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BFM136 Application Note

1. INTRODUCTION

One of the main issues that arise when addressing sub-metering projects is the retrofit issue. Many existing commercial buildings are interested in applying sub-metering solutions. At the same time, penetrating this market segment requires multi-channel capability to facilitate multi-tenant commercial sub-metering as well as retrofit wiring configurations support. This Application Note provides general hints about using the 3-phase multi-channel branch feeder monitor (BFM 136) for US commercial applications.

2. WIRING CONFIGURATIONS

2.1 Single-Phase Two-Wire  

 Fig. 1. Single-Phase Two-Wire Distribution Circuit
Fig. 1. Single-Phase Two-Wire Distribution Circuit

 The single-phase two-wire configuration is supported by the BFM136 feeder monitor. The device can provide sub-metering for up to 36 single-phase tenants. Unused voltage inputs should be shorted to the neutral (VN) input to avoid erroneous phase-to-phase and phase-to-neutral voltage readings.

2.2 Two-Phase Three-Wire

Fig. 2 Two-Phase Three-Wire Distribution Circuit
Fig. 2 Two-Phase Three-Wire Distribution Circuit

The two-phase three-wire configuration (see Fig. 2) is supported by the BFM136 feeder monitor. The device can provide sub-metering for up to 18 two-phase tenants. Unused voltage input should be shorted to the neutral (VN) input to avoid erroneous phase-to-phase and phase-to-neutral voltage readings.

 

 

2.3 Three-Phase Three-Wire Delta

Fig. 3. Three-Phase Three-Wire Delta (No Neutral) Distribution Circuit
Fig. 3. Three-Phase Three-Wire Delta (No Neutral) Distribution Circuit

The three-phase three-wire Delta (no neutral) configuration is supported by the BFM136 feeder monitor. The maximal phase-to-phase voltage allowed for the BFM136 device is 480V (tested by SATEC Ltd). The device can provide sub-metering for up to 12 three-phase tenants, for three-phase applications only. The phase to neutral voltage readings for this wiring configuration has no physical meaning and should be disregarded. Certainly, these readings do not affect energy metering.


2.4 Three-Phase Four-Wire Delta ("Red Leg" Delta)

Fig. 4. Three-Phase Four-Wire Delta Distribution Circuit ("Red Leg" Delta)
Fig. 4. Three-Phase Four-Wire Delta Distribution Circuit ("Red Leg" Delta)

The three-phase four-wire Delta ("Red Leg" Delta) configuration is supported by the BFM136 feeder monitor. The neutral (VN) input must be connected to the ground of "Red Leg" Delta. The maximal phase-to-phase voltage allowed for the BFM136 device is 480V (tested by SATEC Ltd). The device can provide sub-metering for up to 12 three-phase tenants.
The BFM136 device supports sub-metering for any combination of 3-phase, 2-phase, and single-phase tenants providing that total amount of current inputs does not exceed 36 (see also "PAS channel assignment" chapter for proper field implementation).

3. Multi-channel sub-metering

3.1 Basic Principle

Fig. 5. Schematic circuit demonstrating basic principle of multi-channel sub-metering by BFM136 branch feeder monitor

Fig. 5. Schematic circuit demonstrating basic principle of multi-channel sub-metering by BFM136 branch feeder monitor

Figure 5 shows schematic drawing (example) of multi-channel BFM136 connection. Figure 5 demonstrates basic principle of multi-channel (multi-tenant) sub-metering by use of the BFM136. Voltage inputs are common for all channels. Same voltages must be supplied to all tenants. Otherwise sub-metering is not supported by the BFM136. The current inputs of BFM136 are fed from external CTs according to a number of phases provided to a specific tenant (1, 2, or 3 CTs per channel). Up to 36 current channels can be monitored by the BFM136. As a result, up to 36 one-phase tenants, up to 18 two-phase tenants, up to 12 three-phase tenants, or any combination of those.

3.2 PAS channel assignment

Fig. 6 Channel assignments for multi-tenant sub-metering by use of PAS SW

Fig. 6 Channel assignments for multi-tenant sub-metering by use of PAS SW

Fig. 6 depicts channel assignment settings to be performed by the PAS software. One can clearly see that Tenant #1 is two-phase (I1 and I2 current inputs are assigned to the tenant), Tenant #2 is one-phase (I3 current input is assigned to the tenant), Tenant #3 is also one-phase (I4 is assigned to the tenant), etc.1 The channel assignment menu is approached by entering to Meter Setup / General Setup / Channel Assignments.

1. Important Note: For proper energy sub-metering all tenants must use the same line voltage since a single voltage input for all channels is implemented in the BFM device.
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