MF12 – 3.11 

Installation, Operation & 

Maintenance Instructions

1200°C Tube furnaces (3-zone) 

types TZF & GZF 

This manual is for the guidance of operators of the above Carbolite products and 

should be read before the furnace is connected to the electricity supply. 

Manuals are supplied separately for the furnace controllers 

(and overtemperature controller when fitted). 

Please read the controller manuals before operating the furnace. 

 CONTENTS

 Section page 

1.0 Introduction 2 

2.0 Installation 3 

3.0 Operation 5 

0 Maintenance 8 

4.0 Repairs & Replacements 9 

5.0 Fault Analysis 12

6.0 Circuit Details 13

7.0 Fuses & Power Settings 16

8.0 Specifications 18 
TZF, GZF 

 

2 MF12 – 3.11 

1.0 INTRODUCTION

1.1 Products Covered 

This manual contains installation and operating instructions for two types of furnace. Both types 

are “three-zone” furnaces designed principally to achieve a single heating zone of extended 

temperature uniformity. 

The TZF range has heating elements comprising a ceramic work tube wound with resistance wire. 

The GZF range has “modular” heating elements of resistance wire partially embedded in vacuum 

formed light-weight refractory fibre. The element modules are 182mm long. Usually the end 

elements (two only) are rated at 1500W maximum, and the centre elements (the remainder) at 

1000W. 

1.2 Switches and Lights 

1.3 Warning Symbols 

Supply Light: when the furnace is connected to the electrical supply the 

light in the adjacent switch glows 

Heat Light: the adjacent light glows or flashes to indicate that power is 

being supplied to the elements 

DANGER of electrical shock– read any warning printed by this symbol.

DANGER – hot surface. Read any warning printed by this symbol.

WARNING: all surfaces of a furnace may be hot. 

DANGER – read any warning printed by this symbol. 

Heat Switch: the switch disconnects power to the heating elements; unless 

this switch is off there is a danger of electric shock when inserting objects 

into the furnace 
 

TZF, GZF 

MF12 – 3.11 3 

2.0 INSTALLATION

2.1 Unpacking & Handling 

When unpacking or moving the furnace always lift it by its base or by both ends of the main body. 

Never lift it by its work tube or the surrounding insulation. For the larger models, or where the 

furnace and control box are not fixed together, use two people to carry the furnace. 

 Remove any packing material from inside the furnace before use. 

NOTE: This product contains Refractory Ceramic Fibre (better described as Alumino Silicate 

Wool) for precautions and advice in handling this material see the ‘Repairs and Replacements’ 

section. 

2.2 Siting 

 Place the furnace in a well ventilated room, away from other sources of heat, and on a surface 

which is resistant to accidental spillage of hot materials. Do not mount the furnace on an 

inflammable surface. 

 Ensure that there is free space around the furnace. Do not obstruct any of the vents in the control 

section: they are needed to keep the controls cool. 

 Ensure that the furnace is placed in such a way that it can be quickly switched off or disconnected 

from the electrical supply - see below. 

2.3 Setting Up 

 A furnace ordered for vertical use has a small clip or plate at one end to prevent a wound tube 

element or a work tube from slipping downwards. Mount the furnace so that this clip is at the 

bottom. In models with one thermocouple the thermocouple should be near the top rather than the 

bottom. 

 If the furnace is supplied with a separate work tube or any accessories fit these into position. 

 For optimum temperature uniformity, insulating plugs should be placed in the tube ends as shown 

in fig.1. With a long work tube, the stem of the plug assembly should line up with the end of the 

tube as in fig.2. Alignment of radiation shields is similar to that of plugs. 

 If stainless steel seals with gas inlets are supplied they are to be fitted as shown in fig.3; the stem 

of any insulating plug should touch the seal. Stainless steel seals for vertical use: a hook and eye 

arrangement holds the upper insulating plug assembly; alternatively a gland nut. 

Horizontal models: if heavy fittings are to be clamped to the end of an extended work tube they 

can increase the bending stress at the centre of the tube. Support such fittings in such a way that 

expansion of the tube is allowed. 

 If a metal work tube is being used in the furnace, ensure that it is earthed. In the case of woundtube models (TZF) it should be mounted so as not to touch the furnace ceramic tube. See the 

safety warning in section 3.4. 
TZF, GZF 

 

4 MF12 – 3.11 

2.4 Electrical Connections 

 Connection by a qualified electrician is recommended. 

 The furnaces covered by this manual may be ordered for single phase A.C. supply, which may be 

Live to Neutral non-reversible, Live to Neutral reversible or Live to Live. Some models can be 

supplied for three phase use; some for use on two phases of a three phase with neutral supply (one 

phase unused). 

