Unsafe safety cables

[CSCTech]

Somewhat off topic, but in regards to safety cable and not using spring loaded 'carabiner clip' type cables for over-head hanging. Is this what is meant?

If so what is the correct type to use on over-head fixtures? As we use one of those on all of our fixtures, they have been there since the original install so I have never second-guessed them. (Didn't even know there was a different kind of safety cable)

 

[shiben]

Shattering clamps like that is exactly why we don't use any of the cast iron clamps on any of our fixtures. Go out and find yourself a rated clamp. We use the Megaclamps, and those are specifically load rated.

I tend to agree with this. Not really sure why the industry as a whole has not been more enthusiastic about moving towards a better clamp design... Even the aluminum C clamps that lightsource sells are far superior in many ways... However, I think its silly to dislike safeties. If something goes wrong, you have the "I installed the safety cable, so my rear is covered" thing going for you, and it takes about, oh, 2 seconds to do right? Takes a lot of instruments for 2 seconds per to actually make any decent time savings. I can think of about 2 dozen ways to speed up hangs before cutting safety cables from the package. Its fast, easy, and cant hurt. So whats the problem with them?

 

[shiben]

Somewhat off topic, but in regards to safety cable and not using spring loaded 'carabiner clip' type cables for over-head hanging. Is this what is meant?

If so what is the correct type to use on over-head fixtures? As we use one of those on all of our fixtures, they have been there since the original install so I have never second-guessed them.

Thats correct, that type of clamp is not actually rated for overhead something or other. A proper attachment would be a shackle or something like that... Never could understand why locking carabiners were not a valid option... I dont buy they wont hold up to shock load and the like, the most I could buy is that they dont have a nice variety of scales...

 

[Footer]

Somewhat off topic, but in regards to safety cable and not using spring loaded 'carabiner clip' type cables for over-head hanging. Is this what is meant?

If so what is the correct type to use on over-head fixtures? As we use one of those on all of our fixtures, they have been there since the original install so I have never second-guessed them. (Didn't even know there was a different kind of safety cable)

There is not a different kind of safety cable. There is nothing unsafe about this safety cable. Just make sure the snap actually closes and your golden.

 

[gafftaper]

First off I want to draw attention to my old post from the Do you use the integrated safety attachment thread:

I was messing around with some lights today and thinking about this thread and had what I think is a GREAT idea of how to attach a safety cable.

1) Pop one side of the yoke off and slide the loop end onto the yoke. This way every fixture always has a safety cable attached... no excuse not to safety.
2) Hang fixture.
3) Pass safety cable around batten.
4) On the way back around and pass the snap link THROUGH the loop which is attached to the yoke. This creates a choke around the batten and sort of a half choke around the yoke at the same time.
5) Pull some of the slack through... not too tight.
6) Snap onto integral safety attachment.

It's a little slower than some methods but I think it's a really safe while keeping the cable permanently attached to the fixture. What do you think?

I have been using this technique for a couple of years now and I am convinced it is the safest way to hang a S4. I've had people tell me it that the safety cable is too short for this to work. I've never once run into a situation with any my fixtures where the safety cable was too short to reach. I believe this is the best way to attach an S4 Ellipsoidal, PAR, and PARnel for several reasons:
1) There is ALWAYS a safety cable attached to the fixture.
2) You can't drop the safety cable while hanging instruments and injure someone or get lazy about going down to retrieve it.
3) The connection to the batten is very secure.
4) The connection to the fixture is by way of the manufacturer's designated attachment point (if it fails, it's ETC's problem not yours).

