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PostPosted: Thu Sep 02, 2004 3:49 pm 
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Finally found this -

2002 NEC, section300 - (quote)
300.3 Conductors.
(A) Single Conductors. Single conductors specified in Table 310.13 shall only be installed where part of a recognized wiring method of Chapter 3.
Section 300.3(A) clearly states that building wire, such as individual insulated conductors identified as THHN, is prohibited from use outside of a recognized wiring method.
(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (4).
This general rule remains consistent with electrical theory; that is, to reduce inductive heating and to avoid increases in overall circuit impedance, all circuit conductors of an individual circuit must be grouped. Similar requirements are found in 300.5(I). (end quote)

The exceptions are ONLY for retrofit of 3 conductor receptacles into older, 2-wire circuits and allow the ground to be connected to almost ANY grounded or grounding conductor - NOT for new installs... Steve


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PostPosted: Sun Sep 05, 2004 8:52 am 
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Hey everybody. I've been doing some heavy reading and such on different electrical contractors forums. The overwhelming majority of electricians beleive that the use of isolated recepticals is a scam! The only time when they are of any use would be for self contained systems such as a computer. Computers and their peripherals must be plugged into the same outlet and even then, there is no protection against irregular currents that could cause damage to our equipment.

So which leads me to my next question, which is somewhat answered from the above...When you plug equipment together from two different circuits via balanced audio cables, in essence, you are losing your isolated ground that you have already tried so hard to achieve? Am I correct or totally off base with this one? Also, talking to electricians, the majority believe, as well, that if there are only a couple outlets per circuit housed in plastic boxes, there should be no problems concerning ground. Nor have they experienced any problems.

Ultimately, I have been advised to wire how I normally would, and if I experience any problems regarding noisy power, run a UPS on the equipment that is generating the ground issue. Any thoughts?

M

Some good reading - - - http://electrical-contractor.net/cgi-bi ... tion=intro


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PostPosted: Sun Sep 05, 2004 10:13 am 
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First, let me state that besides being an experienced Audio/Video tech for several years, I am licensed as an electrician (two different, overlapping licences) in order to do my job as an instrumentation and control tech in heavy industry in the state of Oregon - so far, I wouldn't even have to take my other hand out of my pocket to count the number of "normal" electricians I've encountered who have the depth of theory understanding or the related experience to make this kind of statement - motors and lights, and even control circuits for the most part, aren't NEARLY as picky about their grounding and power requirements as audio gear, assuming you want QUIET audio gear.

In my opinion, listening to most generic electricians about grounding of technical audio power is like getting a Yugo mechanic to advise you on optimum combustion chamber shape for an Indy race car...

As for interconnect causing loss of isolation on a ground system, this is a real possibility - which is why I mentioned the rack isolators or using wooden rails with threaded inserts for studio racks - some semi-pro gear now has plastic cases so isn't susceptible to this, but if you run isolated power with star grounding and then plug several rack units into the same outlet, if their chassis touch each other you may still get a slight hum from that short ground loop (ground at receptacle, thru one power cord and chassis, to the other chassis, and back thru its power cord to the ground pin at the wall) -

Inputs and outputs are usually designed so that as long as all chassis have the same ground point, it's not necessary (or in some cases even desirable) to have both ends of an audio wire's shield connected to ground. Ideally, only ONE end should be grounded, so that the shield is incapable of carrying any current whatsoever - its only function is as a shield, which is fulfilled by one end being at ground potential. Grounding the other end of the shield just makes it more likely to get a loop in most cases. Single-ended shielding is called a Telescoping Shield.

There is even a way to (sort of) accomplish this with UN-balanced wiring - you use twisted shielded pair, connect the black to ground on both ends, the red (or white) to the hot lead, and the shield to ground, but ONLY ON ONE END of the shield - that way, your shield is still a shield but can't pass current - in extreme cases of tracking down that last dB of noise, sometimes you can use a standard coaxial un-balanced cable and just clip the shield at one end (normally the source, or output, end) - I don't recommend this unless these leads are going to be permanently installed though - it's too easy to forget, unless you label each end (good idea anyway) that this is a special cable and can't be expected to work in all situations.

Having a dedicated, star type, safety ground system in place is a MANDATORY requirement for safety if you use single-ended shields.

A lot of UPS's don't use a true sine wave, and can introduce distortion into the power supplies of some gear - if you're going to use a UPS and still want quiet, you should find one that puts out a true sine wave. Some UPS's offer what's called "modified sine wave" - this is nothing more than a trapezoidal wave instead of a square wave - better than square, but NOT as good as a true sine output.

