CT Configuration Options

CT Configuration Overview

For most installations, CTs must be installed. Care must be taken to install them correctly and to place them in the proper location in order for various functions of the ReliaHome Smart Panel to work correctly. 

Warning: CTs are often installed on service conductors or feeders with exposed live parts. Contact with live uninsulated parts can result in serious injury or death. If at all possible, de-energize equipment before placing CTs. If de-energizing is not possible, use extreme caution and only proceed if you understand the risks involved and how to minimize them.

Caution: CTs can become saturated and permanently damaged if they are clamped around the primary source wires while being disconnected from the ReliaHome Smart Panel. Always connect the CT leads before clamping the CTs on the conductors being measured, and always unclamp the CTs before disconnecting the CT wiring leads.

A ReliaHome Smart Panel ships standard with one pair of 200-amp CTs. Proper CT placement depends on the intended purpose of the ReliaHome Smart Panel and the site's electrical configuration. Select one of the two use cases below to view recommended CT configurations.

Panel Guard (Avoiding Service or Electrical Panel Upsizing)

Service or Main Panel Upsize Avoidance

When using the ReliaHome Smart Panel to avoid upsizing the service entrance conductors, main breaker, or main service panel, Main CTs should be placed on the service conductors so that they will capture all power being received from the electrical utility. 

CT config for service upsize avoidance

Subpanel or Feeder Upsize Avoidance

If the ReliaHome Smart Panel is being used only to avoid upsizing a portion of the electrical system such as a subpanel or a feeder to a subpanel, the main CTs should be placed on the feeders for that subpanel. This will ensure that the subpanel will not draw more than the current limit set in the ReliaHome mobile app. The app will not display information about the main electrical panel's consumption and the data in the app will not represent the total amount of power being consumed by the utility. 

CT config for subpanel or feeder upsize avoidance

Service Upsize Avoidance with Backfed Solar PV

When net-metered PV (without storage) is present, it must be measured by auxiliary CTs as an additional power source. Auxiliary CTs are not included with the standard ReliaHome Smart Panel package but can be ordered from any ReliaHome Smart Panel distributor. In these cases, main CTs should be placed on the service conductors between the main load center and the utility meter, while the auxiliary CTs should be placed on the inverter output circuit between the inverter and the backfed PV breaker in the load center.

Note: If a battery energy storage system is present, configure CTs according to the Off-Grid Manager guidance in the next section of this article.

Main and aux CT config for service upsize avoidance when solar PV is present

Off-Grid Manager (Energy Management for Battery Energy Storage Systems)

A ReliaHome Smart Panel ships standard with one pair of 200-amp CTs. Most ReliaHome Smart Panel installations use these as the Main CTs and clamp them on the feeders between the Microgrid Interconnect Device (MID) and the load center.

Installers and contractors can contact their ABB distributor to purchase an additional pair of 200-amp CTs for enhanced monitoring. This second set can be connected to the ReliaHome Smart Panel Auxiliary (Aux) CT leads and used to measure the combined PV and battery output. In this Main + Aux CT configuration, the Main CTs should be moved to the feeders or service wires between the meter and the MID.

Currently no Rogowski coils are compatible with the ReliaHome Smart Panel.

The diagrams below illustrate the most common ReliaHome Smart Panel CT configurations. Systems incorporating certain inverter or battery solutions may require slightly different CT placement; see the bottom of this article. If applicable, also consult the article titled Wiring for Multi-LSP Locations.

Note that for simplicity, the following diagrams do not show placement of the Grid Detection Circuit (GDC). The GDC is an essential element of a ReliaHome Smart Panel installation. Please refer to documentation in the installation manual and GDC installation article for placement requirements.

Note: Ensure that CTs are clamped on the correct feeders, respecting ReliaHome convention for identifying A/B phase. Refer to the ReliaHome Installation Manual, steps 9-18 for more information.

Manufacturer-Specific CT Configurations

• Enphase IQ-Series Storage System
  
• Sol-Ark
• Sonnen
• Tesla Powerwall

Enphase IQ-Series Storage System

Note: When utilizing the Main + Aux CT Configuration, ReliaHome CTs should be installed in the IQ System Controller, ensuring the following:

1. Main CTs are on the feeders from the main or service. The side of the CTs reading This side toward grid should face the utility meter.
   • Main CTs should read positive wattage when solar and battery are disconnected. If this reading is negative, swap each CT to the opposite leg's feeder.
2. Aux CTs should clamp around both the PV inverter output circuit and the battery circuit. Extra wire length may be required to accommodate CTs on these circuits inside the IQ controller. Alternatively, the CTs can be clamped on these wires in a nearby pass-through box installed for the purpose. Ensure that both wires in each CT are of the correct phase/leg and that the side of the CT reading This side toward grid faces the utility meter (away from the PV and battery).
   • Aux CTs should read negative wattage when power is flowing out of the PV or battery. Unless grid charging of the battery is enabled, these CTs should not display significant positive wattage (it is normal to notice some standby power consumption by the Enphase equipment at night). ReliaHome aux CTs in this configuration read the net power supplied by the PV and battery together. Note that if all PV output is charging the battery (not supplying other loads in the home or back feeding the grid), the aux CTs will read 0 watts as the outflow of the PV and the inflow of the battery charging will cancel each other out.
   • If using aux CTs in this configuration, use the device list in the ReliaHome app to edit the aux CT circuit so that it is descriptively named. Change the category to Solar and Storage.

