Studio Electrical Discussion from Utility to Outlet deleted

[SSLtech]

[quote author="mediatechnology"]The result? B-flat hum....[/quote]

What... -You no like?

Try life in Europe... It's a very slightly off-pitch 'G'. -Tune your Bass Guitar top string an octave above it, and you're close enough for the count-off! :wink:

Bob, I'd like to come round again some time soon and have a peep at your handiwork, if you don't mind...

Keith

 

[SSLtech]

240V works better on Soprano Sax... -you get a better arc for cutting it in half! :wink:

Keef

 

[bobkatz]

[quote author="SSLtech"][quote author="mediatechnology"]The result? B-flat hum....[/quote]

What... -You no like?

Try life in Europe... It's a very slightly off-pitch 'G'. -Tune your Bass Guitar top string an octave above it, and you're close enough for the count-off! :wink:

Bob, I'd like to come round again some time soon and have a peep at your handiwork, if you don't mind...

Keith[/quote]

If you don't mind the key of G minus!


Take care,


Bob

 

[bobkatz]

[quote author="mediatechnology"]Right on the money Bob.

In the past we all were freaked out about ground loops and breaking shields without really thinking about where that loop current comes from. It ain't no mystery - it's hum! And what's the source of hum? Power!

I do think matters have gotten worse over time with more and more gear having a proper line filter and loads having greater power factors.

I think you can parallel the secondary windings on the Topaz for true single phase 120V i.e. 120-0 not 120-0-120. Did this at DSL in Irving. What voltage would you be using to feed the primary? 240V? Send me a pic of the Topaz if you can. I've got an old full-line catalog and I'll match pictures. (mediadialupATmindspringDOTcom)


[/quote]

I'm talking to the "new Topaz" right now to get a schematic. I can psyche it out without them, but it would be real nice to confirm that it really has two independent electrostatic shields as those two wires are not marked. The nameplate is off of this transformer. Maybe that's why I got it for $125!

Anyway, I'll be feeding 220-240 volts to the primary and the secondary I'd like to split that into two split 120 volt secondaries with a grounded neutral. As for "balancing loads" I know it is not fully possible, and with heavily non-linear loads the concept of balancing current is out to lunch. But I do see some potential advantaqe for putting, say, the heavy duty power amplifier on one leg and other equipment on the other. Or, maybe, some of the dirtiest digital gear on one leg and analog gear on the other, thought that gets dicey.

It's not really possible to truely balance your loads. Consider the following example. Two 75W lamp "resistive" loads one on leg A the other Leg B. Now in a 120-0-120 system the vector (and algebraic) sum will be zero in the neutral. So where does the current flow to light the lamps? From leg to leg. Lifting the neutral in this example wouldn't change anything: Both lamps would light and it is still balanced.

I'm not sure I follow you. If one lamp is hooked to one phase's hot and the "neutral", and the other lamp is hooked to the other phase's hot and the neutral, if you lift the neutral wire to either lightbulb, you get nothing, no light! If you lift the central neutral from the transformer, you end up with nothing... So I don't see what you are leading to.

But back to the issue of legs on the transformer. Is it really possible to double up the current by paralleling the two secondaries and having a single phase system?

If you can I would try to make everyting in the room on the same phase 120-0. Just make sure that all of your neutrals are dedicated and home-runned just like iso ground other wise they'll be overloaded. If you can do a 240 primary leg-to-leg you should.

Yes, I'll be doing a 240 primary leg to leg (no neutral involved). On the secondary, I'd like to see some further arguments against using two phases instead of paralleling the secondaries as you are advising. My instincts are two secondaries... not to "balance the loads" per se, but perhaps to have a bit of isolation between the loads.

I know we have three threads going on. I'm trying to pick the thread that's closest to my question so as not to start a fourth!!!

Thanks, all,

BK

 

[CJ]

OK, I looked up Two Phase circuits in an old AC power book, and it does exist. It is just a generator with the poles spaced 90 degrees, so you get two signals 90 degrees apart.
You can then tie in a common point, so it's kind of like a 120-N-120 type wiring, only with the phasing whacked.

