The sub panel could be a "tenant" panel, feed to a garage, or another large load such as a central air unit.

(enlarge)

In this example, the main panel energy would be represented by CH1 and the secondary load (sub-panel) would be CH2.

One important note to make. CH1 energy will include that of the sub panel. In order to represent the main panel consumption, not including the sub panel, subtracting CH2 from CH1 is required.

NOTE:

This method is not applicable for panels supplied by a three phase service.

(enlarge)

This method is applicable only for 120V/240V "split-phase" systems.

The "summing" procedure consists of putting the two currents in series.

Although the signals are AC, polarity is very important here. One polarity will give you the sum of both currents and the other will result in the difference.

Changing the phasing is done in one of two ways:

1. Reversing the leads of either (but not both) current transformers (CT).
2. Un-clamping either (but not both) CT and re-installing it in the opposite direction (180 degrees).

The proper phasing will result in the highest output.

This method can only be applied using the same type of CTs in series, although each channel may have differing types.

For example, in the example above, two SPLIT-200 CTs are used for the main panel on CH1 and two SPLIT-60 CTs for the sub-load on CH2.

One last note of caution has to do with the maximum amperage before overloading the channel. Since the two outputs are summed, the maximum signal into the channel is now doubled. This may be corrected in one of two ways:

1. Using CTs rated at twice the panel current. For example, using two SPLIT-200 (200A CTs) for a 100A panel.
2. Inserting a resistor voltage divider to reduce the output by half. This would require reducing the "CT Range" value by one.

Brultech plans on providing an "adaptor" type solution in the near future. This would house the resistors and provide a "phase reversal" switch, greatly simplifying this entire setup.

(enlarge picture)                    

This is mostly the case in light commercial and industrial environments, however there are instances where residential service panels may be supplied by a three phase source.

This situation can be determined by:

•  "120V/208V" panel marking. Notice the 208V value which is not twice the 120V value.
• The feed wires being "Blue & Black" or "Blue & Red".

If you're not sure, have a qualified person measure the "neutral to line voltage" (120V) and the "line to line" voltage.

For a split-phase service, the line to line voltage will be ("neutral to line voltage" x 2).

EX: 120V x 2 = 240V

For a three-phase service, the line to line voltage will be ("neutral to line voltage" x 1.73).

EX: 120V x 1.73 = 208V

Contact support@brultech.com for more information.