FAQ - Field terminals -
FAQ - Field terminals
| Q |
What field terminals are used for THC and RTD modules in Zone 2 / Div 2 applications? |
| A | MTL8605-FT-TC & MTL8606-FT-RT field terminal blocks are keyed as ‘Non-Incendive’ types since THC and RTD field circuits are inherently non-incendive. They can therefore be used in applications where the field wiring enters Zone 2 / Div 2, as well as safe area applications. The reason there are Non-Incendive and Non-Arcing versions of other field terminals is to allow the user to avoid unnecessary complication by selecting the standard type in non-hazardous applications regardless of whether the module is non-incendive or non-arcing. Note that for intrinsic safety applications the terminal blocks would be : THC MTL8625-FT-IS RTD MTL8626-FT-IS |
| < back | |
| Q |
Do the field terminals for IS modules have the barrier in them? |
| A | No. All Hazardous Area protection circuitry is within the I/O Module. This allows all Field Terminals to contain only passive components. (Some Systems Integrators and Users specify that the level of qualification required to install components containing active circuitry is higher than that to install passive components. The MTL8000 Series allows all wiring connections to be made to passive system components, with active system components being pushed home and secured with a single retaining screw). |
| < back | |
| Q |
I can not read the terminal number on a terminal block when it is installed? |
| A | The Field Terminals have moulded-in terminal identification numbers (1-16) which can normally be seen during installation. If the position of the cable or conduit is such that the numbers cannot be seen clearly, the Field Terminal Tag Strip can be used to more clearly indicate the terminal identification numbers. (The Tag Strip has odd numbered identification numbers moulded in to it at an angle to those moulded in to the Field Terminal itself). |
| < back | |
| Q |
Are cage clamp terminal blocks available ? |
| A | The design of the MTL8000 Field Terminals allows for a number of different wiring connection methods which include cage clamp and multi-pole connector style. The MTL8000 2/2 system currently uses multi-pole connectors as standard, whilst the MTL8000 1/1 system uses a cage clamp approach. |
| < back | |
| Q |
Why are there separate ‘Safe Area’, ‘Non-Incendive’ and ‘Non-Arcing’ field terminals |
| A | In Zone 2 & Division 2 applications (ie, where the field wiring from an MTL8000 I/O module enters a Zone 2 or Div 2 hazardous area), the certification authorities require that incendive voltage and current levels must not enter the hazardous area due to accidental interchange of I/O modules - ie by plugging the wrong module type into an existing installed field terminal. Hazardous area wiring Zone 2 and Division 2 circuits fall into one of two types: ‘Non-incendive’ circuits, which carry only low levels of voltage and current because they are ‘energy-limited’ within the field circuit. These circuits can be live-worked in a similar way to intrinsically safe circuits. ‘Non-arcing’ circuits, which carry high levels of voltage and current, and which must not be live-worked in the hazardous area. Their safety is ensured by not allowing arcs or sparks to be produced, usually by means of mechanical protection of wiring and by eliminating unprotected contacts. With the MTL8000, the type of field circuit (ie ‘non-incendive’ or ‘non-arcing’) is often defined by the I/O module type. For example, 4-20mA AI & AO modules have non-incendive field circuits, whereas AC & DC DO modules typically involve ‘non-arcing’ circuits. The published MTL8000 data sheets show which type of field wiring each I/O module type has, accompanied by the recommended field terminal type. The certification requirement is that the MTL8000’s keying system should prevent an I/O module with non-aring field circuits from being plugged onto a field terminal belonging to an I/O module with non-incendive field circuits. This situation could present an unsafe condition. Non-incendive modules are therefore keyed differently from non-arcing modules, so that they will only plug into the appropriate type of field terminal. A diagram of the different field terminal keys is illustrated in the MTL8000 Installation Guide, document reference INM8000. Hence the correct type of either Non-Incendive and Non-Arcing field terminals must be selected for Zone 2 and Division 2 applications. Safe area wiring In applications where the field wiring is located in a safe area only, the certification requirements do not apply, and there is no necessity to differentiate between Non-Incendive and Non-Arcing wiring. The selection and use of the different types of field terminal would be an unnecessary complication, so a ‘safe area’ variant of field terminal may be selected. The safe area field terminals (available in fused and unfused versions) will support the use of Non-Incendive or Non-Arcing modules. Exceptions Some field terminal types (eg, for RTDs, thermocouples and typically 4-wire transmitters) are not available in seperate ‘safe area’ and ‘hazardous area’ variants, since they are always keyed according to whether they are non-incendive or non-arcing. This type is used even in safe area applications. |
| Q |
What functionality can a terminal block have, IS protection, signal conditioning etc.? |
| A | The Field Terminal provides screw clamp connectors for field wiring and offers optional fusing and loop disconnection. All signal conditioning and Hazardous Area protection circuitry is within the I/O Module itself, not in the Field Terminal. The exception to this is the cold junction compensation sensor for Thermocouple Input Modules, which must be sited as close as possible to the connection point of the thermocouple compensation cable (the cold junction), and is therefore mounted within the field terminal itself. |
| Q |
Do 2/2 DI modules need fused field terminals ? |
| A |
Fused terminals can be used for all Digital Inputs. The fuse provides two functions:
Examples are : |
| Q |
What is the advantage of having seperate, removable, field terminals? |
| A | Using separate, removable field terminals provides a number of advantages: 1. The principle advantage is the ability to make field wiring connections independent of the I/O Module. This allows the wiring connection to be done quickly and easily - by removing the Field Terminal from the Carrier, and then making the wiring connections holding the Field Terminal in one hand and screwing down the terminal clamps with the other. Any mistakes that are made in wiring the connectors—e.g. misalignment of the wire or crimp, leaving stray strands etc.—are then easily seen. 2. If the module needs to be changed, the wiring stays in place, ensuring that the original wiring is maintained and mistakes in rewiring are avoided. 3. If any of the Field Terminals become damaged through rough handling they can be easily replaced. |
| Q |
Is there cable size recommendation for the LAN connection? |
| A | The Screw type LAN interface connections are detailed in the Node Services Carrier data sheets and the Installation Manual. The cable size of screened twisted pair cable which can be accepted by the screw terminals is as under : 1. For single stranded wires the terminal can accept any size between 0.14 mm to 4 mm conductor with a nominal size of 2.5 mm. 2. For multi stranded wires the terminal can accept 0.14 mm to 2.5 mm conductor. Typically, for such applications, and depending on distance, a twisted pair cable of 22AWG and 150ohm / km resistance is selected corresponding to a Belden cable type 9182. This is typical, the choice depending on the distance to the host and the speed of the LAN selected. The level of mechanical protection (eg steel wire armour or resilient plastic sheath) would generally be determined by the requirements of local site standards and their codes of practice. |
| Q |
Do all Field Terminals have fusing? |
| A | Field Terminals for General Purpose I/O Modules are available in Standard (unfused), Fused, Thermocouple & RTD versions. The data sheets for each I/O Module recommend the type of Field Terminal that should be used with that module, perhaps also qualifying its use. Fusing is not required where the maximum short circuit current can be handled by the electronic protection within the I/O Module itself, or where fusing would normally be sited close to the field instrument. An example of the latter is the Isolated Discrete Input Module, which is powered by an external supply to the field instrument, and which should be fused close to the power supply itself. |
Displaying all Legacy Products
There are no legacy products in this category