Setup: Marley ABH Basin Heater Control User Manual

Overview

The ABH Basin Heater Control is a stand-alone control package for protecting the cold-water collection basin of a cooling tower from freezing conditions. It monitors basin water temperature through a platinum PT-100 RTD sensor and switches the basin heater on or off through a power contactor.

This guide is intended for qualified personnel responsible for installing, operating, maintaining, or troubleshooting Marley ABH basin heater systems. Read the complete guide before working on the control panel, heater element, or cooling tower.

Specifications

• Product: ABH basin heater control package.
• Control enclosure: Outdoor NEMA 4X fiberglass enclosure with hinged lid and snap-type latches.
• Available supply ratings: 208 V, 240 V, 380 V, 480 V, or 575 V at 50/60 Hz.
• Control panel protection: Main thermal-magnetic molded-case circuit breaker with integral overload and short-circuit protection.
• Standard short-circuit current rating: 5,000 A; a 65,000 A option uses a fused disconnect instead of the standard breaker.
• Temperature sensor: Platinum PT-100 RTD with combined temperature-sensing and low-water cutout functions.
• Standard sensor lead: 30 feet (9 m); field extension is permitted to a tested maximum of 200 feet (60 m).
• Sensor extension cable: 18-gauge stranded copper conductors with a shield, installed according to local electrical requirements.
• Controller display: Two-line display showing PV process temperature and SV setpoint temperature.
• Factory temperature setpoint: 42°F (5.5°C).
• Heater cut-in temperature: 40°F (4.5°C).
• Heater cut-out temperature: 45°F (7.2°C).
• Low-temperature alarm: Contact closes at approximately 35°F (1.7°C).
• Heater coverage: One centrally located heater can protect up to 300 square feet of basin surface area from ice damage.
• Heater mounting clearance: Keep the heater at least 7/8 inch above the basin floor.
• Sensor mounting: 1/2-inch NPT bulkhead fitting installed through a 1 3/8-inch clearance hole.
• Sensor position: At least 1 inch above the highest point of the heater and at least 6 inches away from it.
• Sensor insertion: Extend the probe at least 4 inches into the open basin.
• Electrical standards: UL 508A, CUL 508A, and NFPA 70 requirements.

Detailed Description

The ABH Basin Heater Control combines a main disconnect, control transformer, solid-state temperature controller, contactor, terminal strip, safety circuits, indicator lights, and basin heater connections in one outdoor-rated enclosure.

The RTD sensor performs two jobs. It measures water temperature for the controller and confirms that the probe is submerged. The heater cannot energize when the sensor detects an unsafe low-water condition. This prevents the element from operating in air.

The controller uses an adjustable thermostatic sequence. Its process-value line displays the water temperature measured at the probe, while the setpoint-value line displays the control target. The normal factory setting is 42°F. When the basin temperature falls to 40°F, the controller energizes the contactor. When the temperature reaches 45°F, the contactor opens and removes power from the heater.

Some heater elements include a two-wire thermal cutout, also called a TCO. This one-time thermal fuse opens the safety circuit if the element overheats. The TCO must be wired through terminals C1 and C2, with the factory jumper removed. When several heater elements are installed, their power connections are wired in parallel and their thermal cutout circuits are wired in series.

The control panel can provide dry contacts for a low-temperature alarm, heater operation confirmation, contactor status, and heater failure indication. Optional provisions include a 4–20 mA temperature signal, remote setpoint selection, remote heater testing, run enable, and fieldbus integration.

Safety

• Disconnect and lock out electrical power before opening the panel, servicing the heater, or working on the cooling tower. Electrical shock or burns can cause severe injury or death.
• Use qualified electrical personnel for installation, wiring, maintenance, and troubleshooting.
• Verify grounding, branch-circuit sizing, overcurrent protection, panel access, and the customer-supplied disconnect arrangement before energizing the system.
• Never operate the basin heater unless it is completely covered by water. An exposed element can become extremely hot, fail, or ignite nearby combustible material.
• Do not bypass, modify, or disable the combined temperature and low-water sensor. A disabled safety circuit can create a fire or equipment hazard.
• Keep the sensor at least 1 inch above the heater and at least 6 inches away to ensure that the heater is submerged before it can energize.
• If combustible material is closer than 10 inches to the heater, install a noncontacting sheet-metal heat shield that extends beyond the element in all directions.
• Seal conduit entries at the enclosure to prevent water vapor and condensation from entering the panel.
• Follow the as-built wiring diagram mounted inside the control-panel door. Special project configurations may differ from a standard diagram.

