How many channels and CT sensors do I need?
NOTE: This section applies to 120V/240V residential services only! These rules DO NOT apply to 3-phase electrical systems or those powered by two legs of a 3-phase source.
A single 32-channel GEM may be sufficient to monitor a panel with 40 or more breaker slots. A typical residential panel will have single-pole 120V and double-pole 240V breakers. The picture below shows the difference between each.
The GEM has 32 channels. Although your electrical panel may have more than 32 breakers, the GEM probably will have the capacity to monitor all loads.
One channel is required for each of the following:
- the main panel feed
- each single-pole breaker
- each double pole breaker
- each pole of a “split duplex” receptacle
- Two large CTs are required for the main panel feed
- One CT is required for each single pole breaker
- One CT for 240V “balanced” loads
- Two CTs for 240V “unbalanced” loads
|Unbalanced 240V Loads||Balanced Loads|
|Electric Range / oven||Electric Baseboard Heating|
|Clothes Dryer||Central A/C Units|
|Hot Tub or Spa||Water Heater|
|Workshop Outlets||240V Water Pump|
|Split duplex receptacle*||Sauna Heater|
|240V Solar Grid Tied Inverter Generated Feed|
A split duplex receptacle has a separate breaker circuit for each half of a standard receptacle. This is typical for kitchen counter outlets as it allows two heavy loads to be plugged without exceeding the current of a single breaker.
See diagram on the right.
Each breaker has a maximum amperage which will cause it to trip. This value is typically located on the breaker toggle such as “15”, “30”, “40”, and so on. A “30 amp” breaker is shown on the right.
The CT used to sense the current of a given breaker must have a value the same or greater than the breaker amperage. The CT amperage is the number at the end of the model number. For example, a SPLIT-60 CT can be installed on a 15A, 20A, 30A, 40A, 50A or 60A breaker.
There are certain exceptions to this rule if your electrical service uses aluminum wiring. This is only likely if your home was built in the 1970’s where aluminum wire was used for new construction due to a copper shortage. The conductor diameter for aluminum wire is larger diameter than that for copper based on a given amperage. Because of this, a Micro-40 CT is limited to 30A aluminum wiring and the Split-30 is limited to 20A aluminum wire, simply due to physical size restrictions.
Not enough channels?
In the case where a 32 channel GEM doesn’t provide enough channels for monitoring your entire panel you have two options:
- purchase a second GEM
- double up two 120V circuits on a single channel (if you are only short a few channels)
You may find that some branch circuits are rarely or barely used. Such circuits may be “outside outlets”, “storage room”, etc. You can benefit by using a single channel for two of such branch circuits. Although both circuits each require a CT, they may be connected to a single channel. Be aware that the energy used for both circuits will be summed together on that single channel. You may also couple two similar type breaker loads together on a single channel such as “kitchen lights” and “dining room lights”.