I run a home business and have recently purchased a large HP 800w latex printer that requires a 220v outlet.

The manufacturer of the printer requires there to be no more than 240v going into the printer. I am sitting at 245v and need to lower it or else I void the warranty on this $30k printer and risk causing damage to it. Is there an easy method of wiring in a regulator so that the 220 outlet will be under 240? Another difficulty I am having is that the outlet required for this printer is a Nema 6-20r non locking and no “plug-in” style of voltage regulator has this. Any help is much appreciated.

  • 8
    NEMA 6-20 means this is us/Canada. My guess is this is a device originally designed for Europe 220 and while they configure it with a NEMA plug for US, they're sticking to a strict +/- 10% from original design voltage. Jun 16, 2022 at 13:11
  • 10
    @manassehkatz-Moving2Codidact - Europe has been OK with 207 to 253 volts since 2003. Jun 16, 2022 at 20:21
  • 11
    For $30,000 I'd be expecting some level of customer support, if not installation. My business Xerox MFD cost 8 UK grand, and a guy turned up to install it. Jun 16, 2022 at 21:14
  • 7
    It’s an hp 800w latex printer. Their tech did install it but I was required to have the 220 hooked up and ready for them at install. I neglected to read some of the fine print regarding not exceeding the 240v. The printer runs fine…and it’s very reputable company, HP. The tech did me a solid and completed the install rather than delaying completion due to the voltage. He simply told me that if I ever encountered problems going forward that one of the first things a tech will do is a voltage check and if it’s over the 240 mark that they could easily void my warranty. I just need a simple fix
    – Rodney
    Jun 17, 2022 at 2:45
  • 5
    I live in Europe and my wall socket voltage (nominally 230V) sometimes does read 245V. No equipment is expected to break all the way to at least 230+10% (this is 253V). If it does break, it ends up as a legitimate warranty claim. If something is known to fail between +/-10% around 230V, one is simply not allowed to connect it to the utility grid.
    – fraxinus
    Jun 17, 2022 at 9:19

6 Answers 6


Note that AC power system voltage drifts all over the plane normally due to ordinary changing demands. So saying "it's 245V" - it may be 239V or 247V in another minute when an A/C unit cycles on or off or the town's aluminum smelter starts a batch. This is normal for AC power, and everything is built to tolerate it.

This is a serious case of miscommunication

Assuming this is bona-fide HP product, it will be certified to domestic safety standards for the market it's sold in, e.g. UL in the United States. Part and parcel of those safety and quality standards is the voltage tolerance on the AC supply. The standard requires them to tolerate the entire range of electrical voltages which power companies are permitted to supply, minus some more for voltage drop within a site.

Not optional. You will not get a UL/CSA/BSI listing without proving that.

Therefore whoever told you that you couldn't exceed 240.0 volts is simply incorrect. Or the product is a fake LOL.

If they're legit, what they surely mean is "Do Not Connect This To 277 Volts", which is "the next voltage up" in the North American spectrum. (it's one leg of 480V/3-phase, which is why it's a funny number).

That 220V "thing"

When Edison started out with DC power, it was a nice round 100V/200V. However Edison wanted to increase the voltage to increase system capacity, so several "voltage bumps" were planned. Edison had light bulb makers make light bulbs for 105V. Then after a few months Edison bumped system voltage to 105V/210V. Then had light bulb makers make 110V bulbs, and bumped system voltage to 110V/220V.

And that's when Edison lost the "War of the Currents" and Westinghouse took over all the legacy Edison systems. The year is 1892.

AC made it possible to sell power to the masses, so a huge publicity campaign ran, promoting "110 / 220 volts". It is now a fixture of popular culture, and that is why you call it "220V" informally.

That is wrong. Since 1892, power companies did three more bumps, now putting us at 120/240V "officially" but leaning toward 125/250V with the tolerances mentioned in the earlier link.

Further, EU is 230 volts -10/+6% (207V-244V).
UK and Australia are 230V +10/-6% (216V-253V).
So clearly, the salesman who told you the voltage spec is very confused. I would talk to someone knowledgeable.

