Safety bonds

[chris512]

morning all,

 

just a quick question, I'm trying to hunt down some safety bonds for our stock of moving lights (mac 500, 300 + 250's).

 

FYI - Mac 500's weigh 30KG, whilst the smaller mac's weigh 20KG

 

just wondering whether when getting these bonds whether its alright to just get 35KG rated ones or do you have to account for the potential force and weight that would be generated should the unit actually fall, therefore would 50KG be better?

 

 

hope that makes sense!

[mac500]

I personally would go with the 50Kg its better to be safe then sorry.

[emj]

if 35kg is the safe working load of the safety that will be fine as that already has a safety factor of any where between 5-1 and 10-1 depending on where you get them from

 

I would speak to Rope assembly's as they manufacture them for most of the company who resell them in the UK

 

Hope this helps

Em

[smeggie]

depending on how much extra it would cost for the additional rating, I would be inclined to for the larger one as it can't hurt to have the extra if [on occasion] they are used for any other bits of kit.

[ianl]

if 35kg is the safe working load of the safety that will be fine

I disagree with this as I think the swl is for a static load, the point of a safety wire is to arrest a dynamic load (dynamic load is bigger than static load) there fore you need a safety with a swl >= dynamic load without using up any of your safety factor

[MarcT]

I asked the same question recently, and was told by a certain large lighting company in Wimbledon that the rating is for a shock load. So, a 35Kg bond should be fine for a 30Kg fixture.

 

Whilst on the subject of safety bonds - if you fit them so as to make a loop around the LX bar through the lantern trunion arm or safety point (ie by clipping the ends together), you half the tension in the safety should the lantern end up hanging from it compared to not having it in a loop...

 

Marc

[TomLyall]

which costs more... replacing a mac and the floor, or buying a higher rating safety bond?

 

I know thats not all it comes down to, but it is a factor

[Ike]

or on a slightly more serious note...a mac falling 30' onto a punter or buying a higher rated bond!

 

Your best bet would be to contact the manufacture of the safety bond, explain how you wish to use it and ask for there advice.

[peter]

I believe, don't quote me on this, that the large lighting hire company based in avonmouth use 35kg bonds on their 250s, 300s, 500s and 600s and 50kgs on their 2000s. I think if you ring up and ask for a safety bond for a Mac 500 then they'll be able to advise you.

[Tomo]

Given what a safety bond is for, the rating should be for a shock load!

 

Also, don't forget that a safety bond should be considered 'one use only' - if it ever has to catch anything, replace it as it probably stretched when it stopped the fixture.

 

The energy has to go somewhere, no?

[Brian]

Given what a safety bond is for, the rating should be for a shock load!

Except that this would require you to work out what the shock load is going to be and then select a safety to suit. How many people know how to do that?

 

The rating on a safety will be the maximum weight of lantern you can use it with, so that if the lantern falls the maximum distance (being half the total length of the safety) if will not exceed the strength of the bond.

 

Also, don't forget that a safety bond should be considered 'one use only' - if it ever has to catch anything, replace it as it probably stretched when it stopped the fixture.

Good advice.

[Kevin Robertson]

To calculate shock loads:

 

Shock Load = [(weight X falling distance) / stopping distance] + weight

 

the most important factor of this calculation is the Stopping distance, when using a steel wire safety bond the elasticity is very small so the stopping distance will be nominal and thus create a larger force in the event of a fall.

 

so on a 30 kg unit falling a distance of 5cm the resultant shock load would be...

 

[ (30 weight X 0.05 falling distance ) / 0 stopping distance ] + 30 weight = 61.5 kg

 

so only falling 50mm will more than double the shock loading on the safety bond.

 

Another interesting point...

 

A secondary safety bond MUST be rated. But the primary fixing doesn't!

[TomLyall]

I assume it is acceptable to use two safety bonds on a larger item? im sure this would be overkill.

 

[edit] another question, would it be ok to use two 30kg ones instead of one 60kg?

[kaareolai]

To calculate shock loads:

 

Shock Load = [(weight X falling distance) / stopping distance] + weight

 

[snip]

 

so on a 30 kg unit falling a distance of 5cm the resultant shock load would be...

 

[ (30 weight X 0.05 falling distance ) / 0 stopping distance ] + 30 weight = 61.5 kg

Mmm, something must be wrong with this formula. Dividing on zero usually gives a _very_ big number ....

[Brian]

I assume it is acceptable to use two safety bonds on a larger item? im sure this would be overkill.

 

[edit] another question, would it be ok to use two 30kg ones instead of one 60kg?

Not really, you couldn't guarantee that both bonds would act at the same time. What would probably happen is that one bond would get the full shock load, so in your example one of the 30kg bonds would cop for the full 60kg. Depending on safety factors it may or may not survive. If it failed the second bond would then carry the full 60kg whilst the first bond falls onto the punters below. The distance the 2nd safety would have to pick up on would probably not be that great and so it would probably take the load. Mind you, there are several probablys in there.