Features and Options

Resistive Elements
Wirewound

Wirewound resistive elements consists of an open helical stainless steel wire wrapped around a tubular porcelain core, allowing for fast and efficient cooling. In general wirewound resistive elements are ideal for low current conditions, offering excellent power dissipation, stable resistance, and shock-proofing.

Wirewound Element

Edgewound

Edgewound resistive elements are strip type elements, essentially a stainless steel tape wound on tubular porcelain insulators. A rod is placed inside these resistive elements to form the resistive assembly. They are used in general for medium-level currents, touting shock-proofing, and compactness.

Edgewound Element

Stamped Grid

Generally used for low resistance and high current, grid resistors are made with punched steel sheet with holes at in each end for mounting. Grids are then stacked on insulated steel rods. Mica washers are inserted between grids for insulation, and the rods are mounted between steel end frames. To obtain the best electrical connection, we weld grids together.

Enclosures
NEMA 1

Enclosures constructed for indoor use to provide a degree of protection to personnel against access to hazardous parts and to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt).

IP20
Protected against solid foreign objects of 12.5mm in diameter and greater. Not protected against water ingress.

NEMA 3R

Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain , sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.

IP23
Protected against solid foreign objects of 12.5mm in diameter and greater.
Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect.

NEMA 4

Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow, splashing water, and hose directed water); and that will be undamaged by the external formation of ice on the enclosure.

IP56
Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact.
Water projected in powerful jets (12.5mm nozzle) against the enclosure from any direction shall have no harmful effects.

NEMA 4X

Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow, splashing water, and hose directed water); that provides an additional level of protection against corrosion; and that will be undamaged by the external formation of ice on the enclosure.

IP56
Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact.
Water projected in powerful jets (12.5mm nozzle) against the enclosure from any direction shall have no harmful effects.

Enclosure Materials
Galvanized Steel

A protective coating of zinc is applied to steel. The zinc provides cathodic protection due to its greater negative electrochemical potential, making it the metal of preference to be consumed (when rusting). It often shows an aesthetic feature known as spangle, crystallites inside the coating. All of our galvanized steel material meets specific ASTM coating standards.

Once the galvanized steel is prepared, it is then treated for painting with a non-metallic iron phosphate coating. This heavily improves paint adhesion and increases corrosion protection if the metal’s paint film is broken. After the steel has been phosphatized, it is then powder coated. Powder coating cures in heat, forming a “skin”. This creates a harder finish, tougher than conventional paint.

Galvanized steel is a generally cost-effective and reliable material to prevent corrosion and damage to your product.

Galv Steel

Stainless Steel

The most widely used stainless steel is the “304” type, comprised of 18% chromium and 8% nickel. We also offer “316” grade stainless steel, comprised of 18% chromium and 10% nickel.

Stainless steel is touted for its resistance to corrosion and staining, and low maintenance needs. If your product will be used in an environment subject to corrosive conditions then we recommend using stainless steel over galvanized steel. The 304 grade steel provides greater resistance to corrosion than galvanized steel, and the 316 grade steel provides even more resistance than the 304.

Because stainless steel is comprised of chromium and nickel throughout the material itself, it provides corrosion resistance for a longer duration as it does not rely on a coating for protection. This leaves painting to be an an optional layer of protection. We generally use stainless steel with a natural finish unless otherwise specified.

If you need the high corrosion resistance paired with long-term usage, then consider stainless steel as a very viable alternative to galvanized steel.

SS

Anodized Aluminum

Anodizing is a process used to increase the thickness of a natural oxide layer formed on the surface of metal. Aluminum when exposed to any gas containing oxygen at room temperature will form a surface layer of amorphous aluminum oxide, which is very effective against corrosion.

We recommend anodized aluminum if you have specific corrosive conditions that are not or cannot be met by stainless steel. It is a very effective method of protecting against certain corrosive conditions.

anod alum

What are Motor Control Resistors?

These resistors are used to control the torque and speed of AC and DC motors, along with limiting in-rush current. To avoid confusion it should be noted that these resistors are used to control energy input into motors while Dynamic Braking Resistors are used to brake and drain energy.

Motor Control Resistors are commonly used with wound-rotor motors as an external resistor circuit. Conductors in the rotor are connected to slip rings, these slip rings provide the contact to the resistor circuit. By changing the level of resistance in the circuit (the Motor Control Resistor), speed and torque can be adjusted. In other words, higher resistance means reduced torque and speed.

For multiple levels of torque and speed control, Motor Control Resistors use “steps” or “speeds”. Steps/speeds essentially provide intervals for levels of resistance. For most applications, a 4-step/5-speed Motor Control Resistor is recommended. 1-step/2-speed resistors are available, all the way up to 10-step/11-speed. In general we recommend that you use a higher number of steps if the motor is powerful and used for large-scale purposes such as mining. Usually there will always be one more speed level than resistor steps, because the maximum speed is achieved with all steps cut out; exceptions occur when a permanent slip resistor is required to reduce internal heating of the motor.

To enable manufacturers to test resistors under the same conditions, NEMA has created resistor classes based on duty and the type of application. We use these classes to conform to standards and making it easier for you to order your product. You can refer to the NEMA Resistor Applications table above, and then the NEMA Resistor Classes to help you determine the class for your motor.