If they indeed can't tolerate more than 240.0 volts, demand they put that in writing. That will force the person claiming it to actually check their facts.

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – BMitch
    Jun 18, 2022 at 20:22

Get a UPS.

Has several advantages:

  1. meets safety standards and insurance cf anything you build.

  2. protects from surges, lightning strikes etc

  3. easily replaced when needed instead of some "magic" black box that no-one else understands (which they might disconnect by accident...

  4. also protects from low voltages aka "brown-outs" at least until the battery is discharged.

Edit based on a comment:

Make sure you get a UPS, not an SPS. The classic difference between an SPS (Standby Power Supply) which has a switching time in milliseconds which is not good for desktop compuiters as they reboot.

While a UPS (Uninteruptible Power Supply) which is separating incoming and outgoing power ALL the time and has no switching time so it is fine for computers, printers etc.

  • 3
    The catch is that there are UPSes and there are UPSes. The former are standby battery packs with surge protection. When in normal range they keep the battery charged and work like a surge protector. When out of range they switch to battery and provide perfect power for a limited time. The latter are double-conversion - they fully process the power all the time. That is what you need here to take 245 to a setpoint of 220. But they are a lot more expensive than standby UPSes. Jun 16, 2022 at 14:13
  • 4
    But UPS has become the common term for anything that provides battery backup. Look at APC - the vast majority of their low-end product (not sure about the high-end as I have not looked at it lately) are labeled UPS but are really SPS. And for the average user the $ saving is worth it. Jun 16, 2022 at 14:30
  • 3
    UPS is too darned imprecise. People throw down that term for a huge variety of specific tasks they think UPS's do, and while some UPS's might do that, others don't. The only thing a UPS can be said to do is battery backup. OP hasn't asked for that. Jun 16, 2022 at 19:40
  • 16
    Most manufactuers use UPS to refer to anything. What you are referring to as SPS is usually called a "line interactive" UPS. The always on type are called either "online UPS" or "double conversion UPS"
    – Grant
    Jun 16, 2022 at 22:59
  • 2
    @manassehkatz-Moving2Codidact Exactly. The ATX standard requires a minimal hold-up time of 17 ms at full rated power (in other words, a compliant PSU needs to keep going at least this long after you pull the plug). That should be more than enough for any line-interactive UPS to switch over, so if the computer reboots, you have a crappy PSU. And given that you rarely run at max rated power, a decent PSU is able to keep going for much longer. (Unfortunately, decent PSUs are a minority on the market nowadays.)
    – TooTea
    Jun 18, 2022 at 19:54

You can use a ferroresonant transformer such as the Sola CVS series. I’ve been using these for voltage regulation since 1976 and they are amazing. They consist of a big, heavy transformer and a bunch of capacitors. They regulate their AC output voltage within +/- 1% no matter what you feed it, even through power surges, brownouts and lightning strikes. They contain no batteries so they don’t help in a blackout, but they purify and condition the power for sensitive electronics. They have no moving parts, no relays, switches or displays – basically bulletproof. They come in various sizes up to 7.5 KVA and it’s best to get one sized appropriately for the load, not excessively oversized.

Note that ferroresonant transformers are not particularly power efficient, typically about 90%. The wasted power is dissipated as heat. They can also be noisy with a 60 cycle hum, but they can be mounted in an out-of-the-way location.

I only have experience with 120V and 240V units, but I’m sure if you contact the company they can connect you with a 220V model intended for the European market. You would be able to feed it with 120, 208 or 240 volts.

  • I used to use and sell a line of UPSes that were based on ferroresonant transformers. Great devices, but big, heavy and expensive. As standby UPSes got better and cheaper, the ferroresonant-based UPSes largely disappeared, at least from the low-end (home, small business) market. Jun 16, 2022 at 17:30

From the datasheet:

Input voltage (auto ranging) 200-240 V two wires and PE; 50/60 Hz (±3 Hz); two power cords; 16 A max per power cord

My theory:

  • Split to two circuits to allow for an easier European install. Because in the US the answer would be to install a 240V 40A circuit, but they didn't allow for that.
  • Range based on allowing for 208V (because that is common enough in the US in commercial usage) to 240V (which covers most stuff). But clearly if they rounded up to 250V the way they rounded down to 200V, it would take care of OP's 245V problem and similar problems elsewhere.

