WARNING: According to the National Electrical
Code (NEC) all fixtures in or within 10 feet of
water (including waterfalls, ponds and other
type of water features) must be powered
by a pool and spa rated transformer. Vista
Transformers meet this rating with the following
modification. In addition to this modification,
transformers must be installed in accordance
with the National Electrical Code (NEC) and
local codes. Failure to do so will void the
warranty and may result in serious injury and/or
damage to the transformer.
This is straight from the instruction manual that comes with Vista's MT series transformers. I did a job where I had one light 7' from the pool and another 9' and it passed with the MT transformer.
This is from an article on the web:
Section 680.22(B)(4) permits luminaires to be installed within 5 to 10 feet horizontally of the pool’s edge only where a ground-fault circuit interrupter (GFCI) protects the luminaires. Since low-voltage landscape luminaires are supplied by a low-voltage power supply, such as a transformer, providing GFCI protection on the primary side of an isolation transformer will not provide GFCI protection on the secondary side. GFCI devices will not operate at the 15-volts or less supplied by the secondary of the power supply. This leaves only two options: one is to locate all low-voltage landscape lighting at least 10 feet from the pool or fountain edge; or, two, to use a special power supply.
There are low-voltage lighting power units that are marked “For Use with Submersible Fixtures or Submersible Pumps.” In this case, a special transformer is used that complies with the requirements in 680.23 for underwater luminaires installed below the normal water level of the pool. This transformer is specifically listed for this use and is an isolated winding type transformer with an ungrounded secondary similar to the low-voltage landscape lighting transformer, as required by 411.5(B). The low-voltage pool lighting transformer has one additional feature in its design. It has a grounded metal barrier or shield between the primary and the secondary. This metal barrier or shield prevents a direct internal short between the primary and the secondary of the transformer. If a short does occur on the primary side, it will short to the metal shield and the primary overcurrent protective device will operate. If a short develops on the secondary side to the shield, the secondary overcurrent protective device, if provided, will operate. If there isn’t a secondary overcurrent protective device and the primary is providing protection through the transformer, the primary device should operate