Design Cable run to truss

[MNicolai]

A rigger and I have gotten into a debate on my current project. We're adding a vertical mast of truss on each side of the apron of our stage and putting a 68' long cross-member on top with additional lift lines to the roof structure. For all intents and purposes, this is a permanent structure. Temporary only in the sense that we could remove it in a painful process of hiring in outside contractors to do it. The only time that might happen is if over the course of the next several decades, we need to hang significantly heavier loads or it is eventually deemed structurally deteriorated and needs to be completely replaced.

We have 8-circuit connector strips on either side of the apron that are inaccessible and unusable. Those circuits we plan to tap and put onto the truss.

The district electrician and I want to pipe conduits of the dimmable circuits out of J-boxes next to the connector strips, up to the beams of the roof structure, and then down to the height of the truss. They would not be physically connected to the truss. From here, 19-pin panel mount connectors would take the electrical into SO multi-cable with break-outs that we could move around as is needed. The multi-cable would have appropriate strain relief grips, also suspended form the beams.

What the rigger wants to do is make custom 8-circuit SO multicables with 2P&G breakouts for the circuits from the connector strips and use a break-in on one end, and the breakout on the other, running no new conduits. The cable would drape up to the roof beams and over to each vertical mast.

Additionally, he wants to take (12) circuits from the dimmer racks and pipe them through the wall in our mechanical room directly onto our catwalk. At our catwalk, a 12-outlet 2P&G plug box would allow for (12) SO cables to individually carry the circuits from the catwalk, in a bundle, to the truss. The cable run would drape down from our catwalk to the truss, with pick-points on to the roof structure beams. Then, the cables would be laid out to have female connectors on 5' centers along the length of the truss.

My electrician and I have several problems with this. SO cable is specifically not allowed for permanent installs for a reason - it dry rots. If my electrician remembers code correctly, SO is only an acceptable use in permanent installs when the flexibility is needed (such as drop boxes) (again, he's verifying this in his codebook when he gets back to his office tonight). Also, in a bundle, they would need likely need to be derated (he's checking his codebook on this for confirmation). Plus, this structure is to be considered permanent for us. The rigger is defending his position by claiming that it is a temporary structure and the cables would be allowed. He did not understand why they would need to be derated. He also claims it provides more flexibility for us because we can add/subtract cables from the catwalk to the truss as is necessary. However, we don't have a lift to get to this cable bundle 35' in the air, and the last thing I need to deal with is having the risk of 2P&G connectors getting disconnected when 19-pin connectors could be screwed on and would almost never need to be looked at.

This is our rigger's way of providing inexpensive power distribution. Granted, we really don't want to spend a boatload of money on a 12-circuit, 60' connector strip, but I think it should not become flexible cable until at the truss. Anything that is a completely permanent cable run (e.g. the 12-cable SO bundle bridging the gap between the catwalk and the truss) should really be in conduit.

Experienced riggers and code-junkies -- what are your thoughts?

Flexible cable bundled together or rigid conduit between the catwalk and the truss?
To derate or not derate?
(12) 2P&G connectors or (2) threaded 19-pin connectors?

I've already gotten into two arguments with the rigger on this, and my electrician agrees with me that a pile of flexible cable for a might-as-well-be permanent install is a poor chose. Additionally, the rigger has had the project manager for a local electrical contractor quote the project for him -- this is the electrical contractor of choice between my electrician and I, but we also understand that theatres aren't his thing and his familiarity with Article 520 of the NEC is shady, at best. We think the project manager may have deferred to the rigger for expertise on the electrical that is misguided. I've tried to contact said project manager, and he has not returned my call.

I really don't need this causing this big of a problem, because this electrical contractor is the one we would hire no matter what, but if he gets caught in the middle of this rigger and his ways, this is going to be a messy situation. Especially because we have multiple riggers quoting this project but already have this electrical contractor as our established go-to guy.

The rigger has already told me he can quote the project without electrical, but that we need to then find someone else who has experience with rigging, rig the electrical on the truss. (Speaking of which, how much experience do you need to get flexible cable on a fixed truss? -- This seems to me like it's an empty threat of sorts)

 

[SteveB]

"The rigger has already told me he can quote the project without electrical, but that we need to then find someone else who has experience with rigging, rig the electrical on the truss."

This sounds like an ultimatum.

My very first read was to ask out loud "why is the rigger involved in the electrical wiring design ?".

Your last paragraph sounded like the rigger is saying "If you don't do the electrical my way, I'm not rigging any of the electrical".

At which point I would diplomatically ask him to clarify his position to ascertain if that was true and if it was and his/her final position, I'd diplomatically fire his/her sorry ass. Or not so diplomatically if it came to it. Your call and you know the political situation.

