Lights and Sound: Phasing issues with theatre power

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Phasing issues with theatre power

Printed From: Community Theater Green Room
Category: Producing Theater
Forum Name: Lights and Sound
Forum Discription: Technical discussion
URL: http://www.communitytheater.org/forum/forum_posts.asp?TID=2448
Printed Date: 5/08/25 at 12:19am
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Topic: Phasing issues with theatre power

Posted By: Mr. Lowell
Subject: Phasing issues with theatre power
Date Posted: 6/11/07 at 5:31pm

Hi guys, I need some professional safety advice from you hardcore theatrical electricians out there.

I'm a lighting designer, so I know squat about AC power, right? But I do have a healthy respect for it. I've felt the "110 rush" a few times over 30 years.

But one big fear I've always had is getting popped with 240 volts due to some kind of phasing fowl-up in the theatre someplace.

Back in the 1970's I heard a horror story about a rock musician holding his electric guitar and touching his lip on a stand mic that wasn't grounded properly. He got a big 220v zap and refused to go on with the concert unless EVERY roadie came out on stage and did the same first...or they were fired! Yes, it might be a silly old legend, but ever since, I've worried about crossing power supplies somewhere on stage.

Here's why it has come up now. The other day I was in the booth under the balcony. I was wearing my Clearcom (wired) headsets. I touched a digital camcorder in the booth and heard a faint buzz sound on the earphone. I touched a laptop computer and heard a faint buzz again.

Both items are plugged into a booth outlet which is powered by a transformer under the balcony. But the Clearcom base station is plugged in backstage, where it is powered by a transformer in the loading dock. I tried touching other units in the booth, such as the mixer and the dimmer board, and I did NOT get a buzz sound on the headset.

Why did the the camera and the computer buzz in my ear? And more importantly, should I be at all concerned? Could a short circuit in the system someday cause damage to equipment or a shock to a crew person?

The 3 phase power coming into the building was installed by expert industrial electricians, of course. But they build general office buildings all the time, not dynamic theatre spaces. I often wonder if they realized that a performer can be standing on stage holding several different items - each of which is powered by three or four different transformers at once. A guitar, a spotlight, a hand mic, a headset, a smoke machine, a worklight...

What if one or two of these fixtures has a short, or crossed ground, or something funky? Will the person get a 240 jolt? (A 120 jolt would be bad enough!)

Am I worried about nothing? Did they think of everything?

Or am I just confusing my different transformer sources with different phases?

Oh, and the booth in the big Theatre and the booth in the Studio are also linked for sending audio between the mixers. AND the Clearcom headset system links both theaters as well.

And another concern of mine is my video prompting system. I have a camera in the Theater booth so the cast can see the show on a monitor backstage. Plus the video is daisy-chained to a monitor in the studio theatre, (used as a greenroom), and sometimes even a monitor in the lobby. So I have a couple hundred feet of video cable connecting the camera to 3 monitors that are each plugged into 3 different power sources. Could this video set-up cause the same potential hazzards as the headsets and mics?

With all this in mind, do you think my system foolproof? Or should I call in a certified electrical inspector ASAP? If so, would a "local" electrician understand the weird wild world of live theater?

If you are a wise electrician yourself, please offer some friendly advice.

Thanks in advance, Dana

Specs. on the facility:

-Brand new with 600 seats, 40 wide proscenium, 6 story counterweight fly system, plus 200 seat black box attached beyond the loading dock.

-No company switch on stage, just architectural wall outlets and 3 stage floor pockets.

-The 192 dimmers in Sensor rack, (plus 16 houselight dimmers in Unison rack), are powered by a LARGE transformer next to the booth, under the balcony.

-The distribution of the 192 dimmers goes to the 4 electrics on stage, pigtails on each corner of the stage, two FOH catwalks, box booms, and balcony rails.

-The ETC Expressions board is powered by the same booth outlet as the audio mixer.

