AC Power Question

clearthink599 posts01-23-2019 2:56pm


noromance"if using two runs off two breakers, make sure they are on the same phase or you could get noise"

That is myth, fiction, and misinformation there is no truth, validity, or basis for this claim where do you think the "noise" will come from!

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almarg8,594 posts05-16-2013 9:59am

Regarding the issue of splitting the load between two AC phases, as is usually the case I am in complete agreement with Jim (and Foster_9 and Pbnaudio who expressed similar positions), at least in situations where the AC draw of the system is not unusually large.

I looked through the ExactPower paper Jim referenced, the relevance of which is captured in its subtitle, "A practical guide for AV designers, installers, and electricians."

As an EE with extensive background designing analog and digital circuits (not for audio) I find the paper to be authoritative and credible. Which is to be expected, considering its authors. Among them, Henry Ott (biography here), is a world renowned authority on numerous aspects of electrical and electronic design. Bill Whitlock (biography here) is certainly no slouch either. Some excerpts from their paper:

Less than 300 microamps of ground loop current can cause hum as it flows in an unbalanced audio interconnect cable. However, harmonics of 60Hz that are generated from lighting dimmers or switch-mode power supplies sound like �Buzzz� mixed with a bit of �Hummm� and are more easily coupled by even smaller currents. Harmonics can add together when equipment is powered from different phases, so clearly there is an advantage to specifying same-phase electrical service to power the electronics systems in most cases....

Any leakage currents on the safety ground wires of split single phase load circuits fed by different phase legs will add together due to the 240V potential difference....

Power conditioners do not solve any of these common problems: Cross phase coupling (doubles hums & buzzes) .... What actually does solve them: Same phase power.

Also, regarding ground loops, I would commend this paper by Bill Whitlock to everyone’s attention, particularly the first page. It seems to me that if leakage current finding its way to the chassis (and safety ground) of a given component, via stray capacitance in the power transformer, EMI/RFI filters, etc., is out of phase with leakage current in another component that it is interconnected with, inter-chassis current flow between the two components, and therefore susceptibility to ground loop-related hum and noise, will have been maximized.

Regards,
-- Al

https://forum.audiogon.com/discussions/dedicated-power-lines  

Bill Whitlock
https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

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Al, (almarg), just does a better job of explaining things.

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Cheers,
Jim



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Multiwire branch circuit.

https://www.youtube.com/watch?v=eVamt9IdQd8

cleeds1,945 posts01-25-2019 7:08am

As my questions should suggest, I understand how these circuits work. What I don’t understand is how the load on one phase can influence the current on the other phase, unless there is something wrong with the electric service in the first place.

Shared neutrals are absolutely allowed under NEC and I see no reason to avoid them

The load on one Hot Line does not affect the load on the other Hot Line. What can be affected is the voltage measured from the hot to neutral due to a severely unbalanced multiwire branch circuit due to voltage drop on the heavily loaded hot to neutral circuit. The shared neutral is part of the circuit.

sleepwalker65 stated in his post a 14-3 w/grd 3 wire multiwire branch circuit feeds the laundry room outlet on the 2nd for the washing machine and a ceiling lighting circuit. (One Hot Line for the wall receptacle for the washing machine, the other Hot Line for a ceiling lighting circuit). The electrical panel is located in the basement on the opposite end of the house. How long, distance, is the multiwire branch circuit?

(First this must really be an old house. For as long as I can remember the circuit for a (laundry area) cloths washing machine per NEC is 20 amp, #12awg minimum copper wire.) A muliwire branch circuit should have never been used in this instance. Does it meet bare minimum NEC code ? Yes..... I wouldn’t have though......

So back to the load on the Hot Line to neutral load created by the washing machine. Say the distance from the electrical panel to the wall outlet for the washing machine is over 100ft, or more. (It could very well be. 3000 sq ft house.) What do you think is happening to the current draw of the motor during the wash cycle? Do you think it is steady or fluctuating? As the current is fluctuating what is the voltage doing on the circuit? I bet it is also fluctuating due to Voltage drop on the line created by the load on the motor in the wash cycle.