 

[PRR]

In the US, in the second half of this 20th century, in residential work, "two phase" means 240V center-tapped.

> I looked up Two Phase circuits in an old AC power book, and it does exist. It is just a generator with the poles spaced 90 degrees, so you get two signals 90 degrees apart.

Right. AC motors can't start with single phase power. There is a dead-spot, and on starting they usually find it and stick. If you manually spin them near 1,800 RPM, they will work fine, until the next time the motor stops.

Same thing on a single cylinder double-acting steam engine. The piston comes to the end of the stroke and stops.

The fix is to use two cylinders 90 degrees out of phase. Walk around a locomotive. The crank-pin on one side is 90 degrees off from the other side. As one side hits the end, the other side is mid-stroke and pushing hard. Assuming no cutoff, torque varies from 100% to 70.7%, but never zero.

In true steam-head tradition, early AC motors were plumbed just like a 2-cylinder steam engine. Two coils at 90 degrees fed two phases 90 degrees apart.

> You can then tie in a common point, so it's kind of like a 120-N-120 type wiring, only with the phasing whacked.

You can't get 240V to power your electric dryer. You get 168V. You can redesign for 168V, but taking power off the two high legs of a 3-wire 2-phase line is very inefficient of copper.

Westinghouse's dwarf worked out the properties of 3-phase, and it has been the standard way to spread the juice ever since.

Oh, so how does your 120V electric fan work? It has 2-phase inside. Big motors use a large capacitor to shift the juice almost 90 degrees, enough to get started. Smaller motors put a short around a small part of the pole which time-shifts the rise of flux and causes a gentle starting action.

And then there are eddy-current clocks. They tend to start but don't care which way they start. Backward running is wrong for a clock. They had a peg that flew out when the clock gained speed, and if it spun backward it caught a ratchet and bounced backward, semi-reliably starting in the right direction.

 

[Boswell]

Speaking at a safe distance from the other side of the pond, two suggestions about the US 240V centre-tapped:

(1) use a transformer with 240:120+120 windings. Connect the primary to the two 120V incoming phases but don't connect the neutral. Either parallel the secondaries (care with phasing!) or use two separate 120V outputs with the 0V grounded to power your rig. What you are doing here is replicating what happens on the pole transfomer, but this time you choose how you connect the secondaries. Then you bring an unpolluted earth in from outside to ground your rack.

(2) (bit radical, this) bring both phases of your 120V mains in and run the equipment switched to 240V across the phases. Run a separate earth in as above.

In both cases, you put no neutral current back into the mains and you avoid interference caused by imbalanced phases.

 

[NewYorkDave]

I think PRR may be thinking of C.P. Steinmetz, not Tesla. Tesla (of Westinghouse) was a tall man, Steinmetz (of GE) was very short. And both were brilliant.

 

[bobkatz]

[quote author="mediatechnology"]

Paralleling secondaries does work great but the phasing of them is worth checking at least three or four times before powering up.

[/quote]

Oh yes, I'd check that a dozen times with my scope before I see that transformer go up in smoke! Maybe even put a variac on the input first!

But is it really necessary (or useful) to have everything in the studio on that single phase? As I said in another post, maybe on another thread (deepest apologies)... I think the whole fear of having two phases in your audio room comes from bad wiring and powering practices. I can see, for example, if you have a surround system and multiple power amps, if you power one amp on one phase and the other on the other phase, all plugged into the same power distribution source, each with its own separate neutral... you can reduce loading, run more efficiently. It seems to me.

BK

 

[SSLtech]

[quote author="Boswell"]Then you bring an unpolluted earth in from outside to ground your rack.[/quote]
I did talk to Bob about this suggestion when I last visited with him.

I THINK though, that this is almost certainly 'counter-code' (against the regs) in this part of the world. -Essentially all electricians are required to carry the power company's ground to ALL outlets.

