EMUSIC-L Digest                                    Volume 36, Number 5


This issue's topic: Fight the (AC) Power


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Date:         Thu, 10 Jan 91 12:47:00 EDT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         "William R(ay) Brohinsky"
<RAYBRO%HOLON%UTRC@UTRCGW.UTC.COM>
Subject:      Grounding (was: Re:  Team Metlay, continued: Networking Considerat

Interesting that you folks should have pegged safety as first priority:
I have been involved in a (sometimes heated) discussion on BIX concerning
noise between a Mac and the user's stereo. Someone suggested that it was
ground-loop induced (I asked for, but never recieved, a better description
of the noise, but everyone seems to have decided it is ground-loop
induced!)

The first `do this' response involved using a third-wire-breaking adaptor
to eliminate the case ground connection on the mac. I responded with
an impassioned plea for safety, and the response was somewhat amazing:
roughly 2/3 of the comments (an admittedly small sample) were in
favor of safety first, and 1/3 felt that I was over cautious and
even wrong to raise such concerns.

I hope it is common knowledge, but 30V can kill! Real, honest to goodness
Dead! Is this fact being taught to our up-and-coming E-musicians at the
schools?  I hope so...

I applaud Team Metlay for their sensible priorities. I personally would
prefer to see a session fail to produce a salable result to seeing any on
[of] the players/techs get hurt. (maybe not good economics, but it isn't
necessary for this choice to even come up with a modicum of planning!)

For my part, I always tree my power. I find the power strips from Radio
Shack to be just fine, and they had the added bene that, when the wind
and a tree branch knocked the neutral line off my house, but left the
hot line attatched, the GE-movs in the strip box fried, and protected
my computer and synths! (also, my TV, VCR, Stereo, etc. I use a lot of them...)

GFI's tend to trip if there's a 5ma difference between the current flowing
in the hot and neutral lines. When a person is sweaty, and in a certain
mood, his/her internal resistance can get as low as 600 ohms. 10ma
of current through a person's chest will kill them. 5ma MAY kill them---
it isn't like 9ma won't but 10ma will! 120V can be lethal. Team Metlay
were probably safer by knowing their systems and maintaining good power
and case grounds than they would have been relying on the GFI!

`Know your equipment, and thyself,' said he, Peloniusly. [forgive the
spelling...]

raybro
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Date:         Fri, 11 Jan 91 10:22:48 GMT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         Nick Rothwell <nick@LFCS.ED.AC.UK>
Subject:      Re:  Grounding

>For my part, I always tree my power.

Me too. I don't know how mains power is wired in houses in the US, but in
the UK all the wall sockets in any room (each socket rated at 13A) are
wired to a ring main, which can carry 30A; each socket therefore has two
circuits to the source. I had a huge amount of mains hum when my studio was
rebuilt after the Electronica gig. I've just rebuilt it again, running
practically everything out of a single socket, and it's fine. Using several
sockets on a ring main means that you've got ground loops around the walls
of the room - not too good, I feel.

When I arrived in the US and we started assembling the Team Metlay
Technorubble, you know what surprised me the most? Answer: some of the
absolute sh*t that people in the US draw 110V out of. Wall sockets are just
cheap plastic boxes with a couple of slits and bits of brass - no
shuttering on the slits or anything. Extension blocks are often cheap bits
of plastic with holes punched through them. Earthing (grounding) seems to
be pretty much a secondary concern ("no problem, I'll just attach it to
this screw here..."), and half the sockets don't accomodate earth pins.
Since the US runs at 110V rather than 240V, the voltage is less dangerous
(marginally...) but there's twice the current and hence twice the risk of
overheating. In the UK, plugs and extension sockets are big and bulky, but
seem a lot more solid.

I've just rewired all my racks for mains power with a switch on the front
of each rack and an internal cooling fan ("whirrrr"), and I went over the
things with a fine-toothed multimeter to make sure the connections were
solid. I still have to install GFI's and surge suppression, although I
can't decide whether to do this for each rack individually or have a master
distribution box.

