# New to C.T. for residential



## Hexamexapex (Jun 9, 2012)

Can someone explain in brief the need for a current transformer on residential service? I understand for any service over 400amps a CT is needed, but haven't quite wrapped my head around the need for it. Thanks for any and all help. 

M

Marcus


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## socalelect (Nov 14, 2011)

Hexamexapex said:


> Can someone explain in brief the need for a current transformer on residential service? I understand for any service over 400amps a CT is needed, but haven't quite wrapped my head around the need for it. Thanks for any and all help.
> 
> M
> 
> Marcus


The ct is for metering purposes , you can only put so much thru a meter , the ct creates a induced current that the meter reads


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## Hexamexapex (Jun 9, 2012)

Ah....never thought about the meters capabilities. Makes perfect sense. Thanks again!


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## aftershockews (Dec 22, 2012)

Hexamexapex said:


> Ah....never thought about the meters capabilities. Makes perfect sense. Thanks again!


Our POCO made us use CT's on a resi 400 amp service one with a demand lower than 300 amps. We ate 800$ on that one and the POCO said oops.


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## Hexamexapex (Jun 9, 2012)

POCO official not understand the code? So the service wires supply the panel with induced current from the CT?


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## socalelect (Nov 14, 2011)

Hexamexapex said:


> POCO official not understand the code? So the service wires supply the panel with induced current from the CT?


Rephrase the questions plz


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## Hexamexapex (Jun 9, 2012)

I was told that the service lateral conductors connect to the CT and the service entrance conductors aren't actually connected to the CT but are run near in the casing, enough that they induce adequate current for panelboards. I thought there was something strange about this for some reason. I am trying to picture what the installation would look like. I have never seen one.


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## socalelect (Nov 14, 2011)

Hexamexapex said:


> I was told that the service lateral conductors connect to the CT and the service entrance conductors aren't actually connected to the CT but are run near in the casing, enough that they induce adequate current for panelboards. I thought there was something strange about this for some reason. I am trying to picture what the installation would look like. I have never seen one.


Picture a donut , the service conductors run thru the center of the donut , the donut has a couple wires that come off it a run to the meter 
So basically your service conductors comes into your ct cabinet runs thru the donuts and then out of your ct cab to your disconnect , then the small wires that come off of the cts run to you meter base


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## Hippie (May 12, 2011)

Hexamexapex said:


> I was told that the service lateral conductors connect to the CT and the service entrance conductors aren't actually connected to the CT but are run near in the casing, enough that they induce adequate current for panelboards. I thought there was something strange about this for some reason. I am trying to picture what the installation would look like. I have never seen one.


The power for the panel is not induced from the CT. Service conductors are connected directly to the load and the current flowing through them creates an induced current from the CT which is measured by the meter


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## socalelect (Nov 14, 2011)

Hippie said:


> The power for the panel is not induced from the CT. Service conductors are connected directly to the load and the current creates an induced current from the CT which is measured by the meter


Much better explanation than mine :thumbsup:


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## Hexamexapex (Jun 9, 2012)

Hippie said:


> The power for the panel is not induced from the CT. Service conductors are connected directly to the load and the current flowing through them creates an induced current from the CT which is measured by the meter


And this induced current is carried to the meter by smaller gauge wires from CT?


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## Hippie (May 12, 2011)

Hexamexapex said:


> And this induced current is carried to the meter by smaller gauge wires from CT?


Exactly


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## KDC (Oct 19, 2012)

Yep. The poco here uses CT metering for anything greater than 200 amps. Really depends on the maximum rating of whatever meters they use are. 

Once you go to a CT meter, you just need to pick CTs with the right ratio and you can meter any service. I think the biggest I've been a part of wiring were 1200:1, normally they're in the range of 40 to 80.


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