 Check the furnace rating label before connection. The supply voltage should agree with the 

voltage on the label, and the supply capacity should be sufficient for the amperage on the label. 

 The supply should be fused at the next size equal to or higher than the amperage on the label. A 

table of the most common fuse ratings is also given in section 7.1 of this manual. Where a supply 

cable is present there are internal supply fuses; customer fusing is preferred but not essential. 

 Furnace with supply cable: either wire directly to an isolator or fit with a line plug. 

 Furnace without supply cable: a permanent connection to a fused and isolated supply should be 

made to the internal terminals after temporary removal of the furnace back panel. 

 Connection by line plug: the plug should be within reach of the operator, and should be quickly 

removable. 

 Connection to isolating switch: this should operate on both conductors (single phase) or on all live 

conductors (three phase), and should be within reach of the operator. 

 The supply MUST incorporate an earth (ground). 

CONNECTION DETAILS supply type 

Supply Terminal label Cable colour Live-Neutral Reversible or Live-Live

1-phase L Brown To live to either power conductor

 N Blue To neutral to the other power conductor

 PE Green/Yellow To earth (ground) to earth (ground) 

supply Terminal label Cable colour

2- or 3-phase L1 Black to phase 1

 L2 Black to phase 2

 L3 Black to phase 3 except 2-phase

 N Light Blue to neutral except delta

 PE Green/Yellow to earth (ground)

2.5 “Universal Wiring” 

From Year 2000, applicable to GZF models which are available as three-phase. 

These models, when ordered for 3-phase supply, are supplied in a form in which they can be 

easily rewired between 1-phase and 3-phase supplies. This applies to 3-phase+N and 3-phase delta 

in the ranges 380/220V–415/240V and 208-240V, but does not apply to 3-phase star without 

neutral (e.g 380V). 

To alter the configuration, remove the back panel and alter the wiring connections between the 

supply terminal block and the EMC filters, using the appropriate diagram from section 6.7. 

Models ordered for single phase only are not affected and cannot be converted to 3-phase. 

If in doubt, please consult Carbolite. 
 

TZF, GZF 

MF12 – 3.11 5 

3.0 OPERATION

 The instructions for operating the temperature controller are given in a separate manual. 

If the furnace is fitted with a time switch, see also the supplementary manual MS03. 

 If cascade control is fitted, see the supplementary manual MS07. 

3.1 3-zone Control Methods 

The models in this manual are typically designed to achieve an extended uniform temperature 

zone by the use of three control zones. The control zones are typically linked so that they are all 

follow the central controller in a master-slave approach; there are two ways of doing this. 

Alternatively independent control zones may be ordered. There are thus three control methods (A, 

B & C). 

A. Back-to-Back Thermocouples 

This is the most commonly supplied option. 

 The central zone of the work tube is controlled directly by the central temperature controller. Each 

end zone thermocouple is wired in opposition to a central reference thermocouple, and the small 

voltage resulting when the zones are at different temperatures is used by the end zone controller. 

The circuit diagram in section 6.1 shown the thermocouple arrangement. 

 Set the "setpoint" of the end zone controllers to zero. Alternatively, a small temperature difference 

(offset) can be created by setting a non-zero value, but the sum of the main controller set-point and 

the slave controller offset MUST NOT exceed the furnace maximum temperature. The "measured 

temperature" display shows the actual offset. 

 To alter the setpoint (with the display at “home”), press Down  or Up  once to display the 

setpoint; press again or hold down to adjust it. The display returns to the measured temperature 

offset when no key is pressed for 0.5 seconds. 

 Sometimes a furnace using this type of control does not cool down: the end controllers try to 

remain at the central temperature. Should this occur, contact Carbolite’s technical department. 

 2132 Slave Controller Navigation Diagram 

B. Retransmission of Setpoint using Broadcast comms 

 When this is ordered there are three independent thermocouples connected to the three controllers. 

The controllers are linked together, the central controller communicating the desired setpoint to 

the end controllers. 

Additional communication modules are fitted in the controllers, rather than an additional 

thermocouple as in A. The communication between the controllers of the Eurotherm 3000 series is 

known as Broadcast comms. 

It is possible to switch off the linked control and allow the controllers to work independently. In 

level 2 of the end zone controllers (see controller operating instruction), scroll to L-r. Where the 

end zone controller is a 3216 use the  up  down and select NO. Where the end zone controller 

is a 3508 use the  up  down to select SP1, (SP1 = Local, and SP2 = Remote). There is no 

need to alter the centre controller. 

