Start with the actual load, then check the transformer's total and per-zone ratings, fixture compatibility and cable voltage drop. Plan my yard can help organize a preliminary fixture count; confirm the final selection against the product instructions.
The one rule
Add the input load of the compatible fixtures, using watts or VA as the transformer instructions require. For the referenced HIBOITEC dual-zone models, plan the connected lamp load within 80% of rated capacity, following the supplied manual. A 200 W rating therefore gives a recommended lamp-load allowance of up to 160 W, with 40 W retained as headroom. Other models may specify different limits.
Keep that 20% headroom in the plan after adding lights; it is not the portion to spend on later additions. Expansion room is the unused portion of the recommended 80% allowance. This headroom is not a measurement of cable losses: check cable length, conductor size, load distribution, connections and voltage drop separately.
Illustrative load: eight 3 W path lights and four 5 W spotlights total 44 W. On a 200 W rated transformer, the recommended 160 W lamp-load allowance leaves 116 W available within that allowance and retains 40 W of headroom. If sizing from the load instead, 44 ÷ 0.8 = 55 W is the example minimum rated-capacity target; do not add the same 20% allowance again. Check compatibility and per-zone limits before selecting a unit. The current HIBOITEC standalone range covers 200 / 300 / 400 / 500 / 600 W: 2-zone models at 200 / 300 / 600 W and 3-zone stainless models at 300 / 400 / 500 / 600 W. The 100 W table row is a hypothetical example.
The table
Illustrative counts with an assumed 20% reserve and one load value per column. These are not verified maximum fixture counts for a particular product. For a mixed run, add the actual loads, check each zone's limit and verify cable voltage drop. Kits with their own power supplies are excluded.
| Transformer | Compatible 3 W fixtures | Spotlights · 5 W | Compatible 2.5 W fixtures | In-ground · 12 W |
|---|---|---|---|---|
| 100 W | 26 | 16 | 32 | 6 |
| 200 W | 53 | 32 | 64 | 13 |
| 300 W | 80 | 48 | 96 | 20 |
| 400 W | 106 | 64 | 128 | 26 |
| 500 W | 133 | 80 | 160 | 33 |
| 600 W | 160 | 96 | 192 | 40 |
The table does not account for cable length, conductor size, load distribution or per-zone limits; the wire guide explains the cable checks. The 20% allowance is already applied in the table. Add planned future fixture loads to the connected load before sizing the transformer, and retain the headroom after expansion; do not automatically apply the same allowance twice.
The taps
Terminal layouts vary. Use only the outputs and connections shown in the instructions for your transformer. Our current 2-zone range has 12 V / 14 V AC outputs; a kit that requires its own 12 V DC supply is a different system. A higher tap must stay within the permitted input range of every connected fixture. Check connections and cable voltage drop first; the wire guide explains the factors.
Photocell and timer
A photocell responds to ambient light. The selected control mode determines when the lights turn off: this may be after a number of hours, at a clock time, or at dawn. Available modes and settings depend on the model; check its instructions.
Our current 2-zone transformer allows the zones to be controlled independently. Group fixtures by the schedule and output they need, then check the load limit for each zone. Confirm whether the selected timer mode uses elapsed hours or a fixed clock time before choosing a setting.
Where it hangs
- On a wall or post beside the outdoor GFCI outlet, off the ground at the height its instructions give.
- Cord straight into the outlet. No extension cord, ever, outdoors.
- Cover closed, and out of the path of a sprinkler head.
- As close to the first light as the outlet allows. The feed from the transformer to the first light carries the whole load; every foot of it costs a little.
When one is not enough
Three cases, and they are planning questions rather than wiring ones.
- Two schedules. Part of the yard should run later than the rest. A two-zone transformer, or two transformers.
- Two sides of the house. A front yard and a back yard, each with an outlet. Two short runs are simpler and brighter than one long one round the house.
- The far end is dim and the feed is already thick. The run is longer than one transformer wants to push. A second transformer near the far end, on its own outlet, is the clean fix.
Two mistakes
- Sizing to today's count. Twelve lights, 36 W, a small transformer that is full on day one. The two lights by the shed next spring mean a new transformer, the cover off, every lead re-landed and the timer re-set. Take the size up now.
- Sizing by the kit's number. A kit's transformer is matched to the kit. The moment you add a spotlight for the maple, it is the table above that counts, not the box.
Questions people ask
What size transformer do I need for landscape lighting?
Add the fixtures' specified input load, using watts or VA as required by the manual. The referenced HIBOITEC dual-zone models use an 80% lamp-load allowance: 44 W ÷ 0.8 = 55 W as an example rated-capacity target. On a 200 W unit, 44 W connected leaves 116 W within the recommended 160 W allowance, while 40 W stays as headroom. Check total and per-zone limits and voltage drop; do not count the same allowance twice.
Can I run two transformers on one yard?
Yes, and there are two good reasons to. One is schedule: if the path lights should run until midnight and the tree lights until ten, that is two timers, which means a two-zone transformer or two transformers. The other is layout: a front yard and a back yard with an outlet on each side are simpler as two short runs than as one long one round the house.
What happens if you overload a low voltage transformer?
Exceeding the manufacturer's load rating can trigger protection or cause overheating and damage. Disconnect power and correct the load or wiring fault before resetting protection according to the instructions. An 80% lamp-load allowance is not a universal trip threshold, and being below it does not rule out voltage drop or a wiring fault.
Does a landscape transformer need a GFCI outlet?
Use the power source and GFCI protection required by the transformer instructions and local requirements. Do not assume an existing outdoor outlet is correctly protected. If a GFCI repeatedly trips, stop resetting it and have the fault investigated; a new or modified household-voltage outlet is work for a qualified electrician.
Next
Transformers — 200, 300, 400, 500 and 600 W, with independent zone control
Next: how to install low voltage landscape lighting
