PT Connection

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ianis

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The CT cabinet in the distribution centre doesnt have any lugs to make the connection from the 3 phases and neutral to the 3 PT's primary. Any idea whats the best and most economical way to make this connection.
 
What is PT? There should be no terminations for you to make in a CT can other than bonding. Your conductors should pass straight through POCO's CT's into your MDP.
 
PT=Potential Transformers for utility metering.

I assume this is a 480/277 VAC service?

In our area the utility makes these connection.

One utility meters at 480/277 the other makes taps of the service conductors, stripping back the insulation to grab three strands and use a small split bolt...Does not look very nice, but it is their deal.
 
brian john said:
PT=Potential Transformers for utility metering.
Click to expand...

Here Poco uses CT's with an assembly for metering that pierces the insulation of the conductor, no need to strip. And what do PT do?
 
yes the Current Transformers (CT) are installed where the POCO conductors run through the 3 CT's. The feed from the secondary at the CT are going into the meter cabinet. The issue is that in the CT cabinet at the bottom are the Potential Transformers (PT- I believe anything over 400V needs PT); and there are no lugs to connect the PT's to the POCO lines on the primary side.
 
oh ..the voltage is 347/600V from POCO and it connects in the Main wireway to the distribution centre. The bus bars (about 4" wide ) then go to the main disconect and then in the CT cabinet where they go through the CT's. The Potential Transformers are also in the CT cabinet. They will be connected phase to neutral with a ratio aof 3 to 1 bringing the voltage from 347 to 120. Because the CT's are closed core the bus bars have bolts in order to remove them and have them go through the CT. I was thinking that a fast and cheap way to do it is to connect lugs to each phase bar and then connect the PT that way. Is that going to bring any concerns?
 
ianis said:
I was thinking that a fast and cheap way to do it is to connect lugs to each phase bar and then connect the PT that way.
Click to expand...

Does the manufacturer have lugs listed for this application?
 
chris kennedy said:
What is PT? There should be no terminations for you to make in a CT can other than bonding. Your conductors should pass straight through POCO's CT's into your MDP.
Click to expand...
PT = Potential (or voltage) Transformer.

Remember, power is a measure of both voltage and current; all watt and watt-hour meters must have a way of sensing both. The voltage can either be directly fed into the meter, or stepped down through a transformer.

The typical 3-phase CT setup has three current circuits and three voltage circuits, all of which share a single neutral conductor. So, there are seven conductors (usually #10) in the 1-1/4" conduit we provide.

As long as the meter is calibrated to convert the representative current and voltage into actual full current and voltage readings, it will read out in actual power over time (watt-hours).

CT's are basically step-up voltage transformers, with the "primary" a single winding (the conductor or bar) and the secondary the number of turns it takes for the application; for example 400:5 is 80 "secondary" turns.

By effectively shorting the secondary with the ammeter portion of the watt meter, the high voltage is instead converted into amps. For every 80 service amps, one amp will flow in the meter circuit.

Without the low-impedance ammeter, or shorting bars for meter removal, the CT would indeed behave as a step-up transformer, and could reach thousands of volts open-circuit, damaging the insulation inside the CT.
 
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