ABB TF42-16 Thermal Overload Relay 13-16 A

TF42-16, ordered as 1SAZ721201R1047, is an adjustable ABB overload relay for motors drawing 13 to 16 A. It is a TF42 thermal relay of trip class 10 that also reacts to phase failure. Because it mounts straight onto AF09 to AF38 contactors, contactor and relay together make a compact motor starter. See contactors and overload relays for more starter parts, including the TA25DU relay.

Technical specifications

Tripping behaviour between 13 and 16 A

Each pole has a bimetal strip that the motor current heats. When the strips bend on overload, contact 95-96 opens to release the contactor and 97-98 closes to signal the trip. Settings are read directly in amperes against the motor rated current; per the data sheet there is no trip at 1.05 x the setting and a trip at 1.2 x. Resistance per pole is 7.79 mOhm, and heat per pole ranges from 1.3 W at the lowest setting to 2.0 W at the highest, a point to watch in closed enclosures.

Mounting and typical pairing

The TF42-16 mounts straight onto the contactor and uses the same 0.75 to 4 mm2 terminal range up to 20 A, with 12 mm stripping length. Its setting window starts where the TF42-13 ends, so a 14 to 16 A motor falls near the middle of the scale. In ABB’s softstarter catalogue the TF42 is the example overload relay for PSR sizes up to PSR37, which makes the TF42-16 a natural fit beside a 16 A or 25 A class starter. Allow for 15 operations per hour without early tripping, or 60 with a 40 percent duty ratio and a starting time of one second or less.

Which motors fall into the 13 to 16 A range

The relay should be set to the rated current printed on the motor nameplate, not to a calculated value. As a rough guide, three-phase motors with a full-load current between 13 and 16 A at 400 V are often around the 7.5 kW size, but nameplate currents vary with efficiency class, pole number and manufacturer, so always confirm against the actual motor. If the nameplate current lies near 13 A or near 16 A, consider whether an adjacent TF42 range gives more margin for adjustment.

Trip class 10 and starting time

Class 10 suits motors that reach full speed within a normal starting time. Loads with long run-up, such as large fans with heavy impellers, centrifuges or loaded conveyors, may need a higher trip class or an electronic overload relay, otherwise the relay can trip during a healthy start. Check the starting time of the driven machine before selecting.

Setting, testing and resetting

• Setting the dial: turn the current setting to the motor nameplate value; where a motor runs in a hotter cabinet than the motor itself, follow ABB guidance rather than raising the setting on instinct.
• Automatic or manual reset: manual reset is generally preferred so an operator investigates the cause; automatic reset is used only where an unexpected restart is safe, for example with a separate start command circuit.
• TEST and STOP: use the TEST function during commissioning to confirm that contact 95-96 opens the contactor coil circuit and 97-98 signals the trip to the PLC or indicator lamp.
• After a trip: allow the bimetals to cool before resetting, and find out why the motor overloaded: jammed load, low voltage, a lost phase or a failing bearing.

Coordination with short-circuit protection

The overload relay protects against overload and phase loss, but not against short circuits. Fit the upstream fuse or circuit breaker listed for Type 2 coordination, 40 A gG in the data sheet, so that after a short circuit the starter remains suitable for further use after inspection.

Motor control panels in Oman and the GCC

Direct-on-line starters with an AF contactor and a TF42 relay are standard in pump sets, cooling towers, air handling units and process skids across the region. Panel temperatures in summer can be high, and although the relay is ambient-compensated between -25 °C and +60 °C, an overheated panel shortens the life of every component. Ventilate or cool enclosures, and keep the heat loss per pole in mind when several starters share one panel. The listed marine approvals are relevant for shipyards and offshore support vessels.

RFQ details

• Model TF42-16 and order number 1SAZ721201R1047, with quantity.
• Matching contactor type (AF09 to AF38) and coil voltage, if a full starter is needed.
• DIN rail mounting kit if the relay is to be mounted separately.
• Motor nameplate current for cross-checking the range.

What to confirm before ordering

In the name TF42-16 the figure is the top of the setting range in amperes, giving 13 to 16 A; quote 1SAZ721201R1047 when asking for a price. Short-circuit protection is required ahead of the relay: ABB gives a 40 A gG fuse for type 2 coordination. Please check the motor full-load current, contactor, voltage and the need for a single mounting kit for DIN-rail fitting before an order. Behind the link is ABB’s TF42 data sheet with order data, circuit data, UL/CSA tables, dimensions and a tripping curve. Quotations come from Seven Star LLC, an independent supplier in Muscat; this page shows neither price nor stock.