Overview

The eGauge ESH044 Sensor Hub is capable of connecting up to four powered sensors or CTid DC CTs. These can be connected to the eGauge sensor ports using the provided RJ-45 breakout cable. For installations requiring the sensor hub to be placed in a separate location from the eGauge, the breakout cable can be joined with a CAT5 cable wired to the T-538B standard, offering increased flexibility in sensor location.

This flexibility can facilitate quite complex setups with many sensors in physically separate locations measured by a single meter. However, there are some rules that should be followed to ensure a successful installation when multiple Sensor Hubs will be used in distinct locations. It is particularly important to power the Sensor Hubs correctly to avoid encountering electrical conditions which may adversely affect sensor readings.

This article will offer several installation recommendations to consider when multiple sensor hubs are needed in physically separate locations. These recommendations are intended to avoid exceeding the common-mode limits of the EG4xxx meter.

Single 5V Power Supply

The preferred solution when multiple Sensor Hubs must be used in physically distinct locations, is to power all of the Sensor hubs from the same 5V source ensuring that no common-mode issues are encountered. This requires wiring the +5V and GND wires of the power supply to each location.

If a CAT5 run already exists between the power supply and the sensor hub and not all twisted pairs are in use, a spare pair can be used to provide voltage to the sensor hub as shown below:

The 5V power supply used must have sufficient capacity to power all attached sensors.  Similarly, the wires used for power need to be rated for the maximum current they are expected to carry.  For example, AWG 24 copper wire as found in a CAT5 cable is rated for up to about 500mA.

Options using Multiple 5V Power Supplies

In some installations, using multiple 5V power supplies may be unavoidable.  If this is the case, the following guidelines should be considered:

Common Negative pole - When multiple power supplies must be used, the most reliable way to ensure that no common-mode issues are encountered is to electrically tie together the negative pole of all 5V power supplies.  Using a shielded CAT5 cable to connect a sensor hub to the eGauge, the shield can be used for this purpose as shown below: 

Grounded Negative Pole - If it's not possible to have a dedicated Negative pole wire connecting all of the power supplies, the next best option is to connect the negative poles of the power supplies to Earth Ground. This should work correctly provided the site at which the power supplies are installed has good, low-impedance ground wiring and the wires are not loaded with significant currents that could cause noise or potential differences.  However, since this essentially ties together the measurement wiring with power wiring, we do not generally recommend employing this solution except when there are no other alternatives. 

Linear Power Supplies - If none of the solutions above are possible, using linear power supplies to power the sensor hubs may be a good option. One model that is generally available and has been tested successfully for this purpose is the Jameco DDU050100RM2270 5V/1A linear power supply.