Nick.
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Date:         Fri, 11 Jan 91 10:27:00 EDT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         CHRIS@FANDMA.BITNET
Subject:      Grounding question

This discussion of the Team Metlay setup reminded me of a wierd statement I
heard recently.  A couple of the guys in the band I'm in were discussing buzz
and hum in the PA system, and one of the guys said he thought the system was
"over-grounded" (apparently meaning we had to many pieces of equipment on the
same common ground, or some such notion), and that by *lifting the ground at
the wall outlet for the entire system* we would get rid of the noise.  To me
this sounded like a recipe for death and destruction of equipment, but I didn't
have enough information to sway this guy's arguement.  Has anyone on the list
ever heard of a condition called "over-grounding", and if so, care to elaborate
on it?  I suspect that lifting the ground *would* get rid of the noise, but I
personally would be afraid to touch any of the equipment once that was done.

-chris
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Date:         Fri, 11 Jan 91 15:58:47 EST
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         ronin <HARNDEN@AUVM.BITNET>
Subject:      overgrounding

'too much ground' usually means that the system is going to ground at two
differnt places, with different floating ground references. when assembling
an ac network, one wants as much as possible to pull all the grounds to
the same place, and spike it to earth, so that all the divices see the same
ground reference. otherwise, there is a danger of hum. lifting the third prong
removes an extra reference from a machine that is already trying to ground
itself by another path, usually the audio lines to the patch bay/mixer.
unless the thing has that ac ground connection wired to its external
casing, you're usually pretty safe doing this. remember, electric shock
occurs when your body provides a current path to a circuit.

----------< Extremism In The Pursuit Of Good Noise Is No Vice >----------
Eric Harnden (Ronin)                 | V.P., Chief Engineer
<HARNDEN@AUVM>                       | Transmedia Music, inc.
The American University Physics Dept.| (202) 347-8050
Washington, D.C                      |
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Date:         Fri, 11 Jan 91 13:44:00 EDT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         METLAY@PITTVMS.BITNET
Subject:      Re: Grounding question

That's a weird term for a ground loop, which is essentially what he's
describing: more than one path to ground for all signals. I do NOT
recommend lifting the ground at the wall! If you have a bass amp set up
near you with the polarity switch set wrong, and you put on the bass
and mute the strings and then touch a mic that's wired to the house PA
to see if it's on-- well, let's just say that's why Uriah Heep had to
audition a new bassist somne years back. There are safer ways to kill
ground loops: cheater plugs at the source are stupid and dangerous.

metlay
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Date:         Fri, 11 Jan 91 13:03:00 EDT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         "William R(ay) Brohinsky"
<RAYBRO%HOLON%UTRC@UTRCGW.UTC.COM>
Subject:      Re: Grounding question

By the way: I've never heard of over-grounding either.

An alternative to treeing your power connections:
get a 40' roll of 3/4" braid, usually tinned copper. Also get a set of
two lugs for each piece of electrical equipment large enough to hold the
braid. Cut lengths of braid to go from an 8' copper pole that is driven into
the ground to each piece of equipment and crimp a lug at each end. Bolt
one end of each braid to the rod, and drill a hole in each piece of equipment.
Use a wire brush (one of those that mount up in a power drill works very
nicely!) and remove all of the paint for a 1/2" radius beyond the hole, and
bolt the other lug to it. This hole should be as close as possible to the
green wire connection inside of the equipment. Now, all equipment will
be at very near the same potential!

This worked just fine for a 10joule laser that was arcing between it's
cabinets. It should work just fine for your next live E-music setup.
It's also much more expensive than sensible routing of power lines in
the first place, and lowers the resale value of the equipment. But it's
lots safer than lifting the ground at the wall for the whole system!

raybro (in a more brief mode)
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Date:         Fri, 11 Jan 91 11:41:00 EDT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         "William R(ay) Brohinsky"
<RAYBRO%HOLON%UTRC@UTRCGW.UTC.COM>
Subject:      Re: Grounding question

Chris,
Grounds are there for a reason. They come in two types, signal and power, but
both types serve the same purpose: to provide a return path for the current
that flows out of a current source. (note that a voltage source is also
a current source: one names the potential (volts) to make current flow,
the other names the measure of current motion (amps).)

Ground loops happen when more than one ground path is available. Normally, a
musician sees a ground loop when he has his instrument plugged into an amp
(through a signal cable) and both instrument and amp have power cords which
have ground lines that are common to the signal ground. Because 60Hz (50Hz in
England) is such a low frequency, filter capacitors must be MASSIVE to
be large enough to successfully remove AC from DC power lines in the
instrument and amp circuits. This AC is normally shunted to ground. That
means that it manifests itself in the (normally negligable) resistance of
the return line. When the return line becomes resistive (which any real
wire is, regardless of its diameter!) then a noise voltage representing
the ac becomes available.

