A new ‘gotcha’
This practice has become more difficult.
It’s dangerous in areas that have energy
usage codes. Engineers are increasingly
moving to expensive light-emitting diode
(LED) fixtures to meet the energy codes.
When asking vendors for a substitute, you
must tell them the fixture packages have
to be energy equivalent in addition to the
other requirements. I have heard several
stories where contractors got in trouble
when they accepted a fluorescent package in lieu of an LED package, since the
fluorescent fixtures required more power.
Branch circuitry presents another
problem when substituting fluorescent
fixtures for LED fixtures. Since fluorescent fixtures draw so much more energy,
be sure to include the cost of additional
circuits in your calculations when you
present a proposal for this type of value
Follow-up to “Out of Control”
Since my January column, “Out of Control,” I have estimated more projects
with 0–10-volt (V) LED dimming controls, and, of course, the control wiring
was not designed. While laying out the
0–10V wiring, I wondered if any of the
metallic cabling (MC) manufacturers
are making a cable with the control wir-
ing included. Sure enough, Southwire
has UL-approved cables in several con-
figurations, including 12/2 with two No.
16 control wires as well as 12/3 with two
No. 16 control wires. This is just what the
doctor ordered for projects that allow MC
and have 0–10V LED dimming fixtures.
I also have a correction to the article
in regard to how 0–10V LED dimming
works. There are actually two protocols.
One protocol is known as “sourcing”
and is used more often in entertainment
technology. This protocol requires the
controller to generate the low-voltage
control signal. The protocol I see on all of
my projects is known as “sinking,” where
the low-voltage control signal is generated at the ballast or driver.
To estimate the cost of a sinking protocol system, first understand that the
dimmer has four wires. Two are at line
voltage and switch the ballast or driver
on and off. The other two wires are purple and gray and handle the 0–10V signal.
The driver or ballast furnishes approximately 10V and a rheostat in the dimmer
alters the voltage. The return low-voltage
signals the driver or ballasts electronics
to “sink” the controller’s voltage, causing
the fixture to dim.
These dimmers have a maximum
amount of current they can handle on
the low-voltage circuit. It varies typi-
cally between 30 and 75 milliamperes
(mA). Calculations need to be made to
ensure the dimmer’s low-voltage side
is not overloaded. Tech support peo-
ple at three companies have told me
that it is possible to overload the low-
voltage circuit while not overloading
the switching circuit.
So, do you think the engineers will
make these calculations? If you do, I
have a bridge for sale. Two calculations
will be required to ensure you do not
overload a 0–10V dimmer. The first calculation is for the rating of the on/off
switch in the dimmer. You will need to
make a standard amperage calculation.
You can find out from the manufacturer how much current is required to
switch the ballasts or drivers. The second calculation is for the rating of the
dimmer’s 0–10V rheostat. Once again,
contact the manufacturer to find out
how much current each ballast or driver
contributes to the circuit. Each ballast
or driver typically contributes 0.5 to 1
mA. After obtaining the amount of current generated in the drivers, you can
make the simple calculation for the control circuit.
Something else important to know
about 0–10V dimmers is the dimming happens at the drivers, not the dimmer. As a
result, you can gang these dimmers without derating them. These dimmers are also
available without switches, for schemes
where the fixture is switched from another
location, such as a motion sensor.
Losing Control Again
Value engineering and LED dimmers
FOR AS LONG AS I HAVE BEEN IN THIS INDUSTRY, material substitutions
have been a way to save money on projects. The process eventually became known as
“value engineering.” Theoretically, the contractor, and maybe the owner, saves money
by replacing a specified product with a less costly one. We usually look at lighting
fixtures first. In the past, it was fairly easy to do. You could simply ask a vendor for
a fixture package based on inexpensive fixture brands instead of the “Rolls-Royce”
fixtures that were specified.
CA RR has been in the electrical construction business since 1971. He started Carr
Consulting Services—which provides electrical estimating and educational services—in
1994. Contact him at 805.523.1575 or firstname.lastname@example.org. I S T
ESTIMATING BY STEPHEN CARR