Home 

List 

Access

List 

°C/F/k ACCS

°C/F/k codE

0.0 

Zone temperature 

difference; use /

to access offset 

home list

for factory access to lists 

and parameters not 

available to the operator





OP.Hi

Outpu

t List

oP



power limit 

setting, if 

present
TZF, GZF 

 

6 MF12 – 3.11 

It is possible to use local trim in the end zone controllers to enter a positive or negative adjustment 

from the centre zone temperature. Once entered this trim will always be added or subtracted from 

the retransmitted set temperature. In level 2 of the end zone controller (see controller operating 

instruction), scroll to LOC.T (local trim) and use the  up  down enter the desired positive or 

negative difference to be added to the end zone set temperature. There is no need to alter the 

centre controller. 

C. Independent Control 

In this case the three controllers are completely independent. Note that it is not possible to 

maintain very different zone temperatures because of heat transfer within the work tube. 

3.2 Operating Cycle 

 The furnace is fitted with a combined Supply light and Instrument switch. The light is on 

whenever the furnace is connected to the supply. The switch cuts off power to the controller(s) 

and contactor (when fitted). There is also a Heater switch which can be used to disconnect power 

to the elements. 

 Connect the furnace to the electrical supply. The Supply light should glow. 

 Operate the instrument switch to activate the temperature controller. The controller becomes 

illuminated and goes through a short test cycle. 

Control methods A & B: Set the slave (end zone) controllers to the desired offset temperature, 

usually zero. Set the main (central) temperature controller to the desired setpoint or program. See 

section 3.1 and/or the separate manual(s) for the controller(s). 

 Control method C: Set the three controllers to the desired temperatures. See the separate 

manual(s) for the controller(s). 

Overtemperature option only. If the overtemperature controller has not yet been set as required, 

set it and activate it according to the instructions in the appropriate manual. 

 Switch on the Heater switch, located on the instrument panel. Unless a time switch is fitted and is 

off, the furnace starts to heat up. The Heat light(s) glow steadily at first and then flash as the 

furnace approaches the desired temperature or a program setpoint. 

Overtemperature option only. If the overtemperature trip operates then an indicator in the overtemperature controller flashes, and the heating elements are isolated. Find and correct the cause 

before resetting the overtemperature controller according the instructions supplied. 

 To switch off power to the heating elements, use the Heater Switch. To switch the furnace off, use 

both the Heater switch and the Instrument switch. If the furnace is to be left off unattended, isolate 

it from the electrical supply. 

3.3 General Operating Advice 

 Heating element life is shortened by use at temperatures close to maximum. Do not leave the 

furnace at high temperature when not required. The maximum temperature is shown on the 

furnace rating label and on the back page of this manual. 

3.4 Operator Safety 

 The ceramic materials used in furnace manufacture become electrically conductive to some extent 

at high temperatures. In the GZF models there are partially exposed heating coils in the chamber. 

DO NOT use any conductive tools within the work tube without isolating it. If a metal work tube 

is used, it must be earthed (grounded). 

 Switch off the Heater switch whenever loading or unloading the furnace. The elements are 

isolated when the Heater switch is OFF. This switch cuts both sides of the circuit directly or via a 

contactor (a contactor is used in models where the rated current exceeds 16 Amps). 
 

TZF, GZF 

MF12 – 3.11 7 

3.5 Tube Life 

 A ceramic work tube may be cracked if workpieces are inserted 

too quickly or at temperatures below 900°C (when the tube is 

more brittle). Large pieces should also be heated slowly to 

ensure that large temperature differences do not arise. 

 Poor thermal contact should be encouraged between the 

workpiece and the tube; crucibles or boats should be of low 

thermal mass and should have feet to reduce the contact with 

the tube (fig. 4). 

 Do not set too high a heating rate. Large diameter tubes are more susceptible to thermal shock 

than smaller. Tubes which extend beyond the heated part of the furnace are more at risk. A general 

rule for maximum heating rate is 400/internal diameter (°C/min); for 75mm i/d tubes this comes to 

5°C per minute. The controller can be set to limit the heating rate. 

3.6 Pressure 

 Work tubes are not able to accept high internal pressure. When gas seals or similar fittings are in 

use, the gas pressure should be restricted to a maximum of 0.2 bar (3 psi). A pressure of about half 

of that should normally be sufficient to achieve the desired flow rate. The customer must ensure 

that the exhaust path from the tube is not blocked, so that excess pressure does not occur. 

3.7 Power Adjustment 

 The furnace control system incorporates electronic power limiting. The power limit parameter 

OP.Hi is accessible to the operator, and can be used to adjust the furnace to the actual supply 

voltage. 

