Managing Electrical Overstress (EOS)


Back in the halogen and incandescent days of landscape lighting, it was a common practice by
many contractors to install lamps while the system was on — especially if a contractor was out
providing maintenance on a lighting system. This action is known as a hot plug-in.

In this era of LED light sources, hot plugging should be avoided. Why? It’s virtually impossible to
be 100% sure there will not be even a slight electrical arc when a lamp is inserted into a socket,
or when a connection is made with live cable. A hot plug-in can cause an electrical overstress
(EOS) on the internal circuitry of an LED lamp or integrated fixture.

EOS happens when an electrical component is operated beyond its maximum rated electrical
limit (according to its rating on the specification sheet) accidently or deliberately. In landscape
lighting, EOS can occur with a hot plug-in, a lighting strike, or a poorly made connection.

Some common signs of EOS:

·         One or more diodes out.

o    In this case, the bonding wires inside the LED device have broken.

·         Burnt smell emitted from the lamp.

·         Back of the lamp may show a burn hole, especially with lightning.

EOS can have an adverse effect on a fixture that requires a remote low voltage driver. If a driver
is connected live when attached to its fixture, an EOS failure can occur.

The question: How do we change the hot plug-in install? One idea —when performing
maintenance on an older system, unplug the transformer before installing the LED lamp or
integrated fixture to ensure the power is off to the socket. Use the same method on new

installations with a standard landscape lighting transformer. If you happen to be working with a
smart app-driven transformer, make sure the remote control has the system off. Most smartphone

apps allow for simple on and off for the transformer.

To avoid EOS, make sure you have solid potted cable connections and no power to the fixtures
upon installation. If lightning has caused EOS, see if the homeowner’s insurance policy covers
lightning damage.