Advantages

  • Limit torque and speed of wound rotor motors to safe levels.
  • Keep motor voltages within safe levels.
  • Reduce overheating.
  • Reduce wasted time during braking.
  • Increase life of the equipment.
  • Improved service reliability.

24 Month Guarantee

All of our products have a minimum 24 month guarantee. We are fully committed to ensuring your satisfaction.

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Information Resources

NEMA Resistor Classes
Approximate Per Cent of Full-Load Current on First Point Starting from RestDuty Cycles
5 Sec On 75 Sec Off10 Sec On 70 Sec Off15 Sec On 75 Sec Off15 Sec On 45 Sec Off15 Sec On 30 Sec Off15 Sec On 15 Sec OffContinuous Duty
2511113114115116117191
5011213214215216217292
7011313314315316317393
10011413414415416417494
15011513514515516517595
200 or over11613614615616617696
NEMA Resistor Applications

Blowers

  • Constant Pressure: 135-195
  • Centrifugal: 133-193

Brick Plants

  • Augers: 135
  • Conveyors: 135
  • Dry Pans: 135
  • Pug Mills: 135

By-Products Coke Plants

  • Reversing machines: 153
  • Leveler ram: 153
  • Pusher bar: 153
  • Door machine: 153

Cement Mills

  • Conveyors: 135
  • Crushers: 145
  • Rotary dryers: 145-195
  • Elevators: 135
  • Grinders, pulverizers: 135
  • Kilns: 135-195

Coal and Ore Bridges

  • Holding line: 162
  • Closing line: 162
  • Trolley: 163
  • Bridge: 153

Coal Mines

  • Car hauls: 162
  • Conveyors: 135-155
  • Cutters: 135
  • Crushers: 134-193
  • Fans: 134-193
  • Hoists, slope: 172
    • Vertical: 162
  • Jigs: 135
  • Picking tables: 135
  • Rotary car dumpers: 153
  • Shaker screens: 135

Compressors

  • Constant speed: 135
  • Varying speed, plunger type: 135-195
    • Centrifugal: 93
  • Bridge: 153

Concrete Mixers: 135

Cranes-General Purpose

  • Hoist: 153
    • Bridge, sleeve bearing: 153
  • Trolley, sleeve-bearing: 153
  • Bridge or trolley, roller-bearing: 152

Flour Mills: 135

Line shafting: 135

Food Plants

  • Dough mixers: 135
  • Butter churns: 135

Hoists

  • Winch: 153
  • Mine slope: 172
  • Mine vertical: 162
  • Contractors’ hoists: 152

Larry Cars: 153

Lift Bridges: 152

Machine Tools

  • Bending rolls, rev.: 163-164
    • Non-rev.: 115
  • Boring mills: 135
  • Bulldozers: 135
  • Drills: 115
  • Gear cutters: 115
  • Grinders: 135
  • Hobbing machines: 115
  • Lathes: 115
  • Milling machines: 115
  • Presses: 135
  • Punches: 135
  • Saws: 115
  • Shapers: 115

Metal Mining

  • Ball, rod, tube mills: 135
  • Car dumpers, rotary: 153
  • Converters, copper: 154
  • Conveyors: 135
  • Crushers: 145
  • Tilting furnace: 153

Paper Mills

  • Heaters: 135
  • Calendars: 154-192

Pipe Working

  • Cutting and threading: 135
  • Expanding and flanging: 135-195

Power Plants

  • Clinker grinders: 135
  • Coal crushers: 135
  • Conveyor, belt: 135
    • Screw: 135
  • Pulverized fuel feeders: 135
  • Pulverizers, ball type: 135
    • Centrifugal: 134
  • Stokers: 135-193

Pumps

  • Centrifugal: 134-193
  • Plunger: 135-195

Rubber Mills

  • Calenders: 155
  • Crackers: 135
  • Mixing mills: 135
  • Washers: 135

Steel Mills

  • Accumulators: 153
  • Casting machines, pig: 153
  • Charging machines, bridge: 153-163
    • Peel: 153-163
    • Trolley: 153-163
  • Coiling machines: 135
  • Conveyors: 135-155
  • Converters, metal: 154
  • Cranes, ladle, bridge, trolleys, sleeve-bearings: 153-163
    • Roller-bearing: 152-162
    • Hoist: 153-163
  • Crushers: 145
  • Furnace doors: 155
  • Gas valves: 155
  • Gas washers: 155
  • Hot metal mixers: 163
  • Ingot buggy: 153
  • Kickoff: 153
  • Levelers: 153
  • Manipulator fingers: 153-163
  • Side guards: 153-163
  • Pickling machine: 153
  • Pilers, slab: 153
  • Racks: 153
  • Reelers: 135
  • Saws, hot or cold: 155
  • Screwdowns: 153-163
  • Shears: 155
  • Shuffle bars: 155
  • Slab buggy: 155
  • Soaking pit covers: 155
  • Straighteners: 153
  • Tables, main roll: 155-163
    • Shear approach: 155-163
    • Lift: 155-163
    • Roll: 155
    • Transfer: 155
    • Approach: 155
  • Tilting furnace: 153
  • Wire standing machine: 153

Woodworking Plants

  • Boring machines: 115
  • Lathe: 115
  • Mortiser: 115
  • Molder: 115
  • Planers: 115
  • Power trimmer and miter: 115
  • Sanders: 115
  • Saws: 115
  • Shapers: 115
  • Shingle machine: 115