Both of those design decisions may be cost-cutting measures - i.e., cheaper to design power circuits that use less power (2 small instead of 1 large) and cheaper to design for a smaller input voltage range. Yet that doesn't really make sense for a high-end product.

And this is a very high-end product. Not your typical office printer. So those places that are installing it will figure out a way to provide the right power. Much as print shops have done for the last 100 years when they've installed big presses.

But in the end, buyer beware. If the specs said 200V - 250V and the equipment came in with a nameplate showing 200V - 240V then it would be a shouting match with HP. But everything matches, even if it is unusual.


If the extra 5V bothers you, its actually amazingly simple to safely and reliably reduce it a bit. You just need a small bucking transformer. Check this: https://blueglowelectronics.files.wordpress.com/2018/11/bucking-transformer-slides.pdf

The first 6 pages are a primer on how transfomers work. Page 7 is where they show how to implement a bucking transformer.

Note a 'bucking transformer' is not a special kind of transformer. It's a standard off-the-shelf transformer, but the way you wire it in series with your existing load is what turns it into a 'bucking transformer'.

You should be able to build one for about $20, maybe less if you have a suitable transformer kicking around.

  • 3
    Note that the DIY solutions probably aren't suited to this size of load, unless you use quite a large transformer. OK. you only have to carry the full current in the secondary, but most are still only rated to a few A and this needs 16A. Choose your transformer wisely (they exist, for fairly big audio amps)
    – Chris H
    Jun 17, 2022 at 9:37

The printer is certified by the CSA

After some digging into the UL issue I found this informational sheet from HP which says (under Certification)

Safety IEC 60950-1+A1+A2 compliant; IEC 62368-1 compliant; USA and Canada (CSA listed);

So it's not UL or ETL certified but what is CSA? This site says

The CSA acronym once stood for the Canadian Standards Association but is not a private testing body. As the name implies, this is a Canada-based group that offers certification for mechanical and electrical products, as well as any general product that carries a high amount of user risk. In 1992, OSHA officials accredited the CSA, deeming it an NRTL alongside the UL.

Why CSA and not UL?

Unlike the UL Mark, a CSA-Listed designation holds value all around the world, not only in its country of origin. For a product to receive this prestigious label, it must also pass extensive tests that align with standards from the following certifying bodies:

  • American National Standards Institute (ANSI)
  • UL
  • NSF International (Formerly the National Sanitation Foundation)

This product is sold around the world, so a broader certification makes sense. It is UL confirming, even if UL didn't certify it.

What does the printer need?

The printer does say 200-240v. And you're buying the US version so their preparation manual says you'll get a NEMA 6-20P plug, which is a 240v plug

NEMA 6-20P plug

You didn't specify where you're getting 245v readings. I'm going to assume this is a main panel reading. Since this machine will need not one but two 240v circuits, you're going to want to subpanel this (two double-20amp circuit breakers, or four slots). Your printer needs 32 amps (2x 16 amp plugs) and I'll assume your printer is 100ft away from the panel. Let's go with 8 gauge aluminum (up to 40 amps). According to this voltage drop calculator, you'd wind up with 238 volts pulling 32 amps (disclaimer: I am not sure if split phase changes this).

As such, the natural voltage drop may be enough to drop you below 240v by the time it reaches your printer. I would consult an electrician about this to verify that my thinking here is correct.

  • 2
    It’s 245v at the electrical outlets, not the breaker. I have two 20amp breakers, one for each of the required nema 6-20 outlets. They both read above the 240v.
    – Rodney
    Jun 17, 2022 at 20:24
  • But presumably 245V at the outlets without the printer connected so drawing no current therefore no voltage drop. However, while there's no error in the calculations in the answer, there's a big flaw in the assumptions: there's no way the printer will be drawing full current all the time; at idle it's like to be drawing less than 1A, with next to no voltage drop. So at idle it will still see more than the stated max voltage
    – Chris H
    Jun 18, 2022 at 20:20

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