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5
FAULT FINDING
If an electrical fault occurs on the appliance
the preliminary electrical system checks
contained in the British Gas Multimeter
Instruction Booklet must be carried out
first. When any service or replacement of
electrical components which has required
the breaking and re-making of electrical
connections has taken place, the following
tests must be repeated:
– earth continuity;
– short circuit;
– polarity;
– resistance to earth.
5. 1
EARTH CONTINUITY CHECK
Appliances must be electrically disconnect-
ed, meter set on Ω (ohm) x 1 scale and
adjust zero if necessary. Tests leads from
any appliance earth point (e.g. inside control
box) see wiring diagrams (section 7) to
earth pin on plug. Resistance should be less
than 1 Ω (ohm). If the resistance is greater
than 1 Ω (ohm) check all earth wires for
continuity and all contacts are clean and
tight. If the resistance to earth is still
greater than 1 Ω (ohm) then this should be
investigated futher.
16
5.2
SHORT CIRCUIT
CHECK
Switches turned FULL ON - meter set on Ω
(ohms) x 1 scale. Test leads from L to N on
appliance terminal block, if meter reads 0
then there is a short circuit.
Meter set on Ω (ohm) x 100 scale. Repeat
it with leads from L to E. If meter reads less
than infinity (∞) there is a fault.
NOTE: Should it be found that the fuse has
failed but no fault is indicated, a detailed
continuity check (i.e. by disconnecting and
checking each component) is required to
trace the faulty component.
It is possible that a fault could occur as a
result of local burning/arcing but no fault
could be found under test. However, a
detailed visual inspection should reveal
evidence of burning around the fault.
5.3
POLARITY CHECK
Appliance reconnected to mains supply and
meter set on 300 V ac scale. Test at appli-
ance terminal block.
– Test leads from L to N meter reads
approx.: 240 V ac.
– Test leads from L to E "
" meter reads
approx. 240 V ac.
– Test leads from N to E "
" meter reads
from 0 to 15 V ac.
5.4
RESISTANCE TO
EARTH CHECK
Appliance must be disconnected from main
supply and meter on Ω (ohm) x 100 scale.
All switches including thermostat on test
leads from L to E - if meter reads other than
infinity (∞) there is a fault which should be
isolated.
A detailed continuity check is required to
trace the faulty component.
IMPORTANT:
These series of checks are the first elec-
trical checks to be carried out during a
fault finding procedure. On completion
of the service/fault finding task which
has required the breaking and remaking
of electrical connections then the
checks 5. 1 Earth continuity, 5.3 Polarity
and 5.4 Resistance to earth must be
repeated.
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