Bob, in Europe the reason for not permitting 2 different phases in the same room (or -in the case of large conference centres and ballrooms- requiring a large minimum distance to be pbserved between outlets on differing phases) is to prevent the possibilty of 415V inter-phase differences meeting human flesh. (we've all heard of people being electrocuted when they touch two faulty bits of gear: like grabbing the mic while their left hand is still on the guitar strings... imagine if the possible failure voltage difference was 415VAC... :shock: )

There may certainly be other equally valid reasons, but in the UK, Ive been quoted that reason by a few electricians, site inpectors & architects.

Personally, I LIKE the clean-ground and fully- isolated power version... even better than the 60-0-60 Equitech solution. However, you're fighting codes that presumably have been made into "paint-by-numbers-and-never-vary-that-way-we're-all-safe" ways of doing things, which have been carved into stone tablets as law.

Keith

 

[CJ]

I have the 120 dual phase problem at home, I ran a big piece of copper braid to each box/rack, and it seemedto do the trick.

You want the amplifiers on the other side of the glass to be grounded to the stuff on the other other side of the glass, I would think.

 

[SSLtech]

Skycraft has plenty of larger-than-0Ga. welding cable. -There's no building steel that I am aware of, though Bob will be able to confirm or correct this.

Do you know if the NEC would allow a local 'dedicated-clean' ground rod to be used, then only tied back to the power company's required safety reference by a single, long fat-as-my-arm welding cable? -Would that be an acceptably safe and yet clean way to achieve 'buzz-free tranquilitee'

Keith

 

[PRR]

> may be thinking of C.P. Steinmetz

Yes. And GE, not Westinghouse. Sorry.

While Tesla and Westinghouse had a deal, I don't think Nicky had much to do with Westinghouse's business aside from licensing the multi-phase AC motor patent. George was a prefectly practical inventor and businessman. He invented the fail-safe Air Brake, which was soon made mandatory; and the railway block-signal system which keeps trains from running into each other. He captured natural gas, which oil-well drills just blew-off. When scientists said you could not run multiple electric streetcars on one track, he did. Many people had tried to move power from Niagra Falls to the mills in Buffalo, his company did it (with AC). He invented the AC Electric Meter we still use today. Skeptics said that Parson's steam turbines would never be practical, Westinghouse made them practical and of course they now dominate most large rotating machinery. This also required advances in herringbone gears. He even worked toward perpetual motion: he wasn't sure it would work (of course it can't) but he knew the Heat Pump would be useful anyway.

Steinmetz came to America a penniless Socialist. But he knew math and he figured out AC like nobody else. He really should be better known. But he had a dark side. Not dark to him, but dark in later US politics. He really believed in socialism, corresponded with Lenin, yada yada... by mid-century, it was not nice to talk about people like that, even if they died before socialism became an excuse for totalitarian dictatorship.




> Then you bring an unpolluted earth in from outside to ground your rack.

Recent NEC has provisions for unusual grounding for hospital and technical situations. Read it! Not so much for when things go right: NEC knows a lot about how things go WRONG and their (evolving) rules really do have reasons.

Personally, I think any gear that lets neutral-crap get into the signal should be fixed (it is probably bad) or tossed. I realize this sometimes may not be acceptable.

 

[bobkatz]

[quote author="SSLtech"]Bob, in Europe the reason for not permitting 2 different phases in the same room (or -in the case of large conference centres and ballrooms- requiring a large minimum distance to be pbserved between outlets on differing phases) is to prevent the possibilty of 415V inter-phase differences meeting human flesh.

Well, in the U.S. that would be 240 but that's lethal enough. I am aware of that potential issue, but in my opinion this would only occur with a hot chassis and improper chassis grounding. I don't consider that an issue.

So, any other objections? Advantages? In my mind, splitting the loads, while not equating to "load balancing" just might reduce the issue of interference. For example, I could put high gain audio gear on one phase and equipment with motors and high power consumption on the other, along with all the computers. This would be far from a "balanced load" but might reduce noise issues.

And to spread the subject, I'd like to ask briefly about grounding and fusing if anyone would like to chime in.

For a 2.5 kva transformer with a 240 volt primary winding, it seems to me I could use a 10 amp slow blow on the primary. How does that sound to you all?

