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Earth Connections
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When fitted with the optional local isolator, the Client internal earth cable connection
on the MFH heater is inside the Isolator Enclosure. Connection is made by the use of
an M6 earth bolt (fitted) with proprietary cable ring crimp (Client supplied). Maximum
cable size is 25mm².
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When not fitted with the optional local isolator, the Client internal earth cable
connection on the MFH heater is inside the terminal enclosure. Connection is made
by the use of a ferrule crimp (Client supplied) connected to the Earth terminal
provided. Maximum cable size is 10mm², if larger cable is required, an optional local
isolator must be fitted.
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The minimum External Earth conductor size permitted is 4mm². The external earth is
made on the M6 stud on the Ex e enclosure, or optionally on the Isolator bracket
fixings (when fitted)
Earth-fault Protection
For safety reasons, it is essential to limit the magnitude and duration of earth-fault currents.
It is impractical to cover all possible systems, however note that, regardless of which system
is used, the product must be protected by a suitable device wired to shut down the product if
the thermostat fails to earth. Suitable devices include a residual current device (RCD) – this
is the preferred method and should be used whenever possible – or an insulation monitoring
device.
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Maximum recommended setting for the RCD: 100mA/10mS. The duration time of
10mS (ten milliseconds) ensures that any fault is detected within a single cycle of a
thyristor system (where applicable).
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Maximum recommended setting for the insulation monitoring device: Insulation
resistance is not greater than 50 ohms per volt of rated voltage.
Ensure that the equipment is earthed in accordance with the plant earthing philosophy.
If fitted, an anti-condensation heater must be protected by a 30mA earth leakage circuit
breaker.
Before commissioning the equipment, the completed installation should be approved by an
authorised & competent person to ensure that it has been carried out correctly and that the
system is safe for commissioning.
Before switching the thermostat circuit on, check that all the relevant requirements, and any
special conditions of safe use have been adhered to, including any additional warning labels
that may be present on the product itself.
WARNING – These heaters MUST BE EARTHED.
5. Installation Instructions
