Subpanel boding/unbonding

[mtne]

250.50, 250.52 and 250.53 cover the grounding and would be damn long if I cut and pasted it.........

The shorthand is that there are 1-8 means of grounding. Any of them present at a structure must be bonded together to make the ground system. If none are present, one of the 4-8 shall be installed and used. Defacto that means a ground rod as it's cheap and easy. 250.53 goes on to require a supplemental electrode for single grounding electrode unless the resistance to earth is 25ohm's or less. So cheap and easy, you set another ground rod cause most little shops don't have the appropriate testing equipment.

Yes this is all 2011 code, the areas I work in all adopt current code, usually within 6 months.............. it's the minimum and they often add stuff above and beyond.

The new arc fault signage **** is out of hand...........

 

[Falcon67]

Good news - glad you got the right wire in there and are off to the next thing!

I am not an electrician, but I have three wires running from the house to the barn. The ground and neutral are tied together in the sub panel, and the sub panel is grounded to ground with two rods.

People wired outbuildings like this for almost 100 years. The electrical inspector approved this 10 years ago, and said it was well done, so go figure.

The part you may have missed is that of the original three wires, the "neutral" was bare and as nehog kindly pointed out, that's no good.

 

[Norcal]

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) sup- plied by feeder(s) or branch circuit(s) shall have a ground- ing electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing ground- ing electrode, the grounding electrode(s) required in 250.50 shall be installed.
Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non–current-carrying metal parts of equipment.

You know the N.E.C. never even mentions the word "sub-panel". Article 250 is the most misunderstood part of the N.E.C. BTW 250.56 is being dropped from the 2011 code. Some of the sub-sections are contradictory. Based on the entirety of article 250 you could argue that as long as you pull a ground conductor from the main panel you do not need ANY ground rod at the garage. Some inspectors want a ground rod some do not. Hell some of them are still using the 1996 code. On a side note. I hope all of the guys doing their own work are NOT bonding the neutral at the sub.

James

The requirement is still there though.....

2011 NEC:

250.53 Grounding Electrode System Installation.
Informational Note: See 547.9 and 547.10 for special
grounding and bonding requirements for agricultural
buildings.
(A) Rod, Pipe, and Plate Electrodes. Rod, pipe, and plate
electrodes shall meet the requirements of 250.53(A)(1)
through (A)(3).
(1) Below Permanent Moisture Level. If practicable, rod,
pipe, and plate electrodes shall be embedded below permanent
moisture level. Rod, pipe, and plate electrodes shall be
free from nonconductive coatings such as paint or enamel.
(2) Supplemental Electrode Required. A single rod, pipe,
or plate electrode shall be supplemented by an additional
electrode of a type specified in 250.52(A)(2) through
(A)(8). The supplemental electrode shall be permitted to be
bonded to one of the following:
(1) Rod, pipe, or plate electrode
(2) Grounding electrode conductor
(3) Grounded service-entrance conductor
(4) Nonflexible grounded service raceway
(5) Any grounded service enclosure
Exception: If a single rod, pipe, or plate grounding electrode
has a resistance to earth of 25 ohms or less, the
supplemental electrode shall not be required.
(3) Supplemental Electrode. If multiple rod, pipe, or plate
electrodes are installed to meet the requirements of this
section, they shall not be less than 1.8 m (6 ft) apart.
Informational Note: The paralleling efficiency of rods is
increased by spacing them twice the length of the longest rod.

 

[kngelv]

The requirement is still there though.....

2011 NEC:

250.53 Grounding Electrode System Installation.
Informational Note: See 547.9 and 547.10 for special
grounding and bonding requirements for agricultural
buildings.
(A) Rod, Pipe, and Plate Electrodes. Rod, pipe, and plate
electrodes shall meet the requirements of 250.53(A)(1)
through (A)(3).
(1) Below Permanent Moisture Level. If practicable, rod,
pipe, and plate electrodes shall be embedded below permanent
moisture level. Rod, pipe, and plate electrodes shall be
free from nonconductive coatings such as paint or enamel.
(2) Supplemental Electrode Required. A single rod, pipe,
or plate electrode shall be supplemented by an additional
electrode of a type specified in 250.52(A)(2) through
(A)(8). The supplemental electrode shall be permitted to be
bonded to one of the following:
(1) Rod, pipe, or plate electrode
(2) Grounding electrode conductor
(3) Grounded service-entrance conductor
(4) Nonflexible grounded service raceway
(5) Any grounded service enclosure
Exception: If a single rod, pipe, or plate grounding electrode
has a resistance to earth of 25 ohms or less, the
supplemental electrode shall not be required.
(3) Supplemental Electrode. If multiple rod, pipe, or plate
electrodes are installed to meet the requirements of this
section, they shall not be less than 1.8 m (6 ft) apart.
Informational Note: The paralleling efficiency of rods is
increased by spacing them twice the length of the longest rod.

You are misreading 250.32. If his household service that he is using to supply his sub-panel meets the criteria explained in sections 250.50-58 then he does not even need a ground rod. Many municipalities require one.

James

 

[Falcon67]

You are misreading 250.32. If his household service that he is using to supply his sub-panel meets the criteria explained in sections 250.50-58 then he does not even need a ground rod. Many municipalities require one.

James

Yep - larger town here requires two methods be used.

 

[smokey_truck]

Yep - larger town here requires two methods be used.

My city inspector said, we don't need additional ground rod since I am using ground from main panel. I don't have any water pipes to connect ground at detached garage

Ganesh