In intrinsically safe circuits, maintain 50 mm clearance from non-Ex i wiring, 6 mm between two Ex i circuits, and 3 mm from earthed metal. Where rail space is limited, a certified partition plate reaching within 1.5 mm of the enclosure wall replaces the air distance. Correct selection of terminal block accessories keeps every one of these gaps intact through installation and service.

The Three Isolation Distances at a Glance

The table lists every separation value required by IEC 60079-14 for intrinsically safe terminal wiring.

Circuit Pair	Air Distance	Partition Alternative
Ex i to non-Ex i	50 mm	Plate, ≤1.5 mm wall gap
Ex i to Ex i	6 mm	Insulating barrier
Ex i to earthed metal	3 mm	Insulated mount
Jumper bar edges	No cutting	Factory-formed only

Which Zone and Gas Group Changes the Numbers

Zone 0, 1, and 2 determine the protection level, not the millimetre values. Zone 0 permits only Ex ia. Gas group IIC, covering hydrogen and acetylene, tightens creepage and clearance per IEC 60664-1. Temperature class T1–T6 sets the maximum surface temperature the terminal must stay below, with a safety margin subtracted from the gas ignition point.

Selection Workflow

Confirm the circuit protection type (Ex ia or Ex ib) and its Zone.
Measure the actual gap between the Ex i group and adjacent circuits on the rail.
If 50 mm fits, keep the air path. If not, select a certified partition.
Verify partition height exceeds terminal height.
Confirm the partition-to-wall gap stays at or under 1.5 mm.
Choose blue terminals or a blue marker carrier.
Fit rail end clamps to lock the group in position.
Check every jumper bar is factory-formed and uncut.

Accessories That Affect Compliance

Partition Plates and Insulating Barriers

A partition must appear in the terminal's Ex certificate. Height must exceed the terminal body. An uncertified plate voids the panel certificate, even when dimensions look correct. One chemical plant lost two weeks of commissioning after field-cut partitions failed inspection.

Terminal Strip Jumper Bars

Cutting a jumper bar on site is prohibited in hazardous areas. Exposed cut edges shorten creepage paths below the accepted limit. Multi-pole bars must not be trimmed to shorter lengths. Bridging inside one Ex i loop is permitted; bridging across a partition boundary is not.

Terminal Strip Marker Carriers

The JHD5-DB-KLM-A carrier holds 44 × 7 mm labels and mounts on NS 32 or NS 35/7.5 rails. Markers sit above the terminal, so labels stay readable during service. Material must meet UL 94 V-2 or better. Both ends of an Ex i loop need the same identifier, and each partition boundary needs a group marker.

DIN Rail End Clamps

An end clamp stops the terminal group from sliding along the rail. Movement can close the 1.5 mm wall gap or shift the 50 mm clearance. Fit clamps on both sides of every group. Screw-type clamps hold better where vibration is present.

Terminal Strip Jumpers

Single-pole jumpers differ from multi-pole bars in current path and rating. The jumper rating must equal or exceed the terminal rating. Bridging across different signal types requires separate proof of intrinsic safety.

Common Acceptance Failures

Failure	Cause	Fix
Gap too small	Group slid on rail	Add end clamps
Partition rejected	Uncertified or short	Replace with certified part
Jumper violation	Field-cut bar	Use factory lengths
Missing marks	No blue ID	Add marker carrier

FAQ

Q: Can standard terminal blocks serve Ex i circuits?
A: Yes. They are passive parts needing no separate certificate. They must meet spacing rules and carry blue marking or labels.

Q: Is 50 mm always required between Ex e and Ex i?
A: No. A certified partition reaching within 1.5 mm of the wall replaces the air distance.

Q: What happens if a jumper bar is cut on site?
A: The installation becomes non-compliant. Cut edges reduce creepage below the accepted limit.

Q: Do marker carriers need Ex certification?
A: No. They are passive labeling parts. Their material must not alter certified spacing.

Q: How is the 50 mm measured?
A: In a straight line through air, or around partitions, between exposed conductive parts of the two circuit types.

Q: Does gas group affect isolation distance?
A: It affects creepage and clearance values for IIC atmospheres. The base 50/6/3 mm figures stay unchanged.

Q: Are blue terminals mandatory for Ex i?
A: Blue is the common identifier under IEC 60079-11 clause 6.2. Labeled markers satisfy the same requirement.

Model	JHD5-DB(KLM-A)
Number of packages	100
Thickness/Height()/Width mm	9.4/37.2/46
Dimensions