As for the original question, the order of what you do is very critical. Far too many people hang the fixture and attach the safety cable last. This is dangerous. The most likely thing to fail is the C-clamp. The most likely time for it to fail is while you are tightening it. The correct procedure for hanging a fixture is:
1) Place fixture on batten and finger tighten the c-clamp with one hand while holding it securely in place with the other hand.
2) Attach the safety cable.
3) Tighten the c-clamp no more than 1/2 turn past finger tight (if you are a wimp with your finger strength then you may need to go up to 3/4 - 1 turn). The point is to never be trying to tighten the snot out of the clamp, that's how you break the c-clamp. It doesn't have to be that tight. Always use a short wrench to minimize the leverage and thus the amount of damage you can do (I carry a 6" wrench, that's really all you need). The only time you really need an extra crank on the clamp is in a situation where the batten is vertical, but even then you don't need to go crazy.

No safety cable, no wrench!

 

[MPowers]

............ This place [sic] it in the weakest part of the light with two standard 1/4" bolts that hold the yoke to the light that combined have a sheer strength of less then 800 pounds..........

Not sure where you get 800# total combined shear strength. A 1/4" bolt is considerably stronger than that.

A 1/4" grade 2 bolt has a tensile strength of 72,000# (sources vary from 72000 to 74000) .
Shear load = Shear area * shear stress
Shear stress = 60% of tensile strength, : 72000*60% = 43,200#
1/4" Bolt body diameter = .244" (Although the thread root is slightly smaller, the shear force in this instance, is borne by the bolt body)
Shear area = body diameter squared *pi/4
.244^2*pi/4 = .059536*.785398 = .04676 sq in
Shear load = .04676 * 43,200 = 2,020 # shear load per bolt.

Second item, the caribiner. There are load rated caribiners, they are used for climbing and safety harnesses, rescue equipment, military recon etc. People climbing 1,000' cliffs trust their lives to them, but they are not rated for overhead lifting. A climber may fall 30 ' and depend on them to stop and hold. They may be rated at 5,000# but not for overhead . That is a different purpose. Use on a safety cable is not "Overhead lifting" and so an appropriately rated caribiner is a perfectly acceptable use of the hardware. FWIW, the approximate shock load of 15lb S4 ERS falling 9" to a foot is just shy of 200#.

 

[Van]

Thanks Michael, you beat me to the math.
For what it's worth, if someone shows up on a light call with anything over a 6" crescent cut the excess off and you shouldn't ever have to worry about clamps failing. If a clamp is being over tightened to the extent that it fails, with the exception of the extremely rare occasion that there is a manufacturing defect, "then the fault, my dear Brutus", lies in the electrician.

 

[gafftapegreenia]

Thanks Michael, you beat me to the math.
For what it's worth, if someone shows up on a light call with anything over a 6" crescent cut the excess off

Have you always been anti 8" wrench?

 

[Pie4Weebl]

Even the aluminum C clamps that lightsource sells are far superior in many ways...

I hate those clamps sooo very much, they take forever to put on and take off! Its especially bad when you're on a ladder, holding the light with one hand while tightening with the other when side hanging a light on a truss tower...

 

[Van]

Have you always been anti 8" wrench?

Well, Ok, I don't mind an 8" wrench in the hands of an EXPERIENCED sparky, but the young and uninitiated really need the 6" torque limitations.
; >

 

[emoreth]

The only time you really need an extra crank on the clamp is in a situation where the batten is vertical, but even then you don't need to go crazy.

What if you have to mount a light on top of a pipe with the yoke below it?

 

[Grog12]

What if you have to mount a light on top of a pipe with the yoke below it?

Same rule applys for top hanging a light. A little extra crank yes but don't go gorilla on it.

 

[chausman]

What if you have to mount a light on top of a pipe with the yoke below it?

Same thing. Tight enough not to move, but not too much. 1/2 turn to 1 turn past finger tight.

 

[Scarrgo]

I use the same safety as pictured above, and something along the gafftaper method, I got into putting the yoke thru the pressed loop so it couldn't be taken off the fixture,(had a problem of people stealing them)unless someone decided to take the yoke off to remove it.
You never had to look for one and if it was extended out for whatever reason, it was long enough to reach.

Sean...