Speaking JUST of power for the moment:
Normally, there are 3 lines on a power connection. One is called HOT, one
is called NEUTRAL. These are the _normal_ current carrying paths for the
power supplies in instruments and amps. Hot is generally attached to the
power source (one of the three phases from the power transformer) and the
other is generally attached to `ground' in the form of a rod driven into the
earth near your home. In my case, the rod is ~1/2inch thick, and 6-10 feet
into the ground. The neutral line is also attached to one of the three phases
from the transformer (a different one, so that you get a voltage difference
between them, of course). If that ground lifts, i.e., some rodent chews through
the wire connecting the fuse/breaker box neutral to the earth-rod, then
the neutral side may appear to be at some voltage well above ground potential.
Since your pipes tend to be metal and tend to run into the ground sooner or
later, this is a life threatening problem: cross neutral to a pipe and fry!

To reduce this kind of problem aboard ships of the US navy, the `HOT' and
`Neutral' lines are 55volts, out of phase with each other. That way, there
is 110v (nominal) between the two lines, but either one is only 55v above
the voltage of the metal ship, reducing by 2 (by 4 if you consider power)
the damage from a short. The damage can still be miserably bad...

Once upon a time, in the US, there were only these two connections to power:
hot and neutral. The metal case of, say, an appliance, would be unconnected,
for safety. Unfortunately, if a heating element broke (the most common
occurance, although worn insulation was a pretty common problem, too) it would
tend to contact the case (being usually spring-shaped). Then, the case would
be connected to hot, or neutral. Depending on the side connected (or the
potential in any case) this could be dangerous. If your toster connected its
case to hot, and the coffee maker connected to neutral,and you tried to move
both of them at once...

So NEC (the national electrical code) and UL (the underwriter's laboratory) and
some other safety agencies decided to catch us up with the rest of the world.
Hence, the green wire. This is truely the GROUND. Whereas the neutral can
float above ground potential (as it surely does aboard ship) the ground pin
MUST be a good connection to ground. An appliance/instrument/amp with a
3-prong plug will have its case attatched to the green wire, which attaches
to this good ground through the third (round) prong. Now, if the element breaks,
the case remains at ground potential, and all that current that could have
run through you runs to ground.  Yes, that may destroy things in a red-
hot spray of sparks, but at least you aren't likely to be attached to
it...

As for signals:
you usually have a signal line and a ground line. The ground may be wrapped
around the signal or braided around it to provide some shielding. This is
so that the ground will absorb any RF interference, and carry it off
before the amp gets it. (If you hear radio stations from your speakers,
check both the grounds and the quality of the signal connections. but we
won't get into radio recievers from dissimilar metal connections here...)
Normally, both signal and ground are connected at both ends to the signal
output and ground at the instrument end, and likewise the signal input and
ground at the amp end. A normal signal will travel from the instrument to
the amp on the signal wire, and the return path is through the ground wire.

If, however, there is another path for the ground return, you can get effects
in the amp you don't want. [let me correct an earlier statement: the grounded
shield blocks RF from the signal wire, usually, rather than `carrying it
off' anywhere]

Current flows through loops. The signal-ground return forms such a loop.
If the signal ground is connected to the power ground (neutral) or the
case ground (3rd prong) at both the amp and inst, then signal current can
flow in the same wires that power noise is being carried off. This is
the canonical ground loop. Another mechanism here (maybe even the more
effective for causing troubles) is that current from the power supply
ground can actually travel through the signal ground, and cause the
potential difference between the signal ground and signal wire to change
at 60Hz. The amplifier will amplify this difference, and hum (or if
it gets distorted, buzz) comes out!

The canonical fix among the incognoscenti is to break the third prong
connection. This MAY break the ground loop! It certainly will reduce
a level of safety in the equipment, and may cause effects from mild
finger-buzzies when you touch your guitar strings or synth case to death.

The canonical fix among techs who have worked in data acquisition is to
lift the signal ground at the instrument input. This breaks the ground
loop for the signal, while allowing ground return through the power
connections. Note, that when you use this cable with a system that doesn't
suffer from a ground loop, or one that doesn't have power-grounds inter-
connected, you won't get any sound out of the system.

