Wiring - PENN Controls - A421ABD - A421AED - Electronic Temperature Control - A421 Off‐Cycle Defrost Model

A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

Product name
A421 Off‐Cycle Defrost Model
Document type
Installation Guide
Document revision
Revision date

Observe the following guidelines.

  • Risk of Electric Shock
  • Disconnect or isolate all power supplies before making electrical connections. More than one disconnection or isolation may be required to completely de-energize equipment. Contact with components carrying hazardous voltage can cause electric shock and may result in severe personal injury or death.
  • Risque de Décharge Électrique
  • Débrancher ou isoler toute alimentation avant de réaliser un raccordement électrique. Plusieurs isolations et débranchements sont peut-être nécessaires pour -couper entièrement l'alimentation de l'équipement. Tout contact avec des composants porteurs de tensions dangereuses risque d'entraîner une décharge électrique et de provoquer des blessures graves, voire mortelles.
Important: Use copper conductors only. Make all wiring connections in accordance with local, national, and regional regulations. Do not exceed the A421 Control's electrical ratings.
Important: Do not exceed the A421 Control’s electrical ratings. Exceeding the electrical ratings can result in permanent damage to the control and void any warranty.
Important: Run all low-voltage wiring and cables separate from all high-voltage wiring. It is best practice to use shielded cable input (sensor) cables that are exposed to high electromagnetic or radio frequency noise.
Important: Make all wiring connections in accordance with the National Electrical Code and local regulations. Use proper Electrostatic Discharge (ESD) precautions during installation and servicing to avoid damaging the electronic circuits of the A421 Control.
Important: Do not connect supply power to the A421 Controls before checking all wire connections. Short circuits or improperly connected wires can result in damage to the modules and void any warranty.
Important: Do not overtighten the terminal screws. Excessive torque can damage the electronic board. The recommended torque is 3 in.•lb.
Important: When you connect an A99 sensor with a shielded cable to an A421 Control, connect the cable shield drain lead to the common (COM) terminal on the sensor and binary input terminal block (TB3). Do not connect the shield at any other point along the cable, and isolate and insulate the shield along the entire length of the sensor cable. If you connect a cable shield at more than one point, transient currents can flow through the sensor cable shield and cause erratic control operation.

Observe the wire size restrictions listed in Table 1 and the electrical ratings listed in Technical specifications.

Observe the following guidelines, procedures, and illustrations when you wire an A421 Series control and A99 Series sensor.

  • Select the appropriate A99 sensors for the ambient operating range that the A421 Control monitors and controls, as shown in Table 2. See Technical specifications for more information.
  • Keep the sensor leads as short as possible in your application. The additional resistance in long sensor cables creates an offset between the actual temperature and the displayed temperature. See Table 1 when you extend sensor leads.
  • A99 sensors are not polarity specific. You can connect either lead to the SEN or COM terminals.
  • It is best practice to use 22 AWG, stranded, twisted-pair cable with a shield to extend sensor cable runs.
Table 1. Maximum sensor cable lengths and wire sizes
Wire gauge Maximum sensor cable length1
16 AWG 500 ft (152 m)
18 AWG 300 ft (91 m)
20 AWG 200 ft (61 m)
22 AWG 125 ft (38 m)
1 At the listed maximum cable lengths, there is less than 1Fº (0.6Cº) error between the temperature sensed at the A99 sensor and the temperature displayed on the LCD.