“Equipment bonding jumpers: are they always necessary?” Massimo Mitolo, Senior Member, IEEE

“Equipment bonding jumpers: are they always necessary?” “Equipment Bonding Jumpers” are equivalent to: “Protective Bonding Conductors” (PE) as per IEC 60364: Maintain continuity of the equipment grounding path. Maintain continuity of the equipment grounding path. Provide Protective Equipotential Bonding. Provide Protective Equipotential Bonding.

Exposed-conductive-part (ECP) Conductive part forming part of electrical equipment which can be touched (even if out of reach) which is not live which is not live which may become live when basic insulation fails.

ECPs shall be bonded to ground so that fault current is allowed to flow to ground, permitting the protective device to promptly disconnect the supply. Grounding is the 2 nd level of protection, the basic insulation being the 1 st. Exposed-conductive-part (ECP)

Piece of equipment with “double” (or reinforced) insulation (Class II equipment), is not considered an ECP and shall not be connected to a PE. shall not be connected to a PE. (!! NEC art Exception n. 3 !!) Additional insulation is the 2 nd level of protection Symbol:

Exposed-conductive-part (ECP) A conductive part which can be energized just because in contact with an ECP, is not an ECP. (it is not required to be grounded, then!)

Extraneous-conductive-part (EXCP) Conductive part not forming part of the electrical system (e.g. piece of metalwork) not forming part of the electrical system (e.g. piece of metalwork) liable to introduce a “zero” potential or an arbitrary potential into the premises.

Extraneous-conductive-part (EXCP) EXCPs shall be bonded to ground Equipotential connections between ECPs and EXCPs will significantly reduce the magnitude of their potential difference under fault conditions. (Necessary but not sufficient condition!)

Extraneous-conductive-part (EXCP)

It’s an EXCP if less than: 1000 Ohms (200 Ohms) (based on the definition of permissible body current and body resistance of a “standard” person As per IEC )

Where do you find PEs? 6 possible cases: 1. PE in equipments 2. PE among ECPs 3. PE among electrostaticly charged objects 4. PE for Lightning Protection Purposes 5. PE among ECPs and metal parts 6. PE among ECPs and EXCPs

1. PE in equipments Clear path to ground = Low resistance PE

1. PE in equipments

2. PE among ECPs

3. PE among electrostaticly charged objects The metal object is isolated from ground (resistance to ground greater than 1 MOhm) The metal object is isolated from ground (resistance to ground greater than 1 MOhm)+ Any mechanism for generating electric charges exists Any mechanism for generating electric charges exists+ An explosive atmosphere is present An explosive atmosphere is present

4. PE for Lightning Protection Purposes Overvoltages are induced in any closed loop with possible electric discharge through the gaps

5. PE among ECPs and metal objects

5. PE among ECPs and metal parts

5. PE among ECPs and Metal objects?

6. Among ECPs and EXCPs Equipotential connections between ECPs and EXCPs will significantly reduce the magnitude of their potential difference under fault conditions.

CONCLUSIONS Basic investigation on the nature of conductive parts is necessary, in order to assess in which category they fall (ECPs or EXCPs). Only ECPs and EXCPs shall be considered for grounding.

“Equipment bonding jumpers: are they always necessary?” Any questions?