Isolation barrier for intrinsically safe circuits: the galvanically isolated barrier used where a zener barrier and its safety earth are not wanted
DIN-rail isolated barriers in the safe area feeding Ex ia field circuits · isolated barrier or zener barrier · entity values Uo, Io, Po, Co, Lo and Um · insulation between hazardous side, control side and supply
Every intrinsically safe loop needs a device in the safe area that limits how much voltage, current and power can reach the hazardous area if something goes wrong on the control side. That device is either a zener barrier, which shunts fault energy to a dedicated earth, or an isolating barrier, which separates the two sides galvanically. The "if required" in this product's name is the design decision: an isolated barrier is chosen where a barrier earth, blown fuses or earth loops are a problem. Buying one means matching its certified entity values to the field device and cable, and checking the insulation it gives between field, control and supply.
Galvanically isolated intrinsic-safety barriers (isolated barriers, IS isolators) mounted in the safe area or Zone 2 on DIN rail or backplane, for analog, digital, temperature and communication signals to Ex ia field devices, with their entity parameters and insulation ratings. Non-Ex DIN-rail signal conditioners and isolators are covered on the Industrial signal conditioner page; component opto-isolators on the Wide-creepage surface-mount opto-isolator page; non-Ex multi-channel optocoupler boards on the DIN-rail optocoupler isolation board page; road safety barriers and safety light curtains are different products.
CNFX editorial research · Sources checked October 19, 2026 · 3 sources
Isolating barrier or zener barrier: safety earth, fuses and earth faults
LGM Products' barrier selection guide states that every intrinsically safe circuit must be protected by a suitable IS barrier, and describes the two types. Zener barriers combine zener diodes, resistors and fuses; MTL700 series barriers must be replaced if the internal non-replaceable fuse blows, while the later 7700 series has electronic fuses; and the negative rail of the compatible zener barriers connects directly to earth, which can cause problems with control panels fitted with earth-fault monitoring. [3]
Galvanic isolating barriers, in the same guide, isolate the hazardous area from the safe area, are fully resettable and contain no fuses, and let the IS circuit be left floating or earthed at any one point, avoiding earth-loop faults that can occur with zener barriers. The guide says they cost more than zener barriers but give a simpler engineering solution, and that barriers of either type must be located in the safe area. [3]
Pepperl+Fuchs' KCD2-STC-Ex1, a 1-channel isolated barrier that supplies 2-wire SMART transmitters, shows what the isolated type carries besides the barrier function: a 19–30 V DC supply over a power rail, a 4–20 mA output repeated to the control side to within ±0.1% in source mode at 20 °C, HART passed through, and SIL 2 to IEC 61508. [1]
State whether the plant uses a dedicated IS earth, whether the control panel has earth-fault monitoring, and how many loops are involved; those decide whether isolated barriers are required.
02
Uo, Io, Po, Co, Lo and Um: the certified values to match against the field device and cable
An isolated barrier's certificate data give the maximum output voltage, current and power at its hazardous-area terminals (Uo, Io, Po), the capacitance and inductance that may be connected to them (Co, Lo), and the highest voltage the safe-area side may see without losing intrinsic safety (Um). Two published examples:
Editorial calculation: in both examples the stated Po equals Uo × Io ÷ 4 (25.2 V × 100 mA ÷ 4 = 630 mW; 15 V × 8.5 mA ÷ 4 ≈ 31.9 mW). The KCD2-STC-Ex1's second terminal pair (3+, 4-) is listed with Uo 7.2 V, Io 100 mA and Po 25 mW, so the values to use depend on which terminals the field device is wired to. [1][2]
Pinghe states its barrier is installed in the safe zone and can connect to intrinsically safe instruments in hazardous areas up to Zone 0, IIC, Zone 20 and IIIC. [2] P+F shows the field side in Zone 0, 1 or 2 and the barrier itself in Zone 2 or the safe area, with a separate Ex nA IIC T4 Gc marking for Zone 2 mounting. [1]
Ask for the certificate number and the entity values for each terminal pair, and compare Uo, Io and Po against the field device's Ui, Ii and Pi, and Co and Lo against the device plus cable capacitance and inductance.
03
How strongly field, control and supply sides are separated
P+F rates the insulation between input, output and supply of the KCD2-STC-Ex1 as reinforced to EN 50178 at 300 V rms rated insulation voltage, and as safe electrical isolation to IEC/EN 60079-11 at 375 V peak between input and output and between input and supply. [1]
Pinghe gives dielectric strength for its PHD-11TC-11 as at least 3,000 V AC for one minute between the intrinsically safe and non-intrinsically safe sides and at least 1,500 V AC between the supply and the non-intrinsically safe terminals, insulation resistance of at least 100 MΩ between input, output and supply, operation from −20 to +60 °C, and EMC to IEC 61326-1 and IEC 61326-3-1. [2]
The two makers express the separation differently, one as rated insulation voltage and peak isolation voltage, the other as one-minute test voltages, so compare them on the same basis by asking each for the test voltage and duration between each pair of sides.
Specify the signal type and count, supply method (terminals or power rail), SIL requirement, ambient temperature in the cabinet and the hazardous-area classification of every field device.
04
What an isolated barrier enquiry should state
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Signal: [4–20 mA in/out; HART; digital; RTD/TC; RS-232/485]
Channels: [per module; total]
Field device: [Ui, Ii, Pi, Ci, Li; zone; gas/dust group]
Cable: [length; capacitance; inductance]
Mounting: [safe area or Zone 2; DIN rail or backplane; power rail]
Safety: [SIL; certificate scheme]
Environment: [cabinet temperature]
2 companies list this product among what they make. Company figures are quoted from each
company's own website; every card states where the relationship came from.
Beijing Pinghe Entrepreneurship Technology Development Co., Ltd.
Manufacturing site to be confirmed for the order
Lists T and H series isolated safety barriers for analog, digital, temperature, frequency and communication signals, with Ex ia certification data.
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 19 October 2026
Buyer questions
Why use an isolated barrier instead of a zener barrier?
LGM Products notes isolated barriers need no fuses, are resettable and let the IS circuit float or be earthed at one point, while zener barriers tie the negative rail to earth. [3]
What does Um mean on a barrier?
The highest voltage the safe-area side may see without losing intrinsic safety; P+F lists 250 V AC and notes Um is not a rated voltage. [1]
How much power can an isolated barrier deliver into the hazardous area?
It depends on the model: P+F's KCD2-STC-Ex1 lists Po 630 mW on its transmitter terminals; Pinghe's PHD-11TC-11 lists 31.9 mW. [1][2]
Sources and what still needs a direct check
Sources checked 2026-10-19. Pepperl+Fuchs and Beijing Pinghe barrier data sheets for entity and insulation values, and LGM Products' guide to choosing between zener and isolating barriers.
