MF47-3.05
14
5.9
Insulation Replacement
Before undertaking any insulation replacement, see section 5.2.
After any replacement of insulation material, run the furnace at 1500°C to burn off volatile matter.
Do this is a well ventilated area. Try to ensure there is some chamber ventilated, but not too much
as this could result in cracked insulation.
5.10
Transformer Tappings
A change of transformer tapping is required if the supply voltage differs from the present setting.
To access the transformer tappings first disconnect the furnace from the electrical supply; then
remove the left-hand side cover (see 5.3). Positions below are given from a viewing position at the
left end of the furnace.
On the left side are the secondary tappings, which should not require change, but can be checked
against the following data:
HTF 17/5 – 27V
HTF 17/10 – 38V
HTF 18/4 – 31.1
HTF 18/8 – 43.8
On the right side is a terminal strip with the following connections (208 to 240V version shown).
The thermal trip connection forms part of the circuit to the contactor coil.
The L and N connection may alternatively be L1 and L2 for a live-to-live supply. The L side
should be connected to the correct tapping to match the supply voltage.
The link wire should be in position as shown unless the supply voltage is always low, in which
case there is the option of moving one end to the +2% terminal.
Important
– Changing the transformer primary tapping (including the +2%) requires adjustment
of the thyristor current – see section 5.4
The terminal between the link connections is not used.
5.11
Fuses
To access fuses disconnect the furnace from the electrical supply and remove the left side cover.
View the compartment from the left hand side of the furnace.
The thyristor fuse, which protects the thyristor unit, is located to the left of that unit.
If supply fuses are fitted they are to the left side of the compartment. If the incoming supply cables
go directly to terminal blocks, then there are no internal supply fuses (F1, section 8.1).
The control circuit fuses (F2) are near the EMC filter unit on the left side of the compartment.
thermal trip
240
230
220
208
+2%
L – connect to the
correct voltage tapping
connect the link to the +2% terminal if the supply
voltage is routinely low – see section 5.4
0%
N
E
in the case of the 380-415V
version, there are three
tappings marked 380, 400
and 415