Setup and Installation

Mount the control panel

Install the enclosure outdoors near the cooling tower in a location that provides safe access for operation and service. Route power and control wiring through the bottom of the enclosure using watertight fittings. Provide a drip path and seal the conduit at the enclosure with silicone or expanding foam to form a vapor barrier. A lower panel elevation can allow condensation to travel toward the enclosure, so take additional care with conduit sealing.

Install the RTD sensor

1. Select a location in the coldest portion of the cold-water basin, normally near the heater and pump suction area.
2. Drill or provide a 1 3/8-inch clearance hole through the basin wall.
3. Insert the sensor probe through the supplied bulkhead fitting and basin wall.
4. Position the probe at least 1 inch above the heater’s highest point, at least 6 inches away from the heater, and at least 4 inches into the basin.
5. Hold the bulkhead fitting so the cord does not twist while tightening the mounting nut by hand.
6. Lightly tighten the nut to secure the gasket and fitting without damaging the assembly.

Install the heater element

Place the heater in the depressed basin area near the outlet while maintaining at least 7/8 inch of clearance above the basin floor. For larger basins, distribute multiple heaters so each protects an approximately equal area. A single heater package can serve no more than two tower cells; towers with three or more cells require additional heater packages.

Use metal heater supports as necessary to keep unsupported heater length below 30 inches. When multiple elements are installed in a cell, connect the elements in parallel and return three power conductors plus ground to the control panel.

Complete field wiring

• Bring incoming utility power from the bottom of the enclosure to the line side of the main circuit breaker.
• Route the contactor load conductors through the bottom of the enclosure to the basin heater.
• Connect the RTD and field devices at the user terminal strip.
• Connect the heater thermal cutout wires to terminals C1 and C2 after removing the factory jumper.
• For multiple heaters, connect all thermal cutout circuits in series and return two wires to the panel.
• Use the wiring diagram inside the panel door for terminal identification and any special options.
• Seal every field-added conduit opening after wiring is complete.

Operation

Automatic temperature control

After the main disconnect is turned on and all safety circuits are complete, the controller monitors the basin through the RTD. The heater turns on at approximately 40°F and turns off at approximately 45°F around the normal 42°F setpoint. Some surface ice can still occur because the system is intended to keep basin water fluid at the discharge area rather than eliminate every trace of ice.

The controller adjustment may be locked to prevent unauthorized changes. Only qualified personnel should alter the setpoint or configure optional operating modes.

Panel display and indicators

• PV: Actual water temperature measured at the sensor.
• SV: Controller setpoint temperature.
• Amber BASIN HEATER ON light: The element is drawing current during a heater-on command.
• Red BASIN HEATER FAILURE light: The heater circuit is defective or the element is not drawing current during the test.
• Low-temperature alarm contact: Closes when basin temperature reaches approximately 35°F.

Test the heater

Use the push-to-test button on the enclosure door only when the heater element is fully covered with water. Hold the button for several seconds to command the contactor on. The amber indicator should illuminate if the element draws current. If the red failure indicator illuminates, de-energize the system and investigate the heater circuit before returning it to service.

A remote dry-contact closure can provide the same test command where the control panel is integrated with a building management system.

Operate the disconnect

Turn the disconnect handle to OFF before opening the enclosure door. The door interlock normally prevents opening while the handle is ON. If qualified service personnel must defeat the interlock for testing, insert a small pin into the opening in the yellow bezel and follow the site lockout procedure.

For lockout/tagout, switch the disconnect OFF, pull out the locking provision behind the pistol-grip handle, insert an approved lock, and secure it before servicing.

Cleaning and Maintenance

Inspect and clean the sensor probe and heater element during normal cooling-tower maintenance. Mud, silt, scale, and other deposits can interfere with water-level detection and prevent proper heat transfer.

