Chain Hoists as permanent install?

[millamber]

I have a client that wants to install some truss over the audience with some LED fixtures to use for house lights, and he wants to have the truss on chain hoists to be able to bring them in for servicing and loading, etc...

As I understood it, chain hoists are really for a temporary type of install -touring shows and such. The idea here is that the motors would be the permanent anchor point for the truss. I have some reservations about going forward with his request as I want it to be done as safely as possible. I know it is a bad idea to do this, but I don't have any kind of documentation to back that up.

Have any of you used electric chain hoists in a permanent installation, and/or can anyone direct me to a specific document allowing or disallowing this type of install?

 

[theatre4jc]

In my chapel all my arial truss in on motors and is basically permanently installed. We used chains hoists so we could move them but our upstage truss hasn't moved since install. Also in my Worship Center I have a truss in my archway that is permanently installed. I believe Atlanta Rigging put it in, but don't hold me to that. But all my items are in hard to get lifts to areas. If the client has a lift, and can use it to access the area I would advise to push them towards a properly rigged permanent setup.

 

[Footer]

Chain hoists are use all the time in permanent setups. The chain hoists that we use in our industry are adapted from chain hoists that are used in general industry every day in harsh environments.

There are two ways though that if you are going to install a chain hoists permanently that you will want to consider. First, your going to want to go with a "motor up" design. This will require you to purchase a hoist that is specifically designed to work in this way. This will not only give you a cleaner look but will allow you to not have to worry about having motor power travel with the truss. The only other thing to consider is how the hoist is attached to the steel. It is not recommended to use steel slings/burlap for a permanent install. Instead, you will have to have some type of permanent point installed such as a beam clamp. Your rigging company will be able to spec what should be used.

You might also be able to go with a line shaft winch. Either way, it can be done.

 

[abbyt]

I know you were not really asking for alternate suggestions, but just a thought...something like this may work for you...

ETC's Prodigy Hoists

 

[derekleffew]

Perhaps this, from CM's FAQs, will further serve to muddy the waters.

Q. Can a CM Lodestar be used to hang loads over people's heads?

A. It is preferred that the load always be tied off (dead hung) with auxiliary chains or cable before access to the area beneath the load is permitted. As an alternative, the system may be designed such that malfunction or failure of one hoist's load bearing components does not cause load loss and/or overloading of any other hoist in the system. Note that in such a system, hoist performance and function must be monitored visually or with the use of load cells.

 

[Footer]

Perhaps this, from CM's FAQs, will further serve to muddy the waters.

There are plenty of statements like that out there. As always any rigging should be designed with a significant safety factor. This statement does throw out standard 120k rigging.


sent from my HTC Incredible

 

[SteveB]

The only issue I've ever been warned about with CH's (and as told to me by Bill Sapsis, if memory serves) for permanent installs, is that chain hoists *generally* need to be serviced once a year, as in taken down, cleaned, etc... the interval being somewhat dependent on usage.

Thus the issue becomes how do you support the load on the deck while the motor is off the rig. With line-shaft type winches, the intervals between servicing is greater and you don't have the same issue as to supporting the load for routine maintenance.

SB

 

[len]

The only issue I've ever been warned about with CH's (and as told to me by Bill Sapsis, if memory serves) for permanent installs, is that chain hoists *generally* need to be serviced once a year, as in taken down, cleaned, etc... the interval being somewhat dependent on usage.

Thus the issue becomes how do you support the load on the deck while the motor is off the rig. With line-shaft type winches, the intervals between servicing is greater and you don't have the same issue as to supporting the load for routine maintenance.

SB

Everything should be serviced, based on what the mfg. recommends. As for what to do with the stuff it is lifting, probably just drop it on the deck and leave it. Chances are, it'll be truss or a speaker array instead of pipe so it'll be easier to move around. And regardless of the type of venue, there is likely some seasonality to it, so they can do maintenance during slow periods, and work around things like worship schedules. Likely, if a motor has to come out for an extended period of time, a rental can be arranged in its place.

 

[Wolf]

Everything should be serviced, based on what the mfg. recommends. As for what to do with the stuff it is lifting, probably just drop it on the deck and leave it. Chances are, it'll be truss or a speaker array instead of pipe so it'll be easier to move around. And regardless of the type of venue, there is likely some seasonality to it, so they can do maintenance during slow periods, and work around things like worship schedules. Likely, if a motor has to come out for an extended period of time, a rental can be arranged in its place.

