Grounding issues on secondary lighting circuits

Thread Starter


Joined Feb 14, 2006
As you probably know, a low voltage lighting transformer converts 120V to 12V (on the secondary side). A faraday shield isolates the 12V side from the 120V side. Secondary lighting cables are split with one leg attached to a common tap while the other leg is attached to a voltage tap.

My questions are about grounding:

1. Is the 12V common tap connected to the same ground as the 120-volt receptacle (a GFCI)?

2. If one contact of the lighting fixture socket is grounded to the mounting surface (such as a metal gutter) that is also grounded (through a grounding wire), is it important that the common leg of the fixture wire be the leg that contacts the gutter?

The reason I ask is because an electrician attached a fixture to such a gutter and he read 12V across the gutter and it tripped the GFCI. When he reversed the fixture leads, it solved the problem.



Joined May 16, 2005
The answer to both 1 and 2 is "yes."

Sometimes, it is difficult to tell which wire is which simply by looking.

Also, "fixtures" are the wet & drippy things the plumbers install. We electricians put in "luminaires.";)