Return-Path: X-Real-To: stagecraftlist [at] theatrical.net Received: by prxy.net (CommuniGate Pro PIPE 4.2.6) with PIPE id 17451690; Sat, 05 Feb 2005 03:00:58 -0800 X-ListServer: CommuniGate Pro LIST 4.2.6 List-Unsubscribe: List-ID: Message-ID: From: "Stagecraft" Sender: "Stagecraft" To: "Stagecraft" Precedence: list Subject: Stagecraft Digest #285 Date: Sat, 05 Feb 2005 03:00:39 -0800 MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Disposition: inline X-Spam-Checker-Version: SpamAssassin 3.0.2 (2004-11-16) on prxy.net X-Spam-Status: No, score=-5.5 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.0.2 X-Spam-Level: X-TFF-CGPSA-Version: 1.4f2 X-prxy-Spam-Filter: Scanned For info, archives & UNSUBSCRIBE, see --------------------------------------------------- Stagecraft Digest, Issue #285 1. Re: Proper sizing of neutrals by Eddie Kramer 2. Re: Periaktoi by Loren Schreiber 3. Re: Welding Shop Equipment by Loren Schreiber 4. Re: Yo, Frank Wood, I gotcher Matchless rightchere! by Loren Schreiber 5. Re: Proper sizing of neutrals by murr rhame *** Please update the subject line of your reply to use the subject *** line of the message you are replying to! Please only reply to *** one message subject in each reply. ---------------------------------------------------------------------- Message-Id: In-Reply-To: References: Date: Sat, 5 Feb 2005 00:53:26 -0500 From: Eddie Kramer Subject: Re: Proper sizing of neutrals Proper sizing of neutrals Curt Mortimore has a brand-new-never-been-plugged-in 24-channel ETC Sensor= portable dimmer rack He wants power from an old 600A three-phase disconnect= about 170 feet away. Facilities services on campus will do this project.= They are planning to under-size the neutral between the 600A panel and the= new company switch. If it's a 24 x 2.4K rack, the load is 160A per phase, but 160 is not a= standard ampere rating of a fuse or a circuit breaker (150, 175, and 200= are) [NEC 240.6(A)], you only need to feed it 160 A per leg. It is OK to= feed it more, you also can give it less, but if the rack is loaded, the= fuse or a circuit breaker may pop. If any of the load is continuous (on more than 3 Hr.) [NEC 100], the rating= of the overcurrent device must be at least the non-continuous load plus 125= percent of the continuous load [NEC 215.3] or 160A x 125% =3D 200A. The rack needs to be fed from a 200A or greater supply. My preference would= be to bring the whole 600A service to your theater (you can never be too= thin or have too much power). But, as this is expensive, I will assume the= plan is only to provide the minimum power. At the old 600A disconnect, a new 200A fuse, or a circuit breaker is needed= to protect the conductors. Dimmer racks produce harmonics (I'm not going= there=8A) so the Code requires the grounded conductor (neutral) to be= considered a current carrying conductor [NEC 310.15(B)(4)(c)]. On a 3-phase= circuit with a grounded conductor (neutral), there are 4 wires. Since the= grounded conductor (neutral) is counted as a current carrying wire [NEC= 310.15(B)(4)(c)], the Code requires that the ampacity of the wire be= reduced to 80% when in conduit [NEC 310.15(B)(2)(a)]. (The reciprocal of= 80% is 125 %). 200A x 125% =3D 250A. So the ampacity of the feeder cables= needs to be 250 A. The cables feeding the new company switch would most likely be THHN which is= pretty much standard for pulling in conduit. 4/0 has an ampacity of 260A= [NEC table 310.16]. While this is more than the 250A required, the next= smaller size cable is only good for 225A. NOTE: We commonly use 4/0 to carry 400A in theaters, yet the NEC lists it at= 260A. This is the rating for a cable in a conduit. It may be installed in a= wall surrounded by insulation, run through an attic, or buried in the= earth. In all these circumstances, there is no place for the heat generated= by the current passing through the conduit (voltage drop) to dissipate.= Theatrical style single conductor portable feeder cable is run across the= floor where the heat can dissipate, so it can get hotter. See Table= 400.5(B). Be aware when you use 4/0 at 400A the feeder cannot be bundled to= gether. All of the discussions about double neutrals made reference to 520.53(O).= However, Article 520 is for theaters. Part IV refers to portable= switchboards (a dimmer rack is a type of a switchboard) on stage. Paragraph= 53 is construction and feeders and says " Portable switchboards and feeders= for use on stages shall comply with 520.53(A) through (P)." The discussion= of 130% neutrals only applies to the portable single conductor cabling= between the company switch and the dimmer rack. 520.53(O)(1) refers to connections inside the dimmer rack. 520.53(O)(2) is= where the 130% requirement is. It says that the neutral shall be considered= a current carrying conductor (this refers all the way back to the service= equipment). It also says when single conductor feeder cables are used and= they are not installed in raceways (NEC speak for conduit and the like),= the neutral shall have an ampacity of 130% of the ungrounded conductors. The 4/0 THHN runs about 170' and has a 1.6 volt drop. This is less than 2%= and is viewed as acceptable. 118V is the delivered voltage The company switch is installed at the end of the conduit run in the= theater. We know it needs to be a 200A switch and we know it can be fed= with a 4/0 THHN. We talk about company switches. They can be either a circuit breaker or a= fused switch. I'm a big fan of fused switches, not circuit breakers. The= advantages of fuses are: in the event of a problem or an overload, the fuse= feeding the bad phase will open and you will lose 1/3 of your lights.