It is a rare occasion that an inquiry for a new crane system even addresses the crane duty cycle. Let me assure you, this is one of the three most important questions to be answered (if not the single most important).

Let me give you an actual example. I once was asked to provide two 10 ton cranes to operate on a single runway. The first crane was a bridge crane used to feed the charging system in a foundry. The crane ran at full capacity, 24/7 and had a magnet. If the crane went down, several hundred people went home and they had to “drop the furnace” (purge it of all hot metal). It was cab controlled with an optional radio control. The crane cost a little over $300,000 and was rated as a class E crane. Compare this to a maintenance crane, pendant operated, same capacity, same span. The crane was used for maintenance once a year. It cost $35,000, but it was a low end Class C crane. Two cranes with the same capacity, the same span, the same lift height and almost 10x difference in price!!!

So here’s the CMAA classification system:

CMAA Crane Service Classes

CMAA has established crane service classes so that the most economical crane for a particular installation may be specified in accordance with Specifications for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes-No. 70 or Specifications for Top Running and Under Running Single Girder Electric Overhead Cranes Utilizing Under Running Trolley Hoist-No. 74. The crane service classification is based on the load spectrum reflecting the actual service conditions as closely as possible. The CMAA

Crane Service Classes are as follows:

CLASS A (STANDBY OR INFREQUENT SERVICE)
This service class covers cranes which may be used in installations such as power houses, public utilities, turbine rooms, motor rooms and transformer stations where precise handling of equipment at slow speeds with long, idle periods between lifts are required. Capacity loads may be handled for initial installation of equipment and for infrequent maintenance.

CLASS B (LIGHT SERVICE)
This service covers cranes which may be used in repair shops, light assembly operations, service buildings, light warehousing, etc. where service requirements are light and the speed is slow. Loads
may vary from no load to occasional full rated loads with two to five lifts per hour, averaging ten feet per lift.

CLASS C (MODERATE SERVICE)
This service covers cranes which may be used in machine shops or paper mill machine rooms, etc. where service requirements are moderate. In this type of service the crane will handle loads which average 50 percent of the rated capacity with 5 to 10 lifts per hour, averaging 15 feet, not over 50 percent of the lift at rated capacity.

CLASS D (HEAVY SERVICE)
This service covers cranes which may be used in heavy machine shops, foundries, fabricating plants, steel warehouses, container yards, lumber mills, etc., and standard duty bucket and magnet operations where heavy duty production is required. In this type of service, loads approaching 50 percent of the rated capacity will be handled constantly during the working period. High speeds are desirable for this type of service with 10 to 20 lifts per hour averaging 15 feet, not over 65 percent of the lifts at rated capacity.

CLASS E (SEVERE SERVICE)
This type of service requires a crane capable of handling loads approaching a rated capacity throughout its life. Applications may include magnet, bucket, magnet/bucket combination cranes for scrap yards, cement mills, lumber mills, fertilizer plants, container handling, etc., with twenty or more lifts per hour at or near the rated capacity.

CLASS F (CONTINUOUS SEVERE SERVICE)
This type of service requires a crane capable of handling loads approaching rated capacity continuously under severe service conditions throughout its life. Applications may include custom designed specialty cranes essential to performing the critical work tasks affecting the total production facility. These cranes must provide the highest reliability with special attention to ease of maintenance features.

This information has been presented for reference purposes only. For more information regarding load spectrum, mean effective load factors, load classes, load cycles and how these relate to the determination of crane service classes, please refer to Specifications for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes-No. 70 or Specifications for Top Running and Under Running Single Girder Electric Overhead Cranes Utilizing Under Running Trolley Hoist-No. 74. These documents are available for purchase online at http://www.mhia.org/bookstore or through the Literature Department at 704-676-1190.

WARNING!!!

After you digest this, you’re not done yet. Next week I will list the dozen specific issues that you MUST include to protect yourself in a buyers spec to “hold your suppliers feet to the fire”. It’s not enough to say, I want it class D. You need to let your suppliers know that you are aware of what a “D” means and you will be checking them.

“Thou shall have overload protection on all lifting devices.”

There it is, just nine words. You may have thought that a mechanical or electrical device to prevent the operator from lifting loads in excess of the safe capacity was already required, but it’s not!!!

Not in OSHA, not in CMAA (Crane Manufacturers Association of America), not in HMI (Hoist Manufacturers Institute)…nowhere. Worse yet, it is such a common sense idea, most crane and hoists buyers just assume that when they insist that their equipment be OSHA and/or CMAA compliant, it will meet this most rudimentary requirement. Well it’s not. Yes, there are rules that prohibit you from lifting loads in excess of the rated capacity of the crane, but no rules that require this to be built into the crane.

I have even met a few buyers that insist that they don’t need overload protection, because they never get loads that exceed the rated capacity of their crane or hoist. Although they may never get larger loads, they do get that one trucker that forgets to take off all the chains or the lathe operator that forgets to un-chuck the shaft. Next thing you know, they are lifting the whole lathe.

Bottom line is it’s up to you. Make sure to write into all your purchasing specs that “Overload” protection is required on all new lifting equipment. If the seller says OSHA doesn’t require it, tell them that you do!

Dr. Frazier Crane
PhD in Craneology (Piled High and Deep)

• Wire rope hoists are NOT required to have any type of overload protection
• Electric Chain hoists ARE required to have some form of overload protection
• There are several brands of overload protection that will fit almost all brands of hoist

The topic of the day is a particular type of “overload protection”, that involves cranes with two hoists. We frequently are asked to supply a crane that has two hoists for flipping dies. In this case either hoist may be required to lift the full load, lets say 5 tons, but never will the sum total of the lift be 5 tons. In other words, we have to supply a 5 ton crane with two 5 ton hoists. This may sound like a ticking time bomb, but with modern controls, there is an easy and economical answer.

LOAD SUMMING

Most hoist manufacturers and several third party after market control manufacturers now supply a small control system that is installed into the hoist control panel that constantly sums the total weight lifted by the two hoists. With this, either hoist can lift the full 5 tons or can share the 5 tons in any combination. As long as the aggregate total does not exceed the 5 ton load limit. the units operation is totally transparent, but in the event 5 tons is exceeded, the hoist will cease to lift and only operate in the down direction.

Dr. Frazier Crane
PhD in Craneology (Piled High and Deep)

I guess you should start with OSHA 1910.179. It quite frankly lays down the law in surprisingly few areas. That is surprisingly few concrete specifics. What it does is, “incorporate by reference”, a couple dozen other reference specifications. In other words, the CMAA 70 and 74 specifications are incorporated by reference, which means they have the same force of law as OSHA 1910.179. That means for example, the two referenced CMAA specs along with about 2 dozen other specs are therefore within the scope of 1910.179.

As if this referenced body of work is not enough, each of the referenced documents, in turn, incorporate by reference other specs. In the case of CMAA, we’re talking another couple of dozen specs which they reference, including such things as the National Electric Code, AWS welding code, etc.

To add one more layer to this circus of specifications, OSHA also “incorporates by reference” the manufacturers “owners manual” as the ultimate authority on that piece of equipment.

So the next time you get asked a question regarding the “legitimate way” to do something on your crane or hoist, be prepared to invest a lot of time wading through a lot of specs. Many of which cost close to a hundred bucks each. Below is a PDF files that is a map to all the related governing bodies and specification for Overhead Bridge Cranes and Hoists. To date, I have 36 listings, I’m sure you will have more to add and would appreciate your input.

Overhead Crane Governing Bodies

Dr. Frazier Crane
PhD in Craneology (Piled High and Deep)