900-00272-01-001 Rev A
21
External CTs
External current transducers (CTs or XCTs) are used with the SkyBox to monitor a combined input from the
utility. When installed and programmed into SkyBox, this moves where the SkyBox senses the utility. Good
news for you! This means you can support your normal, unprotected loads and still not export power to the
utility. Also, if the main panel is not right next to the SkyBox, you can extend the total length of the CT leads
up to 10 meters.
An installation document, the SkyBox XCT Install Guide (
), is available with more details.
How does the SkyBox know what loads are protected and what loads are not? Let’s look at an example.
Figure 15 Standard SkyBox Block Diagram
In Figure 15, the SkyBox senses power coming from and going to the grid at location
A
. In this figure, it is the
physical connection which we’ll call the grid port. This is the connection to the main service panel, located
inside the wiring compartment of the SkyBox. When configured for the
Non-export
profile, the SkyBox
changes its power usage so that no power goes out from the inverter to the utility through the grid port.
When in the
Self-consumption
profile, the SkyBox minimizes power coming
in
through
A
but
does not
limit
any power going
out
.
With external CTs installed, the sensing location
A
moves. Now the grid port is irrelevant and the SkyBox
manipulates power at the CT location. See Figure 16.
A
9