 

[CSCTech]

That's good to hear, I had never done any math on it but I had always thought that one of the safety cables we (and I am pretty sure are the most commonly used?) use could withstand much more then the force of one of our fixtures.

Generally what we do is loop the cable around the batten and yoke arm so there isn't too much free space, making the fall shorter. Although I might have to try out gaff's method some time.

And although it probably isn't necessarily we use two safety cables on the Far Cycs and Border lights we hang.

 

[MPowers]

........although it probably isn't necessarily we use two safety cables on the Far Cycs and Border lights we hang.

Not necessary.....??, for the safety and preservation of the people below, Yes. For peace of mind and the safety of the lighting units, two safeties is a great Idea.

 

[Les]

Borderlights and Cyc's are definitely a good candidate for two safety cables. Ideally, they will be attached in such a way that if the/one of the clamp(s) were to fail, the unit wouldn't swing down. Some fixtures are long enough to knock someone out if they are hanging by an end. One safety cable per clamp (strip lights), and two on linear fixtures (ex: 3+ cell Cyc with one long bracket and single clamp) is usually my rule of thumb - again, try to make it so that if the clamp were to fail, the fixture can't hang vertically (safety cable(s) at one corner of the yoke).

 

[AdamHVLS]

Shattering clamps like that is exactly why we don't use any of the cast iron clamps on any of our fixtures. Go out and find yourself a rated clamp. We use the Megaclamps, and those are specifically load rated.

I agree completely! Nothing like a little piece of mind on a rated piece of hardware.

 

[BanditRO]

I am looking to see if any agrees with me about safety cables not really being safe? With a standard electrician coming in and hanging a light they will place a safety cable straight through the yoke and around the batten. This place it in the weakest part of the light with two standard 1/4" bolts that hold the yoke to the light that combined have a sheer strength of less then 800 pounds. The design of a c clamp causes the forces to be pushed against a piece of metal that is almost an inch thick. Basically meaning your pipe will fail before you break a clamp. And on top of all that a light should in theory 3 times before any performance should occur under it, once while hanging, once while focusing, and once by the lead electrician. I find that people use them a cheap insurance meaning they are putting their trust in a piece of hardware that is not rated or designed for hanging over head. I can find OSHA rules on not using the clip on safetys as well. I have a hard time believing that they are as safety as some people say and might even call them unsafe to use. Does anyone agree or is you all just going to call be dumb?

I worked a theatre with NO safety cables... They trusted the twistlock to do the job!!

I fought for years, before quitting, to get them to buy safety cables though.

The biggest thing to bear in mind is that a safety cable will never overcome stupidity. It may diminish the effects of said stupidity though and for that reason alone, they are worth having, whether through an integrated attachment point or just a yoke.

In the UK and Europe, one is required to purchased safety "bonds" that must be rated to a minimum of 250# and have a locking clip...making them far more expensive.

 

[MPowers]

Posted by shiben Even the aluminum C clamps that lightsource sells are far superior in many ways...

I hate those clamps sooo very much, they take forever to put on and take off! Its especially bad when you're on a ladder, holding the light with one hand while tightening with the other when side hanging a light on a truss tower...

Are you sure you are talking about the same thing? The Aluminum Light source "C" clamp known as a Mega-Clamp
Mega-Clamp Photo
works exactly the same way as any other "C" clamp.

BTW, at the 2010 USITT Delbert broke some "C" clamps on his test rig and the aluminum Mega clamp was FAR stronger than the cast iron.

Test Group #12 – Lighting C-clamps
WLL: unknown/600 lbs

Test #12A - Cast iron C-clamp (WLL: unknown)
BS: 2426 lbs

Test #12B - Cast iron C-clamp (WLL: unknown)
BS: 2651 lbs

Test #12C - Mega-Clamp Aluminum C-clamp (WLL: 600)
BS: 4833 lbs

Note: All clamps broke at the same place on the C-clamp