Thermon Electric Heat Tracing - Manual (Page 8)

Electric Heat Tracing
7
Circuit Protection Requirements . . .
1. Over-current protection (typically circuit breakers) is
required for each branch circuit. This protection must
isolate all power conductors from the supply.
2. For typical installations (with TT and TN grounding
systems), a means of protection against earth faults is
required that includes a residual-current protective device
for each branch circuit. For fi xed-level earth/ground-
fault circuit interrupters, a minimum 30 mA trip level is
recommended. The preferred trip level for adjustable
devices is 30 mA above any inherent capacitive leakage
characteristic of the heater as specifi ed by the heat
tracing supplier. Where conditions of maintenance and
supervision ensure that only qualifi ed persons will service
the installed systems, and continued circuit operation
is necessary for the safe operation of the equipment
or processes, earth-fault detection without interruption
is acceptable if alarmed in a manner to assure an
acknowledged response.
3. For IT grounding systems, a means of protection
against earth faults is required that includes an electrical
insulation monitoring device that shall disconnect the
supply whenever the electrical resistance is not greater
than 50 ohms/volt of rated voltage.
Thermal Insulation . . .
1. Before installing thermal insulation, insulation resistance
test should be conducted. The cable should be tested
with a test voltage of at least 500 Vdc. However,
for polymer insulated heating cables, 2500 Vdc is
recommended. The minimum acceptable level should not
be less than 20 megohms.
2. The need for properly installed and well-maintained
thermal insulation cannot be overemphasized. Without
insulation, heat losses are generally too high to be offset
by a conventional heat tracing system.
3. In addition to piping and in-line equipment such as pumps
and valves, all heat sinks must be properly insulated. This
includes pipe supports, hangers, fl anges and, in most
cases, valve bonnets.
4. Regardless of the type or thickness of insulation used, a
protective barrier should be installed. This protects the
insulation from moisture intrusion, physical damage and
helps ensure the proper performance of the heat tracing
system. Seal around all penetrations through the thermal
insulation.
5. Apply “Electric Heat Tracing Caution” labels to the
insulation vapor barrier on 3m intervals or as required
by code or specifi cation. The labels are supplied with
Thermon connection kits.
Final Inspection and Documentation . . .
1. After the installation of the thermal insulation and
weather barrier but BEFORE ENERGIZING THE HEATING
CIRCUIT, the insulation resistance test should be
repeated. This should call attention to any damage to
the heating cable that may have occurred during the
insulation installation.
(Record 3 on Insulation Resistance Test Page 9 and 10.)
For Series Heating Cables, measure the electric loop resistance
and record measured Ohms (Record 3 on Page 10.)
2. It is recommended that the circuit be temporarily
energized so that the volts, amps, pipe temperature and
ambient temperature may be recorded. Take the values
after 5 minutes of energizing. This information may be of
value for future reference and should be maintained for
the historical operating data log.
(Record 4 on Insulation Resistance Test Page 9 and 10)
3. Stabilized design can be used for self-regulating, power-
limiting and constant watt heating cables without a limiting
device to determine the T-class through the use of the
Thermon CompuTrace software or Thermon Engineering.
4. Series heating cable output and T-rating are dependent
upon supply voltage, cable resistance, temperature
conditions as well as additional variables through the
use of the Thermon CompuTrace software or Thermon
Engineering.
5. The maximum temperatures provided by Thermon’s
CompuTrace software and by Thermon engineering are
calculated to the methods and requirements of
EN-IEC 62086-2 and EN-IEC 60079-30.
6. If stabilized design is used, the end user must record the
system parameters and the area T-class, and keep these
records for the time the heating cable is in operation.
7. Inspect system on a regular basis at least once per year.
Record all information after conducting test. If the system
fails any test, refer to Thermon’s Maintenance and Trouble
Shooting Guide for assistance. De-energize circuits affected
and make the necessary repairs immediately.
8. Verify the setting of the maximum control device, if
provided to limit the T-rating for the circuit design, to
ensure it limits the maximum surface temperature to be in
compliance with clause 4.4.3 of EN-IEC 60079-30-1.
Maintenance and Repair . . .
1. Refer to form TEP0066-Electric Heat Tracing Maintenance
and Trouble Shooting Guide.