Truss protectors and 1 1/4" pipe
- Thread starterBillConnerFASTC
- Start date
BillConnerFASTC
Well-Known Member
The drawings clearly call for the correct pipe and it was marked up on the shop drawings. No one argues that.
BillConnerFASTC
Well-Known Member
The last theater I worked on, the GC inadvertently over-sized the hanging pipes in the main lobby's coat check. (He went with 2" ID schedule 40, approximately 2-3/8" O.D.) It was welded and ground in place before the problem was discovered then someone sourced coat hangers with over-sized hanging hooks. It was definitely more than capable of holding up heavy, wet, Canadian winter-wear.
At some point in the future a house manager will need to source new, replacement, hangers.
Toodleoo!
Ron Hebbard.
Jay Ashworth
Well-Known Member
BillConnerFASTC
Well-Known Member
Hi Bill,
To answer your question, no I would not consider using a PVC truss protector in a permanent installation application. To err on the side of safety, I would ensure metal to metal contact in a temporary or permanent application by whatever means possible. Would I employ a stainless steel PermaPenny for continuity as well as truss protection in a permanent application? Yes, though I'm not familiar with anyone too terribly concerned about damaging truss in a permanent install.
That being said, I spoke with a theatre manager while attending the Barbizon Extravaganza who was shocked while working on the grid because of a short in the lamp base of a fixture. That fixture was temporarily installed using a PVC truss protector and was obviously isolated. Not a good thing-
To answer your question, no I would not consider using a PVC truss protector in a permanent installation application. To err on the side of safety, I would ensure metal to metal contact in a temporary or permanent application by whatever means possible. Would I employ a stainless steel PermaPenny for continuity as well as truss protection in a permanent application? Yes, though I'm not familiar with anyone too terribly concerned about damaging truss in a permanent install.
That being said, I spoke with a theatre manager while attending the Barbizon Extravaganza who was shocked while working on the grid because of a short in the lamp base of a fixture. That fixture was temporarily installed using a PVC truss protector and was obviously isolated. Not a good thing-
BillConnerFASTC
Well-Known Member
The permapenny does not seem to do the function I'm after - adding a 1/4" or so of girth to the pipe - so you don't have to run the clamp bolt so far when moving the fixture.
I'm still struggling to see how with a grounded building and the pipe rail welded to it and grounded by the steel frame and connected to the electrical ground by the all steel plug box that the fixture is plugged into that what happened to you could happen here. I don't know how the fixture in your example was isolated if it were cord and plug connected to a grounded receptacle. The fixture ground would have to have failed and the hot would have to be shorted to the body.
Reminds me that my college theatre - two wire no grounds - had electrics with plug strips and I guess there was a problem which they had solved by using ceramic insulators in the lift lines - so there was no continuity between batten/plug strip and lift lines/loft blocks/structure. The aluminum ladder against masonry was not a problem but if you reached out and touched a metal part of th building - which I did - just once - you knew there was a problem.
I'm still struggling to see how with a grounded building and the pipe rail welded to it and grounded by the steel frame and connected to the electrical ground by the all steel plug box that the fixture is plugged into that what happened to you could happen here. I don't know how the fixture in your example was isolated if it were cord and plug connected to a grounded receptacle. The fixture ground would have to have failed and the hot would have to be shorted to the body.
Reminds me that my college theatre - two wire no grounds - had electrics with plug strips and I guess there was a problem which they had solved by using ceramic insulators in the lift lines - so there was no continuity between batten/plug strip and lift lines/loft blocks/structure. The aluminum ladder against masonry was not a problem but if you reached out and touched a metal part of th building - which I did - just once - you knew there was a problem.
GreyWyvern
Well-Known Member
Sorry, didn't mean to cause a thread hijack. I was just responding to someone's post about pennies not staying in place.
-Grounding is not required by the clamp; your cable should probably do that. If you think otherwise, you need to go back to school.
-ETC supplied crap clamps will tighten down on much smaller pipes, but they are crap.
-C-clamps are garbage and should not be used anyway.
-you cannot use amps on my truss..okay you can, just give me a $1000 deposit per stick of truss.
-PVC "truss condoms" Are for people who are too cheap to buy the right clamps.
-If you are doing a theater tour and only have c-clamps, just say so and I will bring you Half couplers to use for free... just to save my truss.
-ETC supplied crap clamps will tighten down on much smaller pipes, but they are crap.
-C-clamps are garbage and should not be used anyway.
-you cannot use amps on my truss..okay you can, just give me a $1000 deposit per stick of truss.
-PVC "truss condoms" Are for people who are too cheap to buy the right clamps.
-If you are doing a theater tour and only have c-clamps, just say so and I will bring you Half couplers to use for free... just to save my truss.
Tell us what you really think Mike!
Toodleoo!
Ron Hebbard. BTW, I promise I'll never use an "amp" on any of your truss.
Malabaristo
Well-Known Member
Well, in the high schools I've worked in, I've run across plenty of poorly wired stagepins where the ground wire is the first to come loose. That means the body of the fixture would no longer be grounded if the clamp was insulated from the batten by PVC. Any further failure could easily result in the body of the fixture being energized without tripping any breakers.