That solution may be ok for DA, but I've never liked it for music: too
much chance of using a knackered cable somewhere else. Very frustrating.
So lets look at the actual cause of the noise:

When you have a power connection, and you use power, current flows in the
ground return. It will tend to take the path of least resistance. The
more power you use, the more current flows. Since the ground is largely
made of cable and wire, the fact that wire has a finite resistance couples
with the current flow to produce a voltage, which can be measured. From
one end of the ground path to the transformer, you may measure less than
half of a volt. Not much, compared to 120V, but what happens when that
.5 volt gets to the input of your 1v-input amp? You guessed.

Power ground loops happen when the ground of system one is connected at one
point in that ground return, drawing lots of current, and system two
gets connected down stream from it. The grounds for the two systems
will be at different potentials, depending on the current and resistance
in the wires from sys1 to sys2. That voltage would cause a current to
flow between sys1 and sys2 if you connected their grounds through another
wire, say the signal ground...

Now you have a ground loop that is causing hum. You can break the ground
at sys1 in the signal wire, and there is still a ground return path. There
is also all that hum current in that path: if the amp is sensitive, that
current will get picked up and amplified. You've reduced the hum, but not
eliminated it.

ENTER THE TREE:
If you ensure that both sys1 and sys2 are plugged into power VERY closely,
then you can be pretty sure that any ground loops you make will not
have current flowing in them (or at least not enough to worry you).
SO, it is a good idea to take a multi-plug box where you are sure that
all the plug connections are good, and all plugs are within a small area,
and use that to plug an instrument, it's controllers and effects, and amp into.
Hence the name tree: a trunk with branches.

raybro
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Date:         Mon, 14 Jan 91 11:01:45 GMT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         Nick Rothwell <nick@LFCS.ED.AC.UK>
Subject:      Re: Grounding question

>ENTER THE TREE:
>If you ensure that both sys1 and sys2 are plugged into power VERY closely,
>then you can be pretty sure that any ground loops you make will not
>have current flowing in them (or at least not enough to worry you).

I can verify that this approach works. I pretty well eliminated the ground
hum from my setup by rewiring each of my racks for mains and running
practically everything from a single socket. The hum is extremely low
indeed (even though the racks have cooling fans wired and running), and
everything is properly earthed.

Don't cut your earth connections. Just say no.

Nick.
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Date:         Sat, 12 Jan 91 15:51:30 EST
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         Jeffrey R Kell <JEFF@UTCVM.BITNET>
Subject:      Re: Grounding question
In-Reply-To:  Message of Fri,
              11 Jan 91 11:41:00 EDT from
<RAYBRO%HOLON%UTRC@UTRCGW.UTC.COM>

No wait a minute; Raybro mentioned a HOT and NEUTRAL side, but the neutral
does NOT have a current potential with respect to ground.  The "three sides
of the transformer" approach is typical 3-phase wiring, but uncommon for home
use.  Three-phase 240v, for example, gives you 240v net in a 3-phase motor;
the voltage between any phase and ground (neutral) is 120v, and between any
two phases around 208v.  Home wiring is true two-phase, each leg being 180
degrees out of phase with the other (as opposed to 3-phase, where they are
120 degrees out).  Home wiring involves three wires to your house (count
'em if you're skeptical).  Two are "hot" and the third neutral.  The voltage
potential between either hot side and neutral is 110-120v.  The voltage
potential between the two hot sides is 220-240v.  The situation Ray mentioned
about case grounds is true, and the same as what I described earlier; but the
neutral is truly neutral with respect to ground (well, there is often a small
voltage potential, but it ain't hot).  And he was equally correct in that
you often ended up swapping neutral/hot from the intended sides, especially
with old 2-prong non-polarized plugs.  The first quick-fix was the polarized
plug (that's why one prong is "fatter" than the other) and the final fix was
the addition of the ground wire (green) which is supposed to go to a true,
honest-to-goodness earth ground at the electrical service entrance rather than
relying on the service ground (neutral) connection.

The problems continue to this day... our latest computer equipment installed
required 3-phase power on a 5-wire circuit - 3 hot phases, 1 neutral, 1 earth
ground, and a max 5v potential between neutral and ground.  The ground is
there as a fail-safe for the neutral (in all applications).  If a rat gnaws
through your hot wire, you're safe (but out of power).  If its the neutral,
then the current seeks out an alternate ground.
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Date:         Fri, 11 Jan 91 11:37:18 EST
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         Jeffrey R Kell <JEFF@UTCVM.BITNET>
Subject:      Re: Grounding question
In-Reply-To:  Message of Fri, 11 Jan 91 10:27:00 EDT from <CHRIS@FANDMA>

Okey dokey... electronics 101 :-)

The big deal here is that with ordinary 110-volt power, one prong is "hot"
and the other prong is "neutral" (and the extra one you broke off should be
a ground) :-)

In many applications, you have a chassis ground (hopefully neutral) since it
makes for a cheap, easily wired system.  If you touch the case and also touch
ground, it won't fry you (yet) since the case is the neutral side.  But then
Murphy's law strikes, something goes wrong, and what can happen?