1. De-energize and lock out the basin heater control before entering the service area.
2. Clean the two conductive sensor surfaces with an abrasive pad until deposits are removed.
3. Clean the heater tubes with an abrasive pad to remove scale and other buildup.
4. Confirm that the heater tubes are not resting in mud or silt.
5. Verify that the sensor and heater are completely positioned beneath the operating water level before restoring power.
6. Inspect conduit seals, terminal connections, heater supports, and the enclosure gasket for deterioration or damage.

The sensor uses conductive surfaces to determine whether it is submerged. Heavy contamination can interrupt this low-water safety function. Scale on the heater tubes can also restrict heat dissipation and cause premature element failure.

Troubleshooting

Panel will not operate

• Confirm that the disconnect handle is fully in the ON position. A positive click should be felt and heard as the breaker engages.
• Check that required circuit points C1, C2, 8, and 9 are complete through jumpers or connected remote devices.
• Verify that all three incoming phase-to-phase voltages are present, balanced, and compatible with the panel rating.
• Check the control-transformer primary and secondary fuses using the panel wiring diagram.
• Confirm that the thermal cutout circuit is connected between C1 and C2 and that the original jumper was removed after connection.
• Inspect any field-installed interposing relay. Its normally required contact must be closed for the control circuit to operate.

Thermal cutout circuit is open

De-energize the panel and disconnect the two TCO wires at C1 and C2. Check continuity through the thermal fuse. An open device must be replaced. The TCO is a one-time protective fuse located in the heater conduit head and is designed to interrupt the contactor circuit after an overtemperature event.

Heater does not energize

• Confirm that the sensor probe is submerged and free of ice, mud, and scale.
• Check the low-water circuit at terminals 17 and 18 with the sensor wires disconnected from the terminal strip.
• To test the sensor loop, temporarily bridge the two conductive sensor surfaces as directed by qualified service procedures and check for continuity.
• Inspect the contactor armature for free movement. It should move when actuated and return to the open position when released.
• Check for welded or damaged contactor contacts if the armature does not respond correctly.

Heater element is defective

With power isolated, measure resistance between each heater phase at the contactor load side. The readings should be balanced for the installed heater size. An open circuit, an extremely high reading, or a significant imbalance indicates a failed element. Typical reference values include approximately 30 ohms for 3 kW, 40 ohms for 2 kW, 60 ohms for 7.5 kW, and 50 ohms for 9 kW elements; actual values depend on the heater configuration.

Temperature reading appears incorrect

• Inspect the probe for scale or contamination and clean it with an abrasive pad.
• Confirm that the probe is installed in the coldest basin area and is not touching the heater.
• Inspect the sensor lead, plug, screw connector, shield, and field splice for damage or loose connections.
• Verify that any lead extension uses suitable stranded copper conductors and follows local wiring requirements.

Replacement Parts and Identification

Panel components and heater configurations can vary. Use the part identification shown on the wiring diagram inside the enclosure door and match the cooling-tower serial information before selecting replacements.

• Platinum PT-100 RTD with bulkhead fitting and 30-foot gray-sheathed cord: Marley item 2667655.
• Platinum PT-100 RTD with bulkhead fitting and 100-foot gray-sheathed cord: Marley item 2667656.
• Platinum PT-100 RTD without cord: Marley item 2597799.
• Low-water cutout card: Marley item A87493.
• FDC-9300 controller without 4–20 mA module: Marley item 2597872.
• FDC-9300 controller with 4–20 mA module: Marley item 2597874.
• 4–20 mA temperature transmitter module: Marley item 2597875.

Field-added relays and other components may not be original panel parts. Inspect the as-built diagram and the actual enclosure before ordering replacements.

Pros & Cons

• Pros: Automatic freeze protection, integrated low-water safety cutout, outdoor-rated enclosure, lockout/tagout provision, dual temperature display, heater test button, and dry-contact building-management integration.
• Pros: Supports single or multiple heater elements, optional remote monitoring, and optional remote operating controls.
• Cons: Correct operation depends on clean sensor and heater surfaces, watertight conduit sealing, complete thermal-cutout wiring, and qualified electrical service.
• Cons: The heater must remain fully submerged, and the system may not prevent all surface ice from forming in the basin.