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Speed Control Technology - Product Guide - Resistor Technology
MG & 3PG RESISTOR BANKS

Why Use MG & 3PG Resistor Banks?

Speed Control Technology (SCT) designs and builds MG and 3PG Resistor Banks. The scope includes AC and DC Motor Control. Our MG and 3PG Resistor Banks have set the standard for reliability and quality for several decades. The grid material is Carpenter 316 stainless steel, with a temperature coefficient of just 5% between ambient and 400C (the nominal operating condition).

An MG Resistor Bank – tap points on alternate grids:

The Resistor Banks are resistant to rust, adjacent grids are argon welded together, to render them independent of rod pressure. A high impedance to earth is ensured by double insulation with epoxy glass tubes between tie rods and grids. There are heavy duty ceramic insulators at grid ends and at end plates. The bank assembly is built to ensure durable operation in tough steel production conditions. Ratings and dimensions conform to NEMA standards. Continuous and intermittent ratings are stated in the subsequent diagram.

MG Resistor Banks

An MG Resistor Bank conforms to the NEMA dimensions, with each grid on the bank identical, and a continuous connection along the assembly.

MG Resistor Bank

ORDERING INFORMATION AMPERE RATING PER NEMA CLASS NUMBERS
BANK OHMS 90 170 160 150 140 130 LIST NO.
MG3􀀀2 0.0465 350 440 513 575 680 792 40601
MG4􀀀2 0.06 310 383 448 507 577 665 40602
MG5􀀀2 0.075 280 319 410 456 537 598 40603
MG6􀀀2 0.09 250 309 362 412 476 551 40604
MG3 0.156 185 232 270 303 358 417 40606
MG4 0.216 162 202 236 267 304 350 40607
MG5 0.25 147 184 216 240 283 315 40608
MG6 0.325 136 163 191 217 252 290 40609
MG8 0.544 109 137 159 178 205 238 40610
MG10 0.72 96 121 140 157 182 209 40611
MG12 0.9 85 107 123 136 160 182 40612
MG16 0.96 80 99 117 130 152 179 40613
MG20 1.52 66 83 96 108 128 149 40614
MG25 2.1 58 74 85 95 111 128 40615
MG31 2.85 51 65 75 83 98 110 40616
MG40 3.92 44 55 64 72 83 95 40617
MG50 7.6 34 42 49 54 64 74 40618
MG62 10 29 37 42 47 54 60 40619
Time On Cont. 15 15 15 15 10 Seconds
Time OFF Cont. 15 30 45 75 70 Seconds

3PG Resistor Banks

A 3PG Resistor Bank conforms to NEMA dimensions, and all grids on the unit are identical but split into three separate phases:

3PG Resistor Bank

ORDERING INFORMATION AMPERE RATING PER NEMA CLASS NUMBERS
BANK OHMS 90 170 160 150 140 130 LIST NO.
3PG3 0.044 185 232 270 303 358 417 40636
3PG4 0.056 162 202 236 267 304 350 40637
3PG5 0.070 147 184 216 240 283 315 40638
3PG6 0.088 136 163 191 217 252 290 40639
3PG8 0.144 109 137 159 178 205 238 40640
3PG10 0.20 96 121 140 157 182 209 40641
3PG12 0.25 85 107 123 136 160 182 40642
3PG16 0.26 80 99 117 130 152 179 40643
3PG20 0.40 66 83 96 108 128 149 40644
3PG25 0.50 58 74 85 95 111 128 40645
3PG31 0.75 51 65 75 83 98 110 40646
3PG40 1.12 44 55 64 72 83 95 40647
3PG50 2.0 34 42 49 54 64 74 40648
3PG62 2.25 29 37 42 47 54 60 40649
3PG80 2.56 26 32 36 41 46 53 40650
3PG150 4.64 17 18 21 24 27 31 40651
3PG200 5.92 10 12 14 16 18 20 40652
Time On Cont 15 15 15 15 10 Seconds
Time OFF Cont 15 30 45 75 70 Seconds

Type 3PG Resistor Banks are ideal slip resistors for small to medium slip-ring motors, with closed-loop thyristor control, such as AC10. A NEMA 90 continuous thermal rating would be standard for this class of control, for which stability of resistance is the essential property.

Enclosed Resistors

Resistor Enclosures for MG banks is assembled from two and three-bank modules. These can be stacked in practical configurations to accommodate any number of resistor banks. High-temperature silicon-insulated cable is used for internal cabling. The standard enclosure colour is B26 Electric Orange.

Enclosure Dimensions

Enclosure Fig 1 1 bank + term chassis H = 587 W = 832 D = 406
Enclosure Fig 2 2 banks + term chassis H = 777 W = 832 D = 406
Enclosure Fig 3 3 banks + term chassis H = 1020 W = 832 D = 406
Enclosure Fig 4 4 banks + term chassis H = 1210 W = 832 D = 406
Enclosure Fig 5 5 banks + term chassis H = 1400 W = 832 D = 406
Enclosure Fig 6 6 banks + term chassis H = 1640 W = 832 D = 406

The enclosures can also be mounted side-by-side. They have knock-out holes for internal cabling.

Resistor Applications

  • Rotor Resistors for Slip-ring Motors

    01

    The principal need is to set an outer limit for the motor at each motor slip point.

  • Discharge Resistors for Frequency Controllers

    02

    The majority of frequency controllers have what is called a passive (un-controlled) front end. This means the controller can pass forward power only: it cannot return regenerated power to the mains system. The implication is that negative power (power developed by the load), must be dissipated within the control system.

  • DC Crane Resistors

    03

    Conventional fixed voltage 230 and 440V dc technology places heavy emphasis on power resistors for starting and control. For hoist motions in particular; the inherent design necessitate bulk resistors to control the armature and field circuits; in particular during lowering.

  • Neutral Earthing Resistors

    04

    The term high resistance earthing pertains to the addition of a resistor into the neutral point of a distribution system; for the purpose of limiting earth fault currents to a controlled pre-determined level.

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