Note that any power limit applies to all three controllers. 

 Some models covered by this manual are are fitted with 208V elements and are designed for use 

over the range of voltages 200V-250; the power limit parameter is set accordingly. These models 

may be relocated to a different voltage within the range: the power limit should be reset to match 

the voltage. See section 7.2. 

To check whether the furnace is a 208V model: 

- look at the OP.Hi parameter – make a note of the value and compare with section 7.2; 

- observe the rating label; if a range of voltages is stated, it is not a 208V multivoltage model; 

- if in doubt, check with Carbolite – each product has its own record card. 

 To alter the power limit 

 Set the Heater Switch to Off to prevent heating while adjusting the power limit. 

 Press Page  until oP (output list) is displayed. Press Scroll  until OP.Hi (Output High) is 

displayed. Press Down  or Up  once to display the value of OP.Hi (it is good practice to write 

down the original value). To alter the parameter to the desired value use Down  or Up . 

 A power setting of zero prevents the furnace from heating: useful for demonstrating the controls 

without taking power. 

 Do not increase the power limit simply “to get more power”. The elements could burn out, or a 

fuse could blow. 

3.8 Running at Low Temperatures 

 The power limit may be adjusted to a low level to achieve better control when running the furnace 

at a low temperature. No hard and fast rules can be given, but, as an example, to run at 

temperatures only up to 600°C try a power limit of 50%. Control stability may fall off again if a 

setting below about 40% is used. 

 Before changing the power limit, record its factory setting for possible future use. 
TZF, GZF 

 

8 MF12 – 3.11 

MAINTENANCE

3.9 General Maintenance 

 No routine maintenance is required. The outer surfaces may be cleaned with a damp cloth. Do not 

allow water to enter the interior of the case, tube or control box. Do not clean with organic 

solvents. 

3.10 Calibration 

 After prolonged use the controller and/or thermocouple could require recalibration. This would be 

important for processes which require accurate temperature readings or which use the furnace 

close to its maximum temperature. A quick check using an independent thermocouple and 

temperature indicator should be made from time to time to determine whether full calibration is 

required. These items can be supplied by Carbolite. 

 Depending on the controller, the controller manual may contain calibration instructions. 

3.11 After Sales Service 

Carbolite’s service division (Thermal Engineering Services) has a team of Service Engineers 

capable of repair, calibration and preventive maintenance of furnace and oven products at our 

customers’ premises throughout the world. We also sell spares by mail order. A telephone call or 

fax often enables a fault to be diagnosed and the necessary spare part despatched. 

 Each furnace has its own record card at Carbolite. In all correspondence please quote the serial 

number, model type and voltage given on the rating label of the furnace. The serial number and 

model type are also given on the front of this booklet when supplied with a furnace. 

 To contact Thermal Engineering Services or Carbolite see the back page of this manual. 

3.12 Recommended Spares Kits 

 Carbolite can supply individual spares, or a kit of the items most likely to be required. Ordering a 

kit in advance can save time in the event of a breakdown. Each kit comprises one of each type of 

thermocouple, one solid state relay, and one heating element (GZF: 2 elements, one of each 

wattage). 

 When ordering spares please quote the model details as requested above. 
 

TZF, GZF 

MF12 – 3.11 9 

4.0 REPAIRS & REPLACEMENTS

4.1 Safety Warning – Disconnection from Supply 

 Always ensure that the furnace is disconnected from the supply before repair work is 

carried out. 

4.2 Safety Warning - Refractory Fibrous Insulation 

Insulation made from High Temperature Insulation Wool 

Refractory Ceramic Fibre, (better described as Alumino Silicate Wool) (ASW) 

This product contains alumino silicate wool products in its thermal insulation. These materials 

may be in the form of blanket or felt, formed board or shapes, mineral wool slab or loose fill wool. 

Whilst there is no evidence of any long term health hazards, we strongly recommend that safety 

precautions are taken whenever the materials are handled. 

Exposure to fibrous dust may cause respiratory disease. 

When handling the material always use an approved respiratory protection equipment 

(RPE-i.e. FFP3), eye protection, gloves and long sleeved clothing. 

Avoid breaking up waste material. Dispose of waste in sealed containers. 

After handling rinse exposed skin with water before washing gently with soap (not 

detergent). Wash work clothing separately. 

Before commencing any major repairs we recommend reference to the European Association 

representing the High Temperature Insulation Wool industry (www.ecfia.eu) 

We can provide further information on request. Alternatively our service division can quote for 

any repairs to be carried out at your premises or ours. 

4.3 Temperature Controller Replacement 

 201. This controller is fitted to the back of the control panel; in many models this can be separated 

from the base by removal of two screws. 