-The amps and mixer are plugged in the booth outlets and powered by a small 120v utility transformer behind the booth, under the balcony.

-The 3 non-dim floor pockets, as well as the backstage architectual wall sockets, (that power the headsets), are powered by a 120v utility transformer in the loading dock.

In addition, the building also has several other misc. transformers:

-One off the lobby for theatre aisle lights, lobby lights and office outlets, etc. (120v).

-One off the lobby specifically for the 277 volt fluorescents throughout.

-Another one in the loading dock dedicated to the 48-dimmer ETC rack in the Studio Theatre.

-A third one in the loading dock for 277 volt works in the Studio.

-And one in a utility room for the building's HVAC system.

That's 8 transformers coming from the main 3-phase Duke Power Company breaker cabinet in the loading dock area.

-------------
Mr. Lowell,
Lighting/Set Designer & Tech Director,
for the Linda Sloan Theatre,
in the Davison Center for the Arts,
at Greensboro Day School

Replies:

Posted By: MikeO
Date Posted: 6/11/07 at 7:31pm

I AM NOT a professional, but here is what I do know. You are likely experiencing a feedback loop, created by your headset system being on a different phase than your other equipment. It is not dangerous, just annoying. The solution is to get your headset system on the same phase as your sound equipment and computer. Considering your setup and the distance between the equipment, this may not be possible. A qualified electrician may be able to do this, as it is imprative that if you switch phases on an outlet or breaker, you must be certain that it has a dedicated common wire, not one that is shared by other outlets or hot wires. Hope this helps.

-------------
I'd rather act, but they found out I can do tech & sets!!

Posted By: P&M Sales
Date Posted: 6/12/07 at 1:07pm

In the UK & Europe, we have 415V across the phases with 220V from each phase to ground, so we are doubly interested to make sure all is well!

There is a building regulations requirement here too that in any building that is served with more than one phase, there MUST be a 6ft (2metre) distance between any socket outlets fed from different phases. Nowadays as well, all socket outlets have to show the phase number or colour (we use red, blue and yellow in the UK) they are connected to.

I would try and find out from the electrical distribution drawings for the theatre, which sockets are served by what phase, and also (very importantly) what phase (or phases) the stage lighting system uses. Unless you use extension cables from the pigtails to lighting positions near architectural/general sockets, you should be OK with these, but check the floor pockets carefully.

Next thing to check is the phase of the sockets serving your audio & video equipment in the lighting and sound booths.

Ideally, every piece of electrical equipment in the auditorium and on stage and in the dressing rooms should be served from just one phase. This can put a large load on one phase, but in most buildings your AC and Heating systems can use another phase, then the kitchen/bar/foyer power and lighting etc can balance it all out on the third phase.

It's always better to have a working knowledge of the entire theatre's power supply system - unless you do have that knowledge you never know if if going to come and bite you!

This almost happened to me once. In our booth we have a couple of stage lighting circuits wired in to use for testing purposes and also occasionally to poke a small follow spot out of the door (don't ask!). Our stage supply was entirely on the blue phase, so imagine my surprise when I discovered (by looking at those electrical distribution drawings for the building) that the domestic power sockets in the booth were connected to the red phase! So we had the blue phase powering the dimmer racks and the red phase powering the lighting and sound desks etc etc. Needless to say, that got changed VERY quickly!

-------------
best regards

David
http://www.stagescripts.com - http://www.stagescripts.com

Posted By: Mr. Lowell
Date Posted: 6/25/07 at 4:32pm

Thanks http://www.communitytheater.org/forum/member_profile.asp?PF=972&FID=20 - MikeO and http://www.communitytheater.org/forum/member_profile.asp?PF=386&FID=20 - P&M Sales for the advice.

An electrician is coming next week to install some new outlets for me, so I'll try to get his opinion on the power situation in the theatre. I'll post his comments here in case others have questions similar to mine.

