Temperature sensor connection heads · housing material and ingress rating, ambient limit of the head and its transmitter, metric or NPT entries, and flameproof versions
A process thermocouple or resistance thermometer ends in a small housing outside the vessel or pipe: the terminal head, or connection head. Inside it the sensor wires land on a ceramic or plastic terminal block, or on a head-mounted transmitter; a cable gland or conduit entry brings the field cable in; a gasketed cover keeps water and dust out. The head is chosen separately from the sensor, and four properties decide it: its ingress rating, the ambient temperature it and anything inside it can stand, the thread of its entries, and whether it must be flameproof.
Terminal (connection) heads for thermocouples and resistance thermometers as components: housing forms and materials, ingress protection, ambient temperature limits of the head and of head transmitters, neck tubes, sensor and cable entry threads, terminal blocks, and flameproof or dust-protected versions. Complete high-temperature thermocouple assemblies with ceramic or metal thermowells for furnaces, kilns and ladles are covered on the Thermocouple assembly page; mineral-insulated thermocouples for direct insertion through compression fittings on the Mineral-insulated thermocouple sensor page; complete RTD and thermocouple probe assemblies, with tolerance classes and thermowells, on the Temperature sensor probes and Industrial temperature probe pages; fluoropolymer sheaths on their own page.
01
The published ratings below come from three makers' data sheets and product pages; the ambient figures apply to the housing, not to the sensor inside the process.
Tempco describes its Bakelite heads as lightweight, non-combustible and resistant to acid and alkali, with a plated chain holding the cover, a choice of 2- or 4-terminal blocks and a grommeted entry for lead wire or flexible cable; its cast-iron head uses stainless steel chain and screws. [3] Endress+Hauser's TA30A has a low hinged cover with an optional window, and carries either a terminal block or a head transmitter with an optional display. [2]
| Head (maker) | Material | Protection | Ambient or service limit |
|---|---|---|---|
| Form B to DIN EN 50446 (JUMO) | Cast aluminium [1] | IP65 [1] | −40 to +100 °C [1] |
| BUZ and BUZH (JUMO) | Cast aluminium [1] | IP65 [1] | −40 to +100 °C [1] |
| NS (JUMO) | Plastic [1] | IP54 [1] | −30 to +130 °C [1] |
| TA30A (Endress+Hauser) | Aluminium, polyester powder-coated [2] | IP66/68, NEMA 4X [2] | −50 to +150 °C [2] |
| Type F and G (Tempco) | Bakelite [3] | O-ring gasketed body [3] | 350 °C (662 °F) maximum service [3] |
| Type H (Tempco) | Cast iron, high-temperature paint [3] | Neoprene O-ring weatherproof seal [3] | Not stated [3] |
State the site's ingress requirement (IP or NEMA), washdown or outdoor exposure, chemical exposure, and whether a display window is needed.
02
JUMO states that the connection head on its screw-in resistance thermometer is suitable for temperatures up to +100 °C, while the thermometer itself is offered for process temperatures from −50 to +600 °C. The gap is bridged by a stainless steel (1.4571) neck tube, 130 mm long on that model, between the process connection and the head. [1]
Fitting a transmitter in the head lowers the limit further: JUMO warns that the permitted ambient temperature is reduced when its head transmitters are used and refers to each transmitter's data sheet; its Wtrans B radio head transmitter, built for Form B heads, works at −30 to +85 °C. [1] Editorial calculation: on these figures a Form B head holding a Wtrans B transmitter is limited by the transmitter, 85 °C, which is 15 °C below the head's own 100 °C and 65 °C below the 150 °C housing rating Endress+Hauser gives for its TA30A. [1] [2]
Editorial note: radiant heat from a furnace wall, hot insulation or steam tracing raises the head temperature as well as conduction along the neck, so give the supplier the air temperature where the head will sit, not only the process temperature.
Give the process temperature, the air temperature at the head position, and whether a head transmitter is fitted, so the neck length and head can be chosen together.
03
JUMO's Form B, BUZ, BUZH and NS heads all have an M20 × 1.5 cable entry. [1] Tempco's heads are threaded to NPT instead: its cast-iron Type H head measures about 3-1/2 in on each side, its standard Bakelite Type F has 1/2 in sensor and conduit openings at about 3-7/8 × 4-1/8 × 3-3/16 in, and its miniature Type G has a 1/4 in sensor opening and 3/8 in conduit opening at about 2-5/8 × 3 × 2-5/16 in. [3]
Editorial note: metric and NPT threads do not interchange, so the head must match both the sensor's neck or thermowell thread and the plant's cable gland or conduit system; state both in the order rather than a head form alone.
04
Endress+Hauser's safety instructions for its TA30A family list Ex db IIC Gb (flameproof, gas), Ex tb IIIC Db (protection by enclosure, dust) and Ex ia IIIC Da markings. [2] JUMO, for thermometers ordered for SIL and PL applications, fits yellow connection heads where the design allows, with exceptions for sensors used in alkaline environments and where freedom from paint-wetting impairment substances (LABS) is required. [1]
Editorial note: an Ex marking belongs to the certified combination of head, cover, entries and glands; ask for the certificate and safety instructions for the exact head and the gland or stopping plug to be used in each entry.
05
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Sensor: [thermocouple type or RTD; single or duplex] Head: [form; material; colour] Protection: [IP or NEMA; outdoor, washdown, chemical exposure] Ambient: [air temperature at head; process temperature] Inside: [terminal block 2 or 4 terminal; head transmitter and output] Entries: [sensor thread; cable entry M20 × 1.5 or NPT size] Hazardous area: [gas or dust zone; Ex protection type]
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JUMO lists IP65 for its cast aluminium Form B heads and IP54 for its plastic NS head; Endress+Hauser lists IP66/68 for its TA30A. [1] [2]
JUMO's Form B head is rated −40 to +100 °C ambient, Endress+Hauser's TA30A −50 to +150 °C, and Tempco's Bakelite heads to 350 °C service. [1] [2] [3]
Yes; JUMO says ambient temperature is reduced with transmitters, and its Wtrans B head transmitter works at −30 to +85 °C. [1]
Sources checked 2026-10-13. JUMO data sheet 902020 (screw-in resistance thermometer with Form B connection head, 2026 edition), Endress+Hauser's TA30A terminal head product page and Ex safety instructions listing, and Tempco's thermocouple heads catalogue page 14-99.
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