Designing or installing machines
for connection to RCD protected
sockets!
Automated machines containing
frequency inverters must not be
connected to circuits protected
by conventional RCDs (RCCB).
Before installing the equipment,
check the machine specification &
inverter characteristics for specific
requirements relating to RCD
protection.
RCCB Protection with Inverters
To comply with Regulation 4(1) 65 Where the precautions taken include
residual current protection to reduce
the risk of death or injury (Regulation
8), the upstream RCD protection must
be suitable for use with inverters
nominal supply frequency (50Hz)
which cannot be detected by
and at various harmonic frequencies.
conventional RCDs. In addition DC
Leakage currents in the higher
residual currents affect the tripping
frequency ranges can be significant
characteristics of AC RCDs, resulting
and from a safety perspective cannot
in a loss of protection due to magnetic
be ignored, as can be seen from the
saturation of the AC trip coil.
connected downstream see Fig 2.
following example.
Electricity at Work Regulation 4(1)
Figure 2 details the frequency range
65 The safety of a system depends
of various leakage currents present
upon the proper selection of all the
in a system
electrical equipment in the system
containing a 4kW
and the proper consideration of
VSD; at 50Hz the
the inter-relationship between the
leakage current is
individual items of equipment.
less than 4mA. The
The inverter design topology will
determine the Type of RCD protection
required. To meet existing laws
on H&S, companies must comply
with the inverter manufactures
recommendations relating to the
Type and characteristics of the RCD
that can be used safely with the
equipment.
AC operational leakage currents: 3
Phase Inverters and the associated
EMC filters and motor cables,
generate leakage currents at
Chaz Andrews – Technical Manager,
Doepke UK Ltd
maximum leakage
current 60mA,
occurs at 8 k Hz.
This equipment
can be matched to
a Type B RCCB that
meets UK 30mA
protection at 50Hz
and fire protection requirements
Doepke
above 150 Hz (see Reg 422.3.9 9 (i) <
300mA RCD sensitivity).
We stock a comprehensive range of
products for immediate despatch to
DC Residual Currents: Under certain
fault conditions 3 phase inverters
produce smooth DC residual currents
customers throughout the
United Kingdom.
www.doepke.co.uk
FDPP - www.fdpp.co.uk 17