 Before handling the controller: wear an anti-static wrist strap or otherwise avoid any possibility 

of damage to the unit by static electricity. 

 Refer to the detailed instructions supplied with the replacement controller. 

 2000 & 3000 series. Ease apart the two lugs at the side; grip the instrument and withdraw it from 

its sleeve; push in the replacement. 

4.4 Solid-state Relay Replacement 

 Disconnect the furnace from the supply and remove the back panel from the base or control box.. 

 Make a note of how the wires are connected to the solid state relay, and disconnect them. 

 Remove the solid state relay from the base panel or aluminium plate. 

 Replace and reconnect the solid state relay ensuring that the heat-conducting thermal pad is 

sandwiched between the relay and the base panel or aluminium plate. Alternatively a thin layer of 

white, heat-conducting silicon paste may be applied between the new relay and the plate. 

 Replace the removed panel. 
TZF, GZF 

 

10 MF12 – 3.11 

4.5 Thermocouple Replacement 

 The coverings and guards which must be removed to gain access to the thermocouple depend on 

the model, its orientation (horizontal or vertical), and possibly other options and fittings. It is 

usually necessary to separate the furnace from its base or stand. On horizontal models (except TZF 

12/38) one outer end-cap should be removed; on TZF 12/38 and vertical models the terminal 

cover. 

 Disconnect the furnace from the supply, and separate the furnace body and/or remove covers and 

guards as necessary. 

 Make a note of the thermocouple connections. Type N colour codings are: 

current models negative: white positive (type K): green positive (type N): pink

old models negative: blue positive (type K): white positive (type N): orange

 Disconnect the thermocouple from its terminal blocks. 

 Withdraw the thermocouple from its sheath and remove any broken bits of thermocouple. 

 Bend the new thermocouple carefully to match the shape of the original (working from the 

terminal end). Should the length differ from that of the original this is usually not important 

provided that the thermocouple tip is within a tube diameter's distance from the furnace centre. 

 Insert the new thermocouple into position, restoring any removed porcelain spacers, and ensuring 

correct polarity. 

 Re-assemble the furnace. 

4.6 Element Replacement 

Please see safety note 4.2 - please wear a face mask. 

 The coverings and guards which must be 

removed to enable replacement of the 

wound tube element depend on the furnace 

model, its orientation (horizontal or 

vertical), and other options and fittings. 

The general procedure is: 

 Disconnect the furnace from the electrical 

supply. 

 Remove all outer guards, meshes and terminal covers from the furnace body. For a horizontally 

mounted furnace remove the furnace body from its base; to reach the bolts or screws which fix the 

body to the base, remove the back panel from the base. 

 Disconnect all electrical leads from the terminal blocks on the furnace case. Note the colours and 

positions of the connecting leads to enable correct reassembly. Take care not to crack porcelain 

terminal blocks - use two spanners where appropriate. 

 Remove the thermocouples. 

 Lay the furnace body horizontally with the split in the cylindrical case uppermost. Remove the 

two metal end-caps from the body. Except TZF 12/38, undo the self-tapping screws which hold 

the terminal strip to the case join. The case should spring open slightly. Remove the ceramic board 

disc from one end. 

TZF: Use a sharp knife to cut right through the insulation down to the wire-wound tube element 

along the whole length of the body, but do not cut either of the ceramic board end discs. The knife 

cut must be in line with the element lead wires. Slide the element gently out through the end of the 

furnace body. 

GZF: Cut through the outer wrap of blanket insulation. Note how the element tails are connected 

and disconnect all of them. Lift out the elements through the end of the cylindrical case. 

Note on GZF Elements

The end and centre elements of GZF models 

look the same but have different wattages. The 

two end elements are 1500W, and all the centre 

elements are 1000W. Ensure that elements are 

correctly replaced. 
 

TZF, GZF 

MF12 – 3.11 11 

 Check the cylindrical case and clean out as appropriate. 

 Remove any insulation sleeving from the tails of the old element and fit to the replacement 

element. 

 Slide in the new element(s). Close up the furnace again, refitting the terminal strip (where 

applicable) and the end-caps. Any cut made in the insulation should close up completely: if the 

insulation appears loose or damaged in any way, please contact our service division. 

 Reverse the rest of the disassembly process. Take care to make all connections to the correct 

terminals. Do not overtighten the connectors in porcelain terminal blocks. 

 Let the furnace heat up at its maximum rate to 900°C without interruption, and then soak for 1 

hour. Fumes may be emitted: this should be done in conditions of good ventilation. 

 Check that the furnace is controlling properly to rule out the possibility that the element failed 

because of a fault in the control system. 

