Safe Hanging

[GregB]

Hanging a instrument from a bar requires:

1. hanging clamp

2. Secondary device/safety bond

 

Do I still need the safety bond if I have two clamps?

(eg. moving lights often come with double hook-clamp/coupler and safety bond, is this over-kill?)

If it is overkill, do we still like to see the safety bond as a reassurance...?

[Just Some Bloke]

Very often you'll find the reason some items have 2 clamps is that one alone would not be high enough rated to take the load (with a sensible margin for error). If that is the case then the two together make one primary suspension and, yes, you would need a secondary.

[Seano]

The main reason that moving heads (nodding buckets) usually have two hookclamps (half-couplers/whatever) is that they have a moving head. When the head pans, there's a reaction torque trying to turn the body the other way.

That's bad news with a single clamp, because it would be constantly getting tweaked as the head pans back & forth. Two clamps spaced as far apart as possible are much better at preventing the body from turning, its a leverage thing.

 

I've never seen a hook clamp fail on a moving light, but I suspect the second would be prone to what they call "cascade failure". That is where the failure of one part changes the circumstances for the next part along, so that its much more likely to fail than it was before. Following the failure of clamp A, clamp B would be subjected to much more torque than before, and therefore be much more likely to fail itself. So even though there are two clamps, they're not truly independent of each other, and there still isn't any redundancy in the system.

 

Also, if you look at it from a cost/benefit point of view, the marginal cost of adding a secondary steel to a moving light is pretty much zero - its cheap, easy and doesn't get in the way of anything. You don't move the body of a moving light to focus it, and so the secondary can be nice and tight without causing you any problems.

 

Sean

x

[GregB]

Assume weight (or movement) is not the issue... If a product was on the market with two clamps and no safety bond would it still be clasified as 'safe' to use?

[Seano]

If the two clamps are not mutually redundant, then the situation is really no different than when there is only one clamp to begin with.

I have never seen a fixture with two clamps where the failure of one clamp would not adversely effect the other - meaning that the clamps are *not* mutually redundant.

[Brian]

If a product was on the market with two clamps and no safety bond would it still be clasified as 'safe' to use?

As JSB says above, if the manufacturer designs it to need two clamps then they together form the 'primary suspension' and so a 'secondary suspension' is still required.

 

Source: Clause 17.6.6, BS EN 60 958-2-17:1989

[Simon Lewis]

Source: Clause 17.6.6, BS EN 60 958-2-17:1989

 

Brian,

 

At the risk of sounding like Kryten, I'm only finding references to "specifications for digital audio interfaces" when searching BS EN 60958...

 

 

Simon

[Brian]

At the risk of sounding like Kryten, I'm only finding references to "specifications for digital audio interfaces" when searching BS EN 60958...

That'll be because I should have typed BS EN 60598-2-17

[Simon Lewis]

That'll be because I should have typed BS EN 60598-2-17

 

BS EN 60598-2-17 Sir? "All nations attending the conference are only allocated one parking space." Is that entirely relevant sir? I mean, here we are, in mortal danger and you're worried about the Chinese delegates bringing two cars.' .... ;-)

[J Pearce]

Erm, that BS number and clause gives me secondary suspension, not parking spaces Simon...

[mumbles]

Erm, that BS number and clause gives me secondary suspension, not parking spaces Simon...

I assume that you've not seen Red Dwarf, and as such, my favourite TV series of all time ;) .

[J Pearce]

I have, and understand the joke, but assumed it was based on a mistype and not just randomnly inserted into the thread.

[Simon Lewis]

I have, and understand the joke, but assumed it was based on a mistype and not just randomly inserted into the thread.

 

For those who have to know, check Space Corp Directive 39436175880932/B

 

It was based on the "not wanting to sound like Kryten" comment..... and the fact that those people who can talk whole sentences just using BS EN numbers are probably a little sad ;-)

 

Brian - thanks for the corrected number. I'll shut up now.....

 

Simon

[GregB]

Thanks gentalmen, thats that sorted.

[Light Console]

Drag an old topic up, kicking and screaming time again folks!

Years ago, in a venue called the Gantry, a pair of EV SX200 speakers were flown in cradles, from fixed bars, and the safety was passed through the handle.

Here is the bracket roughly attached to the speaker.

http://img171.imageshack.us/img171/8428/dscf0002fh0.th.jpg

http://img171.imageshack.us/img171/8083/dscf0001qb1.th.jpg

7 years later I would like to rig these same speakers on a Truss, which is flown in and out quite often over the course of a year. Now, I want to add washers and proper bolts to the connections to the speaker from the bracket, but where do I attach a secondary safety? I don't think the handle is shock proof, so I don't want to re-use that method. Now the hole in the bracket leads to the screw which holds the compression driver in place, so that is not an option. So the last hole available is on the bottom of the speaker. My guess is I will need an M8 eye-bolt and safety wire of suitable length.

http://img171.imageshack.us/img171/8779/dscf0003im2.th.jpg

My concern with this method is that if the two bolts holding the speaker in were to fail, would the speaker gather enough momentum to rip the safety wire connection's metal insert out of the body of the speaker? Or is an additional bond through the handle worth trying?