical support. Let's start with his statement of the generator spiking. Technically a 10 kw generator can only spike to 10 kw and I doubt the governor would let it get that high. There is more of a chance you get a sag (low voltage) or a stall (loss of hertz) than a spike. Also if what he told you is true I would think that that would be listed in a tech report somewhere. What I am trying to figure out is how would any of this effect the electronics of a smoke detector?

The only thing I can think of is maybe some of the exhaust is getting into the house and setting off the detector.

I would suggest contacting a the generators tech support, or a competitor's tech support and repeat what the manufacturer's tech support said and see what they have to say. Also if you contact the manufacturer's tech support again I would ask for an engineer and see if he could give me something better than what you were originally told or ask for some documentation. Because if what the tech has told you is true, I would say they have a very bad problem.

Hope this helps.

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California also requires battery backup for hardwired detectors. So you could separate that circuit from the generator safely.

Most consumer level power generators do not produce the same quality of power as the power company. Total harmonic distortion (THD) may be much higher. Generac is a good company, but they don't specify a THD on the data sheet for their 11/10kW Guardian Series generators.

I find that regular loss of power sets off hardwired detectors. I just consider it a power failure alarm and move on. The switchover from the power company to the backup generator will never be 100% smooth at this price level.

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I've never heard about the "no generator" thing, but I do know that low batteries will cause this dilemna. Replace all the batteries, in all the detectors.

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