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HST, VST
CIRCUIT DIAGRAMS
Safety Switches type A: a 2-pole Heater Switch is fitted directly in the element circuit in models
up to 16A rating. Two “door switches” are also fitted in the element circuit up to 25A rating.
Safety Switch type B: a Heater Switch is fitted into the contactor coil circuit in models over 16A.
A door switch is fitted into the contactor coil circuit over 25A rating.
7.1
Single Phase
Supply ligh
t
Instrument Switch
coil
temperature
controller
overtemp.
controller
thermocouple
safety
switch B
PE
L
N
SSR
e
l
e
m
e
n
t
(s)
F3
F3
safety
switches A
F1
F2
i
f
f
itted
Filte
r
(if fitted)
contacto
r
if fitted
hea
t
on
thermocouple
7.2
2-phase with neutral
As 3-phase, with phase L3 not present, and with two SSRs and element circuits. In models up to
25A safety switches type A are fitted in the L1 and L2 circuits instead of type B in the contactor
coil circuit.
7.3
3-phase with neutral
e
l
e
m
e
n
t
(s)
e
l
e
m
e
n
t
(s)
F1
N
L2
L3
F2
L1
PE
e
l
e
m
e
n
t
(s)
Supply light &
Instrument Switch
coil
temperature
controller
overtemp.
controller
safety
switch
SSR
hea
t
on
F3
SSR
SSR
hea
t
on
F3
hea
t
on
F3
i
f
f
itted
thermocou
p
le
thermocou
p
le
contacto
r
Filter
(
if fitted
)
note on 3-phase: depending on filter(s) fitted, there may be 3
separate neutral wires from the elements to the neutral supply.
12 MF13