If you intend to use balanced power for several dB MORE quieting, you need to size the UPS large enough that the balanced power transformer can be run from the UPS - the reverse order isn't possible with any UPS I've seen.

When you're trying to get your studio quiet enough to justify those Grace preamps and Benchmark DAC's, every last bit of improvement is worth going for - this is the part most electricians don't get - it's not that they're stupid, it's just a lack of experience and knowledge in that particular area. The human ear is so much more sensitive than most test gear, you'll hear things your test gear can't even show you in a lot of cases... Steve


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PostPosted: Sun Sep 05, 2004 10:38 am 
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That leads me to another question, if the isolated circuits are a moto point, they why is there such a buzz around them and why is it now used as a specification for technical equipment?

While I am posting, I was wondering if anyone has seen and/or tried these yet?
http://www.psaudio.com/products/powerport.asp

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Carl Fuehrer
Pulsar Audio Lab
http://www.pulsaraudiolab.com


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PostPosted: Mon Sep 06, 2004 10:32 pm 
I totally understand Steve...and in absoltely no way was I questioning your expertise in this matter. I was swayed to go with the typical wiring and I hope there are no problems! I've since wired the whole studio and we'll be putting up the insulation tomorrow! If I do have problems, are there any "quick fixes" so to speak? Hope so! Wish me luck. Thanks again Steve.

M


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PostPosted: Tue Sep 07, 2004 12:26 am 
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Carl, you're preaching to the choir :wink: - and I'd not seen those IGR's - that seems a bit extreme to me, when for the same price you can buy 6 of these -

http://www.dale-electric.com/detail.cfm ... =16262-IGI

They're available in several colors, including bright red if you want -

M, you must be having sign-in problems, you're showing up as a guest - As to wiring, I'm sorry you were convinced by people who don't do what you're trying to do, and don't know enough to know that they don't know enough - if you've wired your place with anything but conduit and individual conductors, there isn't any reasonable way to change it once it's a done deal - as I posted earlier, grounds are required to be run in the same cable or conduit or raceway with all other conductors in a circuit, so it isn't practical or legal to add them later unless you can get to the original wiring. You may be stuck with what you have in this case.

I'm not trying to be sarcastic here, I really AM sorry - this sort of thing happens all too often, because people in the trades usually don't want to be seen as ignorant, so they give answers whether they know or not.

IF your power requirements are relatively small, you might be able to just use ONE outlet (actually one duplex, or two outlets) to run ALL your audio gear - you can run a surprising amount of gear from one 15 or 20 amp circuit with no problems. That would clean up most grounding problems pretty well - if you have ANY gear that uses "wall warts", it's much more important to segregate those noisy atrocities from audio wiring as much (and as far away) as possible.

Other than that, you may have to take this on a case-by-case basis... Steve


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PostPosted: Tue Sep 07, 2004 11:19 am 
I am an electrical contractor, and have been an electrician for over 15 years, and I have a down to earth "for real" opinion on the isolated ground thing. I have a big hum on my subwoofer in my home theatre as we speak. So this is of huge interest to me.

If you need can lights, outlets, switches, circuits, fished in or added to your house, I am the man- qualified to the hilt. Many electricians are. But when it comes to home audio, or any install like this, Just being an electrician and running 'dedicated circuits' to things like home theatre does in no way qualify me to adress the ground loop problem. I have a problem in my theatre now and was baffled for over three years with it. Soon I will attemt to apply the isolated ground and see if I find a cure.

Then you have a guy like knightfly who is in both industries and can comment with authority that most electircians are trained in one specific area. Hey, man, I may be licenced to pull any dang wire that someone can manufacture, and pull a permit to install it, but that does not mean I know all there is to know about some of these other areas of electircal.

I happen to be baffled and amazed with home automation, high end theatre, any install that has a computer needed to run it. I believe that there is something to the Isolated ground. Line voltage wiring is on / off, big power, etc..

Low voltage has multiple transformers, (which makes each unit a "separately derived system,..doesnt it :shock: in theory) lots of sheilding, wire shielding, bla, bla, and a lot of this is bonded or grounded to the body and thus the equipment ground. It is not beyond my belief that special precautions should be taken to treat these signals and communications with the best care for the most optimum performance....

g


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PostPosted: Tue Sep 07, 2004 11:20 am 
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that was me, forgot to sign in.... :oops:

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PostPosted: Tue Sep 07, 2004 2:32 pm 
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G, thanks for the vote of confidence, I meant no disrespect to any electricians as you obviously realized, it's just a matter of training and experience.