* If the neutral side is shorted, the current will now seek you out as a
  ground and you get fried.  Thus the invention of the ground wire, its a
  secondary neutral.

* If you're playing around with plugs, you might plug it in backwards (which
  can be done easily enough without the ground wire).  Now the case is hot,
  but no damage yet since the neutral is still intact.  But if you touch
  another case with a proper plug (and neutral case) then fzzztttt...

* If the building is wired for 220v then individual outlets may be on
  different phases (ie, for 220v you go hot-to-hot between two sides of
  opposing polarity).  If you screw up as above you might get 220v instead
  of 110v, and it will *greatly prefer* you over the ground.

* This 220v differential phasing is what creates ground loops.  If you
  complete a path between grounds of *opposing* phases, you get induced eddy
  currents and RF fields (and a nasty 60Hz buzz).

The idea is to have *everything* on a *common* ground, fed by a *common* phase
of current.  It doesn't *have* to all come from one outlet (if you are damned
sure how and how *well* they are wired) but that's one way to be sure.  And
everything should be in phase.  If you lift a ground you can avoid some of the
ground-loop problem, but you have to be real sure there's a good ground in the
overall system.  I have heard recommendations to pull grounds on everything
except the power amps; while this usually works, and is theoretically sound,
it still isn't all that safe.  If you have a ground fault, you still leave a
prettly long path to ground, and you might end up well done.

/Jeff/
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Date:         Mon, 14 Jan 91 11:39:00 EDT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         "William R(ay) Brohinsky"
<RAYBRO%HOLON%UTRC@UTRCGW.UTC.COM>
Subject:      Re: Grounding question

Jeffry Kell is quite right that home wiring is not true three phase, and
almost right in that the neutral `does not have a current potential with
respect to ground'.

I apologize for the misstatement: my experience has been as an ET, both
onboard a ship, and as a civilian for both military and industry. Since
I am not always intimately focused on the power mains, I do sometimes
cross the two experiences: in civilian and industrial life, the 110v
line is often 117-120 volts and the neutral is supposed to be really
neutral to ground. On a US navy ship, the two lines are both `hot', but
there is SUPPOSED to be no connection between  the generator and the ship's
metal structures: hence, both sides do `not have a current potential with
respect to ground'. We were always warned not to screw with safety/case
grounds, though, because it was ALWAYS possible that the connection could
be there. In the Nav, the possibility comes with emergancy, war, or any
occurance that can shake up or damage a ship. At home, the proverbial
rat in the conduit will suffice!

Still and all, it boils down to this: don't mess with the green wire!

raybro
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Date:         Mon, 14 Jan 91 13:49:00 EDT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         CHRIS@FANDMA.BITNET
Subject:      Another grounding question

Many thanks to all who responded to my question on grounding, especially
Jeff and Raybro who went above and beyond the call of duty.

I understand the tree design, but in my case it's not practical:  we have
three 800-watt amps driving the main PA and another 800-watt amp driving
the monitors, in addition to two guitar amps, a bass amp, a keyboard amp
and the rest of my keyboard setup all on stage.  I doubt that we could
drive all of that off one circuit.  Even if we could, there's still the
mixing board to power up, which is at the end of a 300 foot snake on the
other side of the room.

So, if a tree layout isn't viable, what's a poor e-musician to do?

-chris
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Date:         Mon, 14 Jan 91 14:28:00 EDT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         "William R(ay) Brohinsky"
<RAYBRO%HOLON%UTRC@UTRCGW.UTC.COM>
Subject:      Re: Another grounding question

Chris,
yours is one of the systems that calls for the 3/4" braid! The idea is to get
the lowest resistance cable possible (preferably insulated) and to
make a `power snake'. Since the mixing board is not the highest current user,
I would put all of the local plugs at the stage, and then run a special
power hookup for the mixer.

You should first have ONE person in the group (or with the roadies) who
is responsible for power, and that one person only should be authorized to
plug things in. He should also have a backup, unless the band can't play
without him.

This one person has to be able to use a multimeter, as a minimum. Some training
in electronics is desirable, so your sound man should make a good first
choice.

