Auxiliary Equipment 8

All discharge sources and low-voltage incandescent sources require the use of

auxiliary equipment to supply the correct current or voltage or both to the source.

Auxiliary equipment falls into two categories:
transformers and ballasts. This auxiliary
equipment consumes a small amount of
electrical power, adding to the total amount
of wattage used by the lighting system.

Transformers

Low-voltage light sources require the use of
a transformerto step down the standard
building service of 120 V to 12 V. The nomi-
nal 120 V building service can vary between
115 V and 125 V; some low-voltage light
sources operate at6Vor24V.Transformers
are placed either within (integral to) the
luminaire or in aremotelocation.
The smaller size of many low-voltage
light sources allows for the design of smaller
luminaires. With recessed luminaires the
transformer is hidden above the ceiling and
out of view. With surface- or pendant-
mounted luminaires that have their trans-
formers enclosed within the housing, how-
ever, the bulk of the luminaire is increased.
Where ceiling conditions permit, surface-
and pendant-mounted luminaires can be
designed with the transformer recessed in
the ceiling and out of view.

Track-mounted luminaires usually con-

tain their transformers. It is also possible to

provide low-voltage service to a length of

track, locating the transformer in the ceiling

or in an ancillary space. The high amperage

of low-voltage lamps strictly limits the

number of track luminaires per transformer

(W÷V=A):a50W,12Vlamp draws the

same amperage as a 500 W, 120 V lamp;

therefore, a 20-ampere-rated track can ser-

vice only four 50 W lamps (50W×4÷12V

= 16.7 A). This problem is reduced by the

use of 50-amp track, which permits ten 50

W, 12 V lamps to be installed on a single

track circuit (50W×10÷12V=41.7 A).

If remote transformers are used to

maintain the compactness of the lighting

element, the increased distance between

the source and its transformer requires

larger wire sizes to prevent avoltage drop

from occurring over the longer wiring run.

See table 9 in the Appendix.

Two kinds of transformers are manufac-

tured for low-voltage lighting: magnetic

(core-and-coil) and electronic (solid-state).

Magnetic transformers use copper

wound around a steel core, which isinduc-