Overview
The eGauge AC voltage inputs can handle up to 277Vrms between any line input (L1, L2, L3) and neutral terminal. If voltages exceed this range, potential transformers may be used to step-down the voltage from the system to the eGauge voltage input terminals.
When using a potential transformer, the eGauge must be configured appropriately to allow for accurate power calculations. Generic options such as 277:120 and 480:120 are available, as well as specific supported transformer models, such as FDT-480-120.
A set of negated transformer values are also available. Choosing this negates the polarity of the voltage. This has the effect of negating all power calculations using this transformer setting.
- This type of installation is categorized under Legacy Support. The guidance in this article is intended to be used for legacy installations that utilized step-down transformers. For new installations it's recommended to use the EV1000 high voltage sensor according to the appropriate installation example.
Prerequisites
eGauge Systems cannot guarantee meter accuracy when third party potential transformers are used. It is recommended to use the EV1000 high voltage sensor when measuring a high voltage system (480V no-neutral, 347V no-neutral or 600V system), or on a different side of a transformer from where the eGauge is connected.
Instructions
Step 1: Access the Installation Settings from the Main Menu by navigating to: Setup → Other Settings, then click Installation to the left.
Step 2: Choose the appropriate PT ratio and click save at the bottom of the page to save your changes. Reboot the eGauge if requested to do so.
Step 3: Access the Channel Checker from the Installation Settings page by clicking on the Tools link at the top right, then Channel Checker at the left. Verify that the line voltage is accurate. The voltage should be equal to the voltage found on the primary side of the installed potential transformers.
Custom PT Ratios (Advanced)
If a custom, unsupported step-down transformer ratio is used but not available in the drop-down menu, a custom scale factor will need to be used.
To calculate a custom potential transformer scale factor, use the following calculation:secondary / primary * model_pt_value = SCALE_FACTOR
Where:
| secondary | is the secondary voltage |
| primary | is the primary voltage |
| model_pt_value | is a model-specific value (see below) |
| SCALE_FACTOR | is the custom scale factor you should use on the eGauge2 and EG30xx |
The model_pt_value number will vary based on what model eGauge is in use, as described below (note values are negated):
| EG4xxx (with LCD display) | -74.0140 |
| EG30xx (no LCD, w/ Ethernet) | -4.003 |
| eGauge2 (no Ethernet, no LCD) | -4.003 |
For example:
EG4xxx with a 277:240 transformer would have a custom scale of -64.128:
240 / 277 * -74.0140 = -64.128
Similarly, an eGauge2 or EG30xx with a 277:240 transformer would have a custom scale of -3.4683:
240 / 277 * -4.003 = -3.4683
Troubleshooting and Tips
-
Issue: After choosing my PT settings the voltage does not read as expected.
- Solution: Confirm that the chosen setting is appropriate for the potential transformer used. If using custom PT ratios, check your calculations.