|
|
This topic comprises 3 pages: 1 2 3
|
|
Author
|
Topic: Booth Electrical Loads
|
|
|
John Walsh
Film God
Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
|
posted 01-03-2003 10:52 PM
At our recently-opened theater in Minneapolis, we specified all audio equipment be on the same phase, and lighting be on the same phase. This was documented in the drawings, and the architect just made every breaker panel the same for every auditorium.
The electrical inspector noted this, and insisted we "break up" the load arrangement because (he said, giving an example) if all the lights are on the same phase at all panels, the phases may be unbalanced.
So, we had to change which phase things went on at each auditorium. Luckly, this theater had 15 auditoriums, so five panels had one arrangment, (lights on phase A for example) the next five a different arrangement (phase B) and the last five on phase C.
I wanted to simply switch around the three power leads inside the breaker box, so the breakers would be in the same location for every auditorium, but on differnt phases. (I really like making all equipment the same since it's easier to train people.) The electrical inspector could not think of anything in the code that would'nt allow this, but "just didn't like the idea" so would not allow it.
Since we use projectors with freq converters, the issue of phase matching for interlocking projector motors wasn't a concern.
Does anyone think this is a bad idea?
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Bruce Hansen
Jedi Master Film Handler
Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999
|
posted 01-05-2003 05:50 PM
With all due respect, Gordon, you may have something confused. If a conductor has 60 volts on it, it is not a neutral; the three phases are out of phase with each other, so how would you phase the neutral you are talking about? I can't see how that would ever work, and it would NEVER NEVER NEVER pass electrical code here in the states. What you may be thinking about is: sending the three phases to a group of outlets, but only one neutral, and connecting all the neutrals on the outlets to this one neutral. If the current flows of the three phases are balanced (the same) there will not be any neutral currnet traveling back to the bracker box, and no voltage drop across the neutral run back back to the bracker box. This concept has been used here for a long time to keep hum down, especialy for long power runs.
| IP: Logged
|
|
|
|
|
|
|
|
|
|
John Hawkinson
Film God
Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
|
posted 01-07-2003 01:17 PM
Huh. This is all interesting and fascinatingly disturbing stuff.
Jeff's last link asserts this is referenced in Article 530(G) of the 1996 NEC. In case anyone was wondering, I decided to go dig around in the NEC to see what it says.
It turns out that it's not in 530 anymore in the 2002 NEC, but there are some references elsewhere. (Article 530 is "Motion Picture and Television Studios and Similar Locations").
Instead, balanced power seems to be the subject of Article 647, "Sensitive Electronic Equipment." They seem to refer to it both as "sensitive electronic equipment" as well as "Technical Equipment," though the term "technical equipment" seems to be used elsewhere within the NEC(*).
I suppose the only terribly interesting comments in the NEC are in Section 647.7 Receptacles, (A) General:
code:
(1) All 15- and 20-ampere receptacles shall be GFCI pro-
tected.
(2) All outlet strips, adapters, receptacle covers, and face-
plates shall be marked with the following words or
equivalent:
WARNING--TECNICAL POWER
Do not connect to lighting equipment.
For electronic equipment use only.
60/120 V. 1{phi}ac
GFCI protected
(3) A 125-volt, single-phase, 15- or 20-ampere-reated recep-
tacle outlet having one of its current-carrying poles
connected to a grounded circuit conductor shall be lo-
cated within 1.8m (6 ft) of all permanently installed
15- or 20-ampere-rated 60/120-volt technical power-
system receptacles.
(4) All 125-volt receptacles used for 60/120-volt technical
power shall have a unique configuration and be identi-
fied for use with this class of system. All 125-volt,
single-phase, 15- aor 20-ampere-rated receptacle outlets
and attachment plugs that are identified for use with
grounded circuit conductors shall be permitted in ma-
chine rooms, control rooms, equipment rooms, equip-
ment racks, and other similar locations that are re-
stricted to use by qualified personnel
(*) For what it's worth, the only way I see to get to Article 647 from Article 530 is a reference in 530.11 "Permanent Wiring" permitting "communication circuits; audio signal processing, amplicfications, and reproduction circuits; Class 1, Class 2, and Class 3 remote-control or signaling circuits and power-limited fire alarm circuits shall be premitted to be wired in accordance with Articles 640, 725, 760, 800." Why is this relevent/interesting? Well, mostly it's not, but Article 640 ("Audio Signal Processing, Amlification, and Reproduction Equipment" defines "Technical Power System" as "An electrical distribution system with grounding in accordance with 250.146(D), where the equipment grounding conductor is isolated from the premises grounded conductor except at a single grounded termination point within a branch-circuit panelboard, at the originaging (main breaker) branch-circuit panelboard, or at the premises grounding electrode." Maybe I'm reading that wrong, but that seems to imply to be incompatible with the idea of "technical power" meaning 60V/120V balanced power. (250.146(D) permits isolated receptacle grounds not tied to the closest panelboard but instead terminating at some central grounding location)
In an additional bit of irony, other parts of Article 640 refer to balanced power as "a seperately derived system with 60 volts to ground" (640.7(B) and 640.9(A)(2)).
Bleh. These NEC/NFPA people could really use a decent techwriter and copy editor. ![[Mad]](mad.gif)
--jhawk
| IP: Logged
|
|
|
|
All times are Central (GMT -6:00)
|
This topic comprises 3 pages: 1 2 3
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
![[Big Grin]](biggrin.gif)
![[Smile]](smile.gif)
![[Frown]](frown.gif)
Printer-friendly view of this topic