What is SGFP?
SGFP is an abbreviation for Secondary Ground Fault Protection. This is a sensing circuit to shut off transformer power when a ground fault
on the secondary side is detected. This transformer is designed to shut off the power within 1/2 second when the ground current (current
flowing from the secondary side to the ground) exceeds 15mA, under the standard of UL2161.
What are Mid-point transformers and End-point transformers?
Mid-point transformers have two separate output windings at the secondary circuit.
End-point transformers have only one output winding at the secondary circuit.
Are all UL2161 neon transformers equipped with SGFP?
No. UL doesn't require SGFP on neon transformers which meet the following exemptions:
The neon transformer generates no more than 33mA (30mA + 10%) and:
the output is rated at 3001V or less with 100Hz or less. This is usually a Standard Transformer, and if it is a mid-point transformer
having two separate outputs, such as a transformer rated 6002V or less, it doesn't require SGFP because each output becomes to half
of the rated voltage. All 60mA standard transformers require SGFP regardless of
the output voltage.
the output is rated at 2001V or less with 100Hz or greater. This is usually an
Electronic Power Supply.
The neon transformer has an isolated output of which the maximum voltage is 7500V
at a frequency of 100Hz or less. Isolated output is defined by UL that the current from
an output lead to the ground doesn't exceed 2mA.
The neon transformer has integral porcelain or glass output receptacles;
it is often called a housing transformer. This transformer becomes an exemption when
neon tubing is interconnected only by a freestanding lampholder without using a GTO
cable.
The neon transformer generates no more than 15mA.
How is the appropriate tube loading measured?
Luminous tube footage chart is normally the guide to match transformers with the required tube loading. However, the circumstances aren't
always ideal; for example, changing temperatures, voltage fluctuation, or the length of metallic conduits may affect the correct transformer
sizing. There are a number of load testing methods to determine the correct transformer size, as follows: (Note: the following methods don't work on electronic power supplies.)
Use an AC milliamperemeter
Measure the short circuit current and the current
connected to your required tube load. If the
transformer chosen is correct, the percentage of the
load current against the short circuit current should
range between 77.5% and 82.5% at the normal
ambient temperature. For cold weather mercury
tubing, it should range between 82.5% and 85%.
Flicker test (on neon filled tubes only)
Use a variable voltage variac to reduce the primary voltage and check the amount of voltage reduced when the flickering starts. It the transformer is rated at 120V, the primary voltage should range between 90 and 85 volts before flickering occurs. As for transformers rated at 277V, the voltage range should be between 208V and 196V.
Voltage test
Connect the required
tube load and measure
the voltage from one
secondary high-voltage
terminal to the ground
lug. Since our
transformers are
midpoint grounded, if
the voltage is plus or minus 5% of 1/4 of the rated secondary voltage, the transformer chosen is
correct. Use a digital voltmeter equipped with a high-voltage probe.
Which situation would be worse; connecting to overloaded or underloaded tubes?
Neither one is good but in extreme conditions, underloading is a little better for the following reasons:
Overloading
The longer the tube, the higher the discharge voltage becomes. However, if the current doesn't follow the voltage increase, this
unbalanced condition will cause unstable discharge. Flickering may occur, and a high frequency voltage will cause insulation failure
inside the transformer. The high voltage spikes may also cause radio interference.
Underloading
The shorter the tube, the lower the discharge voltage becomes. Therefore, discharge will stabilize quickly. However, if it is extremely
underloaded, the current increases too much, and this excessive current will cause the transformer to run hotter (overheat)
Is it necessary to reduce the footage when a flasher or adimmeris connected to signs?
Yes. However, the amount of footage reduction isn't precisely determined because it depends on the specifications of the particular flasher
or dimmer. The dimmer, in general, is designed to cut out the AC sinewave or to lower the voltage in order to reduce the energy of the input
power for dimming. Therefore, it is important to make allowances for these energy reductions. Use the the industry standard, which is to
reduce the maximum recommended footage chart by a factor of 15 -20%.
