Mikey brings up a good point talking about miners being resold possibly multiple times: You included the point of "free electricity" in the OP. The only reason that should matter is if you are getting used & older, less power efficient, hardware. Point being the question for you that should bring is, "the hardware is x years old, how much longer will it last?"

Are you looking at using/getting old to very old gear?

Why would you even care?
However, to answer:
  Using OEM firmware - no.
  Using 3rd party firmware, because they periodically mine to a special DEV fee pool -- maybe.

Any particular reason you are asking these security-related questions? Are you mining in a country where it is illegal? If you are - BAD idea!

Free electricity is irrelevant and by design miners are intended to run 24x7x365.

That said, it depends on the make and model. If kept reasonably clean and ran in reasonable temperatures the Avalons from Canaan can easily last many many years. I have over a dozen A841's from 2018 that are still running perfectly with zero maintenance (but in clean environment).

Miners from Bitmain are more of a crapshoot. I have a R4 from 2017 that still runs flawlessly and 2 others that died in about 2 years. Early s9's were near bullet-proof up to around batch-9, later ones up to a 15-20% failure rate within 2-3 years OR LESS.

That I do not know so you will most likely have to do a search for it. Most of what I've seen about VPN's suggests that you will need to setup a pc/laptop to act as a bridge running the VPN and connect the miners to that.

Don't you mean maximum power per-rack? As a max it would make more sense because as you said, 4.8kva in a full rack is a lot for just powering servers and switches. But, a 42U high rack could easily pull over 20kva if filled with miner hardware.

My guess is that the data centers were forced to not only look at distributing that kind of dense power but also how to get rid of the heat generated. Most were designed and built to be data centers -- not mining farms.

edit: Got a PM and yes it is a minimum power per-rack. In short, it seems many clients op-sec requirements are demanding that only the clients and providers hardware be in a rack with no other (different) clients hardware allowed. That led to unused rack space which folks were filling with miners.

Moving back to on-topic, I'm hoping for -5.69% as that is my guess in the .01BTC "who can guess the closest" giveaway Kano is running in his Discord channel for folks mining at his pool

If living in an area that gets cold during the winter an Avalon A841 works great as a space heater. Throttled down to 9THs and fan limited to 40% it's nice and quiet while pulling about 750w.

Of course there is also Sidehacks R606 which has threads here as well.

Bet the cable was a charger cable. They lack the wires used for data transfer. The USB cable MUST be one that supports both charging and data transfer.

Ran into this a couple times when running Avalons and using cables I have laying around.

The miners could care less about a brownout, they will run as normal until the PSU cuts off and will restart the the PSU comes back online.

The PSU's are a different story: Running at a very low line voltage (below their nominal rated minimum voltage, usually around 190VAC) puts a lot of stress on their input circuits and will no doubt shorten their life. When the line voltage drops below a certain minimum the PSU *should* shut off but that feature is up to whoever makes the PSU.

Please read the stickied post at the top of this area... Mainly point-3:For BTC, trying to mine with anything other than an ASIC-based miner is beyond useless even when using free or stolen power.

For some alt crapcoins - maybe, but that discussion would belong in the altcoin areas not here in the Bitcoin area.

That is why I suggested to try running through a VPN as a test. If the country is having the ISP's block mining why the Bitmain miners can connect is odd but it's possible something about the Avalons trips the barriers while the Bitmain ones do not.

Oh, instead of opening another new thread about it, you can just move this thread to the other area. At the bottom-left of the webpage for any topic create is a button "Move Topic" to do that.

HagssFIN went through Canaan's training a couple years ago. His A10 review/troubleshooting guide starts here.

Definitely weird. Again with all 12 going down it is highly unlikely something broke in all 12 of them at the same time. Something is hinky about their connection to the network.

Question: From the A10 on up the Avalons support running 1 network cable between the router/switch and then daisy-chaining more miners onto that 1 connection by using both LAN ports on the miner. eg, router > miner1 > miner2 > miner3 > etc. Are you doing that or does each miner have its own cable running to the router/switch? Folks have had issues with doing the daisy-chain configuration.

Is it possible for you to move 1 miner to a different location and try it from a different network connection?

Correct - if you are using Compassmining. You should change the title of this thread to reflect that vs sounding like a blanket statement about all BTC mining.
Find a place with cheaper hosting fees and it is a different story. As has been said numerous times in the past, you need to find cheap power (and/or hosting where power is cheap). Only then is there a good chance of profitability.

Considering you say all 12 miners are offline odds are this is not a problem with the miner hardware. Either your router does not work (can you access the internet from a PC connected to it?) or it is possible your internet provider is blocking them. Can you run through a VPN to bypass any filtering your ISP might be doing?

If you are talking about a different miner on the planet mining to a different node/pool that is an entirely different matter. Is it possible they may get the same work at the same time? Sure.

It is also bloody unlikely because the work sent to them is completely random and is defined by the node they get the work from. Not only can/will the work ID's be different but the underlying data itself will be as well because the node/pool picks what Tx's to process and again that results in different work being sent. Also keep in mind that even the fastest hardware cannot sequentially process all possible values before someone, somewhere, finds a block and forces new work to be started. 2³² is a huge, huge number...

Sorry to be bouncing you around the Forum but since you are inquiring about the nuts and bolts of how mining works you might want to move this discussion to the Development & Technical area of the Forum where you will get more eyeballs looking at your questions.

No. As explained before the software feeding work to a miner DOES NOT ALLOW THAT. All miners pointed at the same pool or private node get different work unless you screw with the code on your experimental node. If a pool does it (sends same work to multiple miners) then whoever operates it is a idiot.

All solo mining means is that you and you alone get the block reward regardless of you mining to your own private node or a pool allowing solo mode such as Kano's or -ck's. The work mechanisms sending/receiving work are the same as mining at a regular pool. The difference between Solo vs shared (pool) mining is more of just an accounting thing. This Help topic from Kano's site may help you understand.

As Kano and I have said in 2 other threads you started: NO!
Solo or otherwise the pool software assigns different ID's and therefore work to the miners. If you are talking about their speed - still no because a miner's hashrate varies quite a bit as it is running. Even any given single miner will have different hash rates and results each time it gets new work.

The only possible way multiple miners would have overlapping results would be if you setup your own BTC node for experimenting and hacked it to not assign different ID's. Which by the way would be a terrible thing to do on the BTC main net. If you decide to screw around like that - use TestNet, that is what it is for...

When buying a transformer, avoid anything called a "travel converter " or "international travel converter" that look like this. Been there, done that and they are CRAP which will burn out very quickly. They are not able to sustain anything near their supposed ratings.

Only use ones that are either commercial or industrial grade such as these as they are properly designed and made to deliver rated power 24x7x365.

AwesomeMiner https://bitcointalk.org/index.php?topic=676942.msg7668661#msg7668661 I've used it for several years for monitoring my farm and it can do all you ask about.