Big news coming from Sound United in 2023!

[lc6]

I would suggest you read the actual rule in the NEC code book for completeness.

Buy NFPA 70, National Electrical Code (NEC) Handbook

Order the NFPA 70, National Electrical Code Handbook. The Handbook explains the NEC fully and is available in various print and digital formats.

catalog.nfpa.org

I found this: Sizing a Circuit Breaker

"NEC sizing rules. Secs. 210-22(c), 220-3(a), 220-10(b), and 384-16(c) all relate to the sizing rules for overcurrent protective devices (OCPDs). The first three all specify the same requirement:

OCPD size = 100% of noncontinuous load + 125% of continuous load.

Sec. 384-16(c) has the same requirement, except that it's stated in terms of the loading of the OCPD. This rule states that an OCPD can be loaded to only 80% of its rating for continuous loads. Remember that 80% is the inverse of 125% (0.80 = 1 ÷ 1.25) and, as such, the rules are indeed identical in their end requirement.

Read the rule closely; the 125% sizing of the OCPD (or 80% loading) is only applicable when continuous loads are involved. CBs and other OCPDs can be sized at 100% of their rating for noncontinuous load applications."

So you are generally correct, but that does not take the power factor into account (which Gene claimed to be 0.75 for a typical AVR). Try this calculator with sample 1,000 W loads of various non-continuous types, and a 120 V circuit single-phase AC, and see how that affects CB size. With the PF=0.75, the CB is 1.33x that with PF=1, all other things being equal. What do you think the safety factor (SF) should be for AVRs? Higher than the 75% for AC or even 100% for a welders (an even more non-continuous load)?

 

[Chromatischism]

Oh boy. In the electrical jargon, service = circuit.

Not here in the states. Electrical service = to the house. Don't exceed the panel's capacity. Each circuit to a room is a different matter and depends on the breaker used for the circuit. You can overload one circuit and not affect the service at the panel.

 

[Chromatischism]

As to the 80% rule, again that's for a continuous load that does not apply to audio devices such as avrs, and power amps. You can in fact exceed the 1440, even 1800 W for a short duration. As an extreme example, motors and transformers can draw many time, 20 times or even higher of its rated continuous load for a few cycles on start-up, that's why the light bulbs in the house may dim when you first turn on a big power amp, or an AVR, or the furnace fan etc., but you obviously know that already..

And we don't even need extreme examples. Everyday hair blow dryers say 1875w on the side of them. Wonder what that means?

 

[peng]

OK, so how many 3800H-type devices is it safe to plug into a single 15 A circuit? Please provide detailed calculations.

No problem with one for sure. Denon does not provide the information for detailed calculations and I think it is because there is really no standard for all to follow. You can do such calculations with light bulbs, electric heaters, even motors etc., that can be expected to draw relatively constant current under a load condition. For audio devices the draw will vary continuously with the input signal.

Gene's write up I linked earlier is as good as any because he said he got the info from Sound United that they follow IEC 62368-1 electrical safety standard for rating power, specifically Annex B for operating conditions and Annex E for test conditions.

To answer your question, the only thing I can do in this case is rely on the power consumption figure provided by Denon. For the 3800, that's 660 W, assuming a conservative power factor of 0.75, current = 660/120/.75 = 7.33 A. I wouldn't plug two into a 15 A circuit for sure, but as a licensed EE, I would consider it in compliance to do so, because an AVR will not be drawing 7.33 A continuously for normal use. The average draw would depend on the specific usage of the individual user, but for most people it will likely be well below 7 A each.

 

[lc6]

I think you may be looking at the information (such as your linked calculator) that is not very relevant for the topic discussed. Power transformers, including those for audio amp applications are generally higher than 90%, more like 95%.

An example:

https://www.farnell.com/datasheets/2279593.pdf

This one is specified as 94% typ.

The smaller one such as those <300 VA may be less efficient but should still be at or near 90%, E-I core or toroidal.

That's just the transformer, the power supply efficiency overall will obviously be a little lower because of other loss however small.
As to the 80% rule, again that's for a continuous load that does not apply to audio devices such as avrs, and power amps. You can in fact exceed the 1440, even 1800 W for a short duration. As an extreme example, motors and transformers can draw many time, 20 times or even higher of its rated continuous load for a few cycles on start-up, that's why the light bulbs in the house may dim when you first turn on a big power amp, or an AVR, or the furnace fan etc., but you obviously know that already..

