CT cabinet need to be grounded ?

Status
Not open for further replies.

Stevenfyeager

Senior Member
Location
United States, Indiana
Occupation
electrical contractor
We've installed a CT cabinet on a 600 amp house. Does that cabinet need to be grounded ? The Elec inspector doesn't know. The POCO will install a meter base next to this cabinet with current transformer wires connecting the two boxes. Thank you.
 
We've installed a CT cabinet on a 600 amp house. Does that cabinet need to be grounded ? The Elec inspector doesn't know. The POCO will install a meter base next to this cabinet with current transformer wires connecting the two boxes. Thank you.
I mean, do I need to connect this outside cabinet to the grounding electrodes (rods) ?
 
Since it's on the line side of the service disconnecting means you would bond the neutral directly to the CT cabinet if the neutral terminals aren't already factory bonded.
 
Sounds like the CT cabinet should be treated more as a wireway in this case. I would have grounded it with the supply side bonding jumper, and called it a day. I can't recall a code that requires us to run a grounding conductor to anything on the supply side, other than a bonding jumper. Let us know what you decide in the end.

Sent from my SM-G950U using Tapatalk
 
If it’s A POCO cabinet then I would check with them. I my area POCO does not want EGC or GEC connected in their equipment. They will fail your inspection for having their cabinet bonded with any ground.


Sent from my iPhone using Tapatalk
 
If it’s A POCO cabinet then I would check with them. I my area POCO does not want EGC or GEC connected in their equipment. They will fail your inspection for having their cabinet bonded with any ground.


Sent from my iPhone using Tapatalk

Do you mean they bond it with the neutral/grounded conductor, or that they leave it floating? If that latter that is hazardous.
 
Yes they leave it floating. It is hazardous and we have brought that to their attention and the inspectors say “that’s our manual.”

We always put a grounding bushing in the service disconnect leading to their cabinet anyways so you at least get it bonded. It could just be their inspectors misunderstanding their own manual, but I have seen services fail for having the can bonded.


Sent from my iPhone using Tapatalk
 
Yes they leave it floating. It is hazardous and we have brought that to their attention and the inspectors say “that’s our manual.”

We always put a grounding bushing in the service disconnect leading to their cabinet anyways so you at least get it bonded. It could just be their inspectors misunderstanding their own manual, but I have seen services fail for having the can bonded.


Sent from my iPhone using Tapatalk

Depending on specifics, it may be perfectly acceptable to bond the cabinet with the raceway.
 
Yes they leave it floating. It is hazardous and we have brought that to their attention and the inspectors say “that’s our manual.”

How is this possible? You're saying that the metal CT enclosure is unbonded and floating so that a fault to the metal cabinet will leave it energized?
 
How is this possible? You're saying that the metal CT enclosure is unbonded and floating so that a fault to the metal cabinet will leave it energized?

CPS in San Antonio directs us to break the ground between a line side connected PV system and the service. They require a PV meter between the PV disco and the service with no grounding of the meter can to either side.
 
How is this possible? You're saying that the metal CT enclosure is unbonded and floating so that a fault to the metal cabinet will leave it energized?
Sounds dangerous.

The 400 amp, 3 phase meter bases GA power gives us are pretty much "pre packaged" CTs with terminals for wires and place to plug the meter in. No current from the loads goes through the meter though.

My point here is that the neutral, or grounded, terminals in these cans are fixed directly to the meter can. There is no insulator. They are relying on that piece of equipment to be bonded to their grounded conductor in the event of a fault. Its a little strange because when you install the supply side bonding jumper you are effectively bonding the ground and neutral in the meter can and the disconnect. But we know this is not the correct. That should be done only in the disconnect.

I have come across a few inspectors who scratch their head at this one.

A CT cabinet is a little different because the are no terminations made. Wires are just passing through it just like a pullbox or wire way. But its on the supply side.

