On a commercial 3 phase service, yes, connect redundant PSUs to separate phases, since each phase on the panel actually corresponds to each phase of the grid.

But if you need enough backup capacity to survive something a multi-state, multi-day blackout [1] that probably gets expensive.

You wouldn't need that for a premium erotic call processor, but a 911 call exchange might, for the portion of their workload they can't pass off to another exchange.

[1] https://en.wikipedia.org/wiki/Northeast_blackout_of_2003

back then running leased lines would've been way too expensive. So what did the kids running the show did? They got wind of a central office in an older part of Budapest have excess capacity so they rented an apartment in the next building and drilled the wall :D no expensive trenching, no expensive equipment to demultiplex landlines, nothing, just a bunch of wires running straight from the CO equipment into retail modems... We had no idea what we were doing, mind you. I was already doing Linux at the time so among the few installers I was the lucky guy who got to install the Internet at a small business who wanted it to be done on a Solaris workstation. That was a fun challenge... Other installs were Trumpet Winsock. The ISP itself ran a custom linux app, you dialed in and landed on a text app or maybe it was Lynx? can't quite remember, it's been 30 years...

In that sense, it is not incorrect about the configuration of utility power because it doesn't say anything about that subject.

The Cold Cranking Amps (pretty much the peak startup current) that they can provide is rather insane. Even my small motorcycle battery provides over 250 CCA.

Double conversion takes power from AC, converts it to DC to charge batteries, takes battery output, and inverts it back to AC. All power drawn from the UPS goes through the battery and inverter stack, and there is no transient/power loss when AC mains are lost. They tend to be more expensive, louder, run hotter, etc.

Line interactive UPSs, on the other hand, tend to be cheaper and are in most cheap consumer products. They take AC mains, convert it to DC, and charge batteries. But AC mains is also connected directly to the output device through switch circuitry that will quickly switch the power source from AC mains to batteries/inverter if power loss is detected.

Reputable UPSs will use pure sine wave inverters for converting DC battery back to AC. Modified sine waves are indeed a lot cheaper but are not suitable for some sensitive equipment.

This has been my experience. There was a corridor between 2 FL counties known for heavy lightning strikes. I serviced small sites that had their IT equip fried (exploded, melted) once or twice a year.

Putting it behind 4-6 decent, consumer-grade surge protectors turned out to be really effective. I was a bit surprised given how lightning can jump over protection during a strike.

To illustrate the area: An XO's home was hit. Char marks lined the walls wherever wiring ran. Pipes burst all over. Nothing plugged in or wired survived. The front door was blow into the street.

His grade school kids were home at the time; they were physically fine.

Although I do think I might have mixed some things up between regular power strips and those outdoors/industrial ones with a long (double/triple digit meter) rollable cable which my dad was a big user of back when he used to work in construction. Basically back when I was little he used to tell me never to plug power tools into a rolled-up “power wheel”, and I think that when I was later heard you shouldn’t daisy chain power strips I must have made that (wrong) connection.

It’s not safe, and it’s expressly forbidden by the NEC, see 11.1.5 below:

> 11.1.5 Extension Cords

> 11.1.5.1

> Extension cords shall be plugged directly into an approved receptacle, power tap, or multiplug adapter and shall, except for approved multiplug extension cords, serve only one portable appliance.

Daisy chaining extension cords is unsafe and not recommended. Only use extension cords that you’ve inspected and are properly rated for the environment (don’t use indoor cords outside, don’t use an outdoor extension cord outdoors unless it’s GFCI protected) and power usage of the device you are powering.

Any time electricity has to flow through a splice or mechanical connection, the possibility of a loose connection causing an arc and subsequent fire exists.

It’s unlikely to happen to you specifically, but it does happen and avoiding electrical fires is a good thing if it can be avoided.

Daisy chaining power strips is also forbidden by the NEC:

> 11.1.4.2

> The relocatable power taps shall be directly connected to a permanently installed receptacle.