Thanks again, Dana

-------------
Mr. Lowell,
Lighting/Set Designer & Tech Director,
for the Linda Sloan Theatre,
in the Davison Center for the Arts,
at Greensboro Day School

Posted By: Gaafa
Date Posted: 6/29/07 at 12:38pm

We have a 440VAc 3 phase & 254VAC single phase here. Also everyone working on presures over 32VAC has to be Licensed under the state Electrical Act by the supply Authority.

You would be some what different as with the UK. Which still Use the 'Ring Mains' system in a lot of situations. (which was an inovative British method of saving on the amount of copper conductors used durning the War to save on the amount of copper cabling.)

Your local 'wire jerker' who fronts up, would be able to advised on your local supply conditions & give you a quick schemtic of the the mains supply distribution - if the drawinging can't be found, as suggested.

There are a lot of factors for the buzzing, including Mains emf harmonics, shielding & power cables running parrel to audio conductors. A good Sparky ould be able to advise you on this.

With the niose a simple line filter can be utalised easily enough, if it's a problem.

As this is primarily an audio problem any audio techie can sort this out for you.

-------------
Joe
Western Gondawandaland
turn right @ Perth.
Hear the light & see the sound.
Toi Toi Toi Chookas {{"chook [chicken] it is"}
May you always play
to a full house}

Posted By: Attreui
Date Posted: 2/19/08 at 1:19pm

You are not going to get "hit" with 220v. As said earlier, this is a grounding issue, not necessarily a power problem. It sounds like there may be a floating ground somewhere that wasn't attached or is attached wrong. One possiblity is that there are some mixed up wires in the headset system. This can happen if pins are swapped somewhere and you become part of the grounding system when you touch something grounded. Also as stated before if you have connections going to other theatre's it's possible you are on different ground planes. One thing that does sound a little wierd is that the sound board etc are in the same outlets as the lighting console. Both those systems should be separate as a rule of thumb. This could cause all kinds of noise problems in the sound system and intercom system as well.

If this is a new facility you need to call the electricians and people who did the intercom and have them check their connections again. We run into this all the time when installing new facilities. It's a lot of connections and one never gets them all right the first time.

Posted By: vickifrank
Date Posted: 2/20/08 at 3:05pm

I'm an electrical engineer not a real electrician, but it sounds like the buzz you are getting is a 60 cycle hum. You see any wire acts like an antenna unless shielded--and even when shielded it still acts somewhat like an antenna. So when power flows thru the wire at 60 cycles it 'transmits' like a radio tower antenna. The other internal wires associated with the camcorder and laptop audio act as small antennas too. They 'receive' the sound (60 cycle hum). But since everything is shielded the antennas don't work as well ( the signal is attenuated), so you only get the hum when the systems are close. If I'm right, this is not dangerous. (But I'm the type of EE that deals normally with computers not power circuits, or antennas). This is sort of like when people with metal fillings in their teeth hear the radio through them when they pass a radio transmitter on the road. The fillings small as they are act as weak antennas and recieve the very strong signal of the transmitter. This also is what you saw and heard on your tv screen in the old days, when running power equipment near the tv--strong diagonal lines and a funny buzz sound.

Different transformer sources will be out of phase by definition--but expert installers ought to have everything grounded. Since ground is ground you should be good. (If you ever get shocked, its the electricity flowing through your body on its path to get to the ground. Electricity takes the path of least resistance. So given a choice of traveling through you and shocking you, or traveling through a nice low resistance thick wire that connects to the ground, the electricity will choose the wire. So that is why we 'ground' equipment by running a thick wire to something already grounded--like a water pipe.)

Having said all this, mistakes are always possible and it won't hurt to have the electrician check it all.

-------------
_____________

http://www.studio-productions-inc.com
1-800-359-2964

The theater scrim people

Posted By: JoeMc
Date Posted: 2/20/08 at 8:10pm

This is all good advice from the previous posters.

I'm sure Lowell's sparky would have sorted the problem out by now with his local Sparky?

