FAQ - Hazardous Areas -
FAQ - Hazardous Areas
| Q |
What is meant by General Purpose, 2/2 and 2/1 I/O? |
| A | General Purpose I/O This is for use in process industry applications where there is no risk of explosion. In traditional IS terminology these applications would be called “Safe” - in contrast to those areas which do have a risk of explosion. Many process operators and specifiers, however, would consider these to be far from safe; for example, they may be hot, heavy, toxic or corrosive and, therefore, viewed as dangerous. It is therefore inappropriate to use the traditional IS terminology of “Safe Area” I/O and the term General Purpose has been adopted. General Purpose Field Terminals allow any I/O Module to be inserted in to any Field Terminal, once the “Module Type” key has been re-positioned by the User. However, General Purpose Modules cannot be inserted in to any Field Terminal other than the “General Purpose” type. 2/2 I/O The “2/2” product is I/O for mounting in North American Division 2 or CENELEC Zone 2, with field wiring connected to devices in the same Division or Zone - hence “2/2”. The I/O Modules are actually identical to “General Purpose” I/O Modules - but the relevant Field Terminal uses a different key position. The use of two names for the same product is to position it correctly for two similar, but different Users.The “2/2” Field Terminals have a key which is coded so as to ensure that Field Terminals intended for use with Non-Incendive I/O Modules cannot be used with I/O Modules for Non-Arcing field connections, and vice versa. 2/1 I/O The “2/1” product is for mounting in Division 2 or Zone 2, with field wiring connections to devices locatedd in Division 1 or Zone 1 / Zone 0 hazardous areas. The “2/1” Field Terminals are coloured blue (for Intrinsic Safety) and are keyed such that it is not possible to insert an I/O Module which carries General Purpose or “2/2” keying in to a “2/1” Field Terminal. |
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| Q |
Can I use the standard MTL Remote I/O product in a European Zone 2 ? |
| A | MTL8000 General Purpose I/O can be used in Zone 2 applications, under the terms of ‘ATEX’ Directive 94/9/EC. The product is marked as suitable for Zone 2 in accordance with the Directive and carries the CE and Epsilon-x marks. Under the Directive, MTL issues its own apparatus certificates and Code of Practice for installation and maintenance. |
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| Q |
What restrictions are there on hot-swapping of modules in Zone 2 / Div 2 ? |
| A | Non-IS MTL8000 system For the MTL8000 Non-IS system, I/O modules can be hot-swapped in Division 2 or Zone 2 hazardous areas provided the following conditions are met: Where a module uses Bussed Field Power, this must first be de-energised before removing or replacing the module. If the isolating switch is itself within the Division 2 or Zone 2, it must be an appropriately (Ex) explosion protected type. I/O modules in this category are: > All module-powered DI and DO versions (AC and DC) > AI, 4-20mA with/without HART > AO, 4-20mA with/without HART > Pulse/Frequency Input module (MTL8123) Where a module receives an input which is sourced from the field, the field power supply must first be de-energised before removing or replacing the module. I/O modules in this category are: > All sinking DI versions (AC and DC) > All un powered DO versions (AC and DC) > Pulse/Frequency Input module (MTL8123) (certain field devices) The node must be powered by MTL’s own power supply module or modules (ie, type MTL8910-PS-DC, MTL8913-PS-AC, MTL8914-PS-AC). Users wishing to use other types of power supply connected to the external power supply terminals on the MTL8000 carriers should consult the Technical Support department since use of such equipment is not specifically covered by the Factory Mutual approvals. When the above conditions are met, the 12V system power energising the carrier ‘Railbus’ operation does not need to be de-energised before hot-swapping is attempted. The node can therefore continue to operate.Note : the user chooses at what point to provide the necessary isolating switches for Bussed Field Power; if a single switch is used in the BFP feed to a large number of modules, then all these modules will lose their power when hot-swapping is undertaken. Individual switches can be used in the feed to pairs of modules if it is required to take the fewest channels out of service. IS MTL8000 system All I/O modules offering an intrinsically safe interface may be hot-swapped in a Zone 2 or Division 2 hazardous area, with the internal 12V Railbus supply energised. Since Bussed Field Power is not used, there are no restrictions, or requirements, for local isolation before removing or replacing a module. The Railbus Isolator may also be hot-swapped, but the power supply modules (type 8920-PS-DC) must be de-energised before they are replaced. |