The first paragraph in 250.2 is "bonding jumper, supply side" that definition is "a conductor installed on the supply side... ensures conductivity between metal parts required to be electrically connected"

If it were my job, I'd have that jumper installed and move on.

If you are using metallic conduit, then you can use a bond bushing. If its in plastic, i would bolt a lug to the CT cabinet.

Sent from my SM-G950U using Tapatalk
 
bonding of CT cabinet

bonding of CT cabinet

It is pure myth that just because a POCO owns the CT that it can be left unbonded. All metallic items on the line side must be bonded in a manner compliant with 250.92. If they want to pull the NESC card, it would also require bonding. There is no such thing as leaving metallic objects unbonded under either code. To do otherwise is an accident waiting to happen. This urban legend indicates that there are a lot of non bonded CT enclosure out there in the wild. I've seen many.
 
Sounds dangerous.

A CT cabinet is a little different because the are no terminations made. Wires are just passing through it just like a pullbox or wire way. But its on the supply side.

Sent from my SM-G950U using Tapatalk

I have never seen a CT cabinet that did not have terminations in it.
 
I have never seen a CT cabinet that did not have terminations in it.
I see them all the time. Its just a big jbox with the CT mounted for you to run the wire through, or the free floating CTs that you'll see at the weather head sometimes.

Maybe the OP could chime in with what he's got.


We get transockets now for residential up to 600 amps


Sent from my SM-G950U using Tapatalk
 
Last edited:
I have never seen a CT cabinet that did not have terminations in it.

I see them all the time. Its just a big jbox with the CT mounted for you to run the wire through, or the free floating CTs that you'll see at the weather head sometimes.
Some CT's are doughnut types where the insulated conductors pass through unbroken, and others are the bar-type where line and load compression terminals are bolted to the bars.
 
I see them all the time. Its just a big jbox with the CT mounted for you to run the wire through, or the free floating CTs that you'll see at the weather head sometimes.

Maybe the OP could chime in with what he's got.


We get transockets now for residential up to 600 amps


Sent from my SM-G950U using Tapatalk

Never seen a utility use the "J-box and donut CT method". Hopefully if they are using donut type CT's, they use split core. We had a 2MW PV system and had to Pull all the SEC through solid CT's. It was a total nightmare (it was customer metering not utility).
 
Never seen a utility use the "J-box and donut CT method". Hopefully if they are using donut type CT's, they use split core. We had a 2MW PV system and had to Pull all the SEC through solid CT's. It was a total nightmare (it was customer metering not utility).
We did a similar job on an existing shopping center that went from private metering to utility. We installed about 20 meters using the same method you did. It was a HUGE pain in the ass. It was us and the poco guys out there at night for a week. Poco provided all the cabinets and CTs (obviously worked into customers bill though).

And since we're on this post... We bolted lugs to the cabinets to ground them FROM the disconnect as requested by utility engineer

Sent from my SM-G950U using Tapatalk
 
CPS in San Antonio directs us to break the ground between a line side connected PV system and the service. They require a PV meter between the PV disco and the service with no grounding of the meter can to either side.

We've discussed some of your AHJs' inane interpretations before, but this one strikes me as shocking - pun intended. :blink:

At a certain point you can't just take it anymore. If I didn't have bonding via metal raceways and listed fittings, I'd probably be demanding a signed document releasing me from liability before I made that 'correction'.
 
We've discussed some of your AHJs' inane interpretations before, but this one strikes me as shocking - pun intended. :blink:

At a certain point you can't just take it anymore. If I didn't have bonding via metal raceways and listed fittings, I'd probably be demanding a signed document releasing me from liability before I made that 'correction'.
I couldn't get a straight answer from the REMC office or from the elec inspector. While the REMC guys were connecting today, I asked them. They said usually there is a ground bar mounted to the cabinet and we run a #6 from it to the neutral line lug. So I installed a ground bar for them and they bonded it with a #6 Cu. I don't know, I got opposing answers on this posting. I still don't know if I did it correctly. Thank you
 
Status
Not open for further replies.
Top