 If you have any problems with this procedure, please contact our service division. 

4.7 Fuse Replacement 

 Fuses are marked on the circuit diagram (section 6.1) with type codes, e.g. F1, F2. A list of the 

correct fuses is given in section 7.1. Depending on model and voltage, the different fuse types may 

or may not be fitted. 

 If any fuse has failed, it is advisable for an electrician to check the internal circuits. 

 Replace any failed fuses with the correct type. For safety reasons do not fit larger capacity fuses 

without first consulting Carbolite. 

 The fuses are near the cable entry point, and access is by removal of the back panel of the base or 

control box. 
TZF, GZF 

 

12 MF12 – 3.11 

5.0 FAULT ANALYSIS

A. Furnace Does Not Heat Up 

1. The HEAT light 

 is ON

 The heating 

element has failed 

 Check also that the SSR is working 

correctly 

2. The HEAT light 

is OFF

 The controller 

shows a very high 

temperature or a 

code such as S.br 

 The thermocouple has broken or has a 

wiring fault 

 The controller 

shows a low 

temperature

 The door switch(es) (if fitted) may be 

faulty or need adjustment 

  The contactor (if fitted) may be faulty 

  The SSR could be failing to switch on due 

to internal failure, faulty logic wiring from 

the controller, or faulty controller 

 There are no 

lights glowing 

on the 

controller 

 The SUPPLY

light is ON

 The controller may be 

faulty or not receiving a 

supply due to a faulty 

switch or a wiring fault 

  The SUPPLY

light is OFF

 Check the supply fuses and 

any fuses in the furnace 

control compartment 

B. Furnace Overheats 

1. The HEAT light 

goes OFF with 

the instrument 

switch 

 The controller 

shows a very high 

temperature 

 The controller is faulty 

  The controller 

shows a low 

temperature 

 The thermocouple may have been shorted 

out or may have been moved out of the 

heating chamber 

  The thermocouple may be mounted the 

wrong way round 

  The controller may be faulty 

2. The HEAT light 

does not go off

with the 

instrument 

switch 

 The SSR has failed 

“ON” 

 Check for an accidental wiring fault which 

could have overloaded the SSR 
 

TZF, GZF 

MF12 – 3.11 13 

6.0 CIRCUIT DETAILS

 Safety Switches type A: a 2-pole Heater Switch is fitted directly in the element circuit in models 

up to 16A rating. 

 Safety Switch type B: a Heater Switch is fitted into the contactor coil circuit in models over 16A. 

6.1 Single Phase (example for TZF, control method A) 

6.2 2- or 3-Phase 

See also section 6.7. for certain models. 

 Each SSR is connected to a different phase. The control circuit is taken between L1 and N. 

 Safety switch A applies for 2-phase. Safety switch B applies for 3-phase. 

 If type F1 fuse is present, one per phase if fitted. If type F2 fuse is present, one is fitted; if type F3 

fuse is present, one per phase is fitted. 

 Note that on 2- or 3-phase models there may be three separate neutrals taken to a common supply 

terminal, depending on EMC filter requirements. 

6.3 Higher Voltages 

 For 254V or above (or 440V, 3-phase) an isolating transformer is 

fitted in the control circuit after the F2 fuses. 

F2 

F2 

transformer

Supply light &

Instrument Switch 

Supply light 

Instrument Switch 

coil

slave

controller 

thermocouples

overtemp.

controller 

thermocouple

safety

switch B

SSR

heat

on 

safety

switches A

F3 

F1 

F2

F3 

N

L 

PE 

Filter (if fitted)

contactor

if fitted

if fitted

master

controller 

SSR

slave SSR

controller 

F3 

F3

main

ref.

slave

slave

+

+

+

–

–

–
TZF, GZF 

 

14 MF12 – 3.11 

6.4 Independent Zones (control method C) 

 When this is ordered there are three independent thermocouples (instead of the four shown) 

connected to the three controllers; the words “master” and “slave” may be replaced by “centre” 

and “end”. 

6.5 Control by Broadcast comms (control method B) 

 When this is ordered there are three independent thermocouples (instead of the four shown) 

connected to the three controllers; the controllers are linked together (not shown), and remain 

“master” and “slave”. 

 The communication between the controllers of the Eurotherm 3000 series is known as Broadcast 

comms. The wiring connections between the controllers are as follows: 

6.6 GZF Models 

 These models normally have end zones of one element each; the centre zone comprises the 

remaining elements wired in parallel. 

 For the “equal zone” models (suffix E) the zones are as equal as possible: in GZF 12/1092 the 

zones are each 2 element modules each. 