Now, about that subwoofer - rather than take this thread on a side trip, why don't you start a new thread and 'splain me some stuff - like when did it start, what kind of sub, powered or unpowered, connected thru its internal crossover to L/R stereo or direct from sub out on reciever, AC power for sub from same or different receptacle, phasing of any multiple receptacles, etc...

Or, I could just be my usual smart-ass self and say "of course it hums - if it hissed it would be called a tweeter..." :wink:

BTW, in 40 years in the technical fields I can only remember ONE time when there was a strange problem in anything that plugs into the wall or a battery, when it WASN'T caused by a GROUND problem... (when I feel more like embarrassing myself, I'll tell you what THAT one was... :cry:


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PostPosted: Tue Sep 07, 2004 4:01 pm 
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Been at least a couple hours since I "stirred the pot", :twisted: so here 'tiz -

http://www.equitech.com/articles/enigma.html

Keep in mind while reading this (it may take a few passes) that these people SELL balanced power systems - their comments about star grounding just being another bandaid with limited effect may be slightly biased as a result :? - still, this is the route I would recommend if you can possibly afford it -

My weather (hilltop with more than adequate winds, etc) caused me to set up my entire studio on a single UPS some time ago, and the next iteration will ALSO be done that way - in addition, I'll need to go one size larger on the UPS, a sine wave model, so that I can drive a balanced power transformer with the UPS and all the gear from balanced power. (Check out the 16 dB noise floor improvement comment in the article)

This in no way means that I don't still believe in a full star-ground system, this is just the next chapter in the story... Steve


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PostPosted: Tue Sep 07, 2004 10:50 pm 
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KNIGHTFLY- i was replying to the thread but didnt sign in so I couldnt edit it after rereading it. I was paying compliment to the fact that it is a rare to find someone who is fluent in both industries, as you are, and therefore your opinion that most electricians are 'electricians' and not experts in other specialty areas. (ie- the yugo thing) And I am living proof. thats all. and I totally agree.

that post did come off wrong, totally unintentional!

g

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PostPosted: Tue Sep 07, 2004 11:03 pm 
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Ill pop in here with my sub woofer problem, as it may be related to this topic.

OK-

I have a 10 RBH powered sub hooked into the home theatre system. Ive been through about 5 different line level RCA cables, each time throwing down more money for better shielding. No difference. I also have an RBH 200 watt amp hooked to two floor mounted virtual drivers/ shakers (best money ever spent!) Both the sub and the drivers will sit there and humm out a low frequency. Both have the auto on feature and when my fridge kicks on, they both turn on. That Im sure is a separate issue in the fact that I can unplug the fridge and the humm is still there.

the only thing that will make it go away is unhooking my cable tv feed. Ive run RG-6 quad to everything. this same thing happened to my last house and the cable tv and sattalite feeds produced this humm. someone sold me on of those $90 'plug in and protect everything' strips. didnt help.

the cable tv has no converter box, and the vcr that plugs into the cable is fed on the same circuit as the sub. The sub sits 10' away like a lot of subs do, same circuit, but a typical lighting circuit.

Its fair to say that the culprit is the cable tv, but I havent the slightest Idea how to fix.

thanx for any input-

g

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PostPosted: Wed Sep 08, 2004 4:14 am 
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First, I was in no way offended by your post - just the opposite. I felt that some electricians may have had reason to get upset by my earlier comments, even though I'd tried to make it clear that my intent was NOT to put anyone down. I was glad you had taken my comments as I'd intended, thats all :)

Second, if you haven't tried one of these

http://www.partsexpress.com/pe/showdetl ... er=180-075

you probably should - (any of the text on that page sound familiar? :wink: )

The downside is this one's F-59, so you'd need to adapt down from the RG-6 into the transformer, then directly into your first RF device (VCR, if I remember correctly - this is an edit, so can't see the rest of the post)

Hey, if it doesn't work it's cheap enough to use for a cat toy... Steve


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PostPosted: Thu Sep 09, 2004 2:28 am 
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G, did you see this yet? Or have you already tried this approach? Steve


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PostPosted: Thu Sep 09, 2004 5:22 am 
Nice lead, i ordered one. the product description is exactly what my problem is... fingers crossed!
thanx!
Ill let yall know how it works.

g


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