FWIW, as an LD and stage electrician of 34 years, I agree that as much as possible all wiring should be in conduit up to the point that it can no longer be. Bundles of 12/3 SOOW is a dumb idea and expensive to boot, in labor alone, as well as heavy to install and support - so why is it a good idea again ?. The rigger is correct that the TRUSS is temporary, but that doesn't mean the electrical is. I also like the idea of using standard 6 circuit multi's, with Soca or similar connectors, as they are industry standard and easy to replace in one unit. Multiple 2P&G connections are all failure points.... and there are other issues as well, but bottom line, the electrics folks design what works for them and the rigger installs it, unless there is some over-riding reason that the electrical design is flawed in some way, and I'm not seeing that here.

 

[MNicolai]

In our initial meeting, I mentioned a specific electricial contractor that I like to work with and the rigger took it upon himself to contact him directly and have him quote the project. He unknowingly skipped over the district electrician and knowingly skipped over myself by contacting the electrician on his own and arranging it through my boss, the arts center manager. I have been the one researching the project with different contractors for months and though It was an effort to make our lives easier, the rigger has stepped beyond the scope we intended him to have on this project.

I will not disconnect him from the project because he is an excellent rigger but in this case he has certainly put our district electrician and myself on alert. I am, however, prepared to tell him to remove electrcal from his scope pending further discussion here and further research on the codes by myself and our district electrician. I will be digging into my NEC2008 codebook later tonight and my electrcian will be tomorrow morning, and then him and I will compare notes.

 

[mstaylor]

As an experienced rigger and an electrician, your rigger is an idiot. He has no business getting into your method of wiring, especially since he is wrong. I assume you are bidding the rigging contract and as such you should write the bid spec to include both rigging the truss and running the soco. Of course, that begs the question, how are you going to get your lights up there and focus once they are. If you are going to have a means to access the truss once it is erected, then you won't need a rigger to run the soco. If you can't access the truss then you will need to hire a rigger everytime you need to change something.
I don't want to start a discussion about how to rig your truss but is the rigger really qualified to do his portion. Run your power in conduit and change to soco and breakouts when you get to the truss.

 

[MNicolai]

@mstaylor

We have scaffolding that we will be able to use immediately once the project is complete. I am also including with all of the bid documents and project proposal a recommendation to purchase either a one-man lift or an articulating boom lift.

The articulating boom lift is overkill for the theatre on average, but my talks with the district electrician have revealed that there is a need for it within the district and a purchase of one would be especially beneficial for the theatre (accessing house lights) and would then be a substitute for the purchase of a one-man lift. The district building and grounds supervisor has already had this subject fly across his desk and is looking into it.

However, the position on the catwalk that the cables would drape down from and onto the truss is obscure and once the truss is installed, would only be accessible by an articulating boom lift. So if any of these cables had a problem it would require extensive labor to remove the cable from the bundle and replace it. (As an aside, such problems may include flaming insulation as a result of being placed in a 12-cable bundle and not being derated appropriately.)

 

[FatherMurphy]

You mention 'the district' which suggests to me a public school setting, with the bidding and budgeting processes that entails. My inclination would be to remind the rigger that since it is your budget of public funds that is being spent, unless he can come up with compelling reasons to ignore codes and standard practices, you will be wiring it the way that you and the electricians prefer. Jumping a step and contacting another contractor on his own was not an appropriate move, imho - that's how things get screwed up.

Since you mention two batches of eight circuits, plus another twelve, this suggests you have 28 circuits available. If it was me, I'd look for two more to bring it to an even 30 (or double two, if I can't find more), and put in five six-circuit Socapex drops on or above the truss. Panel mount outputs are one way, tails of some length coming out j-boxes with Kellems grips would help eliminate connection points. All should be homeruns in pipe back to the rack. Six circuit Soca wiring is more common than eight circuit versions, and would give you a few more division options.

 

[MNicolai]

You mention 'the district' which suggests to me a public school setting, with the bidding and budgeting processes that entails. My inclination would be to remind the rigger that since it is your budget of public funds that is being spent, unless he can come up with compelling reasons to ignore codes and standard practices, you will be wiring it the way that you and the electricians prefer. Jumping a step and contacting another contractor on his own was not an appropriate move, imho - that's how things get screwed up.

Since you mention two batches of eight circuits, plus another twelve, this suggests you have 28 circuits available. If it was me, I'd look for two more to bring it to an even 30 (or double two, if I can't find more), and put in five six-circuit Socapex drops on or above the truss. Panel mount outputs are one way, tails of some length coming out j-boxes with Kellems grips would help eliminate connection points. All should be homeruns in pipe back to the rack. Six circuit Soca wiring is more common than eight circuit versions, and would give you a few more division options.

We also have an additional couple 20A non-dim circuits we want to add onto these drops, so our division options are still pretty good.

And yes, it is a school district that operates the arts center. I've managed to avoid a lot of politics thus far and have only done a competitive bid process for my own pleasure. I don't feel it's necessary to further alienate him though by not only saying, "We don't want you doing our electrical," but rubbing it in to say, "We wouldn't trust you with an extension cord."

