The voltage required to start the tubes depends on their length, the type of gas and its
pressure and on the design of the electrodes. The manufacturers normally quote the
running voltage per metre of tube and the voltage drop at each pair of electrodes, from
which the designer can calculate the voltage which has to be provided from the secondary
of the transformer. A magnetic shunt is provided inside the transformer to enable the tube
current to be adjusted when the sign is commissioned. This is not a task to be undertaken
lightly, because of the very high voltages involved.
Stringent safety regulations for high-voltage advertising signs have been drawn up by
the Institution of Electrical Engineers, and recommendations are also given in BS
559:1998. No part of the installations may have a voltage to earth greater than 5000V.
and if the centre point of the secondary side is earthed the voltage available between the
opposite ends of the series of tubes is 10000V. This limits the length of tubes which can
be served from one transformer. If greater lengths are required, the sign must be split into
several lengths each having its own transformer. The transformers are normally housed
inside weatherproof steel containers which are fitted on the outside of the building. A
transformer rated at more than 250VA must be supplied on a separate final circuit not
serving any other equipment or any other transformer. If the transformers are smaller than
this, up to four of them may be put on a common sub-circuit, but the total rating of one
circuit may not exceed 1000VA. Particular care must be taken with the high-voltage
wiring which should be lead-covered armoured cable. It must be restrained from swaying
in the wind because this would strain both the conductor and the insulation.
A typical circuit is shown in Figure 7.13. A lockable switch is provided so that anyone
doing maintenance on the installation can be sure that no other person can inadvertently
turn the supply on. The fireman’s switch is mounted outside the building in a prominent
position but out of reach of the public. It is for the use of the fire brigade, who want to
turn off all high-voltage sources before spraying water anywhere near them. A choke is connected in each highvoltage
circuit to suppress radio interference.
pressure and on the design of the electrodes. The manufacturers normally quote the
running voltage per metre of tube and the voltage drop at each pair of electrodes, from
which the designer can calculate the voltage which has to be provided from the secondary
of the transformer. A magnetic shunt is provided inside the transformer to enable the tube
current to be adjusted when the sign is commissioned. This is not a task to be undertaken
lightly, because of the very high voltages involved.
Stringent safety regulations for high-voltage advertising signs have been drawn up by
the Institution of Electrical Engineers, and recommendations are also given in BS
559:1998. No part of the installations may have a voltage to earth greater than 5000V.
and if the centre point of the secondary side is earthed the voltage available between the
opposite ends of the series of tubes is 10000V. This limits the length of tubes which can
be served from one transformer. If greater lengths are required, the sign must be split into
several lengths each having its own transformer. The transformers are normally housed
inside weatherproof steel containers which are fitted on the outside of the building. A
transformer rated at more than 250VA must be supplied on a separate final circuit not
serving any other equipment or any other transformer. If the transformers are smaller than
this, up to four of them may be put on a common sub-circuit, but the total rating of one
circuit may not exceed 1000VA. Particular care must be taken with the high-voltage
wiring which should be lead-covered armoured cable. It must be restrained from swaying
in the wind because this would strain both the conductor and the insulation.
A typical circuit is shown in Figure 7.13. A lockable switch is provided so that anyone
doing maintenance on the installation can be sure that no other person can inadvertently
turn the supply on. The fireman’s switch is mounted outside the building in a prominent
position but out of reach of the public. It is for the use of the fire brigade, who want to
turn off all high-voltage sources before spraying water anywhere near them. A choke is connected in each highvoltage
circuit to suppress radio interference.
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