Low Frequency Complaint

All clocks that are synchronised with the incoming mains frequency will run slow.

It depends on the device design. If it has an input rectifier to create DC, then it probably won't be damaged, unless you overvoltage it. If it has an input transformer or is a AC motor not designed for that frequency, it will not generate the back EMF to prevent excess current flow, and will release it's "magic smoke" forever (assuming it has no protection device).

ignator

transformers will get hot, and maybe even burn up.

There are always "transformers".....grrr.

Cook more chicken.

Your electric cook top will work just fine, but don't believe the clock or you might overcook it.

It depends on a lot of things not specified.

First, if this is the implied AC power distribution frequency then the rotational speed of synchronous motors will be slower. Many transformers in your appliances will get hotter and you will draw more power for the same or less work performed. Some DC power supplies may not be as well regulated with the lower power line frequency. It will also depend greatly on how far below 50 HZ the AC power drops. A drop to 49 HZ may be difficult to notice the above effects with the exception of power grid referenced clocks loosing time. In contrast, a power distribution frequency drop to 30 HZ will produce significant problems to all of your home appliances.

Second, if the low frequency is the low bass notes of a musical instrument (pipe organ, synthesizer, kick drum, etc.) running through your audio amplifier then it will more likely depend on the quality of your speaker or sub-woofer to turn this signal into sound than the electrical engineering of your amplifier. If your speaker is up to this task but your amplifier is not, then a whole lot of damaging power can be dumped into the tweeters of your speakers. Get a more powerful amplifier.

If this low frequency is a sound coming from an appliance (washing machine, vacuum cleaner, etc.) then you may have a mechanical failure that is excessively loading the induction motor of the appliance. Hopefully, nothing is also wrong with the electrical engineering of the appliance and eventually a protection device like a fuse or thermal breaker will prevent a fire from happening.

Utility suppliers are obliged to achieve frequency because of all the above. If the frequency is low, then cause the utility supply company a problem by making a commercial complaint. If enough customers do this, then the problem will be resolved without the customer needing to take any further action.

I'm sure they'll send their ace lineman out in a blink to fix it for him. Here's a pic used at his last safety awards banquet.↓

More importantly what are you using to accurately measure the line frequency?

And also as asked before how far below 50 Hz are you talking?

Motors start to "whine" and get all hot under the collar.