When you arrive on site, he should ensure that there are two 30-amp services
available (it should actually be arranged before arriving:-), and he should
make measurements on the grounds to ensure that they do not have a resistance
between the two services. (allowable is well under .1 ohm). He should
have a power snake that consists of the following:

-two three prong plugs, whose grounds are connected thru the low-resistance
cable, which also connect to two power-distribution centers. The
PDC's should be able to be placed onstage far enough apart to provide
power to everything. The ground cable between the plugs must be long enough
to stretch between the services. One of the three-prong plugs should also have
...actually, a picture may be better:


       ||                         ||
       L/                         L/
       |  plug for one service    | plug for other service
       |\________________________/|\
       |  3/4" braid, jacketed    | \
       |                          |  \
       |                          |   \
       | power lines (3-cond)     |    \
       | to PDC's (30-amps max)   |     \
       |                          |     | 3-conductor cable (5-amp) with
       |                          |     | 3/4" braid(jacketed) ground
       |                          |     |
    --------                 ---------- |
    |      |                 |        | |
    |      | PDC's (2) with  |        | |
    |      | enough plugs for|        | |
    |      | stage equipment |        | |
    --------                 ---------- |
                                        |
                                        | long enough cable to reach to rear
                                        | of room (same length as snake +
                                        | power lines)
                                        |
                                        |
                                       / \
                                      L__|  plug for mixer

Use hospital-grade (with the green dot) plugs and jacks, and don't be
afraid to spend what it takes to do it right. Don't use the green wires in
the 3-conductor cables (and make sure that the cable you use will handly
[handle] 30 amps!) and either have an electrician build it or at least
have one check it.

This will ensure a few things: first off, you will have one person, at least,
in the group who understands ground loops, and you will have a mechanism
ready to avoid them.
Second off, you will have ensured that your power distribution problems are
limited to what the site offers, and you won't introduce any yourself.
Third, by adding breakers to the distribution boxes, you may be able
to avoid plunging the room into darkness...

This is a drastic solution, but one that will guarantee a minimum of danger
for the players, and a minimum of hum.

raybro
-------------------------------------------------------------

Date:         Mon, 14 Jan 91 15:27:23 EST
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         Jeffrey R Kell <JEFF@UTCVM.BITNET>
Subject:      Re: Another grounding question
In-Reply-To:  Message of Mon, 14 Jan 91 13:49:00 EDT from <CHRIS@FANDMA>

On Mon, 14 Jan 91 13:49:00 EDT <CHRIS@FANDMA> said:
>I understand the tree design, but in my case it's not practical:  we have
>three 800-watt amps driving the main PA and another 800-watt amp driving
>the monitors, in addition to two guitar amps, a bass amp, a keyboard amp
>and the rest of my keyboard setup all on stage.  [...]
>
>So, if a tree layout isn't viable, what's a poor e-musician to do?

Find somebody that really (really) knows some basic electrical wiring (if you
have a friend in NECA it would help <grin>).  I would not advise doing this as
a bathtub experiment.

The basic idea is to build your OWN service box.  A short rack on casters is
great and will hold the box, cables, and outlets.  It should house a fair-size
distribution box with independent breakers.  Have your ETech friend rig the
outlets.  Now, the trick part, wire the supply-side of the distribution box
to a 240-v circuit breaker plug and plenty of outdoor-rated feed cable.  When
you arrive at a gig, go to their distribution panel, pop out an existing
breaker, and pop in your plug.  Whammo... an entire service, common ground,
overload protected, that can handle up to the supplying panel's main breaker
current rating.  This is pretty common practice in mid-size road shows.  The
larger shows request taps directly to mains.  Some shows here at our arena
have requested up to 300kVa mains for lighting (that'll seriously cook your
goose) and smaller, separate mains for PA (reduces dimmer pack "buzz" too).

/Jeff/
-------------------------------------------------------------

Date:         Mon, 14 Jan 91 16:17:00 EST
Reply-To:     miller@SOL.CS.ROCHESTER.EDU
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         Brad Miller <miller@SOL.CS.ROCHESTER.EDU>
Subject:      Re: Grounding question
In-Reply-To:  <9101141423.AA28156@cayuga.cs.rochester.edu>

Just a couple very minor points on all the mostly very accurate stuff that
has already been posted:

If your house has polarized plugs, the larger one is supposed to be neutral
(in case you need to futz with it).

