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I would like to remove an existing cable from the breaker panel, that feeds a single home run outlet, and wire it to a consumer UPS that I will locate near the panel, through a junction box.

Questions:

  1. To join the power cord from the UPS to the junction box can I put a NEMA 5-15 inlet on the box and use a consumer power cord?
  2. Instead of a NEMA inlet (a) could I do it with an IEC C14 inlet? (b) could I just insert a consumer power cord into the box with strain relief and splice wires inside the box? This would all be on the surface near the breaker panel, nothing inside walls but also no conduits.
  3. As a further optional step, if the junction box additionally is fed raw power and I add a switch to bypass the UPS, can I just switch the hot or must the neutrals be switched too? The grounds? I assume the UPS input and output grounds are bonded but I don't know about the neutrals. The inlet hot would never be connected to the raw power hot, but is there still any unacceptable danger in this arrangement?

enter image description here

This question is instructive but the answers focus on the practicality of running new cable from room to room. My situation is to use existing, to-code, wiring from the basement to the room, and adds the idea of switching to raw power.

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    Now I'm wondering what the actual point of this is. Specifically (a) a typical consumer UPS provides automatic transfer with no "gap" - doing all of this means that even if you anticipate power loss, you will still end up with a brief power loss when you flip the switch (because it must be break-before-make in a basic setup like this) and (b) a typical consumer UPS provides relatively short-term power (a few minutes to perhaps a couple of hours, depending on power usage).
    – manassehkatz-Moving 2 Codidact
    Mar 31, 2021 at 20:22
  • Yeah, I was wondering about the Why, as well. All my UPSs do automatic switching when the wall power drops so the computer attached to it never notices that the power goes out. It's that drop in power that causes file damage and, potentially, hardware damage. Having to manually flip a switch defeats the purpose of a UPS. If, OTOH, the goal is to simply have a battery backup for a non-computer system, then by all means, have at! (But I'm still not sure why it needs to be wired into the wall like this)
    – FreeMan
    Apr 1, 2021 at 16:36
  • Why is a good question but it devolves into why do I want a UPS at all. I tried to keep that aspect out of my question. It's more like, if a UPS exists that does all the things I want at a reasonable cost, how might I wire it up. I'm glad I kept the question narrow and got an answer.
    – jay613
    Apr 1, 2021 at 16:45
  • Why THIS arrangement: I have my modem, router, and other network gear in the basement near the panel, I have a couple of Wireless Access Points elsewhere and my home office in another room (not the basement). The modem, router, and WAPs won't survive an outage more than about half a second and take minutes to recover. The office has enough electronics to be worth protecting from dirty power esp from the generator. Putting aside that I'm not sure how to get all the things I want from a UPS, if I could get them, this arrangement provides it to all the desired devices throughout the house.
    – jay613
    Apr 1, 2021 at 16:53

3 Answers 3

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Yes.

You can run an isolated electrical line, using normal in-wall wiring methods, from a single inlet to outlets.

The inlet will need to be in the NEMA family. A C13 inlet won't cut it for at least 2 reasons off the top of my head: first it lacks the necessary ampacity, and second it is voltage-agnostic, and the inlet needs to be keyed to reject a power source of the wrong voltage.

As far as having a built-in switch, same rules apply as for a generator. You must have exactly one neutral-ground bond in the entire system. Not zero, not two. ("two" is its own special kind of 'bad'). If the power source bonds neutral and ground, then you must switch neutral. If it does not, then you must not.

The best bet is to switch neutral, but not bond neutral around the switch - have the isolated circuit draw neutral only from the switch. These types of switches are expensive, so I'd just do cord-and-plug myself.

You would never have a reason to switch safety ground.

