Chandeleir Rigging

The sanctuary of our church is certainly one of the key features of our space.  In the center of the very large room is the chandelier.

The original room was lit only by the chandelier... this turns out to be woefully inadequate for our current needs... but that is for another post.  What I wanted to highlight here is the way the chandelier was and is now supported above the ceiling.  Many people may be surprised to know the chandelier can be lowered down to the pews.

This is of course to be able to change light bulbs out.  But how is this done?  Well it was attached with a cable and winch.

      

While the odds of something breaking during the 4 or so hours a week the sancturay is full enough to have people underneath the chandeleir is low this is still a potential safety concern.  We had known for a while we wanted to change out how it is secured and the hardware that raises and lowers it.  Our first step was to weigh it to make sure whatever hardware we used was strong enough.  We used the strain gauge load cell my dad got...

So we found it weighed 430 pounds... it also needs to be able to be lowered 9 feet to the pews... During the process of figuring out the components to replace I looked at the current cable holding it.  It is a 1/4" diameter galvanized steel 6x7 with a fiber core... pretty old type.  New cable of the same type has a breaking strength of 1840lbs which means it is plenty strong right?  Well it is over 4 times the weight it is carrying so that seems like a lot.  Well in reality what we want is a factor of saftey of 8-9 (breaking point 8-9 times the load http://www.engineeringtoolbox.com/factors-safety-fos-d_1624.html).  So 9 times 500 = 4500 pounds should be the breaking point of any single component.  So already the cable alone is well below the recommended factor of safety. But there was a secondary safety cable that was added...

See that hook hanging off the side well if the main cable breaks it would take the load right?  Well yes but notice how loose it is?  The chandeleir would drop 6" then this cable would take the load but the shock load on it would be much greater than the weight of the chandeleir alone... So it really wasn't a good setup.  Not to mention the cable attachment to the eye hook doesn't use a thimble and they saddled a dead horse... and the winch is pretty worn... and the cable has deteriorated...

So enough of scaring you about the chandelier... it has worked for almost a century.  We replaced all this cable and improper rigging with new components.

What we now have is a static and dynamic setup.  Normally the chandelier hangs from web slings that go over the main upper beam and we have all the proper anchor shackles and chain in place so we can sinch it up with a load binder to get it nice and tight.  When lowering and raising it (dynamic setup) we have a chain hoist attached to custom metal straps that connect to the beam and the post above it that goes into the cupola

So how strong is it now?  Well the weakest component for the static setup is a the 3/8" chain that has a Working Load Limit (WLL) of 2650lbs.  A WLL usually means a factor of safety of 5 so the chain would break at 13,250lbs or a factor of safety of 30!  I think we are safe;)  For the dynamic setup the chain hoist is rated for 1 ton which is plenty.  Doing some mechanics of materials on the custom straps and being conservative we are still over the 9 factors of safety.

Now I haven't addressed what is below the eye hook.  We would eventually like to add some re-reinforcement to the chandeleir itself but that would involve a fairly complete re-build of the entire chandeler to keep it from looking too ugly... that will be for another day...