The aim of the document is to provide examples to choose the right combination of Auditor and CTs or Rogowski-Coils (or R-coils for short) for your projects.
In order to work out which Auditor is right for the project, the first step is to select the right CTs or R-Coils. This is due to the fact that R-Coils only work with the Auditor 3RM and are NOT compatible with the Auditor 6 range.
Current transformers and Rogowski Coils can only capture alternating current (AC) and do not support direct current (DC) applications.
Only Low Voltage 120/208V and 230/415 V applications are supported.
How to choose the right combination
Three simple steps to determine the right combination of Auditor and sensors:
- The opening of the CTs or R-Coils has to be big enough to be properly clamped to the conductor.
- The rating of the CTs or R-Coils has to be at least equal to or greater than the rating of the breaker or the maximum current carrying capacity of the conductor.
- Pair the right sensor with the right Auditor
Available Current Transformers and Rogowski Coil
Example 1 - XLPE-CU Cable
Determine the right combination of CTs or R-Coils and the Auditor monitor the 16mm2 XLPE-CU cable.
Let’s populate the characteristics of 16mm2 XLPE-CU cable:
As the diameter of the cable is only 9.3mm, but as the cable is rated for 86A, the right CT to monitor the 16mm2 XLPE-CU cable is 120A CT.
Note that the Wattwatchers warranty is void if the CTs or R-Coils or Auditors are damaged due to excessive current above its rated capacity.
Example 2 - Commercial Site with Single Line Diagram (no cable sizes)
Determine the right combination of CTs or R-Coils and Auditor to monitor the Net Grid Consumption and the Solar Generation as indicated in the single-line diagram below.
Let’s use the logic outlined earlier to assess the situation.
As the size of the cables is not specified, we are relying on the rating of the breakers to determine the right combination of CTs or R-Coils and Auditors.
Starting from the left, the Utility Meter. As the breaker is rated at 630A, the correct approach is to upsize to 3000A R-Coil. This means that it requires Auditor 3RM.
Moving on to Solar PV, as the breaker is rated at 63A, we need to upsize to 120A CT. This means it requires Auditor 6. That being said, 60A CT can also be applicable if you are certain that the maximum load is equal to or below 60A.
Example 3 - Commercial Site with Single Line Diagram (with cable sizes)
In some circumstances, the size of the cable is already specified in the single-line diagram. If that’s the case, refer to the document in the link below for the CT sizes for the commonly used cable types and sizes.
CT sizing based on common cable sizes
Please refer to the simplified SLD below:
Using the information from CT sizing based on the common cable sizes document, we require 600A CT to monitor the Utility Meter paired with Auditor 6. Also, 120A CT to monitor the Solar PV paired with Auditor 6.
Example 4 - Private billing submetering for commercial tenants
Scope the following SLD to determine the right combination of Billing CTs or CET Meters and Auditor to charge the tenants for their electricity consumption as indicated with the red dots on the SLD below:
Starting from the top is L1 Shop 1. As the breaker is rated at 150A per phase, we require the CET PMC-340-BB CT-coupled meter with 600A Billing CTs to capture billing approved electricity consumption data paired with the Auditor 6M+One and 600A Auditor CTs.
A similar configuration can be applied to L1 Shop 2.
Moving on to the second floor, we have L2 Shop 1 with a single-phase breaker rated at 63A. Therefore, we need the CET PMC-220 direct connect meter paired with the Auditor 6M+One and 60A Auditor CTs.
Note that when assessing L2 Shop 2, although the breaker is rated at 40A, however, it is three-phase. Therefore, we need the CET PMC-340-BA direct connect meter paired with the Auditor 6M+One and 120A Auditor CTs.
Lastly, L2 Office with a breaker rated at 100A per phase, we need the CET PMC-340-BA direct connect meter paired with the Auditor 6M+One and 120A Auditor CTs.
I have assessed the situation and couldn’t find the right combination
If after doing the exercise above and it appears that there is no CTs or R-Coil that fit for the project, please contact us by clicking on the ‘Submit a request’ link above.