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    Should probably clarify (since OP asked, so apparently not obvious, though I think it is once you think about the way a UPS works) that neutral must be switched together with hot in a setup such as this one.
    – manassehkatz-Moving 2 Codidact
    Mar 30, 2021 at 19:46
  • @manassehkatz yeah, probably best in most scenarios.
    – Harper - Reinstate Monica
    Mar 30, 2021 at 20:03
  • I accept the advice that neutral must be switched and that doing so is prohibitively expensive ($45 for something off-label that will fit in a standard box, $100 to $200 for anything with "transfer" in its name). So no switch. That just means that UPS maintenance requires a brief outage.
    – jay613
    Mar 30, 2021 at 21:49
  • I do not accept however that this is obvious. On the contrary. I don't see documentation for any of the mass market consumer UPSs about whether the output is isolated, whether the neutral passes through, or wether the output neutral and ground are bonded. Some of them have very hazy descriptions about how battery-backed sockets may or may not be fed directly by the input when it is alive. Because of this lack of information I would keep the output completely isolated.
    – jay613
    Mar 30, 2021 at 22:00
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    @jay613 I have a hunch you're shopping on Amazon because I had the same experience there. Amazon opened its site to third party sellers, and has basically turned into eBay. Anytime the Chinese make a cheapo or counterfeit thing, 1000 different sellers glut Amazon with listings upranked by fake reviews, and just bury any listings for legitimate product. I don't have the patience to dig down to page 44 lol. Best advice: don't buy electrical on Amazon. Better shops will have the junction-box kind.
    – Harper - Reinstate Monica
    Mar 31, 2021 at 3:49
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Here I'm planning a nice implementation of the advice in the accepted answer. This plan provides raw and UPS power to the basement location and also through existing house wiring to a den outlet. It includes a UPS bypass switch allowing for UPS service.

The trick was to find a DPDT switch that would switch live and neutral at reasonable cost, and an inlet, both of which would fit in a standard multigang box with some feasible cover arrangement. I could have done it with sectional box covers for about the same price but this plan uses a standard 4-gang Decora plate. It's easier to build and looks better.

It's all limited to 15A, which works perfectly for what I'm planning.

The key is two devices I found:

  • The Leviton 5686-2W switch. This is a 15A DPDT switch. It's intended use is to switch 2-pole power between two devices, but it works here. And this specific model is in Decora profile and costs less than $50.
  • The Midlite 4642-W recessed inlet. It's intended use is to connect a knee-height outlet to a shoulder-height TV routed through a power conditioner at the lower level. But it's perfect here because it completes the project without requiring a special cover plate.

The Midlite inlet requires a deep box so I've included a Raco 698, and I'll also replace the den outlet with a red one and put a switch guard over the switch.

The outstanding problem is to pick a UPS that does all the things I want at reasonable cost. Probably time for some illusions to be shattered.

Here's the design: enter image description here

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    All UPSes suck; most especially all remotely affordable UPSes suck. Some of the lithium battery items work well, but "reasonable cost" is not presently compatible with lithium batteries. With Lead Acid batteries, UPSes are very good at killing the battery, rather than having intelligent and capable charge management. Best I can suggest for consumer-grade UPS is to put the UPS and a much larger battery or batteries into a safe enclosure, as the much larger battery is harder for the UPS to kill (but you can't leave the teminals exposed, due to the way most UPSes work.)
    – Ecnerwal
    Mar 31, 2021 at 20:37
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    Because UPS's are made for emergencies only, and the battery is going to die anyway of old age in 3-5 years, so if you're having 1-2 outages a year, there's no harm in bottoming the battery 3-10 times in its useful life. If you had an outage a week, then yeah.
    – Harper - Reinstate Monica
    Mar 31, 2021 at 21:58
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    One of the other problems is that typical (and I am talking name-brand) UPSes will often fail in a mode where they try to switch to battery and can't because the battery isn't up to the task. If it is a true power outage then that's life. If it is a < 1 second outage, it can sometimes result in a computer losing power (because of the recovery time for the UPS to switch back to AC) when if there was no UPS at all, the computer power supply would ride through the power glitch.
    – manassehkatz-Moving 2 Codidact
    Mar 31, 2021 at 22:11
  • Keep in mind, the transit time of the switch is not zero.
    – Harper - Reinstate Monica
    Mar 31, 2021 at 22:38
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    Basically, you can (pretty much have to) build that from "solar" parts. 300W TSW inverter, way more battery than you think you'll need unless you go for lithium, and a decent/intelligent charger. At which point throwing some actual solar panels at it begins to make sense.
    – Ecnerwal
    Apr 1, 2021 at 16:01
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You could install one of these upstream of the outlet: https://ezgeneratorswitch.com

I am not affiliated with them in any way.

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