So, you're absolutely right that the cable should provide a protective ground, but in school I learned that having a single point of failure is never the best design
Well, in the high schools I've worked in, I've run across plenty of poorly wired stagepins where the ground wire is the first to come loose. That means the body of the fixture would no longer be grounded if the clamp was insulated from the batten by PVC. Any further failure could easily result in the body of the fixture being energized without tripping any breakers.
So, you're absolutely right that the cable should provide a protective ground, but in school I learned that having a single point of failure is never the best design
I have also seen many fixtures and cables with the ground leads falling out of the terminals in the connectors. However -- while it is often true that PVC may insulate the fixture from the pipe, particularly if the clamps are painted -- with coated chains at lift lines, spansets, portable lighting booms, etc, you cannot reliably assume any particular batten or lighting position is bonded one way or another to a safety ground. The best you can hope for if you have a fixture with lifted ground is that something else on that pipe is grounded and making sufficient contact with pipe to provide a low-impedance path to ground.
I would be curious to see how many fixtures out there in the LED market with plastic bodies do or do not bond the yoke to the ground leads.
GreyWyvern
Well-Known Member
This is good to keep in mind. Ran into this a handful of times while touring out of the country. There was a ground bond for the truss system. More than once, it turned out the ground wasn't properly connected at the venue's panels; tied to neutral instead or not connected at all or not a good enough ground connection. With the state of equipment on the truss, mainly the old S4 pars, there was almost always some voltage energizing the truss. Normally not a problem when the ground was good, but if it wasn't, there was a tingling sensation when you touched the truss. When running on generators, it could sometimes be an issue as well.
Allow me to play both sides here...
The contractor should be held to the design. If it wasn't important it would not have been a called-out design specification. The suggestions regarding PVC truss protectors are a misapplication of that product, they are intended only to keep the C clamp set screw from gouging or denting a truss chord, not to take up slack.
On the other side, the issue here seems to be primarily one of convenience. If a precious snowflake squint must turn a C clamp screw a few more times, so what? Unless the clamp will not fully engage the batten/pipe/truss in a safe & secure manner, there doesn't seem to be a significant issue.
If the contractor is either so sensitive that making him correct the problem of his creation will cause him to cry, pout or otherwise ruin his day; or if he is sufficiently petty and vindictive as to sabotage other aspects of construction, you have more issues that the size of pipe.
The contractor should be held to the design. If it wasn't important it would not have been a called-out design specification. The suggestions regarding PVC truss protectors are a misapplication of that product, they are intended only to keep the C clamp set screw from gouging or denting a truss chord, not to take up slack.
On the other side, the issue here seems to be primarily one of convenience. If a precious snowflake squint must turn a C clamp screw a few more times, so what? Unless the clamp will not fully engage the batten/pipe/truss in a safe & secure manner, there doesn't seem to be a significant issue.
If the contractor is either so sensitive that making him correct the problem of his creation will cause him to cry, pout or otherwise ruin his day; or if he is sufficiently petty and vindictive as to sabotage other aspects of construction, you have more issues that the size of pipe.
BillConnerFASTC
Well-Known Member
Based on over 35 years of working in the design and construction business, I disagree with this as a blanket rule. You try to find solutions to their problems, and they will help try to solve yours. If you think a multi million dollar building can be designed and documents with never an error or miss, or constructed and turned over with everything "perfect", you are dreaming.
First of all, I am of the opinion that if a designer/consultant/architect/etc. goes to the trouble of specifying a dimension or a tolerance, it should be met. If the tolerance is +/- 1" that doesn't mean that you can be -2" just because the error window is 2" wide... If the material is supposed to be 1-1/2" BIP then that is what should be installed. If the contractor or buyer or sourcing agent is confused by the spec, they should ask, not just buy what they think is correct. Granted, I don't know the rest of the structure around these pipes, but as a rigging element, pipe diameter and schedule make a huge difference and affect how much support is required and how much weight can be supported. Installing the wrong product *could* have very dangerous results. I understand not wanting to piss off contractors, but it is their job to build to spec.
That said, if you aren't going to correct the error, the best solution is to make sure all the lighting equipment has C-clamps that will mate correctly with the pipe. I don't think should be terribly difficult, and if want to make the contractor buy all new c-clamps for the entire lighting inventory, maybe that is the way to go. It really is not such a big deal to spin the bolt a couple more times, and really, once you don't need a wrench to loosen the bolt, most folks can spin them out quite quickly. I would not mess around with pipe-condoms or other modifications to the pipe. Pipe-condoms will just get lost and ultimately end up not being used. Modifying the pipe, by welding bits to it kind of negates any time and cost savings to having the correct product installed. The problem will really only rear up if the venue wants to hang gear with half-coupler style clamps.
That said, if you aren't going to correct the error, the best solution is to make sure all the lighting equipment has C-clamps that will mate correctly with the pipe. I don't think should be terribly difficult, and if want to make the contractor buy all new c-clamps for the entire lighting inventory, maybe that is the way to go. It really is not such a big deal to spin the bolt a couple more times, and really, once you don't need a wrench to loosen the bolt, most folks can spin them out quite quickly. I would not mess around with pipe-condoms or other modifications to the pipe. Pipe-condoms will just get lost and ultimately end up not being used. Modifying the pipe, by welding bits to it kind of negates any time and cost savings to having the correct product installed. The problem will really only rear up if the venue wants to hang gear with half-coupler style clamps.
