PQube User Manual 2.1
Page 30 of 113
Setting up Your Optional Current Module
Setting Current Transformer Ratio
If you are using a CT4 current sensing module, you don’t need to set a CT ratio – your PQube will
set it automatically.
If you are using an XCT4 current sensing module, you will need to set the CT ratio so that your
PQube can correctly display the amount of current, as well as correctly calculate power and energy
usage.
For example, to use your PQube on a system with 200 amps flowing in the power conductors, you
might choose current transformers rated at 300 amps, with a 5-amp secondary. In your PQube’s
Setup.ini file, you would set
Current_Transformer_Ratio=300:5
If you have a current transformer with voltage output, simply enter the primary current and
secondary voltage into your CT ratio. For example, if you have a current transformer rated at 300
amps, with 0.333V secondary, then you would set
Current_Transformer_Ratio=300:0.333
Inverting Current Channels
During installation, it is easy to make a mistake in your current transformer connections, either by
reversing the secondary connections (when using an XCT4) or by feeding the main power
conductor through your current transformer backwards (when using a CT4 or XCT4).
You will know when the current transformers are installed backwards by looking at your power
(watts) readings. If you are expecting positive watts values and you are getting negative watts (or
vice versa), then you know your current transformers need to be inverted.
Of course, you can always correct your wiring; but an easier alternative is to use your PQube’s
Setup.ini file to invert one or more of your current channels. If you realize that you have installed
your L2 current transformer backwards, you can fix this easily:
Invert_L1_Current_Channel=OFF
Invert_L2_Current_Channel=ON
Invert_L3_Current_Channel=OFF
Invert_N_Current_Channel=OFF
Why Bother?
It is important to correctly connect your CTs (or use the method above to correct a wiring
error). Power (watt) calculations are made by multiplying the instantaneous current by the
instantaneous voltage. If one or more of your current transformers is incorrectly set up,
your PQube will calculate negative power for that phase.
Calculating Current With a Missing CT
You do not need to connect CTs to all of the conductors that you want to monitor. When current
flows through a system, the net current is always zero. Because of this, you can connect one fewer
CT than you have conductors (for a delta system, you only need two CTs, for a wye/star system you
only need 3 CTs, and you must calculate the Neutral current). Your PQube can calculate the
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