As for grounding, without tremendous effort I'm stuck with a "dirty ground" going to the first floor and then I insulated a ground to the second floor. There is an (estimated) 50' run of bare maybe #4 equivalent multistranded "ground" wire from the main box to the interior box that is bonded to the interior box and to the neutral. So the ground has been "contaminated" along its way, though no official neutral current ever flows in this ground.

My feeling about grounding is it is all relative. That's why we can have functioning airplanes with clean electronic gear and navigation, and make noise-free audio studios on the top of tall buildings. I feel that as long as I use the power isolation transformer to generate my own neutral on the secondary, even though I connect this neutral to the "dirty ground", I am using it strictly as a chassis safety and all my audio equipment will follow good shielding and grounding rules.

I am concerned about using unbalanced audio gear, but again, if you are already on the second floor, the usual "when is a ground not a ground" question applies. Everything in studio B will reference to the chassis of the isolation transformer, dirty or not. That's my rule. Comments?

BK

 

[CJ]

Steinmetz was cool. Use to float around in a boat so he could think.
Also helped young kids out a lot.
Anybody have the volumes? Worth a mint nowdays.

 

[SSLtech]

[quote author="bobkatz"]but in my opinion this would only occur with a hot chassis and improper chassis grounding. I don't consider that an issue.[/quote]
I agree on grounds of common sense: the worst case which I envision is a pair of hot chassis on different phases... which leads me to the probable cause of Jimmy Page's power-tool-phobia:

About a year or two ago I had to look at a noise problem (mid-session) with an ampeg bass rig. -There was an "A/B" switch for noise problems, (what the hell does that do? -Something to do with connecting the chassis to either live or neutral via a capacitor, I suspect...) and an (I THINK) unpolarised 2-pin power plug. At one point I -holding the bass guitar- unplugged it from the DI box (grounded) while the A/B switch was in a particular position (we were trying different combinations of AB switch and ground-lift on the DI, then removing the DI from the equation...)

Basically I got a jolt from my left hand on ths strings to my right hand on the DI... Probably a good 110V "tickle". -Anyhow, for British bands who move from country to country and set up using different powering/ grounding setups night after night this must be tempting fate. -I seem to remember a fad in the 1970's for trying to "bow" electric guitar strings (think of an electric hurdy-gurdy, or "the Gizmo") using power tools such as eectric drills. -Whaddayawanna bet that Mr. Plant got a jolt when one hand was fretting strings connected to a tube amp while the other was grabbing a metal-cased (in those days) Black-and-Decker...?

Personally I think the best that you can do is to reduce it to the basics, and I think Bob's on the right track:

1) Get a good local ground. If the NEC demands that this be bonded somehow with the incoming power ground then you can't fight the law and win...

2) We're all smart enough people who can keep poorly-planned, wide loop-area distribution systems from developing. (easiest thing in teh world.. -right?!)

3) Star all grounds back to good, low-return-impedance ground "kills".

4) Prevent current flow along power ground lines for any reason other than "Live-To-Ground" safety protection reasons.

As for the rest, I still have a sneaky suspicion that in single-phase or dual-phase systems, much radiated noise is CURRENT based rather than actually being voltage-based. If you keep the conductors in a single-phase system close together, then the field generated by current flowing "to and fro" along the live conductor is precisely opposed by the field generated by current flowing "fro and to" along the neutral conductor. -If you separate load types on a 2-phase system, the different timing of the complex waveform on the neutral might be able to create a situation where parts of the cable distribution (Neutral particularly) are carrying non-canceling fields... -Or am I missing something? -Now, bond that to ground carelelssly, and you have a modulated (noisy) local ground.

Naturally, if you always feed everything as "home runs" from the power source comprised of a single live and neutral, then the field cancelation should be much more consistent (assuming that I'm not worrying about irrelevant crap... -Anyone got an opinion here... -or better yet a correction/clarification?)

Anyhow, whether it's a simple loop or a complex multiphase distribution arrangement, the AREA is important, and reducing any current flow or current imbalance over a distributed area is of dominant concern to my present way of thinking.