This would also be a perfect time to also do general maintenance on any fixtures hanging on the truss, house lights or other.

 

[tk2k]

I would be extremely warry.

We have a 3 motor per-bar chain system, and it has been nothing but problems over the 10 years we've had it. Sometimes the chain bags misfeed, and chains can rain down on the stage from 30ft (only when raising), it's loud, and it often gets off balance. Honestly, I would strongly recommend against it.

 

[bishopthomas]

I would be extremely warry.

We have a 3 motor per-bar chain system, and it has been nothing but problems over the 10 years we've had it. Sometimes the chain bags misfeed, and chains can rain down on the stage from 30ft (only when raising), it's loud, and it often gets off balance. Honestly, I would strongly recommend against it.

Please tell us more about your system. It sounds like you either have the wrong equipment, it was installed improperly, you're not using it correctly, or a combination of the above. CM Lodetar is the industry standard, but there are several other equally suitable chain hoists. There's a new Lodestar out that is supposed to be quieter in operation, so if noise is an issue check them out. I don't know how it could possibly get "off balance" if the system was installed properly. This includes a controller that allows you to operate each hoist independently or as a group. In your case you probably never need to operate the three motors independently, and the easiest method is to install and wire a wall switch that will raise/lower all three at the same time.

If you are having these problems I would call the installation company and have them do it the correct way this time. If that is not an option then get a qualified rigger who is familiar with chain hoists and motor control (there are many good lighting companies in your area who can do this job) and have them correct the issues you are having. It sounds like maybe your signature has something to do with your issues...

 

[LightStud]

I don't know how it could possibly get "off balance" if the system was installed properly.

By "off balance," I'm assuming the poster means "out of trim" (not level).

In your case you probably never need to operate the three motors independently, and the easiest method is to install and wire a wall switch that will raise/lower all three at the same time.

This is particularly bad advice, as all electric chain hoists will vary slightly in speed due to power cable length (voltage drop) and weight of load supported. One will always need to "up a bump"/"down a bump" individually when operating multiple chain hoists.

This is one of the best reasons for NOT using chain hoists in a permanent installation. A system using a single motor, such as a line-shaft system, is a better option. As said above, check out Prodigy, Vortek, and others similar.

 

[bishopthomas]

By "off balance," I'm assuming the poster means "out of trim" (not level).

This is particularly bad advice, as all electric chain hoists will vary slightly in speed due to power cable length (voltage drop) and weight of load supported. One will always need to "up a bump"/"down a bump" individually when operating multiple chain hoists.

This is one of the best reasons for NOT using chain hoists in a permanent installation. A system using a single motor, such as a line-shaft system, is a better option. As said above, check out Prodigy, Vortek, and others similar.

Sorry for the bad advice. I stand by my original point that tk2k's post should not be a derterent for using hoists in a permanent installation. It is very common practice, but you should have a qualified person do the installation (and, obviously, I am not).

 

[mstaylor]

I would be extremely warry.

We have a 3 motor per-bar chain system, and it has been nothing but problems over the 10 years we've had it. Sometimes the chain bags misfeed, and chains can rain down on the stage from 30ft (only when raising), it's loud, and it often gets off balance. Honestly, I would strongly recommend against it.

The biggest reason for chains running is improper placement of the chain in the bag. The dead end of the chain should be put in the bag first then feed the rest of the chain in until the entire live end is on top. Many people just take both sides of the chain and dump it in. This puts part of the live end to be under the dead end and starts the chain runout. A twisted bag will do it too but less often.
If you are going to use motors in a permanent location try to use a hard safety once you reach trim. Some locations doesn't allow this to be done easily but is a good idea when possible.

 

[tk2k]

Company is ******, they put in the system 10 years ago and come back every few years, the last time they were out here the service rep told us that "they would never recommend a system such as this" for which we replied "yes, you did, 10 years ago"

The problem is it is a tri-lift system with three motors per bar. The motors do not track linearly (I. E. all up for 10 seconds will result in a slanted bar). It does allow for individual motor operation, center, left, right, but that means we need to rebalance almost every time. I love chain motors for temp use, hanging truss, etc, I use it all the time at convention centers, however for a theater space it has been nothing but trouble for us. The motors have been reconditioned by the manufacturer twice (for free) but problems keep coming back up. At this point, I would gladly trade for a 'dumb' balance based rigging system. I guess the one advantage is it is idiot proof in the sense you can't overload a bar and kill someone, but...