If you are referring to the 92% efficiency figure which I assumed for the sake of a quick calculation, it was for the entire unregulated non-switching power supply (i.e. incl. transformer, rectifier, block caps and related circuitry) and not just the transformer (whose efficiency is likely in the mid- to upper-90s%).

The dimmed halogen lights in my HT room, connected to the same 15 A circuit that powers my old AVR, actually go out every time the AVR is powered on (unfortunately, unlike in the previous home, I do not have a dedicated 20 A line for the A/V equipment). So, yes, I do realize the CB will not trip with a massive but short overload.

 

[lc6]

And we don't even need extreme examples. Everyday hair blow dryers say 1875w on the side of them. Wonder what that means?

Per @peng and NEC rules, a 15 A circuit supports up to 120 V * 15 A * 1.25 = 2,250 W continuous power, so 1,875 W hair dryer (unless operated non-continously) is less than that.

 

[Mnyb]

Consider the crest factor of music for a while even when playing loud your average single figure watts in the main channels peaks may still clip the amp .

The highest load any of these amps will ever see in practice is when someone bench them into a dummy load with a continuous sine wave.

 

[lc6]

No problem with one for sure. Denon does not provide the information for detailed calculations and I think it is because there is really no standard for all to follow. You can do such calculations with light bulbs, electric heaters, even motors etc., that can be expected to draw relatively constant current under a load condition. For audio devices the draw will vary continuously with the input signal.

Gene's write up I linked earlier is as good as any because he said he got the info from Sound United that they follow IEC 62368-1 electrical safety standard for rating power, specifically Annex B for operating conditions and Annex E for test conditions.

To answer your question, the only thing I can do in this case is rely on the power consumption figure provided by Denon. For the 3800, that's 660 W, assuming a conservative power factor of 0.75, current = 660/120/.75 = 7.33 A. I wouldn't plug two into a 15 A circuit for sure, but as a licensed EE, I would consider it in compliance to do so, because an AVR will not be drawing 7.33 A continuously for normal use. The average draw would depend on the specific usage of the individual user, but for most people it will likely be well below 7 A each.

That is all fine, but the 660 W figure is allegedly based on the IEC testing at only 1/8th the nominal power. As an unlicensed EE who built his first amp before Gene was born, I'd rather be conservative with power circuits.

Anyway, FedEx keeps screwing up the delivery of my new 3800H, which supposedly is sitting in their local "destination facility" for the second day in a row, and their system keeps spewing out all sorts of excuses and imaginary delivery time windows. But at least I used all that time to pull the furniture out and replace my old power strip (prompted by @amirm 's "near accident" experience with the PS Audio box). Once I have the AVR, and the power meter with min/max capture arrives as well, I can post some concrete data on power consumption.

 

[Chromatischism]

Didn't know they were available for purchase already. They really waited until manufacturing was done and inventory was adequate before even making the announcement. I look forward to seeing them in the wild.

 

[HarmonicTHD]

Didn't know they were available for purchase already. They really waited until manufacturing was done and inventory was adequate before even making the announcement. I look forward to seeing them in the wild.

Yep. It’s called pipeline fill.

 

[lc6]

Didn't know they were available for purchase already. They really waited until manufacturing was done and inventory was adequate before even making the announcement. I look forward to seeing them in the wild.

Yep. It’s called pipeline fill.

I believe Denon first made the 3800H available for purchase on their website late on Thursday 9/22. I could not place the order then, despite creating an account -- the system kept claiming that "the combination of your city, state and zip code is invalid" (???) But when I logged in again next day, it still remembered my shopping cart and allowed me to automatically proceed to the payment step (and yes, the aforementioned bug was still there when I tried to go back to the first step to double-check the free expedited shipping). By Monday 9/26, Denon declared it was "out of stock" on the 3800H. I was not willing to wait till March '23 to try the 4800H. And, despite the otherwise fine looks, I find the design of the "porthole" on the Marantz Cinema models ugly and useless (even though in his review Robinson claimed it could be electrically disabled).

 

[peng]

So you are generally correct, but that does not take the power factor into account (which Gene claimed to be 0.75 for a typical AVR). Try this calculator with sample 1,000 W loads of various non-continuous types, and a 120 V circuit single-phase AC, and see how that affects CB size. With the PF=0.75, the CB is 1.33x that with PF=1, all other things being equal. What do you think the safety factor (SF) should be for AVRs? Higher than the 75% for AC or even 100% for a welders (an even more non-continuous load)?

0.75 pf is very a very reasonable assumption, though a little on the conservative side imo (a good thing for safety). I would avoid using SF on things related to electrical safety codes because SF will typically mean service factor, not safety factor.