 Note that a 3-phase GZF 12/1092 may have 4 x SSR; in this case phase 1 is for the end zones (2 x 

SSR); phases 2 & 3 are for the centre zone (2 elements per SSR). 

 There are many possible electrical configurations for GZF models covering 1- 2- or 3-phase, 

including 3-phase delta. 3-phase GZFs are made with “universal” wiring as explained in sections 

2.5 and 6.7. 

HD 

HE 

HF 

HD 

HE 

HF 

HD

HE 

HF 

master

slave slave
 

TZF, GZF 

MF12 – 3.11 15 

6.7 3-phase “universal” wiring 

 Fuses F1 are always present in this wiring design. 

 Fuses F2 could be absent in some circumstances, if the circuit does not exceed 10A. 

 Fuses F3 are present if the circuit exceeds 25A, but otherwise are usually absent. 

 

Supply light & 

Instrument Switch

coil

temperature 

controller

overtemp. 

controller

thermocouple

safety 

switch

SSR

heat

on

F3 F1 F2 

F3

SSR

SSR

F3 

heat

on

F3 

e

l 

e 

m

e 

n 

t 

(s)

heat

on

F3

F3

if fitted

Contactors

(2 or 3) 

Filters (if fitted)

e

l 

e 

m

e 

n 

t 

(s)

e 

l 

e 

m 

e 

n 

t 

(s) 

coil

L 

N 

L 

N 

L 

N 

thermocouple

Applicable to certain models only: see section 2.5

A model made to this diagram can be 

converted by the customer between the 

following supply voltages: 

between 3-phase + neutral in the range 

380/220V – 415/240V 

and 3-phase delta in the range 

220V – 240V 

and single phase in the range 

220V – 240V 

208V model: convertable from 208V delta 

to 208V 1-phase

3-phase + neutral 

Circuit no. 1 

N

L 

N

L 

Circuit no. 2 

Circuit no. 3 

N

L3 

L2 

L1 

Supply 

Terminals 

N

L 

Fuses or 

EMC filters 

PE 

Not 

used 

3-phase delta 

Circuit no. 1

N

L 

N

L 

Circuit no. 2

Circuit no. 3

N

L3

L2

L1

Supply 

Terminals

N

L 

Fuses or 

EMC filters

PE

1-phase 

Circuit no. 1

N

L 

N

L 

Circuit no. 2

Circuit no. 3

N

L3

L2

L1

Supply 

Terminals

N

L 

Fuses or 

EMC filters

PE

Not 

used
TZF, GZF 

 

16 MF12 – 3.11 

7.0 FUSES & POWER SETTINGS

7.1 Fuses 

 F1-F3: refer to the example circuit diagram.

F1 Internal 

supply 

fuses 

Fitted if supply cable fitted. 

Fitted on board to some types of EMC filter. 

on-board and up to 16 Amps: 

32mm x 6mm type F 

other: GEC Safeclip 

F2 Auxiliary 

circuit 

fuses 

Fitted on board to some types of EMC filter. 

May be omitted up to 25Amp/phase supply 

rating. 

2 Amps glass type F 

On board: 20mm x 5mm 

Other: 32mm x 6mm 

F3 Heat Light 

fuses 

May be omitted up to 25 Amp/phase supply 

rating. 

2 Amps glass type F 

32mm x 6mm 

Customer 

fuses 

Required if no supply cable fitted. 

Recommended if cable fitted. 

See rating label for amperage; 

see table below for fuse rating. 

 Access to internal fuses is by removal of the back panel of the furnace base or control box. 

Model phases Volts Supply 

Rating 

Volts Supply 

Rating 

TZF 12/38/400 1-phase 200-240 7A 110-120 12.5A 

TZF 12/65/550 1-phase 200-240 10A 110-120 20A 

TZF 12/65/550 2- or 3-phase + N 380/220 - 415/240 5A 

TZF 12/75/700 1-phase 220-240 12.5A 110-120 25A 

TZF 12/75/700 1-phase 208 15-16A 100 30-32A 

TZF 12/75/700 2- or 3-phase + N 380/220 - 415/240 7A 

TZF 12/100/900 1-phase 200-240 20A 110-120 40A 

TZF 12/100/900 2- or 3-phase + N 380/220 - 415/240 15-16A 

GZF 12/546 1-phase 200-240 20A 

GZF 12/546 3-phase + N 380/220 - 415/240 10A 220-240 delta 12.5A 

GZF 12/728 1-phase 200-240 25A 

GZF 12/728 2-phase + N 380/220 - 415/240 12.5A 

GZF 12/728 3-phase + N 380/220 - 415/240 10A 220-240 delta 12.5A 

GZF 12/910 1-phase 200-240 25A 

GZF 12/910 2-phase + N 380/220 - 415/240 12.5A 

GZF 12/910 3-phase 380/220 - 415/240 12.5A 220-240 delta 20A 

GZF 12/1092 1-phase 200-240 30-32A 

GZF 12/1092 2-phase + N 380/220 - 415/240 15-16A 

GZF 12/1092 3-phase 380/220 - 415/240 12.5A 220-240 delta 20A 

other models or voltages: check the rating label for details of the supply. 
 

