Sizing of grounding conductor

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chocho77

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How do you size the grounding conductor in the raceway(s) between the
CT can and MDP?The "bull's eye" is at MDP(bonding of the neutral to MDP
enclosure and Ufer ground and EGC)
 
You would not install an EGC in that raceway(s) since it would become a parallel path with the grounded conductor. The requirement is that if the raceway is a metallic conduit that it be bonded on one end.
 
Frequently the neutral isn't bonded to the CT can. In that case, our POCO requires a #6 ground to a driven rod, or to the grounding electrode system if nearby.

It doesn't make sense to base it on the service main breaker size since it is upstream of that. In fact, there probably is no OCPD in the circuit upstream of the CT cabinet to operate. You're just dealing with touch potentials.

Jim T
 
jtester said:
Frequently the neutral isn't bonded to the CT can. In that case, our POCO requires a #6 ground to a driven rod, or to the grounding electrode system if nearby.

It doesn't make sense to base it on the service main breaker size since it is upstream of that. In fact, there probably is no OCPD in the circuit upstream of the CT cabinet to operate. You're just dealing with touch potentials.
Click to expand...

You're correct that it doesn't make sense to base the size of this conductor on the main breaker. 250.102(C) requires bonding jumpers on the supply side of the service to be sized using Table 250.66.

My concern is that the #6 ground to a driven rod does not accomplish the bonding of the CT can required in 250.4(A)(3). 250.4(A)(5) prohibits the earth being considered an effective ground-fault current path. The driven rod will have too much resistance to ground to allow enough current to clear a fault. 250.92(A) requires the bonding of various items. CT cans seem to fit squarely in item (2) of that list. 250.92(B) lists acceptable methods for bonding. A conductor to a driven rod is not one of them.
 
Around here the POCO requires the grounded conductor to be bonded in all CT cabinets and meter pans. Running an EGC between the CT cabinet and the first disconnect would be unnecessary.
 
I forgot to mention- the raceway is NONMETALIC(PVC conduit).
I call this conductor Bonding Jumper on the line side of the service equipment
and I did size it by Table 250.66.
Is anybody on the same page?
 
Chocho,
Even with nonmetallic conduit there is no reason to install this jumper...it would be a violation of 310.4. All of the grounding of the electrical equipment on the line side of the service disconnect as well as the disconnect itself is done by a connection to the grounded conductor.
Don
 
Bea said:
Trevor is correct and the bonding jumper sized based on 250.66
Click to expand...

I have never seen a meter or CT can that I had to install a jumper in, all arive to me factory bonded, the neutral connections are bolted directly to the steel enclosure.
 
iwire said:
I have never seen a meter or CT can that I had to install a jumper in, all arive to me factory bonded, the neutral connections are bolted directly to the steel enclosure.
Click to expand...


The ones that we install are bolted directly to the CT cabinet also. We never have had to install any type of jumper.
 
don_resqcapt19 said:
Chocho,
Even with nonmetallic conduit there is no reason to install this jumper...it would be a violation of 310.4. All of the grounding of the electrical equipment on the line side of the service disconnect as well as the disconnect itself is done by a connection to the grounded conductor.
Don
Click to expand...
Thank you,Don!
Would you clarify the violation,please!
 
Unless the bonding jumper is the same size as the grounded conductor, you will have a violation of 310.4(3).
Don
 
They must make CT cans both ways, because I've never seen one with the grounded conductor bonded to the pan.
We only use metal conduit (RMC or IMC) so it's not a problem.
In this case (Non Metalic Raceway) I don't see any reason not to use 250.122.
 
russ said:
They must make CT cans both ways, because I've never seen one with the grounded conductor bonded to the pan.
We only use metal conduit (RMC or IMC) so it's not a problem.
Click to expand...

Are you talking about a CT Meter socket or the enclsure that actully houses the the CTs?

In this case (Non Metalic Raceway) I don't see any reason not to use 250.122.
Click to expand...

The reason we can not use 250.122 is because the NEC tells us to use 250.66 or 12 1/2%

250.102 Equipment Bonding Jumpers.

(C) Size ? Equipment Bonding Jumper on Supply Side of Service. The bonding jumper shall not be smaller than the sizes shown in Table 250.66 for grounding electrode conductors. Where the service-entrance phase conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the bonding jumper shall have an area not less than 12? percent of the area of the largest phase conductor except that, where the phase conductors and the bonding jumper are of different materials (copper or aluminum), the minimum size of the bonding jumper shall be based on the assumed use of phase conductors of the same material as the bonding jumper and with an ampacity equivalent to that of the installed phase conductors. Where the service-entrance conductors are paralleled in two or more raceways or cables, the equipment bonding jumper, where routed with the raceways or cables, shall be run in parallel. The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable.

The bonding jumper for a grounding electrode conductor raceway or cable armor as covered in 250.64(E) shall be the same size or larger than the required enclosed grounding electrode conductor.
Click to expand...



250.122 is based on the OCPD that it must trip.

There is generally no OCPD supplying a meter socket, that being the case we must use 250.66 or 12 1/2% of the circuit conductors.

But that can all be forgoten if his CT cabinaet is factory bonded to the neutral,
 
russ said:
They must make CT cans both ways, because I've never seen one with the grounded conductor bonded to the pan.
We only use metal conduit (RMC or IMC) so it's not a problem.
In this case (Non Metalic Raceway) I don't see any reason not to use 250.122.
Click to expand...
That's my case-the neutral is "floating" in the CT cabinet(NOT bonded)
That's why I bonded it to Ufer ground and enclosure in MDP.
Another option is to bond the neutral to the CT can and Ufer ground
and leave it "floating" in MDP.
For both options I still need Equipment Bonding Jumpers sized per table 250.66.
I was going to use the second option-bonding the neutral to the CT can
and grounding rods instead of ufer ground,but the grounding rods and wire
got stolen twice.
Also there is NO OCPD between utility transformer's secondary and MDP-
that's why I could not use Table 250.122.
 
Chocho,
Another option is to bond the neutral to the CT can and Ufer ground
and leave it "floating" in MDP.
Click to expand...
Why not bond it in both places...the code permits the grounded conductor to be used for all required bonding on the line side of the service disconnect.
Don
 
chocho77 said:
For both options I still need Equipment Bonding Jumpers sized per table 250.66.
Click to expand...

Yes you need a BJ from the cans to the grounded condutor but not a BJ from one can to the other.
 
don_resqcapt19 said:
Chocho,

Why not bond it in both places...the code permits the grounded conductor to be used for all required bonding on the line side of the service disconnect.
Don
Click to expand...
Yes,I agree with you,Don!This was the easiest fix after the wire and rods
got stolen.Even I do not need any ground wire (ebj) in the raceways between
the CT can and MDP-just a chunk 4/0 aluminum to bond the CT can to the
neutral bar(the service entrance conductors are 2x750kcmil Al per phase)
and call it good! But... I'm not AHJ and ...
Anyway,I passed the inspection and just wanted to see if I was right.
Thanks!
 
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