He is willing to quote the rigging without the electrical, but he refuses to help suspend cables installed to another solution that his own. He's picky; I understand why, and I respect that. This case is a bit of an exception, but if you see a client making a "bad" decision with something like rigging, it's your duty to be stubborn about what constitutes a good decision and why. In this case, he's moved beyond his expertise though.

 

[Dionysus]

I would use flexible conduit, you seemed to not realize this as an option.

YES, SO cable is not intended for permanent install when at all avoidable, however I find that various forms of flexible conduit replace the need for SO or similar cable in certain situations.

YES, when bundling cables you are required to de-rate by the letter of the code.

There are various forms of flexible conduit you can use, and you can also go with what is commonly known as TECH cable (essentially a cable covered in flexible conduit, similar to Bx (aka AC90) but with a black plastic coating). It is armoured and waterproof. It is the only 'extra hard usage' permanent install cable allowed (here anyways).

You can not use rigid conduit, EMT conduit, PVC conduit, etc onto the truss either.

I'd have to get my codebook from my truck to quote the rules involved so I won't. Plus mine is not the US code, so the rules are slightly different (however almost identical in many ways).

You CAN technically use SO cable for this project, but you should talk to your local inspection authority first. It's really their call if they will allow it in this instance. Your electrician really should have their number to ask an inspector directly. If you use SO cable it should only be for the "removable" parts that goto the truss, not the entire amount leading up to it. Up to that point it should be conduit (flexible or not).

This is off the top of my head, but I am an electrical apprentice (soon to be journeyman if all goes well.).

 

[SHARYNF]

In another thread I raised a question that Dionysus or someone else might be able to answer.

If you were running conduit for this system there was a need for running non dimmed lines from a sub panel, along with the dimmed lines from the dimmer rack, would this be allowed? Or do all the ac carrying lines in a single conduit need to be from the same source/system? Reason for my question is that typically when the metal conduit is attached to the panel box or dimmer rack it bonded to the ground connection, and I wondered if there would be a code issue with having the bonding basically be connected to two source/system locations

Thanks
Sharyn

 

[Dionysus]

In another thread I raised a question that Dionysus or someone else might be able to answer.

If you were running conduit for this system there was a need for running non dimmed lines from a sub panel, along with the dimmed lines from the dimmer rack, would this be allowed? Or do all the ac carrying lines in a single conduit need to be from the same source/system? Reason for my question is that typically when the metal conduit is attached to the panel box or dimmer rack it bonded to the ground connection, and I wondered if there would be a code issue with having the bonding basically be connected to two source/system locations

Thanks
Sharyn

Usually the bond goes back to the same place, there is usually one ONE 'ground' for a building. This 'ground' is 'bonded' in the first main panel (connecting the bonds through the building to the 'ground' and the 'neutral'). However if they are independent bonds to separate grounds, they should NOT be put together. However sometimes it is allowed.
You cannot have two connections to ground, there MUST only be one.

It is common practice to run two conduits side-by-side in this circumstance, especially if at a different potential, different potential to ground, or if one is part of an isolated system. If circuits from seperate panels are run together that SHOULD be clearly labeled at every connection point, junction box, etc that there are multiple independent power sources (along with where each is).

DO NOT please run them down the same CABLE. This is VERY bad practice. And usually found as against code...

I'd err on the safe side and run two (or more) conduits. This is MUCH safer.

Plus I am a good electrician, I always label every box with it's circuit(s) to keep people safer.

Anyways so YES run these in a raceway (of whatever kind, be it PVC conduit, or rigid conduit, or flexible conduit, or whatever...) But keep circuits from independent power sources separate.

You also can NOT share the Identified or Neutral conductors for these separate power sources. As long as they come back to the same point it's okay, but here they would not.

 

[SHARYNF]

Got the answer to my question, there is no problem running power from two different feeds in the same conduit (say dimmer rack and Breaker Panel)

Sharyn

 

[MNicolai]

I've heard back from the electrical contractor. He's going to put two quotes in, one for the the plan described here, and another for the plan that our district electrician and I have been planning on for awhile.

After digging through my codebook, I noted the various articles where the above plan has code violations and have discussed it with the district electrician. Him and I agree that it violates the following sections:

• 400.8 - This states that flexible cords and cables may not be used as a substitute for fixed wiring of a structure.
• 520.44(B)(1) - A reiteration of 400, "Cords and Cables shall be employed only where flexible conductors are necessary.

Additionally, with (12) SO cables and (1) 8-circuit multi-cable bundled together, with (4) 20A circuits, the number of current-carrying conductors in a single bundle would require that all of the conductors be derated to 50% of their listed ampacities, which would require 10AWG conductors.

This is likely not a viable solution for us, which is why the electrician and I are setting up an additional meeting with the electrical contractor for an additional meeting to have the project quoted a second way.