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Old 02-04-2011, 07:31 PM   #1
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Proper way to ground a subpanel


I'm working towards putting in a 60A sub-panel with a generator breaker lockout device (SquareD that has a 60A main panel breaker and a 30A generator breaker).

It will be fed using a 60A single pole breaker using #6, with the neutral going from an empty hole in the main panel's neutral bar to the (isolated) neutral bar in the sub-panel.

I'll be using a 1-1/2" offset nipple to mechanically join the panel (200A CH) to the sub-panel, which bonds them. Do I run a separate #10 green ground wire from the sub-panel's equipment ground bar and connect it to the same ground clamp to which the main panel's ground is connected? Run #10 bare ground from the subpanel's equipment ground to the main panel's ground bar? #6?

Thanks for the assistance.


Last edited by chieftaing; 02-04-2011 at 08:28 PM. Reason: I had some gauges incorrect.
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Old 02-04-2011, 08:29 PM   #2
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Proper way to ground a subpanel


First, lets talk about the 1-1/2" offset nipple. You'll need a bond bushing (looks like a lock ring but has a ground lug and plastic chase built in) on one end of that with a #12 wire connected to the ground bar in the main panel.
Run the ground from the isolated ground bar in Sub Panel to the ground bar in main panel. #6

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Old 02-04-2011, 08:45 PM   #3
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Proper way to ground a subpanel


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Old 02-04-2011, 10:41 PM   #4
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Proper way to ground a subpanel


You do not have to double ground the main.......I think thats what you were asking with the 10 bare......


I would not personally bond using the nipple and bushing. Those things are expensive. Its much cheaper to get a 3 foot piece of 10 thhn green........Just run 4 wires from the sub to the main.......

Also i see you are using a "single pole" 60a main breaker/feeder breaker for the panel........uh....why are you using such a high amperage breaker? Maybe you are confused by the QO series of breakers.........Those have one handle for the double poles.......

I havent heard of a 120 volt subpanel, especially with a 60amp MB. unless you got this custom made you are mistaken.
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Old 02-04-2011, 11:37 PM   #5
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Proper way to ground a subpanel


IF your in IL --- you have it in pipe( from panel to panel) that is considered grounded for a sub panel. For the rest of the country I would listen to the guys above.
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Old 02-05-2011, 12:18 AM   #6
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Proper way to ground a subpanel


wouldnt running a separate ground be above and beyond the code therefore making it permissible (im not from IL, but just reasoning this)
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Old 02-05-2011, 12:23 AM   #7
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Proper way to ground a subpanel


Yes you can- I was prepared to drive another 8 foot rod of copper into the ground to ground the new sub panel I put in. The inspector came out and I had the rod in hand and I ask him about grounding it. I explained to him that it is grounded running pipe between the two. He agreed and then said if you would like to spend the money on grounding it again be my guest if not go take it back and save yourself the 60ish bucks lol.

Yes that inspector and I are on great terms he is my normal inspector on 90 percent of my jobs in that area and I always have his coffee ready for him too lol
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Old 02-05-2011, 10:55 AM   #8
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Proper way to ground a subpanel


You dont need a Grounding rod unless it is a separate structure.
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Old 02-05-2011, 11:32 PM   #9
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Proper way to ground a subpanel


Quote:
Originally Posted by LyonsElecSupply View Post
You dont need a Grounding rod unless it is a separate structure.
Correct- for me in my instance it was cheaper to run another ground rod on the addition side then run almost 100 feet back in wire since I would of had to run another line over in conduit.
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Old 02-06-2011, 07:04 AM   #10
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Proper way to ground a subpanel


Quote:
Originally Posted by proremodel View Post
I was prepared to drive another 8 foot rod of copper into the ground to ground the new sub panel I put in. The inspector came out and I had the rod in hand and I ask him about grounding it. I explained to him that it is grounded running pipe between the two. He agreed and then said if you would like to spend the money on grounding it again be my guest if not go take it back and save yourself the 60ish bucks lol.
You and your inspector need to study up on exactly what grounding and bonding are.

A ground rod has absolutely NOTHING to do with the ground wire run between a main panel and a sub-panel, and one does not negate the other. A ground rod does NOT ground anything as far as an equipment ground is concerned.

Your equipment ground comes from an equipment grounding conductor, and the neutral to ground bond in a main panel, NOT a rod stuck in the dirt.

A ground rod is/was required at a detached structure served by a feeder regardless of what type of feeder is/was run.
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Old 02-06-2011, 01:07 PM   #11
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Proper way to ground a subpanel


Petey is right. You need 4 wires to a subpanel. A ground rod is a second means of bonding for that structure. IIRC you can also use the metal structure, metal conduit (if continuous) or water lines (if metal) ran to that structure for bonding......These are rare for out buildings in this area, so its almost 99% of the time that a ground electrode is used as the bonding system.

And pro, you should have ran 4 wires in that conduit anyways......H/H/N/G
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Old 02-06-2011, 02:08 PM   #12
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Proper way to ground a subpanel


Quote:
Originally Posted by LyonsElecSupply View Post
Petey is right. You need 4 wires to a subpanel. A ground rod is a second means of bonding for that structure. IIRC you can also use the metal structure, metal conduit (if continuous) or water lines (if metal) ran to that structure for bonding......These are rare for out buildings in this area, so its almost 99% of the time that a ground electrode is used as the bonding system.

