size of equipment ground conductor

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sticko

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Location
nothern virginia
They are pulling (20) 10-4 MC cables to a 24 X 24 pullbox, then by using (2) FMC nipples to a PDU. The grounding conductors are terminated in an added ground bar in the pull box. The plan was to pull one #10 grounding conductor in each of the FMC nipples to the ground bar in the PDU. The main breaker in the PDU is rated at 225 amps. The MC cables are rated at 20 amps each. I thought the grounding conductor needed to be sized per NEC 250-122. For a 225 amp OC device, a #4 AWG grounding conductor was needed. Can you tell me if I'm wrong? All 20 MC cables terminate in the pull box, under the floor and the grounded and ungrounded conductors are routed through the nipples to the PDU. I hope I am clear with my description. Thanks.
 
Dennis Alwon

Dennis Alwon

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Chapel Hill, NC
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If you are talking about the 20 10/4 mc cables then only one #10 equipment grounding conductor is required to ground the box. You do not need one for each cable if they terminate at the same place. You would use t. 250.122 for the sizing along with 250.122(B) which makes the equipment grounding conductor #10.

You would only use the 225 amp breaker size if you were sizing the feeder that is being fed from the 225 amp breaker. I am confused as I don't know why the 225 amp breaker even enters into the equation.
 
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sticko

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Location
nothern virginia
each cable has it's own grounding condutor. Each of the (20) grounding conductors terminate in the pull box ( a ground bar was added) . Since the 20 grounding conductors do not terminate to the ground bar in the 225 amp PDU, dosen't the conductor from ground bar (in the PDU) to the ground bar in the pull box need to be sized for the main breaker instead of just one #10 for the (20) MC cables. They only have one #10 conductor between both ground bars to ground / bond them together.
 
J

jap

Senior Member
Occupation
Electrician
From what he's saying the Ground Wires stop in the J box before the PDU. They only carried the Hots and Neutrals to the PDU.

now they're looking at a Ground Wire Jumper from the Ground Bar in the PDU to the Ground Bar they installed in the J-box.

I'd use a #4 or whatever I had on the truck of that size or maybe even bigger also without even thinking about it wether I needed one that big or not.
 
J

jap

Senior Member
Occupation
Electrician
I am curious as to why the EGC's were not continued onto the PDU along with the rest of the circuit conductors?
 
S

sticko

Member
Location
nothern virginia
Yes. thanks for explainig it better. Each MC cable are multicircuits. If they were all the same circuit, I could understand. That's why I am thinking they need to size the jumper to the main OC device.
 
Dennis Alwon

Dennis Alwon

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Chapel Hill, NC
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Retired Electrical Contractor
If the largest circuit in the pull box is a #10 then a #10 equipment grounding conductor is all that is needed. We are not taking about a bonding jumper but an equipment grounding conductor as far as I can tell. If there is metallic conduit between the box and panel then no equipment grounding conductor is even required- if one is used than a #10. If we are talking 480v perhaps then a bonding jumper is needed.
 
F

fmtjfw

Senior Member
Location
Fairmont, WV, USA
If you have a junction box with a bunch of raceways or cables coming into it, you can connect all the EGCs to a single grounding bar. The grounding conductor size needed for the feeder conduit is the largest of the EGCs not the size required for the sum of the ampacities of the circuits fed.

250.122

(A) General. Copper, aluminum, or copper-clad aluminum
equipment grounding conductors of the wire type shall not
be smaller than shown in Table 250.122, but in no case shall
they be required to be larger than the circuit conductors supplying
the equipment. Where a cable tray, a raceway, or a
cable armor or sheath is used as the equipment grounding
conductor, as provided in 250.118 and 250.134(A), it shall
comply with 250.4(A)(5) or (B)(4).

(C) Multiple Circuits. Where a single equipment grounding
conductor is run with multiple circuits in the same
raceway, cable, or cable tray, it shall be sized for the largest
overcurrent device protecting conductors in the raceway,
cable, or cable tray. Equipment grounding conductors installed
in cable trays shall meet the minimum requirements
of 392.10(B)(1)(c).
 
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J

jap

Senior Member
Occupation
Electrician
Just be sure not to pull any circuit that would require an EGC larger than #10 out of the PDU without pulling the ground all the way to the PDU if ground wires are required to be installed.

This type of install always make me shake my head when I see things done like this.:happysad:
 
L

Lectricbota

Senior Member
Location
Rocky Mountain Region
jap said:
Just be sure not to pull any circuit that would require an EGC larger than #10 out of the PDU without pulling the ground all the way to the PDU if ground wires are required to be installed.

This type of install always make me shake my head when I see things done like this.:happysad:
Click to expand...

Why?

This makes perfect sense to me. I recently had to move a panel 15 feet in a remod--why would you extend every EGC 15 feet if you don't have to?
 
J

jap

Senior Member
Occupation
Electrician
Lectricbota said:
My point---nothing.
Click to expand...

So I'm curious what size EGC did you extend to the Relocated panel if it was a subpanel or what size Neutral conductor did you extend to the relocated Panel if it was at the Service Entrance?
 
J

jap

Senior Member
Occupation
Electrician
Lectricbota said:
Why?

This makes perfect sense to me. I recently had to move a panel 15 feet in a remod--why would you extend every EGC 15 feet if you don't have to?
Click to expand...

I never said that I would extend everyone. I'm just saying if theres a panel with an EGC landed on a ground bar, and I extend the ground bar to another location, I will extend the Full size equipment grounding conductor to that location also, so it will be large enough to accept a larger EGC if a larger circuit is installed in the PDU.

In the OP's scenario all of the branch circuits were #10 and the #10 ground wire pulled to the remote Ground Bar in the Junction box was fine. But if a 100 Amp Breaker was installed in the PDU and a #8 EGC was required to be pulled, would you stop it short in the J-box also and let the #10 carry it to the PDU? I wouldnt. although not required if its there to begin with , and I extend a single EGC to a remote Ground bar you can bet it will be full size because of the possibility of a larger circuit being installed from PDU through the J-Box.

If I build a full size dog house and have a chuaua at the present moment but know I could get a St Bernard at almost any minute, I'm going to cut the door large enough for the St. Bernard, not just large enough for the Chuaua, that way I dont have to turn right around and enlarge the door on the doghouse I just got finished building. It's not rocket science just common sense.
 
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curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
jap said:
I never said that I would extend everyone. I'm just saying if theres a panel with an EGC landed on a ground bar, and I extend the ground bar to another location, I will extend the Full size equipment grounding conductor to that location also, so it will be large enough to accept a larger EGC if a larger circuit is installed in the PDU.

In the OP's scenario all of the branch circuits were #10 and the #10 ground wire pulled to the remote Ground Bar in the Junction box was fine. But if a 100 Amp Breaker was installed in the PDU and a #8 EGC was required to be pulled, would you stop it short in the J-box also and let the #10 carry it to the PDU? I wouldnt. although not required if its there to begin with , and I extend a single EGC to a remote Ground bar you can bet it will be full size because of the possibility of a larger circuit being installed from PDU through the J-Box.

If I build a full size dog house and have a chuaua at the present moment but know I could get a St Bernard at almost any minute, I'm going to cut the door large enough for the St. Bernard, not just large enough for the Chuaua, that way I dont have to turn right around and enlarge the door on the doghouse I just got finished building. It's not rocket science just common sense.
Click to expand...

If you add an additional 100 amp circuit to the pull box later you will pull a correctly size EGC with the new 100 amp conductors. I don't see any reason to increase the EGC for circuits that don't exist.
 
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