Transcript Protective bonding conductors: an IEC point of view

“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.
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 may become live when basic
insulation fails.
Exposed-conductive-part (ECP)
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 2nd level of protection,
the basic insulation being the 1st.
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.
(!! NEC art. 250-110 Exception n. 3 !!)
Additional insulation is the 2nd 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)
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)
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 60479-1)
Where do you find PEs?
6 possible cases:
PE in equipments
2.
PE among ECPs
3.
PE among electrostaticly charged
objects
PE for Lightning Protection Purposes
5.
PE among ECPs and metal parts
6.
PE among ECPs and EXCPs
1.
4.
1. PE in equipments
Clear path to ground = Low
resistance PE
1. PE in equipments
ECP
A
Zi
Zph
Vph
Vt
Z
RN
V t  V ph
PE
Z PE

Z i  Z ph  Z PE
B
2. PE among ECPs
2. PE among ECPs
3. PE among electrostaticly charged
objects
•
•
•
The metal object is isolated from
ground (resistance to ground greater
than 1 MOhm)
+
Any mechanism for generating
electric charges exists
+
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?