Sol-Ark

Standard Sol-Ark Partial-Home Backup CT Configuration Using Only Lumin Main CTs

As is true for other Main-CT-only Lumin configurations, this arrangement only measures consumption on the protected loads panel. It does not measure total home consumption or solar export to the grid. 

Notes:

• All CTs should be phased with respect to Lumin phasing convention (steps 9-18 in the installation manuals).
• In this configuration CTs should be oriented so that the This side towards grid sticker is facing toward the Sol-Ark inverter.

Sol-Ark Enhanced Data CT Configuration (Requires Two Sets of Lumin CTs)

This configuration provides detailed power flow information about:

• Grid import
• Grid export
• Total home grid consumption
• Net export of PV power
• Net consumption of PV and battery power

Aux CTs are placed around both the grid and load lines of the Sol-Ark inverter. When the protected loads panel consumes grid power, the Aux CTs register no wattage as the power flows in both directions through those CTs, with a net reading of 0 watts. When solar or battery power is consumed by either the main or protected loads panels or exported to the grid, power will only flow through one direction on the Aux CTs, causing a non-zero Aux CT wattage reading. This configuration requires a second set of Lumin CTs (available for purchase from Lumin).

Notes:

• All CTs should be phased with respect to Lumin phasing convention (steps 9-18 in the installation manual).
• All CTs should be oriented so that the This side towards grid sticker faces away from the Sol-Ark inverter.

Sol-Ark Whole Home Backup (Commonly Seen on Sol-Ark 15k Systems)

This configuration provides detailed power flow information about:

• Grid import
• Grid export
• Total home grid consumption
• Net export of PV power
• Net consumption of PV and battery power

As the Sol-Ark 15k is capable of 200-A pass-through, both the grid-in and load-out lines will often be 2/0 AWG. It is not possible to fit two conductors of this size in a single Lumin CT. The recommended approach is to acquire two pairs of Aux CTs (in addition to the one pair of Main CTs that comes standard with a Lumin Smart Panel). Splice both A-phase Aux CTs to the Lumin Aux CT A wire lead and splice both B-phase Aux CTs to the Lumin Aux CT B wire lead. WAGO connectors are ideal for this purpose. After the CTs have been spliced together and connected to the Lumin Smart Panel, place one pair of CTs on the Sol-Ark grid line and the other on the Sol-Ark load line.

Notes:

• All CTs should be phased with respect to Lumin phasing convention (steps 9-18 in the installation manual).
• All CTs should be oriented so that the This side towards grid sticker faces away from the Sol-Ark inverter.

Sonnen

Systems integrating Sonnen batteries are unique in that they typically feature PV feeding into an electrical panel separately from the grid + battery feeder. This presents a monitoring challenge whereby it is essentially impossible to correctly measure all power flowing through the system with a single pair of CTs. Full measurement of the power flows in an energy storage system with Sonnen requires four pairs of Lumin CTs: one pair of Main CTs, and three pairs of Auxiliary CTs, all spliced together and feeding the "Aux CT" leads of the Lumin Smart Panel. The Aux CT pair placed between Sonnen and the protected loads panel should be oriented "backwards", with the stickers reading This side towards grid facing away from the utility meter.

Tesla Powerwall

Powerwall systems should have CTs configured in the standard Lumin configurations. If utilizing Aux CTs, please note that they can either be clamped around both the inverter and Powerwall conductors inside the Tesla Gateway. Alternatively, if using the optional internal panelboard in the Gateway as a PV and battery combiner, the Aux CTs may be placed around the U-shaped rigid conductors supplied with the panelboard, as these carry the combined current of PV and Powerwall. 

Note: Tesla CTs and Lumin CTs are inter-compatible, so unused Tesla CTs can be repurposed as Lumin Aux CTs, if desired.

Note that the Lumin GDC can be landed on the non-backed-up terminals in the Gateway. Ensure that proper overcurrent protection is used to protect the GDC.

TABLE OF CONTENTS

• CT Configuration Overview
  • Service or Main Panel Upsize Avoidance
  • Subpanel or Feeder Upsize Avoidance
  • Service Upsize Avoidance with Backfed Solar PV
• Off-Grid Manager (Energy Management for Battery Energy Storage Systems)
• Enphase IQ-Series Storage System
• Sol-Ark
  • Standard Sol-Ark Partial-Home Backup CT Configuration Using Only Lumin Main CTs
  • Sol-Ark Enhanced Data CT Configuration (Requires Two Sets of Lumin CTs)
  • Sol-Ark Whole Home Backup (Commonly Seen on Sol-Ark 15k Systems)
• Sonnen
• Tesla Powerwall