TZF, GZF 

MF12 – 3.11 17 

7.2 Power Settings 

The models covered by this manual are designed to run on 100% power, with the exceptions 

below. 

Model Volts: 200V 208V 220V 230V 240V 380V 400V 415V 

Equal zone models: 

TZF 12/38/400E 

TZF 12/65/550E 

100 100 89 82 75 - - - 

Custom Models: 

TZF 12/25/550 

TZF 12/38/550 

TZF 12/75/550 

TZF 12/75/900 

100 100 89 82 75 - - - 

Standard Model: 

TZF 12/100/900 

(from April 2000) 

100 100 89 82 75 89 82 75 

 

208V Models 

Models may be supplied to the USA market with 208V elements, and use power limit if connected 

to higher voltages, as follows: 

Model Volts: 200V 208V 220V 230V 240V 380V 400V 415V 

all GZF 208V models 100 100 89 82 75 89 82 75 

Other possible exceptions: 

 Further custom furnaces based on the standard models may be designed with power limits other 

than 100%. 

 Furnaces supplied for use on 254 Volt typically have a power setting of 89% of the limit for the 

corresponding 240V model. 
TZF, GZF 

 

18 MF12 – 3.11 

8.0 SPECIFICATIONS

 Carbolite reserves the right to change specifications without notice. 

8.1 Models Covered by this Manual 

MODEL Max. 

Temp. 

Max. 

Power 

Work

Tube 

Bore 

Work

Tube 

Length 

Heated

Length 

Uniform

Zone 

Length1

Net

Weight2

 (°C) (kW) (mm) (mm) (mm) (mm) (kg)

Tube furnaces with a ceramic work tube wound with resistance wire

TZF 12/38/400 1200°C 1.5 38 450 400 305 15

TZF 12/65/550 1200°C 2.0 65 600 550 392 25

TZF 12/75/700 1200°C 3.0 75 750 700 510 28

TZF 12/100/900 1200°C 4.5 100 950 900 745 35

Tube furnaces with modular vacuum formed elements with embedded resistance wire

GZF 12/546 1200°C 4 170max 750/1200 (3) 546 45

GZF 12/728 1200°C 5 170max 900/1400 (3) 728 50

GZF 12/910 1200°C 6 170max 1100/1600 (3) 910 55

GZF 12/1092 1200°C 7 170max 1300/1800 (3) 1092 60

also models based on the above, but of other diameters or lengths, supplied to special order

 note 1: The figures for uniform zone length are for ±5°C and are based on 

measurements with the furnace horizontal and fitted with insulating plugs in both tube 

ends. They assume the use of master-slave control. 

 note 2: Weights are approximate for horizontal models and do not include fittings 

or vertical stands. 

 note 3: GZF tubes: recommended lengths for type C / D tubes are shown 

 (C = no fittings; D = long enough for gas fittings etc.). 

8.2 Environment 

 The furnaces contain electrical parts and should be stored and used in indoor conditions as 

follows: 

temperature: 5°C - 40°C

relative humidity: maximum 80% up to 31°C decreasing linearly to 50% at 40°C
 

TZF, GZF 

MF12 – 3.11 19 
Copyright © 2012 Carbolite Limited

For preventive maintenance, repair and calibration of all Furnace and Oven products, please contact: 

Thermal Engineering Services 

 Telephone: UK: 0845 3308035 Int: +44 1433 623335 

 Fax: UK: 0845 3308036 Int: +44 1433 623336 

 Email: service@thermalserve.com 

The products covered in this manual are only a small part of the wide range of 

ovens, chamber furnaces and tube furnaces manufactured by Carbolite for 

laboratory and industrial use. For further details of our standard or custom built 

products please contact us at the address below, or ask your nearest stockist. 

Carbolite, Parsons Lane, Hope,

Hope Valley, S33 6RB, England.

Telephone: (01433) 620011 Int: +44 1433 620011

Facsimile: (01433) 621198 Int: +44 1433 621198

MF12-3.11 11/01/12 TZF/GZF E-mail: info@carbolite.com