The A1P is a proportional, infinitely variable power controller capable of delivering 0-97% of the applied line voltage to the directly connected electric heaters. The A1P will not control transformers or motors. This is accomplished by phase angle firing a pair of inversely connected SCR's. Modular construction allows for simple and solderless field serviceability. There are four field replaceable items:
  • Printed circuit board
  • Fuse
  • Dual SCR package
  • MOV (metal oxide varistor)
Unit of Measure


Voltage Designations

N/A 208 to 240 VAC 50/60 Hz


N/A 200 AMPS

Output Voltage

N/A 0 to 97% of input voltage

Control Signal

N/A 4 to 20 mA at 5 volts DC, 250 Ohms


N/A < 5% deviation

Response Time

N/A <12 mS (std unit, non soft start)


N/A Convection: 30-100 amps
Fan (120VAC): 150-1200 amps


N/A 190 ºF (fan cooled units only)

Power Dissipation (Watts)

N/A 1.2 x maximum current

Net Weight

N/A 14 Pound

Shipping Weight

N/A 23 Pound

Minimum Wire Gauge (Copper Wire Only- 90 ºC Temp Wire)

N/A 3/0 AWG

Wire Lug Torque (90 ºC Temp Wire)

N/A 250 lb/in

Lug Size (90 ºC Temp Wire)

N/A 250MCM - 6


Soft Start

N/A S02-2 Seconds S05-5 Seconds S10-10 Seconds S20-20 Seconds

Current Limit

N/A CL- Current Limit CLP-Current Limit with Panel Mount Potentiometer

Voltage Limit

N/A VL-Standard 1 Turn PCB VL25-25 Turn PCB



  • UL 508 listed
  • Compact and light weight
  • I2T sub cycle fusing standard
  • 100 % solid state circuitry
  • Over-rated dual SCR power modules
  • Thermostat std on fan cooled units
  • Over-sized heat sink
  • Full power ratings up to 50 °C (122 °F) ambient temperature
  • Optically isolated 4-20 mA input standard
  • Electrically isolated chassis and heat sinks to 600 amps
  • MOV protection on all power SCR's
  • SanRex, SemiKron, International Rectifier and Fairchild semiconductors
  • Double sided FR4 VO-94 rated glass epoxy PCB's
  • Theory of Operation

    The graphs below show phase angle fired voltage output on a 240V power line.
    The standard input signal (4-20 mA) is applied to the blue input terminal block, processed and fed to an optical coupler. The output of the optocoupler feeds the drive circuitry which is then fed to a pair of inversely connected SCR's. To obtain superior linearity, the line voltage is monitored and optically fed back to the input stage of the controller. An I²T fuse connected in series with the SCR's provides over current protection in the event of external wiring shorts, and or too large of a heater load. Additionally, a MOV (metal oxide varistor) is connected in parallel with the SCR's, providing voltage spike protection to the controller.