Terminology: HOT carries the current from the service box to the appliance.
One HOT for 120, two HOT for 220. Normally this wire is white (in 120).
Local code may differ on color scheme.

NEUTRAL carries the current from the appliance back to the service box. One
needed for either 120 or 220. Normally this wire is black (in 120). Local
code may vary on color scheme.

GROUND used for safety purposes. Required (by code) for 120v lines only, but
may be present as a fourth wire in 220. This wire is required to be green
universally to my knowledge.

The third pin (green wire GROUND) and neutral are connected together in the
service box (at least according to local code), but that does NOT mean they
are the "same" at the application end (where you plug something in). In
particular, the GREEN GROUND is inteded to be a safety feature for the user
only. That is, a metal case connected to green ground will prevent a
internal HOT wire shorting to the case electrocuting the user, as has been
mentioned.  If a device shorts internally NEUTRAL to GROUND they are in
violation of code, and create a ground loop. The only place these are to be
connected are at the service box (i.e. where your circuit breakers and/or
fuses are) and nowhere else. One does not normally want to use GROUND as
NEUTRAL because 1) the safety feature of having separate paths is gone, and
2) a small amount of voltage might appear on the surface of appliances that
are on this branch. If the user were to touch both this appliance and another
on a different branch... 3) you can get a ground loop as mentioned... 4) you
will trip any GFIs on the circuit, regardless of the presence of an actual
fault.

All cold-water metal pipes in the building must be connected to EARTH
GROUND. This is normally taken from the cold water service into the building
(since it's copper and well grounded), a wire is used to connect the EARTH
GROUND from one side of the water meter to the other. Electrical GROUND
should be connected to EARTH GROUND at one point, only, but EARTH GROUND
provided by metal pipes may be used as an alternative to GROUND for user
service in the building (but not for neutral). Technically this should only
be needed for old construction, since newer construction all require a
separate green wire GROUND be provided at each service outlet, so I don't
know why one would need the EARTH GROUND provided by the pipes for service
reasons.

I'm not an electrician, but I had to study up on the code to rewire my
basement :-).
----
 Brad Miller		U. Rochester Comp Sci Dept.
 miller@cs.rochester.edu {...allegra!rochester!miller}
-------------------------------------------------------------

Date:         Mon, 14 Jan 91 16:30:00 EST
Reply-To:     miller@SOL.CS.ROCHESTER.EDU
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Comments:     corrections added
From:         Brad Miller <miller@SOL.CS.ROCHESTER.EDU>
Subject:      Re: Grounding question (CORRECTED VERSION)
In-Reply-To:  <9101141423.AA28156@cayuga.cs.rochester.edu>

Just a couple very minor points on all the mostly very accurate stuff that
has already been posted:

If your house has polarized plugs, the larger one is supposed to be neutral
(in case you need to futz with it).

Terminology: HOT carries the current from the service box to the appliance.
One HOT for 120, two HOT for 220. Normally this wire is WHITE (in 120).
Local code may differ on color scheme. < PREVIOUS MESSAGE SAID WHITE. OOPS.
IN FACT IF YOU USE WHITE, YOU ARE SUPPOSED TO WRAP EACH END IN BLACK
ELECTRICAL TAPE TO SIGNAL THIS. > 220 SEEMS TO DIFFER MORE THAN 120. SOME
USE BLACK/ RED GREEN - THERE IS NO NEUTRAL BECAUSE THE 2 LEGS ARE USED
TOGETHER. WHITE NEUTRAL MUST ONLY BE PROVIDED IF THE TWO LEGS WILL BE USED
SEPARATELY WITH RESPECT TO NETURAL (for instance stoves with convenience
outlets of 120).

NEUTRAL carries the current from the appliance back to the service box. One
needed for either 120 or 220. Normally this wire is WHITE (in 120). Local
code may vary on color scheme.

GROUND used for safety purposes. Required (by code) for 120v lines only, but
may be present as a fourth wire in 220. This wire is required to be green
universally to my knowledge. IT MAY ALSO BE BARE.

