The motor generator set is the elevator industry’s most argued about survivor. Depending on who you ask, MG sets are obsolete relics that belong in a museum, or they are rugged, serviceable machines that keep running for decades when the buildings around them are on their third lobby renovation. After generations of rebuilding these machines in our Trenton shop, our position is simpler than either camp: the MG set is a tool, and the right answer depends on the building, the budget, and the timeline in front of you.
This post lays out how we think contractors and consultants should actually weigh the decision, including the situations where our own advice is to modernize rather than pay us for a rebuild.
First, Respect What the MG Set Is
For readers newer to older buildings: a motor generator set converts the building’s AC power into the variable DC that a DC hoist motor needs, using a rotating machine set instead of electronics. It is the classic Ward Leonard arrangement, and it moved most of the tall buildings in America for the better part of a century.
The relevant engineering fact is that MG sets are electrically simple and mechanically honest. Nearly everything that goes wrong with one is repairable: brushes, bearings, commutators, windings, insulation. There is no control board that goes obsolete, no firmware, no proprietary lockout. A shop with real winding and machining capability can return a sixty year old MG set to original specification, and machines of that era were built with iron and copper worth restoring.
The Case for Repairing the MG Set
The rest of the system is healthy and the budget is real. A full modernization is a capital project measured in months and six or seven figures. An MG set rebuild is a repair measured in weeks. When a building’s controller, hoist machine, and fixtures still have life in them, rebuilding the MG set buys years of reliable service for a small fraction of modernization cost, and it preserves the option to modernize later on the building’s schedule instead of an emergency’s schedule.
Downtime tolerance is low. Modernization takes cars out of service for extended stretches. A planned MG rebuild, particularly with exchange equipment, keeps outages short. Our warehouse stocks rebuilt MG sets and built armatures for exactly this reason, because a machine that ships while yours is in our shop changes the downtime math entirely.
The building has heritage or logistical constraints. Some machine rooms cannot physically accept the rigging a full equipment swap requires without major construction. Some ownership groups are holding a property and will not fund capital work. In those cases the MG set is not a compromise. It is the correct engineering answer for the situation.
Condition supports it. This is where testing replaces opinion. We electrically test the armature, fields, and interpoles and evaluate the mechanical condition before quoting anything. A machine with sound core iron and good bones is a rebuild candidate. A machine with core damage is not, and we say so.
The Case for Modernizing Instead
We rebuild MG sets for a living, and we will still tell you plainly: there are buildings where modernization is the right call, and steering an owner away from it to sell a rebuild would be malpractice.
The whole system is at end of life. If the controller is failing, the selector is tired, and the ride quality complaints are constant, replacing the drive system with a modern solid state drive as part of a full modernization solves the building’s actual problem. Rebuilding one component of a dying system just relocates the next failure.
Energy and operating costs are a priority. A rotating MG set consumes power whenever it runs, and modern drive systems are meaningfully more efficient. For a building with long operating hours and an ownership group focused on energy performance, the efficiency gap is a legitimate factor in the capital case, and industry groups such as NEII publish resources on modern elevator technology and its building performance implications.
Code and scope triggers. Alteration work on elevator systems falls under the ASME A17.1 safety code, and the scope of a project can trigger requirements that change the economics. A contractor’s code consultant should weigh in before the repair or modernize decision is final, and publications like Elevator World track how modernization practice and code requirements continue to evolve.
One honest tiebreaker. If a modernization is genuinely funded and scheduled within the next two years, do not rebuild the MG set now. Bridge it with targeted maintenance instead. We would rather perform a motor cleaning and maintenance service that carries a machine safely to its planned retirement than sell a rebuild the project will orphan.
The Middle Path Most Articles Skip
The repair or modernize framing hides a third option that serves many buildings best: restore now, decide later, with data. A major maintenance overhaul with full electrical testing returns the MG set and hoist motor to documented good condition and produces the numbers an ownership group needs for honest capital planning. The building gets reliability today, and the modernization decision gets made deliberately in a boardroom instead of reactively in a dark lobby.
For contractors, that documented test data is also cover. When you can show an owner recorded insulation values and a condition trend, the recommendation stops being an opinion contest between vendors.
Where the Work Actually Gets Done
Whichever direction a building takes, the MG set path runs through a shop that can genuinely do the work: winding, machining, balancing, and testing under one roof, with rebuilt exchange inventory when turnaround is critical. That combination is rarer than it should be, because most of the industry’s MG expertise has retired or been absorbed into corporate consolidations, which is precisely why contractors nationwide ship these machines to Trenton.
Our elevator motor repair services cover MG sets, DC hoist motors, and gearless machines of any vintage, with field service available for machines that cannot leave the building. Call Electrical Motor Repair Co. at (609) 392 6149, or send us the machine details for a rebuild quote, and you will get a recommendation from people who profit from repairs and modernizations alike, and therefore have no reason to shade the answer.
Frequently Asked Questions
Yes, fully. MG sets are electromechanical machines with no proprietary electronics, so every wearing component, including brushes, bearings, commutators, and windings, can be restored. A properly rebuilt MG set returns to original specification and can serve for many additional years.
A planned MG set rebuild is typically measured in weeks, while a full modernization is a capital project measured in months. Rebuilt exchange equipment can shorten MG outages further, since a stocked unit can ship while the original machine is being serviced.
Usually not. If a funded modernization is scheduled within roughly the next two years, targeted maintenance that bridges the machine to its planned retirement is a better use of money than a full rebuild the project will replace.
The machine’s nameplate data, a description of the symptoms or failure, photos if available, and whether the machine can be shipped or requires onsite service. With that in hand we can scope the work, quote turnaround, and advise whether exchange inventory can shorten the outage.