If you are asking about safety factor consideration for an AVR load, I don't have an answer. You can understand why if you consider some examples:

A) Someone using an AVR to power 5 speakers with 92 dB/W/m sensitivity, sitting 3 meters and listening to 10 dB below reference:
Power required = about 3.5 W, assuming eff at such low output level = 15%, power consumption = 3.5/.12 = 23.3 W, current = 23.3/120/.75 = 0.324 A, or 5X.324 = 1.62 A

B) Someone using the same AVR to power 5 speakers with 89 dB/W/m, same seating distance, same listening spl:
Power required = 7 W, assuming the same efficiency, Power consumption = 7 W/0.15 = 46.67 W, current = 46.67/120/.75 = 0.519 A, or 5X.519 = 2.6 A

C) Somone using the same AVR for the same conditions but listens to reference level (this means 105 dB peak with just one speaker):
Power required = 175 W, Power consumption would then be about 175/120/0.8/0.8 = 2.28 A, or 5X2.28 = 11.4 A

So if you consider scenario C) above, for some who always listen at reference level, at 3 meters distance using 89 dB/W/m speakers in 5 channel stereo mode, current draw will still be below 12 A (80% of 15 A).

But it depends so much on the individual's speakers and listening habit so it doesn't seem practical to consider "safety factor". Besides, it is an audio device that is protected by not only the circuit breaker, but also the device's protective system that nowadays almost always offer protection against short circuit current, overcurrent, thermal overall current, dc offset, and potentially more. Also, unlike baseboard heaters, fan, pump motors, audio devices naturally don't get as much attention from the regulatory authorities, and are not even mentioned specifically in electrical code books.

Think about his, we even have a thread on ASR named "FTC may drop the amplifier rules", that tells you how keen the regulatory authorities are on audio devices. I guess to them they are low risk, never resulted in much major accidents (may be the odd small fires), injuries etc..

FTC may drop amplifier rules

https://www.stereophile.com/content/ftc-proposes-eliminating-its-amplifier-rule Seems strange and short sighted to drop the whole rule rather than modify it. Then again it appears there is pretty much zero enforcement. Still hard to see how this benefits the consumer. Heck they need a new rule...

www.audiosciencereview.com

 

[wseroyer]

You’re forgetting that “signature” Marantz sound

the Marantz sound is cutting off half of the human hearing spectrum apparently.

 

[wseroyer]

Noteworthy is that the X4000 series and up can play Nintendo 64 out to your HDMI-connected TV, whereas the X3000 series can not.

THIS!

 

[peng]

Per @peng and NEC rules, a 15 A circuit supports up to 120 V * 15 A * 1.25 = 2,250 W continuous power, so 1,875 W hair dryer (unless operated non-continously) is less than that.

No, I never said such a thing.

 

[Doodski]

120 V * 15 A * 1.25 = 2,250 W

What is the 1.25 stuff. I don't get that part.

 

[peng]

If you are referring to the 92% efficiency figure which I assumed for the sake of a quick calculation, it was for the entire unregulated non-switching power supply (i.e. incl. transformer, rectifier, block caps and related circuitry) and not just the transformer (whose efficiency is likely in the mid- to upper-90s%).

The dimmed halogen lights in my HT room, connected to the same 15 A circuit that powers my old AVR, actually go out every time the AVR is powered on (unfortunately, unlike in the previous home, I do not have a dedicated 20 A line for the A/V equipment). So, yes, I do realize the CB will not trip with a massive but short overload.

It isn't a "If", I was clear in my post, even attached a data sheet that is for the transformer only.

 

[peng]

What is the 1.25 stuff. I don't get that part.

I think he might have referred to what was said in the article he linked, that talked about sizing circuit breaker, that is not the same as sizing the feeder cable for the load. Two different, though somewhat related topics. For example, the feeder may be rated for a continuous load that draws 12 A, the circuit breaker could be sized (or rated) for up to 1.25X12, or 15 A. Distinction needs to be made between "non continuous load" and "continuous load". AVRs are clearly not considered "continuous load", I think we can all agree on that..

 

[lc6]

It isn't a "If", I was clear in my post, even attached a data sheet that is for the transformer only.

Well, so where in my post did I say that the transformer was less efficient than the 94% sample figure you quoted to prove me wrong?

 

[lc6]

What is the 1.25 stuff. I don't get that part.

From the NEC rules for continuous loads (e.g. a hair dryer, unless "pulsed" for fun); see my earlier post.