CT Cabinet

[rlfrazee]

So the service utility feeders run thru these donuts in the CT cabinet...
http://www.ohiosemitronics.com/productimages/lcct.gif
to the lug base and then from there each 200 amp breaker panel ohm installed recieves its feeders from this lug base? So the meter is stand alone only driven by the donut sensors? Is the meter mechanical or digital or can it be both? So you have some sort of ring terminal interface that you wire the donuts to and then provide your wiring to the meter from this? Lastly do you treat this panel like any other panel as for grounding? i.e. you run a grounding electrode conductor to the grounding electrode (water line and rods)?
Would you size it to 600 amps at the CT cabinet?....RL

If this involves too much sorry thats no problem just let it go but I'm curious
I will delete post in a few days if too much to explain

[rlfrazee]

Ok I see I am unable to delete the post sorry for asking someone to write a book for me. Im that darn curious type when it comes to things like this.....RL

[mdshunk]

So the service utility feeders run thru these donuts in the CT cabinet to the lug base and then from there each 200 amp breaker panel ohm installed recieves its feeders from this lug base?
Yes.

So the meter is stand alone only driven by the donut sensors?
Yes. It might get a "trickle" of power from the line, but I forget.

Is the meter mechanical or digital or can it be both?
Either one, depending on what the utility uses in youre area.

So you have some sort of ring terminal interface that you wire the donuts to and then provide your wiring to the meter from this?
Yes, but the utility makes up these connections. You only supply an empty conduit between the CT can and the meter can. Normally, they install a "CT rack" which has the CT's and the CT wire terminal strip and such already mounted up on a backpanel.

Lastly do you treat this panel like any other panel as for grounding? i.e. you run a grounding electrode conductor to the grounding electrode (water line and rods)?
We don't "ground" CT cabinets in my area. The service grounding is done at the disconnects. Think of the CT cabinet and the meter base as "one big meter", just in two pieces.

Would you size it to 600 amps at the CT cabinet?
Yes, you and the utility engineer determine service size, and they tell you what dimensions of CT cabinet to use, so that they can mount the CT equipment. A typical CT cabinet is 36" X 36", with hinged double doors. All you do is install the service conductors and the lugs and conductors from the lugs to however many 200 or 225 amp panels you "hang" off of this. The utility installs the CT rack and the #12 conductors from the CT's to the special meter via the 3/4 or 1" pipe you installed between the CT can and the meter. The limiting factor (amperage wise) on a CT metering system is the size of the main service drop or service lateral coming into the CT can. The CT's themselves (I believe ) can often meter up to 1000 amps or better before they need upsized. When you're doing services big enough to involve CT metering, you're generally working pretty closely with the utility's engineer. This isn't something you have to deal with all by your lonesome.

[Wgoodrich]

mdshunk hit it pretty well. Not much to add.

Rl. Remember we are busy and are not getting to the forum as often as we normally do. Your questions were not too many we just hadn't got to them yet. Be patient sometimes.

Good Luck

Wg

[rlfrazee]

Thanks a bunch Mdshunk for taking the time for this as Wg reminded me you guys are very busy this time of year. Been a while since I was on your kind of schedule and I promise to be more patient in the furure.....Thanks Mdshunk.....Thanks for the reminder Wg......RL

[mdshunk]

While we're on the topic...

Some CT metering is done without a CT cabinet. On a larger farm, they sometimes mount the CT rack on top of the yard pole (on a little crossarm or alley arm). Then, they run the CT leads through a little wee weatherhead, down a little conduit to a meter on a pole. Then, you can have many arial service drops to many buildings. Even though the metering is centralized, each building is a seperate service, with it's own disconnect and grounding system.

Sometimes, if a utility's padmount transformer serves just one large customer, they'll mount the CT's around the loadside conductors inside the padmount transformer and bolt the meter to the outside of the padmount transformer. Did a large rec center/gymnasium a couple of years ago that was metered in just this way.

Just thought (since you were interested in CT's) that you'd want to know about these other methods of using CT's in metering.

[rlfrazee]

You know at our new parts plant we have a pad transformer serving the building and it sounds like it may be set up in exactly this manner. Might check it out and see next time the utility company has it opened up.....RL

[volt]

Most Power Companies have what is called an SESR (Standard Electrical Service Requirements) or similar titled manual. It's usually available from the Engineering Dept. or if you're lucky a lineman will have an extra one on his truck. The SESR will have all the info and detailed diagrams that you'll need to install any electric service in their area.

[suemarkp]

One final note. I have a transfer switch and subpanel in my basement. The panel is a normal loadcenter and I wanted voltmeters and ammeters on it so I could monitor generator performance. I bought an ammeter kit, and since this is a 100A feeder I had to buy one with CT's instead of just a giant ammeter shunt.

So a I have two donuts that go over the feeder conductors just above the lugs in the subpanel. The wires on the CT's then go to volt/amp monitoring panel that I'll mount next to the subpanel. The CT's are stamped "20:1" I think, which means when 100A is flowing through them, 5A will be produced on the wires coming out of the CT. My meter equipment must then have a 5A ammeter with the scale relabeled to 20X normal (i.e. 5A is now 100A). The company that sold the kit provided the box, CT's, and correctly labeled meters (they say 5A on the back, but read from 0 to 100A).