Please tell us more about your system. It sounds like you either have the wrong equipment, it was installed improperly, you're not using it correctly, or a combination of the above. CM Lodetar is the industry standard, but there are several other equally suitable chain hoists. There's a new Lodestar out that is supposed to be quieter in operation, so if noise is an issue check them out. I don't know how it could possibly get "off balance" if the system was installed properly. This includes a controller that allows you to operate each hoist independently or as a group. In your case you probably never need to operate the three motors independently, and the easiest method is to install and wire a wall switch that will raise/lower all three at the same time.

If you are having these problems I would call the installation company and have them do it the correct way this time. If that is not an option then get a qualified rigger who is familiar with chain hoists and motor control (there are many good lighting companies in your area who can do this job) and have them correct the issues you are having. It sounds like maybe your signature has something to do with your issues...

 

[WooferHound]

I had been told that 3 phase 240vac motors will operate in sync with each other and travel up the chains at perfectly equal speeds. But that single phase 120vac motors would not sync and speed would depend on voltage or cable length. My experience has shown me that this is correct.

Is this true or not ?

 

[len]

I had been told that 3 phase 240vac motors will operate in sync with each other and travel up the chains at perfectly equal speeds. But that single phase 120vac motors would not sync and speed would depend on voltage or cable length. My experience has shown me that this is correct.

Is this true or not ?

I've run many different brands (even some I've never heard of) of motors at various sites. Never paid attention to voltage, but invariably they get out of sync. You still need human eyes, paying attention to what's going on, and still need to make sure everything is straight. Technology will take you so far, but I'll trust my brain before I'll trust a machine.

 

[Chris15]

I had been told that 3 phase 240vac motors will operate in sync with each other and travel up the chains at perfectly equal speeds. But that single phase 120vac motors would not sync and speed would depend on voltage or cable length. My experience has shown me that this is correct.

Is this true or not ?

According to electrical machine theory, an AC motor's speed is altered by changing the frequency of the supply, hence variable frequency drive systems... Voltage should not be the controlling factor.

However practical reality says that motors WON'T stay in sync when operated together...

Now I'm assuming that chain motors operate using induction motors, since they make up the majority of industrial motors in use today. Because of the way that an induction motor works, it will always run slower than the supply frequency.

So that adds a degree of individuality to every motor and when you combine that with slightly different loading and slight variations in current consumption and thus voltage drop and all of those little things that vary between units...

I've run many different brands (even some I've never heard of) of motors at various sites. Never paid attention to voltage, but invariably they get out of sync. You still need human eyes, paying attention to what's going on, and still need to make sure everything is straight. Technology will take you so far, but I'll trust my brain before I'll trust a machine.

Load cells have improved things quite a way and you can get control systems to self correct reasonably well...

 

[janitor]

I don't spend much time with single phase motors, but am quite familiar with the CM 3-phase units. Their speed will vary based upon load. As you approach their rated load the effect becomes more noticeable, (and current draw shoots up). There is no synching going on, although I would expect a truss with a uniformly distributed load to generally stay pretty flat. The problem so often is that there is a cable bundle somewhere, which gets heavier as you go up, causing one motor to work progressively harder.

Regarding chain hoists and permanent install, we don't leave loads suspended over the head of an audience without them being safetied, unless we have sufficient motors on the item that the failure of any one wouldn't cause something to hit the deck.

A sobering thought for those of us who walk around under loads suspended by chain hoists: Many crane guys can be seen using the worlds twistiest, kinked wires, but won't go near chain because they regard every link as an opportunity for sudden catastrophic failure.

We've seen chains break in the past in this industry, you don't get a warning and it's alarming.

 

[Ezekiel]

I agree with Janitor, when working with significant loads over the heads of an audience a safety cable should be used. Although I will say this is done mostly in arena rigging and almost never done in convention/corporate shows where I rig. Im not really sure why its done in one and not the other. As someone who has just taken the CM class, if there is one thing that was stressed more than anything, it was the chain. As Janitor said, each link of chain presents a potential failure point. I would recommend using chain hoists as a last resort in any type of permanant installation, and if used would incorporate a very high safety factor.

And as for chain hoists running equally, keep in mind I'm no elecrical engineer, its very rare to level a 8 hoist truss with a uniformly distributed load at 4 feet off the ground, run it up 40 feet and have it still be level. There are too many factors playing a part as Chris15 stated. Fly cable length, condition of fly cable, condition of hoists, etc.