Pfannenberg FLZ 541 Twin Thermostat, 0 to +60 °C

Two independent thermostats in one DIN-rail housing

The Pfannenberg FLZ 541 is a twin thermostat: two bimetal switching units with separate dials in one housing, so a heater and a fan, or two stages of cooling, can be switched at different temperatures without a second device. The family is built in three contact combinations: FLZ 541 with N.C. and N.O., FLZ 542 with two N.C. contacts and FLZ 543 with two N.O. contacts.

A twin thermostat also avoids the overlap problem of a single changeover thermostat. With a changeover contact the heater and fan share one set point and can cycle against each other near it. With two dials, the heater can be set at, for example, 10 °C and the fan at 35 °C, leaving a wide, energy-saving dead band in between.

Technical specifications

Which twin version to choose

The three versions differ only in what the two contacts can do. The FLZ 541 pairs a normally closed contact with a normally open contact, which is the usual arrangement for one heater and one fan: the N.C. contact keeps the heater energised until the heater set point is reached and the N.O. contact starts the fan when the upper set point is exceeded. The FLZ 542 gives two N.C. contacts for two heater stages or for a heater plus a high-temperature alarm that opens on rising temperature. The FLZ 543 gives two N.O. contacts for staged fans, or for a fan plus a warning contact that closes when the enclosure is too hot.

The ratings follow the single thermostats: 10 (2) A at 240 V AC on the N.C. side and 15 (2) A at 120 V AC on the N.O. side, with the inductive value in brackets applying to motor and relay loads. Larger heaters or several fans should be switched through a contactor.

Setting and installing the dials

Set the heater dial lower than the fan dial and leave at least a few kelvin between them, remembering that the switching difference is below 7 K and the point tolerance is +/-4 K. Fit the thermostat on the profile bar where it sees typical enclosure air, not directly above a heater or in the airflow of a fan. The sheet lists a hygrostat, article number 17207000000, and an internal enclosure fan, article number 18110000000, as matching accessories for a complete climate loop.

Before ordering, confirm the number of loads, the supply voltage and the contact rating of each, because the contact combination is fixed by the article number and cannot be changed in the field.

Documents and quotation

The Pfannenberg FLZ 541/542/543 product sheet is attached to this page and is the manufacturer’s own document, not a Seven Star summary. It also shows the housing dimensions and the contact schematics. Related climate products are in HVAC & Combustion.

State the contact combination (N.C./N.O., N.C./N.C. or N.O./N.O.) in the request. Seven Star LLC, an independent supplier in Muscat, quotes the FLZ 541, FLZ 542 and FLZ 543 against your application data; send the enclosure size, ambient temperature, supply voltage and quantity so the correct variant and article number can be confirmed before an offer is issued.