And pro, you should have ran 4 wires in that conduit anyways......H/H/N/G
Sorry, I can't find the definition of a bonding system. Could you help me out?
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Old 02-06-2011, 02:45 PM   #13
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Proper way to ground a subpanel


Quote:
Originally Posted by LyonsElecSupply View Post
A ground rod is a second means of bonding for that structure.
Lyons, it's not even that.

A grounding electrode serves a very specific, and pretty close to useless, function.

A grounding electrode's purpose:
Quote:
(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

(2) Grounding of Electrical Equipment. Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.

An equipment ground, or bond's purpose:
Quote:
(3) Bonding of Electrical Equipment. Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

(4) Bonding of Electrically Conductive Materials and Other Equipment. Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.
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Old 02-06-2011, 02:58 PM   #14
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Proper way to ground a subpanel


NEC section 250.....

250.2:

(A) Grounded Systems.
(1) Electrical System Grounding. Electrical systems that
are grounded shall be connected to earth in a manner that
will limit the voltage imposed by lightning, line surges, or
unintentional contact with higher-voltage lines and that will
stabilize the voltage to earth during normal operation.

This is your ground rod and service neutral, all ground rods do is provide another location to stabilize voltage to ground, NOT to ACTUALLY provide a fault path. Note, it says LIMIT voltage, not provide a path. Note also this says ELECTRICAL SYSTEMS....This is the theoretical electrical system.

(2) Grounding of Electrical Equipment. Normally non–
current-carrying conductive materials enclosing electrical
conductors or equipment, or forming part of such equipment,
shall be connected to earth so as to limit the voltage
to ground on these materials.

This is your metal enclosures, device boxes, conduit etc, this provides for GROUNDING, note "limit voltage to ground" section. Note the difference from above, this says ELECTRICAL EQUIPMENT, which is NOT the same as the ELECTRICAL SYSTEM

(3) Bonding of Electrical Equipment. Normally non–
current-carrying conductive materials enclosing electrical
conductors or equipment, or forming part of such equipment,
shall be connected together and to the electrical supply
source in a manner that establishes an effective groundfault
current path.

This is BONDING, which is how all the above mentioned (sec2) are to be CONNECTED, aka Bonded together, note the "Effective ground fault current path" which is why you should use BONDING BUSHINGS when using metallic conduit. Connections are not longer rated as en "Effective GF current path" in commercial structures per 2011.

(4) Bonding of Electrically Conductive Materials and
Other Equipment. Normally non–current-carrying electrically
conductive materials that are likely to become energized
shall be connected together and to the electrical supply
source in a manner that establishes an effective groundfault
current path.

This section provides for your WATER system if it is Ferrous or Copper based. This is why you jump water heaters, water meters and connect your electrical system to the water system. This also provides yet ANOTHER way to stabilize to ground, should your water pipes from the city be metallic and conductive and run at least 10 (i think) feet out.

(5) Effective Ground-Fault Current Path. Electrical equipment
and wiring and other electrically conductive material
likely to become energized shall be installed in a manner that
creates a low-impedance circuit facilitating the operation of
the overcurrent device or ground detector for high-impedance
grounded systems. It shall be capable of safely carrying the
maximum ground-fault current likely to be imposed on it from
any point on the wiring system where a ground fault may
occur to the electrical supply source. The earth shall not be
considered as an effective ground-fault current path.

This is why your 4th conductor for a subpanel is necessary. this is the reason you have a service neutral(SN provides a return path for current and also another fault current path)/subpanel ground

All the ground rod does for a detached structure panel is provide a LOCATION that STABILIZES your voltage to ground. Your ground wire actually is the one that carries the current should a fault occur.....

Remember electricity follows the path of least resistance. There may be more resistance at different areas of the property and throughout the system. By putting ground rods through out different locations, you provide a means to stabilize your ELECTRICAL SYSTEM.....it has nothing to do with carrying current or grounding equipment.........

However, should you lose your Service neutral, which does happen believe me, your ground rod MAY become your neutral leg along with your water system. Doing this, depending on resistance, may cause you to get electrocuted should your ground rod not be installed correctly. However with city water, it should not as the pipe extends for hundreds or thousands of feet with constant contact to earth.

this is also why well systems require 2 separate ground rods as the water system (while still required to be bonded) is NOT a second grounding system (you need 2, one electrode and 1 alternative)

And this is why you have a ground rod in your panel or meter on the same bus that your service neutral is on. (IE your bonding jumper is connected.)

250.24 Grounding Service-Supplied Alternating-Current
Systems.
(A) System Grounding Connections. A premises wiring
system supplied by a grounded ac service shall have a
grounding electrode conductor connected to the grounded
service conductor, at each service, in accordance with
250.24(A)(1) through (A)(5).
(1) General. The grounding electrode conductor connection
shall be made at any accessible point from the load end
of the service drop or service lateral to and including the
terminal or bus to which the grounded service conductor is
connected at the service disconnecting means.


Phew, If anyone wants to add or edit anything feel free. I think this explains it...
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Last edited by LyonsElecSupply; 02-06-2011 at 03:02 PM. Reason: Added 250.24
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Old 02-06-2011, 03:41 PM   #15
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Proper way to ground a subpanel


It is a grounding electrode SYSTEM. It is not a bonding system. What about a ufer ground? True or false? Ground rods are not required with a ufer ground.

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