= However, if a circuit breaker pops, you lose all your lights. If you need= to supply a smaller amount of current than the switch is rated for, you can= use a fuse reducer to put in a smaller size fuse. In the service under= discussion, if you decided to feed a panel that only needed 100A from your= new company switch, you could get a 200A to 100A reducer. However, with a= circuit breaker, you would have to tie in a 100A disconnect. The Sensor SP12 rack comes with camlok inputs. It is a portable/touring rack= and not designed for permanent installation. Single conductor portable= feeder cable is used between the company switch and the rack. This cable is= not in conduit so the reduction to 80% of ampacity does not need to be= taken. It is protected by a 200A switch so the cable must have an ampacity= of at least 200A. The grounded conductor (neutral), as we have seen above,= needs to have an ampacity of 130% of the hots and therefore must be rated= for 260A. In the entertainment industry, 2/0 single conductor portable= power feeder cable is used as a 200A cable and this will serve for the hots= and ground. 4/0 single conductor portable power feeder cable is used at= 400A and will serve as the neutral. I would recommend getting your entire= single conductor portable power feeder cable in 4/0 because you can use it= on any size distribution you are likely to encounter. This is, of course, only my personal opinion and not an official= interpretation of any NFPA, NEC, ESTA, IEEE, or other standards. If you= want to talk about harmonics, I only do that in person. It requires too= much typing and besides, that way you get to hear me sing:-) -- -------------------- Eddie Kramer IATSE #1 Member NEC Panel 15 ------------------------------ Message-Id: <6.1.1.1.2.20050204222008.03130b20 [at] mail.sdsu.edu> Date: Fri, 04 Feb 2005 22:30:08 -0800 From: Loren Schreiber Subject: Re: Periaktoi In-Reply-To: References: I used several periaktoi loaded with 10 PAR cans each for a Doug Schmidt design some years ago. I suspended the six steel-framed, heavy-as-hell units from the grid with 1/4" 7/19 galvanized aircraft cable, and trapped the bottom with a one inch shaft in a flange bearing. Rotation was provided by a sprocket on the shaft, wrapped with a chain pulled by a small pneumatic cylinder. All six ran on the same chain and cylinder. There was no bearing or anything like it on the cable. A half dozen turns in each direction was absorbed by the cable twisting. Didn't seem to hurt the cable none--according to my belt-and-suspenders rigger at the time. Loren Schreiber, Director of Technology and Production School of Theatre, Television and Film, San Diego State University http://www-rohan.sdsu.edu/faculty/schreibr/index.html ------------------------------ Message-Id: <6.1.1.1.2.20050204223155.03180f30 [at] mail.sdsu.edu> Date: Fri, 04 Feb 2005 22:48:19 -0800 From: Loren Schreiber Subject: Re: Welding Shop Equipment In-Reply-To: References: Lincoln, Miller, Hobart and Victor are a few of the best names in welding equipment in the States. We own a Miller and a Lincoln MIG, a Lincoln mini flux-core/MIG, a Lincoln 275 TIG, a Miller spot welder, a Victor Oxy-acetylene rig and a Hobart plasma cutter. We also have a Doringer 350SA auto-feed cold saw, a Milwaukee abrasive cut-off saw and a Dakes metal-cutting band saw with blade cutter/welder. I have no complaints, but I'd like a good horizontal band saw and a plasma cutting attachment for our CNC router. Loren Schreiber, Director of Technology and Production School of Theatre, Television and Film, San Diego State University http://www-rohan.sdsu.edu/faculty/schreibr/index.html ------------------------------ Message-Id: <6.1.1.1.2.20050204225522.03153390 [at] mail.sdsu.edu> Date: Fri, 04 Feb 2005 23:08:55 -0800 From: Loren Schreiber Subject: Re: Yo, Frank Wood, I gotcher Matchless rightchere! In-Reply-To: References: Hey Frank, why don't you join us for the Long Reach Long Riders, "Out of the Wings and Into the Wind" ride for Broadway Cares, Equity Fights AIDS? I started my riding on an English bike--a 400 pound Matchless 350. Took a little while to get used to the handlebars being on the wrong side and all, but it was pretty cool for a 1958 model. You can smoke to your heart's content while in the wilds of the western US deserts (policing your butts, of course). The ride might chip a little off that curmudgeonly demeanor and reveal the disappointed romantic beneath. Frank Wood--the new T. E. Lawrence--gotta nice ring to it. I'm serious! I hereby throw down the gauntlet! (Let's see you be "neutral" about this!) Loren Schreiber, Technical Director and Long Reach Long Rider, Western Contingent School of Theatre, Television and Film San Diego State University http://sapsis-rigging.com/LRLR.html ------------------------------ Date: Sat, 5 Feb 2005 04:40:00 -0500 (EST) From: murr rhame Subject: Re: Proper sizing of neutrals In-Reply-To: Message-ID: References: If you have to double the neutral in a three phase stage lighting system, you'd be using one and two-thirds full sized conductors per hot leg. Does the neutral have to be larger than the hot legs in a 240V single phase system? If not, a 240V single phase system would provide one hot leg for every one and a half full sized conductors. For a given amount of total power, the 240V single phase option uses significantly less copper. Why use three phase at all for stage lighting? At a casual glance, a three phase service doesn't seem to have any advantage for stage lighting. - murr - ------------------------------ End of Stagecraft Digest #285 *****************************