In any situation, should lower voltage transformers be used to avoid nuisance trips?
No. If a 12kV transformer is used instead of 15kV and if this causes the transformer to be overloaded, this will create much higher voltage
stress than using a 15kV transformer. Transformer overloading is potentially dangerous and creates a higher possibility of tracking. SGFP
will shut off the power when it is detected.
Which wiring method would be better; conventional wiring or virtual wiring methods?
Either one is fine, but there are concerns about both of them. First of all, it is important to keep the high voltage wires away from any other
metallic surface. Second, it is good for the transformer to have balanced wiring. Therefore, there are benefits and drawbacks for either
method, but the Virtual Wiring Method is recommended for the following reasons:
Conventional Wiring Method
With this method, it is good to secure a
balanced tube load. However, it is likely to
connect longer high voltage wires with the
metallic conduit directly from the transformer
outputs. Long lengths of wire from the
transformer outputs create capacitive coupling
along the conduit run due to the high voltage.
This capacitive coupling causes not only the transformer to operate overloaded, but GTO
wires may deteriorate. The ideal wiring installation is where no metallic conduits are required, such as inside sign enclosures, and use
tube supports to keep the GTO wires away from any grounded conductive surface at least 2 -1/2 inches.
Virtual Wiring Method
This method is good for keeping the GTO
wires short for the transformer outputs.
However, it is difficult to keep the tube load
balanced for some sign applications. Since
our transformers are designed so that the
output windings are internally connected to
the grounding (mid-point grounded
transformer), no voltage is generated at the
dead center of the secondary circuitry.
Therefore, if the right and left tube loads are
unbalanced, the dead center of the secondary circuitry moves to either side depending on the degree of unbalanced tube loading. There is
a possibility that voltage leaks will occur inside metallic conduits. However, as long as the unbalanced loading is not so extreme, the
amount of voltage leaked inside the metal conduits is much smaller than the leaked amount which is created by the Conventional Wiring
Method and long metal conduits connected directly from the transformer outputs.
Caution for Virtual Wiring Method
A border tube application is one of the ideal wiring situations for the Virtual Wiring Method because it doesn't necessarily need the long
length of metallic conduit directly from the transformer outputs. However, unlike the Conventional Wiring Method, both outputs are
likely to be installed close together. Since they are electrically attracted to each other, be sure to have some distance between them, at
least 2-1/2 inches.
What is the difference between normal power factor (NPF) and high power factor transformers (HPF)?
The power factor of an electrical device relates to the position of the waveform of its voltage relative to the waveform of the current. The
typical power factor for a NPF neon transformer will average between 45% and 50%. An HPF unit utilizes a capacitor connected to the
primary coil of the transformer that will increase the power factor to 90% or greater.
The secondary output of a NPF and a HPF neon transformer are basically the same, but the primary current of a HPF unit is much lower
than an NPF unit. An HPF and NPF transformer both consume the same amount of energy (wattage). However, an HPF unit does not
save the user any money based on kilowatt consumption, but it does allow for more transformers on a given primary circuit.
How should a transformer be mounted to best dissipate heat?
For conventional (CB) units, mounting the transformer so that one or more sides are contact with the raceway or transformer box will increase the dissipation of heat. If raising the unit is required, instead of double-nutting, we recommend that a solid plate be used to create a proper heat sink conducting heat away from the unit. A properly ventilated enclosure is paramount to reduce the heat build up within the enclosure.
Enclosed (EB) units inherently operate much cooler than conventional units that are mounted within an enclosure but it is still very important to mount the enclosed unit in a well ventilated crawl space or attic area. Mounting enclosed units in a transformer box or raceway is not recommended.
What is the ambient temperature range of a neon transformer or neon power supply?
Neon transformers and power supplies, from any manufacturer, will last the maximum amount of time if they are not subjected to abnormal ambient temperatures for extended periods of time. The optimum ambient temperature range for LECIP transformers and power supplies is: - 20C to +40C ( -4F to +104F )
voltage. 
Voltage test 
