CT's and residential

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aftershock

aftershock

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Memphis, TN
Im doing a 400 amp service for an addition. The POCO issues our meter sockets and when doing an addition we have to turn in a load. Apparently if the load exceeds 48Kw then we have to use CT's. I have never installed a service in this manner.

Since my service wires will not go through a meter and I will be having 2-200 amp panels, can I just run a mast pipe from the top of each panel or will I have to parallel the service into a trough and splice from there into each 200 amp panel? Is there a code section in the NEC that addresses this?

Another question: Is there a wiring diagram I can obtain that shows the wiring from the CT can to the donuts?
 
If you are using CT metering you would have to enter a CT cabinet. As far as the meter wiring most poco's do this themselves, you just need to mount and pipe the socket.
 
aftershock said:
Since my service wires will not go through a meter and I will be having 2-200 amp panels, can I just run a mast pipe from the top of each panel or will I have to parallel the service into a trough and splice from there into each 200 amp panel? Is there a code section in the NEC that addresses this?
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I don't see how that would work. The CT's need to be around the service conductors before they split off. No NEC requirements addressing CT's at the service to my knowledge, POCO thing.

Another question: Is there a wiring diagram I can obtain that shows the wiring from the CT can to the donuts?
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POCO wires that.

Here is a picture of a CT can.(on the right)

DSCN0389.jpg
 
Definitely a "discuss with POCO" situation. I work with multiple POCOs and one has a POCO supplied CT cabinet, another requires a contractor built cabinet, still another installs their CTs at the source (pole or pad). All have diagrams as to their specifications.
 
I did some further investigation during lunch yesterday. The CT cabinet is what I want to go with. My boss feels we will need to mount the CT's on the mast. We will be getting with the POCO rep today. We got the CT's yesterday and they have 200 stenciled in each one and this will be a 400 amp service. I hope they gave me the right one.

The picture is what I have on the wall now. The socket is temporary and there will be another 200 amp panel.I would like to place the CT can where the meter is now.
 
Locally we use a class 320 socket and use double lugs to split off into two runs, to two 200 amp panels. You would use a CT can and mounting bracket for the CTs with double lugs, and then as above.
 
your poco should have supplied you with a green book where you can view the service configurations they require. some pocos are very specific about what heights they want certain ct's and meter sizes, and what they allow for grounding/bonding, etc. some pocos supply ct cabts, others don't. etc.
 
I was issued today a 24 x 24 CT can today. What I was thinking of doing was service wire come down the mast parallel (4-2/0 2-1/0), passthrough the CTs then split (without splice) to two seperate 200 amp panels. Section 310.4 on parallel conductors (5) Be terminated in the same manner makes me think I may need to terminate in a trough then splice to my 200 amp panels?
 
Most utility CT's I have seen are not the "doughnut" type. The wires connect to them with lugs. So you could size the "load" side lugs to fit your needs.
 
chris kennedy said:
Here is a picture of a CT can.(on the right)

DSCN0389.jpg
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Other than on the forums I have never seen a CT cabinet like that.

Ours look much more like the disconnect switch, the CTs bolt in kind of like the fuses and all the conductors land on lugs. That way the power company can replace the CTs without unconnecting the large conductors.

More like these ones

d_11788.jpg



HoffmanTransformerCabinets.jpg
 
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The setup I have is this:










And do my service wires need to go in one direction into these CT's? I looked all over these 2 and could not find a direction indicator.
 
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There will be a white or yellow dot on the CT's and this faces the incoming service. We sometimes hear the expression "Dot toward the pot".
 
When the CT cab is on the outside of the building and the MDP is 20' away on the inside its a real wrestling match to thread them and pull them inside.
 
this crude diagram shows how I would like to install and wire this. This assumes I do not have to terminate all conductors in a trough then splice from it to the service panels.
 
chris kennedy said:
When the CT cab is on the outside of the building and the MDP is 20' away on the inside its a real wrestling match to thread them and pull them inside.
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In that case we would order the MDP with a built in CT section. :cool:

We would have to run an 1.25" conduit from the CTs to wherever the power company tells they want the meter to be located.
 
iwire said:
Other than on the forums I have never seen a CT cabinet like that.

Ours look much more like the disconnect switch, the CTs bolt in kind of like the fuses and all the conductors land on lugs. That way the power company can replace the CTs without unconnecting the large conductors.

More like these ones

d_11788.jpg



HoffmanTransformerCabinets.jpg
Click to expand...

I see those a lot up north, but in the south, they mount doughnut ct's in a cabinet, or if it is a large service, the doughnuts are on the lug posts in the POCO's transformer. Either way we have to mount the ct meter base on the building or a POCO supplied post, with a 1" or larger (depending on POCO specs) ridgid conduit from the cabinet or transformer to the ct meter base.
 
aftershock said:
I'm doing a 400 amp service for an addition. The POCO issues our meter sockets and when doing an addition we have to turn in a load. Apparently if the load exceeds 48Kw then we have to use CT's. I have never installed a service in this manner.

I have never heard of such a requirement, CT's at 50% of the rating of the service?
we are allowed a 320 meter for our single phase 400 amp services. 3-phase up to 200 amp 7 jaw, before we have to CT, make sure there not giving you 3-phase requirements, if this is a single phase service let them know.

Here we install the CT cabinet that Bob posted the photo of, unless we have a transformer mounted Ct's, in which we use a junction box, with lugs in it, but I have seen a few installs where both sets of 2/0 go up the riser pipe and the Ct's hang on the conductors at the weather head, with another 1" RMC stubbed up there with a weather head back down to a meter socket
Click to expand...
 
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