If a clamp on amprobe was clamp on the neutral at the end of the 14-3 where it splits off to 2 two wire circuits, (one for the washing machine, the other for the lighting), you will see the varying amperes of the motor load. If you measure the voltage from either Hot Line to the common neutral you will also see the voltage fluctuating. If the ceiling lights are incandescent bulbs you will see the voltage fluctuations caused by the voltage drop on the neutral wire.

As for light bulbs burning out faster than they should normally, I would be looking for a loose or corroded neutral connection starting at the electrical panel neutral bar connection to the junction where the circuits split off the 14-3.

Also worth mentioning Motors are rated in HP. As the voltage drops due to voltage drop current goes up. More current more heat. Too much heat will cause terminations to overheat, corrode, and can eventually cause them to fail.

As for the use of multiwire branch circuits. They have been around ever since 3PH 4 wire polyphase and split phase single phase distribution power transformers. Common place especially in office buildings and industrial facilities.
They save/saved money. Less wire and fewer conduits and smaller sized conduits. Less labor cost man hours.

Then came the age of computers. Starting in the 1980s data centers in office buildings. PCs, (Personal Computers), started showing up on workers desks connected to the main frame. 1990s even more PCs on workers desks. Around the early 2000s problems were starting to show up. All the while, more PCs were being installed in office buildings. Electricians were being called to trouble shoot electrical problems on 4 wire multiwire branch circuits. What they found was the neutral conductor at the electrical panel connection to the neutral bar was corroded, burnt, and the insulation on the wired was discolored and in some cases burned near the termination. HARMONICS! All them PCs.

The solution to the problem? Increase the size of the neutral one size larger than the phase conductors. So if the phase conductors are # 12 the neutral conductor is #10. Did that work? Yeah, for the branch circuit wiring........

Then come the 2008 NEC code edition. Something new for multi wire branch. For electrical safety reasons all ungrounded conductors of multi wire branch circuits shall be required to have all ungrounded conductors of the multi wire branch circuit to be de-energized simultaneously. Either a multi pole breaker or if single pole breakers are used an approved common tie device must be used that opens all breakers with one movement. What do you think this did for the benefit of using multiwire branch circuits in office buildings build after the 2008 NEC was adopted by AHJs across the US? (For many years there were, still may be some, AHJs that did not adopt this section of the 2008 NEC. My State did in Jan of 2009)

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tecknik151 posts01-25-2019 8:13pm

I use Acoustic Revive EE 2.6 solid copper 10g. in wall cable

I don’t think that cable could be used in the USA for in wall branch circuit wiring. Is the cable NRTL safety testing Listed? Such as UL?
https://www.osha.gov/dts/otpca/nrtl/nrtl_faq.html

Acoustic Revive EE 2.6 solid copper 10g. in wall cable
https://www.ebay.com/itm/Acoustic-Revive-EE-F-S-2-6-mm-PC-TripleC-power-cable-2-00m-NEW-/17365209792...

this is a huge improvement over standard Rominex 10g. stranded wire

I couldn’t find anything on " Rominex 10g. stranded wire".
Here in the US we have Romex 10ga solid copper wire.
(Romex is a registered Trade Mark Name product of NM sheathed cable.) (NM, Non Metallic)
https://www.homedepot.com/p/Southwire-By-the-Foot-10-2-Solid-Romex-SIMpull-CU-NM-B-W-G-Wire-28829099...

noromance1,688 posts01-28-2019 7:29am

+1 @millercarbon
I tried initially using two runs and ran into hum issues. Now I use one run of 8 gauge on a 20A breaker into a Hubbell L20R/L20P.

The problem could be with your equipment. Anything is possible.... Or it could have been the type of wiring and wiring method you used.

As for the use of multiple dedicated branch circuits to fed audio equipment, that is connected together by wire interconnects, it’s done all the time without any ground loop hum problems. Again when the type of wiring used, and the wiring method used for the installation of the branch circuits is done correctly. And that includes long branch circuit runs.


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