General Electric produced a very popular line of medium voltage (2.3kv-15kv class) circuit breakers over a 30-year timespan with literally tens of thousands of units in service across the U.S., Canada, and other areas. This product line, known as the Magne-Blast or AM breaker, has been upgraded over the years with improvements and life extensions to add even more value to the customer.
One of the maintenance items that needs to be addressed periodically is what the industry calls the “Raise Lower Mechanism.” This is a mechanism that lifts the breaker from ground level and assures proper alignment and connection to the primary disconnects on both the line and load side.
Maintaining Raise Lower Mechanisms for Your Circuit Breakers
There are several versions of this mechanism that need to be identified properly when service is needed. First, we will address the two most common mechanisms, the “Cast” and “Fabricated” or “Fab’d” mechanisms. GE classifies these mechanisms into two groups depending on the width of the switchgear cabinets they are in because they also include the shutter and connecting chain. GE identifies the Cast Mechanisms as either M26H or M36H because the cabinets they go in are either 26” or 36” wide. The fabricated design is simply designated as M26 and M36.
There is a well-known table in a GE publication that details the supposed application of these devices with particular breaker models and frame sizes. However, we have found both discrepancies in actual field applications as well as contradictions within the table itself. See the Illustration 1 Cast vs Fab mechs pdf for reference.
The easiest way to identify which mechanism you may have (they are not interchangeable), is by looking at the housing at the top of the mechanism that contains the gears. The cast style is obviously heavier duty, thicker, and has pit marks from the sand that was used to sand cast the original parts. The fabricated style is built with plate steel that is lighter duty and welded together.
See Illustrations 2 and 3 for reference.
NPE regularly stocks both of these mechanisms. They are completely rebuilt and ready to install for those “unscheduled outages” and we can even take your damaged or worn out mechanism in for a core rebate. For customers that want to rebuild the mechanisms themselves, we offer both cast bushing kits and fabricated bushing kits and years of experience and expertise to help you along the way.
Raise Lower Mechanism Exceptions
While these mechanisms comprise 90% of what is found in the market, there are some exceptions that should be noted.
The first mechanism is designated in the first illustration with the “HH” suffix. These mechanisms will be found in the largest of the Magne-Blast product line, particularly in the 1000 MVA breakers. See 7A in Illustration 1 for reference. They are the heaviest duty mechanisms and have two vertical screws to lift these frames into place.
On the opposite end of the spectrum, the smallest Magne-Blasts made are the 50 and 75 MVA class and are built for 18”-wide switchgear. These cells utilize a single lifting screw mechanism mounted on only the right side of the cell.
The last group of mechanisms are the oldest versions made for the AM 5 and AM 15 versions of the Magne-Blast line that utilize a double secondary coupler. While not many of these breakers are left in service, there are designs for updated/retrofitted breakers that still use the old switchgear. This last set will have the double vertical screw on both sides, similar to the “HH” version, except that these are much lighter duty. When replacing these, you will need to know if the motor that operates the lift is mounted in the front of the cell or all the way in the rear.
Raise Lower Mechanism Aftermarket Parts to Help Keep Switchgear Going
In addition to Raise Lower Mechanisms, NPE manufactures and stocks many of the common parts that you will need to keep your switchgear running. Raise lower motors, motor clutch parts, and bearing kits are all the things you will need to properly operate and maintain your equipment. You can find these parts in our Aftermarket Parts Store on our website.
• AM 4.16 -350 3000 Amp Shutter (Cell)
• AM Motor Coupler
• AM Raise Lower Mech Bearing and Bushings Kit (Cast)
• AM Raise Lower Mech Bearing and Bushings Kit (Fabricated)
• AM Raise Lower Motor (120 AC/125 DC), with Switch
• AM Raise Lower Motor (120 AC/125 DC), without Switch
• AM Raise Lower Motor (220 AC/250 DC), without Switch
• AM Raise Lower Motor (220 AC/250 DC), with Switch
• AM Raise Lower Motor Base Plate
This may seem complicated, but at NPE we face these questions every day. Our knowledgeable staff has the expertise to walk you through the various steps to identify what you have. Contact us online, give us a call, or send us an email with pictures of the nameplate if available and we will help you get the right parts, at the right price, right now!