As a general rule, I wouldn’t run tools past 50 feet on anything smaller than 12 AWG (and really, 14 AWG is the smallest I’d go for any length; anything smaller isn’t safe for most loads).

Daisy chaining a power bar with it's own circuit breaker can be ideal if it prevents someone from making the mistake of using a circuit in a way that trips a panel breaker, ie preventing your spouse from plugging a vacuum into a circuit shared by several rooms.

If I plug in a heater pulling 10A then sure, the 5A fuse will blow.

Daisy chaining multiways will increase the resistance in the earth wire which could mean you end up with a class 1 device with a fault connecting live to earth which would only punting say 8A to earth due to a high resistance (but then your circuit's RCD would trip with that), but is it a major problem?

With the US system, do you not have wires capable of 3A (say 24 AWG) which you can connect to a normal socket which also takes a 10A vacuum?

If that lamp has a fault where it pulls 6A, what protects the 3A wire -- i.e. there's a fault with your lamp which is plugged into a 15A circuit breaker, and the lamp draws 10A, it wouldn't trip the breaker, and that nice thin 3A lamp cord would melt.

If you have said combination of electrical devices, and if you're assuming we're using an undersized UPS A + the combo of devices, why does the UPS B matter?

If you're going to overload the UPS A you're going to overload the UPS A regardless of UPS B, no? Daisy chaining or not, that doesn't seem like the actual problem to a knee-jerk thinking.

Not necessarily. There are “power strips” which turn one receptacle into several. Then there are sure protectors which are typically built into power strips. So not all power strips are surge protectors but almost all surge protectors are also power strips.

Technically different, but often combined functions. The splitting bit is a "power strip", or sometimes a "power bar". The surge protection is switching off when there's a short or overvoltage in the supply, or other larger than expected power draw.

surge protector = a device with electrical circuitry to help protect angaist surges and spikes.

https://en.wikipedia.org/wiki/Surge_protector

Those little switcher bricks are horribly inefficient: the 15W one I just pulled out of a drawer draws 0.8A on the primary. Realistically you're going to max out a 15A circuit around 20-30 of those, not 96 (1440/15).

I believe some UPS brands might also void parts of your warranty if you use them with a surge protector plugged in.

https://www.apc.com/us/en/faqs/FA158852/

I mean, look for any mention of "slow-roast it for 12 hours" in your favourite web search engine (I notice a couple of those say "overnight", yikes).

The DC will have its own UPS system, but in the event it all goes wrong (which happens more often than I'd like) you probably want something in your cab that can give your equipment notification and time to shut down safely, and provide surge suppression and maybe some level of isolation from the inevitable back-emf caused by the rest of the hall going dark.

Explaining what are the conditions that need to be met for one UPS not to cause issues to another daisy chained off of it would help the reader understand why that's a bad idea.

At least from my experience of owning multiple APC UPS devices, they have a customizable acceptable power quality setting. In such cases setting them to accept the absolute worst quality of power could probably stop them from tripping on bad power input.

No idea if this affects the end devices, however there's probably a reason other than simply extra profit for the default power quality tolerance setting on those devices. Generally they are set to rather low tolerance threshold as the expected usage scenario is servers and other relatively sensitive equipment.

The models I own aren't really the most expensive either, some of the lower end tower models and they still have configurable acceptable power input settings available. Regarding them tripping on bad input and being "absolute worst", I consider this tripping a feature more than an anti-feature, especially as it is user configurable.

EDIT: Also wanted to add that it is actually _preferable_ for UPS to trip as immediately as possible on bad power input. That is the only purpose of such product after all: to protect the devices attached to it from bad or otherwise inadequate power input.

Also, not particularly caring about efficiency currently as we always have more energy than we can use, and I’m currently looking at filling a shipping container with sand as a dump.

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I bought three UPSs, all them used independently; but I had to stop using all of them. They all had a capacitor whine that was driving me crazy.