Landscape Lighting Transformer

[infinity]

I was looking at a 600 Watt landscape lighting transformer and although it's called a 600 W transformer the spec's say that it can only be loaded to 70% or 420 Watts. Besides being required to follow the manufacturers instructions is there any code reason why a transformer would not be permitted to be used at its full capacity?

600 Watt Low Voltage Transformer for low voltage outdoor lighting, landscape lighting, lawn lighting, and garden lighting.

Maximum Load: 70%

• Multi-Tap Output Voltage for Longer Wire Run - Input: 120V AC / Output: 12V-13V-14V-15V AC
• Dual Protection - Primary: Auto Reset Thermal Circuit Breaker / Secondary: (2) 25A Magnetic Circuit Breaker
• Heavy Duty Stainless Steel
• Timer (Not Included) & Photocell (Not Included) Port Available - Allow to add a timer & photocell anytime.
• Power Cord: 70” black 18 AWG SJTW cord and plug set
• High-Performance Toroidal Core - Quiet Operation, Great Reliability, and High Efficiency.
• Suitable for Indoor and Outdoor use.
• Product Dimension - Length: 7.2 inch / Width: 6.8 inch / Height: 14.6 inch
• ETL Listed

 

[retirede]

Most of these lighting transformers with secondary taps are only capable of full power at the max voltage tap. The secondary winding limit is based on the current, thus max power varies by voltage.

I don’t know if that’s the case here, but thought it worth mentioning. Maybe they were too lazy to list power at each voltage?

 

[synchro]

Perhaps the toroidal transformer itself is rated for 600W, but the thermal circuit breaker is only guaranteed not to trip when the load is 70% or less of the transformer's rating. That could be due to the tolerance range of the breaker and to cover its operation over temperature, etc. Also, maybe they want some extra margin for nonlinear loads such as LEDs but they didn't want to complicate it with more specific and detailed requirements.
Or maybe the 600W is just a marketing ploy. But no, I don't know another code reason than what you mentioned.

 

[infinity]

I'm guessing that the inflated rating is because this is from a cheaper Chinese transformer sold on Amazon. I've seen another Chinese brand transformer with the same 70% limit which to me is false advertising. The much more expensive transformers like those from Kitchler do not have a limit below the watt rating of the transformer. I've even read somewhere that there is a code limit of 80% loading.