{it is amasing what can be achieved with a screwdriver & a bloody big nudge venier [hammer]!

But I think this throws up an important factor & on going situation problem that may pop up & bite now & then.

That of PAT [Portable Appliance testing] & other good housekeeping praactices in theatre.

I would imagine this to be a particular problem there, with the lower Voltage [EMF] & higher current [Amperage] when using the same wattage as they do here [254VAC] on mains ppower supply.{[It is the Amps that will kill, not because that of the voltage] 120Volt 1000Watt Lamp = 8.33 Amps - 254V 1000W = 3.937 Amps ( effectiivly using half of the Amperage)}

As one can't see, hear or smell electrical current, only feel it. It is a very efficeint killing machine.

Unfortunatly well meaning techies & others can create unkowingly a silent assign, while doing thier jobs.

One of tricks used by the 'Niose Boyz' if they experiance audio intererfearance, caused by the mains power. Is to disconnect or cut off the Earth cable, to fix it.

The hiccup is they never seem to get around to reinstating the earth circuit & the equipment remains in that condition. Untill something internally goes wrong & mains current is passed to the frame, usualy resulting in some poor soul being zapped or fried. It could have worked without an effective Earth bonding for years, unless regular Portable Appliance Testing [PAT] is carried out, which could save sioling a pefectly good body bag in the future & a heap of paper work as well!

Unfortunatly near accidents such as receiving a slight shock are hardly ever reported & usualy just waved off, as being one of those things. Or when a fuse blows & circuit breakers trips out, they are just rewired or rest, without any investigation as to why it happened. Normally the attitude is 'Well we know now the fuse or Breaker actualy works" or "Not to worry that is what they are designed to do!'. Without the incident being logged or even keeping an incident record book in play, for future reference. Which can save a lot of perspiring of the eyes & heart ache later on, by the record hiighlighting that there is a problem, after the problem keeps repeating Or when housekeeping general maintenance servicing is carried out.

If I find a problem with equipment, if it is electrical, I chop off the electrical plug or with mechanical problems, tie a knot in the cable. untill i get to fixing the problem later, invarably I won't have a 'Danger Tag' handy & this is a quick mefthod of giving the signal that there is something wrong, before anyone uses it hopefully!

Also there is always the problem of when something goes bung or is broken on a piece of gear. To hide it the fact & the equipment, leaving it to be someone elses problem?

Here industrialy every appliance & equipment, has to be tested each 3 months, by a qualified Licenced Electricain [minimum required is a 'Restricted Licence'] with a detailed coloured test tag applied to the equipment. [red. Blue. Yellow & Green] giving a visual signal, when last it was tested & by who & licence Number]

Commercial it only has be tested each year with a Black Test Tag attached.

However theatre & the entertaiment venues have fallen thru the cracks & some how become exempt from this compliance, under the Act.

{But lobying by Gaafa the yoyo & other characters, may change this situation & have theatre included - but I won't hold my breath! for now!

The main objection from proeatre is the cost & inconvience of finding or employing a sparky to do this & with Comeatre getting thier hands on a licenced techie. Which misses the piont that normal [PAT] testing can be performed by experiance & competant techies, without them being licenced to comply with the OH&S Act.

Anyhow it is good policy to instigate at least equipment inspection on a regular basis & keep an up to date log book, it may save a life or cut down on the eyes perspiring & heart aches in future.

-------------
[western] Gondawandaland
"Hear the light & see the sound!
TOI TOI CHOOKAS
{may you always play to a full house!}

Posted By: vickifrank
Date Posted: 2/21/08 at 5:33pm

Good comments Joe. In US industry we have a set of standards for "Lockout/tagout" that cover a similar ground. You lockout devices by use of a lock that attaches normally to the 'on' switch or like and prevents the device from being used while the technician is working on it. For instance you would not want a punch press to be turned on when a technician is servicing it.