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| Q |
How do I tell which modules can be live worked ? |
| A | The list of 2/2 modules which are non-incendive for which the field circuits can be live worked in a Division 2 and Zone 2 application is as below: 1. 8101-HI-TX * (Analogue Input Module with HART) 2. 8104-AO-IP * (Analogue Output Module) 3. 8105-TI-TC (Thermocouple Input Module) 4. 8106-TI-RT (RTD Input Module) 5. 8110-DI-DC * (Non Isolated Digital Input Module) * Note that the use of Bussed Field Power supplies may prevent removal of the modules whilst this power source is live. The 2/2 data sheets for the above modules indicate the special field terminal required to be used for application in Division 2 or Zone 2 area. This terminal will ensure that accidental interchange with other modules does not take place. All other 2/2 modules are Non-Arcing and cannot be live worked in Division 2 or Zone 2 Hazardous Areas. Seperate marking is given on the module to indicate whether it is Non-Incendive or Non-Arcing. A definitive description of the types of circuit and permitted live-working practice is clearly documented in the AN8001 Code of Installation Practice. |
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| Q |
If the system is installed in Div 2 or Zone 2 is it normally non arcing or non-incendive ? |
| A |
Some parts of the installation are Non-Arcing and some are Non-Incendive, depending on the levels of voltage and current present at the individual connections. In general, all power supply connections (including Bussed Field Power) are non-arcing because the amount of energy in these circuits is not controlled and is therefore capable of causing ignition. (Note that the term ‘Non-Arcing’ implies that the circuits are not permitted to produce an arc or spark when operating normally, since this could be capable of igniting the gas.)
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| Q |
Can I connect a 2/1 module next to a 2/2 module ? |
| A | Railbus Isolator forms an integral part of an MTL8000 system structure where intrinsically safe interfaces are required, and interconnects the Non-IS and IS sections of the system. It limits the level of energy available to the IS interface section of the system, but also provides the inherent requirement of a 50 mm physical seperation between Non-IS and IS circuitry. It is not possible to omit the Railbus Isolator device when building up such an IS system due to the physical arrangement of the carriers employed. Hence, 2/2 and 2/1 modules can only be mounted on either side of the Railbus Isolator. |
| Q |
Can IS and non-IS be mixed on the same node? |
| A | Non-IS and IS modules can share the same MTL8000 node. A Railbus Isolator forms an integral part of an MTL8000 system structure where intrinsically safe interfaces are required, and interconnects the Non-IS and IS sections of the system. It limits the level of energy available to the IS interface section of the system, but also provides the inherent requirement of a 50 mm physical seperation between Non-IS and IS circuitry. It is not possible to omit the Railbus Isolator device when building up such an IS system due to the physical arrangement of the carriers employed. Hence, 2/2 and 2/1 modules can only be mounted on either side of the Railbus Isolator. The ability to mix the types of protection for field devices is particularly useful for customers who use, eg, IS transmitters and Flameproof (Explosion proof) valves. |
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| Q |
What isolating switches must be used in Zone 2 ? |
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For an MTL8000 enclosure located in Zone 2, any isolating switches in the power supply circuits must be Ex certified, to avoid any ignition risk.
It also applies to the Bussed Field Power circuits. If the user requires to “hot-swap” I/O modules where the Bussed Field Power supply creates a Non-Arcing environment, then the BFP must be isolated first. |
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