Keith

 

[SSLtech]

[quote author="mediatechnology"]That night I don't think he could have even felt the shock however.[/quote]
:green:

Would've been worth the price of a ticket though! :wink:

Keef

 

[CJ]

Well, Eddie used a cordless for Pound Cake.
Did they have those back then?

Just a note, leakage currents go up as fy=use ratings of system go up.

Much more leakage on a 1000 amp servive than a 30 amp service.
I know, useless info.


O.K Quiz for the day.

Lets say I have a single phase power meter.
I am usuing it on a wye system, on one leg, voltage between neutral and line. CT on one of the lines.
Multiply by three to get power (balanced reasonbly, of course)


How would I use this meter on a delta to get total power?
(this is not easy, my company submitted a patent on this, but they screwed it all up by adding other common stuff to the patent)

Hint:use vectors

 

[bobkatz]

[quote author="SSLtech"]

1) Get a good local ground. If the NEC demands that this be bonded somehow with the incoming power ground then you can't fight the law and win...


[/quote]

I'm praying that calling the chassis of the isolation transformer the reference for the star ground will do the trick.

Let me give you an example. I used to see Florida lightning storms blow out Ethernet switches and Ethernet ports on my computers. It was very frustrating. I then bought some heavy-duty Ethernet protectors made by Furst (NOT CHEAP). Someone on Pro Audio advised that I have a real earth ground and ground those Ethernet protectors to those. I took the position that the lightning bolt is going to raise the potential on ANY ground wire which is more than a few inches from the REAL ground, so, what's the point of the real ground. I run the 4" ground leads from these Ethernet protectors to the chassis of my UPS, or to the chassis of the computer it is protecting. Four years since taking this practice, I have not lost a single Ethernet port in that time. EXCEPT for one time when the screw came loose on the ground wire and it was disconnected on one of those Furst guys. One big lightning hit and that thing smoked and fried like crazy, lost it and the switch it was protecting.

When is a ground not a ground? !!!

Keith wrote...

2) We're all smart enough people who can keep poorly-planned, wide loop-area distribution systems from developing. (easiest thing in teh world.. -right?!)

3) Star all grounds back to good, low-return-impedance ground "kills".

Good thing I'm building a mastering room and not a multi-room studio complex. I don't have the head to figure out loop area in those cases!

Anyway, what is the definition of a low impedance ground in an airplane or on the 103rd floor of the World Trade Center? Ask me how I wired some ceiling microphones on the 103rd floor of the World Trade Center (year was 1988) so as to avoid the incredible RFI from 30 Television antennas 50 feet above me. Answer: It's proper shielding, not grounding, that prevents RFI.

As for the rest, I still have a sneaky suspicion that in single-phase or dual-phase systems, much radiated noise is CURRENT based rather than actually being voltage-based. If you keep the conductors in a single-phase system close together, then the field generated by current flowing "to and fro" along the live conductor is precisely opposed by the field generated by current flowing "fro and to" along the neutral conductor. -If you separate load types on a 2-phase system, the different timing of the complex waveform on the neutral might be able to create a situation where parts of the cable distribution (Neutral particularly) are carrying non-canceling fields... -Or am I missing something? -Now, bond that to ground carelelssly, and you have a modulated (noisy) local ground.

You're right on keeping live and return close together. And Muncy taught me that this should be extended to the audio cables as well, because the power and the audio are all part of the same circuit. The audio cables and the power cables should be bundled TOGETHER, not apart. Think loop area. So, I have the sneaky suspicion that I can run two phase power as long as the neutrals and all the audio cables and ground returns take the same general route. That's like the idea of "home runs" but includes the audio cable routes in the same plan.

Goes against the old "conventional" wisdom that you're supposed to separate audio and power. But makes perfect sense.

The neat thing is that if my theory doesn't work out, I can rewire the secondary of the isolation transformer for parallel single phase in the blink of an eye. I'm mounting a single duplex outlet on there that's spit to the two phases and I can join that in an instant.

 

[bobkatz]

[quote author="CJ"]
Hint:use vectors[/quote]

I can't use vectors, against my religion... that's where I hire the pros like you!