Pumping/VSD Installation Fires
What do you do about RCCB
Protection?
To safely install pumping equipment containing VSDs requires a detailed
understanding of the operational leakage currents and residual currents
associated with the EMC filter / VSD / Motor combination including the
local installation requirements.
R
emote pumping stations/
distributed process
installations subjected to
wide temperature changes
create conditions for condensation on
de-energised electrical equipment. A
build-up of dust on insulated surfaces
subjected to moist damp conditions,
can create an additional fire hazard.
Under these conditions relatively low
levels of leakage current - less than
80mA travelling across an insulated
surface can ignite combustible
material and fluids containing simple
contaminates such as detergents.
Scintillations forming on the insulation
surface create conductive tracks which
result in a cascade effect and increased
leakage current and resultant fire
hazard. See video “How do RCDs
prevent fire” http://www.doepke.
co.uk/
If the electrical specification for
the installation does not cover the
detection of safe levels of earth
leakage current there is an increased
risk of an electrical fire, especially if
equipment is mounted out of sight and
or subject to infrequent maintenance.
Where conventional protective bonding
cannot be relied on to achieve the
required level of electrical safety,
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PECM Issue 16
and RCD protection is required under
the regulations, only Type B RCDs
can be used with 3 phase VSDs: see
GAMBICA Installation Guide 4th Edition
- Page28. 4.2.3 and manufactures
installation instructions.
If the electrical
specification for the
installation does not
cover the detection
of safe levels of earth
leakage current there
is an increased risk of
an electrical fire
BS7671 Compatibility of Electrical
Equipment
Installing equipment containing 3
phase VSD and EMC filters (see Fig
1.) requires a detailed assessment of
the leakage current associated with
the equipment. BS7671 Regulation
331.1 gives some guidance on the
assessment of characteristics of
the equipment that impact on the
safety of the installation – referred
to as “harmful effects”. This includes
amongst other safety issues; earth
leakage currents, high protective
conductor current present under
normal operation, d.c. feedback and
high-frequency oscillations.
Operational Leakage currents and
residual currents associated with
VSD installations
Drive installations produce operational
leakage currents across a wide
frequency spectrum see Fig 2:
Under normal operating conditions
the leakage currents flowing in the
protective conductor should not
cause unnecessary operation of the
RCD. Comparing the operational
characteristics of the drive installation
against the RCD characteristic will
identify any weakness in the proposed
design based on the protection
level required i.e. <30mA personal
protection. >30mA <300mA fire
protection.
Fixed Leakage Current: The EMC
filter - internal or external to the VSD
produces a fixed leakage current to