The third pin (green wire GROUND) and neutral are connected together in the
service box (at least according to local code), but that does NOT mean they
are the "same" at the application end (where you plug something in). In
particular, the GREEN GROUND is inteded to be a safety feature for the user
only. That is, a metal case connected to green ground will prevent a
internal HOT wire shorting to the case electrocuting the user, as has been
mentioned.  If a device shorts internally NEUTRAL to GROUND they are in
violation of code, and create a ground loop. The only place these are to be
connected are at the service box (i.e. where your circuit breakers and/or
fuses are) and nowhere else. One does not normally want to use GROUND as
NEUTRAL because 1) the safety feature of having separate paths is gone, and
2) a small amount of voltage might appear on the surface of appliances that
are on this branch. If the user were to touch both this appliance and another
on a different branch... 3) you can get a ground loop as mentioned... 4) you
will trip any GFIs on the circuit, regardless of the presence of an actual
fault.

All cold-water metal pipes in the building must be connected to EARTH
GROUND. This is normally taken from the cold water service into the building
(since it's copper and well grounded), a wire is used to connect the EARTH
GROUND from one side of the water meter to the other. Electrical GROUND
should be connected to EARTH GROUND at one point, only, but EARTH GROUND
provided by metal pipes may be used as an alternative to GROUND for user
service in the building (but not for neutral). Technically this should only
be needed for old construction, since newer construction all require a
separate green wire GROUND be provided at each service outlet, so I don't
know why one would need the EARTH GROUND provided by the pipes for service
reasons.

I'm not an electrician, but I had to study up on the code to rewire my
basement :-). SORRY FOR THE PRIOR ERRORS
----
 Brad Miller		U. Rochester Comp Sci Dept.
 miller@cs.rochester.edu {...allegra!rochester!miller}
-------------------------------------------------------------

Date:         Mon, 14 Jan 91 16:51:00 EST
Reply-To:     miller@SOL.CS.ROCHESTER.EDU
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         Brad Miller <miller@SOL.CS.ROCHESTER.EDU>
Subject:      Oh foo.

Rereading my "corrected" copy, I realize it still may be confusing. So in
one sentence, 120 service,

HOT is black. Short blade of outlet.
NEUTRAL is white. Taller blade of outlet.
GROUND is green or bare. Round or upside-down U blade of outlet.

Whew. Next time I write the message and wait a day before posting :-).
----
 Brad Miller		U. Rochester Comp Sci Dept.
 miller@cs.rochester.edu {...allegra!rochester!miller}
-------------------------------------------------------------

Date:         Tue, 15 Jan 91 19:27:46 GMT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         "Benjamin M. J. Ellis :->" <bmje@UKC.AC.UK>
Subject:      Re: Earth loops

Yo!
   All this earthy stuff is very interresting, and brings back
so many good (sic) memories for me 8-)
   There is, however, one solution no one has mentioned which
also works REALLY well, and is REALLY safe!!! I discovered it
when I noticed my record deck was humming... this was due, of
course, to an earth loop. The problem was, there shielding of
the audio cable connecting it to the pre-amp was earthed, not
only that, but also the record deck motor was earthed as well
but none the less, separately... problem... nice big unwanted
loop, since the motor was connected to the chassis, and the
chassic to the audio connector ground... etc... etc... any the
at the time I wanted to fix it quickly (I had a new record to
[
list to okay?!??!)... the solution was to run and EXTRA ground,
later I found this invaluable in PA work... you set up, get a
humm... don't know the bands equipement, have 1 hour to sound
check, no time to faff around, so just run a few extra earth
wires to get rid of all those unwanted potention differences
(voltages)... well it works, its hap hassard, but ALOT less
dangerous than "lifting the earth"

     eeekkk...
                 -Benjamin
                  U.K.C. England
---------------------------------------------------------------
P.S. in the next two weeks or so I'm test the bass synth so
     thanks to everyone for the pick up advice, lets pray it
     works!!!!
-------------------------------------------------------------

Date:         Wed, 16 Jan 91 11:36:20 GMT
Reply-To:     Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
Sender:       Electronic Music Discussion List <EMUSIC-L@AUVM.BITNET>
From:         Nick Rothwell <nick@LFCS.ED.AC.UK>
Subject:      Re: Oh foo.

>HOT is black. Short blade of outlet.
>NEUTRAL is white. Taller blade of outlet.
>GROUND is green or bare. Round or upside-down U blade of outlet.

.which confused the hell out of me last weekend when I was rewiring some
American mains cables (black == live indeed...). The old British system
used to be:

   LIVE: red
   NEUTRAL: black
   EARTH: green.

Now we've adopted the European system, which is

   LIVE: brown
   NEUTRAL: blue
   EARTH: green/yellow stripe.

Just in case this is of use sometime...

Nick.
--------------------------
End of the EMUSIC-L Digest
**************************