You tagout a device by placing a prominant tag on the device warning to not use it. (Your 'danger tag' is probably similar.)

I especially like the thought of chopping off the plug--no mistaking the message there, eh?

There is one thing I would add. You can't smell current, but you can smell some of the damage that can lead to electric shock. If you ever smell something like burning rubber or burning lacquer around a device, you might be smelling insulation or dialectrics burning. Either can result in damage to equipment or people, or fire. So don't ignore a smell around electric or electronic equipment.

-------------
_____________

http://www.studio-productions-inc.com
1-800-359-2964

The theater scrim people

Posted By: JoeMc
Date Posted: 2/21/08 at 9:31pm

Commercial & Industrial situations using circuit breakers, have provision for Lockout. In fact I always carry a couple of my key locks in my tool box, ensuring no one but me has the key.

with rewireable fuse wedges, I always remove them, along on with any other that are laying around in the Main switch board. putting the wedge in my pocket & taping over the open wedge base.

There is a heavy fine for anyone removing a tag, except the original electrician, who's name is on the tag.

however this does not stop the average wombat from doing so!

With domestic circuit breakers there are lockout clips, which in my view are as useless as boobs on a bull!

It is far better to just disconect the live delivery circuit cable & rendering the CB inactive.

Many years when I owned Catering engineers, i had a service call to a prominant city restuarant. Complaining thier baine marie & fridge kept blowing fuses. Upon inspection I found the Baine Marie [15A] had it's 15a Earth ppin filed down to fit the 10A outlet socket on a multi-way distro board, with other appliances piggy back stacked into it as well. Checking the Mains fuse board I found someone had replaced the fuse wire with virtual fence wire & cobbled the circuit, to an over load state. Without being daring,game enough & completly chicken, because of the destinctive aroma of melting plastic, to open the fuse panel. I would have imagined the incoming feed was red hot & the conductor getting to melting piont. I isolated the circuit & found the fridge & another appliance were down to frame. So I chopped off the plug tops & adviced the owner of the problems. Unfortunatly the owner abused me for cutting off the plug tops & threatened to sue if I didn't reinstate them imediatly. I attempted to piont out that the next thing that would happen, if he continued to use the equipment in the same manner. Would be for him to check his fire insurance policy & see if stupidity was not an exclusion?

To this he ordered me out of the place & said he would find someone to put the plugs back!

Luckily the Electrical Inspection Office was only a block away. So i informed the Chief inspector of the situation.

The Inspector checked the restuarant almost imediatly & found the the owner replacing the plug tops. So the Inspector went straight outside & pull the Pole fuses, then issued an infringement notice, effectivly closing the premises & carrying a $1000 fine + Court fees if they were found guilty.

I believe it cost the owner some $1500 in fines & fees. Along with $5000 bill from an Electrical contractor to upgrade his premises. To boot he refused to pay for my $60 Service Call, so I issued & served my own summons. He neglegted to respond in time to the Local Court summons, so natural I had a warrent of exercusion serve on the owner, which cost him a further $276 + the $60 & all nin all it was a costly outcome for the owner being a prat & I possibly saved his premises &/or some ones life? But he didn't appreciate it - the idiot!

Anyway back to the topic I agree to use your sences & 'Be Preared' to ask the silly questions [which are not Stupid!] as to why it smells or keeps blowing fuses? Or at least have it 'Idiot checked' asap!

-------------
[western] Gondawandaland
"Hear the light & see the sound!
TOI TOI CHOOKAS
{may you always play to a full house!}

Posted By: Mr. Lowell
Date Posted: 2/21/08 at 11:24pm

Hi guys, thanks for all the new comments and suggestions lately. Sorry I can't reply right now...this is tech weekend for "Seussical" and I am working 16 hour days! Maybe later...

Thanks again, Dana

-------------
Mr. Lowell,
Lighting/Set Designer & Tech Director,
for the Linda Sloan Theatre,
in the Davison Center for the Arts,
at Greensboro Day School