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Discussion Starter · #1 ·
Why is this necessary in a residential development?







 

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Slave to the grind
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Probably too large of a service for a direct socket.
 

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Discussion Starter · #3 ·
CopperSlave said:
Probably too large of a service for a direct socket.
It's fed with 2 paralleled 3/0 AL SEU. That's 310A in the NEC. What would the service size be according to poco?
 

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This is POCOs?

Amperage is more than what a plug in socket can do. Some pocos do CTs when the service is over 200 amps or 400 for 3 phase.
 

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It's fed with 2 paralleled 3/0 AL SEU. That's 310A in the NEC. What would the service size be according to poco?
310 to 400 amps. Maybe 450 at the most. Actual service might be 4000 amps. POCO spec conductor based on the actual load to be served. They know most NEC calculated services don't go to 80% of the rating. Some resi 200 amp services don't go above 40 amps. Hence why #8 AL might be feeing it.
 

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Discussion Starter · #9 ·
Does pulling the meter kill the load side of the service?
 

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Discussion Starter · #13 ·
Thanks for the info guys. So what does CT stand for?




Does the left side of this nameplate on the trans inside the cabinet have any thing to do with the intended amperage of the service? 200-200 to 5A.
 

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Data Tech/Apprentice.
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Thanks for the info guys. So what does CT stand for?

Does the left side of this nameplate on the trans inside the cabinet have any thing to do with the intended amperage of the service? 200-200 to 5A.
Current transformer?
 

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NJ-IEC
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CT stands for current transformer. The meter measures kilowatts because of the size of the conductors.
 

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Bilge Rat
motors and controls.........
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A current transformer is a type of transformer that changes the amount of current in its secondary in proportion to the the amount of current flowing in its primary.

It has nothing to do with voltage, only current.

There is always a ratio on the nameplate. The first number is the primary current, the second is usually 5. In the OPs example, the ratio is 200:5. This means that if 200 amps are in the primary, there will be 5 amps in the secondary. If the primary current is 100 amps, the secondary will be 2.5 amps.

These are used mainly because metering and protection equipment cannot easily be built to handle large amounts of current. Also, if the voltage in the primary conductors is high, a CT will isolate the metering/protection equipment from the high voltage.

CTs are more common than you think, they are found in large motor starters (the heaters for a 400 amp motor may be rated at 5 amps if the CTs are 400:5), overload protection of large transformers, differential protection of transformers and feeders, and many more uses.

Every GFI has a CT. This is the most basic form of differential protection. The primary of the CT contains both the hot and neutral conductors. If the current is the same in both conductors, the CT doesn't see any current. (This is why a clamp-on amp meter needs to be around only one conductor). If there is a difference in current, the CT will see it and cause the GFI to trip.

One important item to note; never have current flowing in the primary of a CT while the secondary is open. VERY high voltage will appear at the secondary if this is done. If there is nothing to connect the secondary to, simply short it out. The CT is perfectly happy with a shorted secondary.
 

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Thumper
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I wish this thread had a better name as this is actually a very interesting topic.

On line drawing practice problems we have often worked with constant current sources which will source nearly infinite voltage to continue providing a set current.

These CT's appear to be the closest non-digital real life approximations.
 

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Bilge Rat
motors and controls.........
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I wish this thread had a better name as this is actually a very interesting topic.

On line drawing practice problems we have often worked with constant current sources which will source nearly infinite voltage to continue providing a set current.

These CT's appear to be the closest non-digital real life approximations.
CTs are kinda the same way, they will push current regardless of voltage, but only up to the point of core saturation. This is where the voltage is high enough that the iron core cannot hold any more magnetism, so it sort of chops off the top of the sine wave and results in a lower output on the secondary.
 

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Bilge Rat
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There could be others, but the only ones I've seen have iron cores.

Sometimes the cores are split so they can be mounted to existing busses or conductors, the majority though are solid.
 
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