IS - Grounding Requirements

[gparker2]

I am designing a barrier for an intrinsically safe circuit. How can I determine to required screw/wire size for grounding the barrier?

Would I be able to use two #6-32 screws in parallel?

Is this requirement different from the NEC vs. the IEC?

 

[FrancisL]

This may help
Earthing And Bonding, Grounding Electrical Equipment Apparatus From MTL

http://www.process-controls.com/MTL/mtl_intrinsic_Earthing.html

 

[FrancisL]

And here's a better link, the same paper but direct from MTL
Select Technical Papers then TP1121

http://www.mtl-inst.com/mtlsupport.nsf

 

[PZas]

This question is quite dependent on where the application is to be used.

In the US this is governed by UL 1203 or FM 3610.

15.3.5 At least one terminal or connection shall be provided on each barrier or barrier assembly for connecting the barrier circuit to ground. The grounding terminal or connection shall besized to accommodate a No.12 AWG(3.3mm2)minimum grounding conductor. The following constructions or their equivalents comply:

a) A No. 8 (4.8mm diameter) wire binding screw that engages the terminal plate by at least two full threads. The terminal plate shall be no less than 1.25 mm (0.049 inches) thick, and shall be provided with up turned lugs or the equivalent to hold the conductor in place.

b) A pressure-type wire connector complying with the requirements for such connectors. Soldering lugs, push-in connectors, quick-connects, or similar friction fit connectors are unacceptable.

c) Bolting the barrier to a grounding bus.

The important thing to remember when designing intrinsically safe equipment is the the end design must be the safest possible. Unlike most codes this some times allows you to break rules. However, the grounding requirements are quite clear.