Hacker News new | past | comments | ask | show | jobs | submit login

> > I had an electrician run two 20A Dual Function (AFCI+GFCI) circuits

> Don't do this. This is a terrible idea if you intend to run a UPS.

Can you please elaborate why someone shouldn't do that? (not who you responded to, I'm just curious about the reasoning behind that statement)




UPS's are notorious for nuisance tripping GFCI's due to the extensive power filtering they usually have inside. It may not happen right away but is dependent on how 'dirty' your power is and on how sensitive your particular brand of GFCI is. All it may take is a neighbour using his AC or power saw and it could generate a spike large enough to knock your system offline (UPS filters spike to ground, leakage current trips GFCI which needs to be manually reset, UPS runs out of battery because no one's home to restore power).

This advice is specific to the US & Canada where GFCI's are calibrated to trip at 5 mA. In the UK, their RCD's trip at 30 mA so it's less likely.

If you read the fine print for your UPS and/or GFCI they will say not to use them together.

What about AFCI's? Well they are basically nuisance devices by design and most electricians hate them. Do not use unless absolutely necessary by code.

The difficulty comes into play because UPS's, servers, etc are essentially industrial equipment while the code is written for such common residential usages as plugging in a lamp (where a dog will chew on the cord, a good way to start a fire hence a perceived need for AFCI protection.)

What if you're stuck because you want to locate your UPS and equipment in an area where GFCI's are required (like a residential basement)? Well I won't tell you what to do in your own home but I'm sure you can devise a creative solution. :)


AFCI's feel like NEC's attempt to create tons of service calls under the guise of "safety". And eventually seems like they will be required for new builds everywhere as areas adopt the newer codes that require them slathered everywhere.

Of course its "for safety" but of course these breakers are famous for false tripping and causing expensive service calls.

anecdote: In my case, small server rack, on circuit a with an AFCI - since "bedroom". No problem.

Until washing machine on circuit b (no AFCI) runs, then trips circuit a's AFCI. Repeatedly, every time(debug on the breaker a returns ArcFault detection reason too). So... either a) don't wash your clothes b) don't have tech or c) quietly violate the code.

Indeed electrician quietly suggested(after a bunch of triage) I swap out the breaker with a normal one. But of course he wasn't allowed to do that... lol

Been here a decade - nary an issue since - so clearly the usual case of nuisance tripping and nothing more.

I suspect the switching power supplies were close to annoying the ACFI, and a beefy motor on an adjacent circuit was enough to push it over the line. Incidentally, swapped UPSes, power supplies(quality Seasonic), etc and nothing improved.


The issues with UPS products tripping GFCI breakers is due to leakage current that is out of spec for the GFCI circuit, this is almost always caused by the load attached to the UPS, not the UPS itself. While most UPS manufacturers do recommend against connecting it to a GFCI outlet, AFCI is required in all new construction for all circuits and GFCI is required for many circuits, including any circuits in basement areas which necessitates a dual function circuit. Since the original thread is about APC, even though I don't use their products, here's what they have to say on the topic: https://www.apc.com/us/en/faqs/FA369034/

FWIW, running my server and network equipment never caused the breaker to trip erroneously while I was still living there. I sold the house when I moved cross-country for unrelated reasons so I can't say what happened afterwards, but my setup was installed according to code and functioned perfectly fine. I used quality UPS and decent quality network and server equipment. Cheap stuff may be farther out of spec and have more issues with leakage current.


> AFCI is required in all new construction for all circuits

This is absolutely false.

Though I'm sure you gave your electrician an earful and he did whatever was needed to keep his customer satisfied and happily took your money. Hope those $50 hospital-grade outlets are working well.


From: https://www.nyeia.com/where-arc-fault-circuit-interrupter-af...

"For new construction, Section 210.12 (A) of the National Electrical Code states that all 120-volt, single-phase, 15- and 20-ampere branch circuits supplying all outlets must be Arc-Fault Circuit-Interrupter protected in the following dwelling unit locations:

Kitchens, Family Rooms, Dining Rooms, Living Rooms, Parlors, Libraries, Dens, Bedrooms, Sunrooms, Recreation Rooms, Closets, Hallways, Laundry Areas, or Similar Rooms or Areas.

Even though it is not listed, this includes finished basements because once the basement is finished, the area becomes one of the rooms listed above.

Adding to the confusion, most people assume that outlets are only plugs or receptacles. However, outlets is defined in Article 100 of the National Electrical Code as “A point on the wiring system at which current is taken to supply utilization equipment”. That means that the requirements for AFCI protection is required in the areas stated above at all 120-volt, single-phase, 15- and 20-amp receptacles, lighting fixtures, switches, smoke alarms, dishwashers, refrigerators, and so on."

So, yes, /technically/ it's not /all/ circuits, however please identify for me a room that's commonly found in a residential property that's not a Kitchen, Family Room, Living Room, Dining Room, Bedroom, Hallway, Laundry Area, Closet or "similar rooms or areas"? Look at the floor plan of most residential properties in the United States and every room noted on that floor plan is on the list. So /technically/ it's not /all/ circuits, so I was /technically/ incorrect, in practice what I said is absolutely true.

Maybe a bit less snark from you and a bit more reading comprehension and you wouldn't come off as such a dick?


You conveniently left out that few jurisdictions are on the 2020 NEC code cycle when this provision was introduced. New codes do not get adopted everywhere immediately. Your town or city needs to adopt it and that can take many years. So, no, not all new construction.




Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: