Detached garage and sub panels

[Rob Hi]

I am new to this forum and need some expert advice. I am receiving conflicting interpretations of the code from one inspector to another for grounding sub panels in a detached garage. Can some one tell me the correct installation, the code reference and reason. Thank you.

 

[Dennis Alwon]

There was a code change on that back in the 2008NEC, I believe. Prior to that a 3 wire could e run to the garage and the neutral and any grounding electrode conductor would be connected together in the panel. Today you need a 4 wire- separate equipment grounding conductor. The equipment grounding conductor would be connected to a ground bar and the neutral isolated from it. The grounding electrode conductor would get connected to the equipment grounding bar.

Check out art. 250.32

250.32 Buildings or Structures Supplied by a Feeder(s)
or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) supplied
by feeder(s) or branch circuit(s) shall have a grounding
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 grounding
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.
(B) Grounded Systems.
(1) Supplied by a Feeder or Branch Circuit. An equipment
grounding conductor, as described in 250.118, shall
be run with the supply conductors and be connected to the
building or structure disconnecting means and to the
grounding electrode(s). The equipment grounding conductor
shall be used for grounding or bonding of equipment,
structures, or frames required to be grounded or bonded.
The equipment grounding conductor shall be sized in accordance
with 250.122. Any installed grounded conductor
shall not be connected to the equipment grounding conductor
or to the grounding electrode(s).
Exception No. 1: For installations made in compliance
with previous editions of this Code that permitted such connection,
the grounded conductor run with the supply to the
building or structure shall be permitted to serve as the
ground-fault return path if all of the following requirements
continue to be met:
(1) An equipment grounding conductor is not run with the
supply to the building or structure.
(2) There are no continuous metallic paths bonded to the
grounding system in each building or structure involved.
(3) Ground-fault protection of equipment has not been installed
on the supply side of the feeder(s).
If the grounded conductor is used for grounding in accordance
with the provision of this exception, the size of the
grounded conductor shall not be smaller than the larger of
either of the following:
(1) That required by 220.61
(2) That required by 250.122
Exception No. 2: If system bonding jumpers are installed
in accordance with 250.30(A)(1), Exception No. 2, the
feeder grounded circuit conductor at the building or structure
served shall be connected to the equipment grounding
conductors, grounding electrode conductor, and the enclosure
for the first disconnecting means.

 

[Rob Hi]

Thank you for the code excerpt. Because I am not a code inspector, and do not want to misinterpret the code, in lay-mans terms. This is exact scenario: detached garage, aluminum feeder, 2 conductor and bare aluminum neutral. Neutrals and grounds bonded in panel on a floating bus bar. I believe this is not allowed in today's code but if this install was is most likely grandfathered. So would this require ground rods, please explain. Again, two different code inspectors giving me conflicting statements.

 

[roger]

Thank you for the code excerpt. Because I am not a code inspector, and do not want to misinterpret the code, in lay-mans terms. This is exact scenario: detached garage, aluminum feeder, 2 conductor and bare aluminum neutral. Neutrals and grounds bonded in panel on a floating bus bar. I believe this is not allowed in today's code but if this install was is most likely grandfathered. So would this require ground rods, please explain. Again, two different code inspectors giving me conflicting statements.

Yes, the detached garage would have to have a Grounding Electrode System which could be rods and this is assuming the three conductor installation was legal when the original install was done. As Dennis points out, today it would require four conductors and it would still have to have a GES but it would only bond to the EGC and the neutral would stay isolated.

Roger

 

[augie47]

Prior to the 2008 code if there were no other metallic paths to the detached garage (piping, CATV, etc.() the three wire would be allowed with a bonded neutral/grounding bar and a grounding electrode system.
The bare aluminum might be a different story depending on a lot of details,.

 

[Rob Hi]

Thank you all for the help. The first code inspector was correct. The sad thing is the other inspector was standing along side two commercial electrical contractors and they were all in agreement that ground rods were not needed in this scenario. Thanks again.

 

[augie47]

"commercial electricians (contractors)" and detached residential garages are not always compatible.

 

[eprice]

Thank you for the code excerpt. Because I am not a code inspector, and do not want to misinterpret the code, in lay-mans terms. This is exact scenario: detached garage, aluminum feeder, 2 conductor and bare aluminum neutral. Neutrals and grounds bonded in panel on a floating bus bar. I believe this is not allowed in today's code but if this install was is most likely grandfathered. So would this require ground rods, please explain. Again, two different code inspectors giving me conflicting statements.

Is this bus bar isolated from the panel enclosure? If so, the enclosure may not be grounded.

 

[Rob Hi]

Yes, the bus bar is floating. Would I be safe in assuming that a sub panel in a detached garage if supplied power through a feeder/branch circuit ( wire between two o.c.p.d) that the sub panel has its own grounding system; hence grounding rods electrodes. I believe that the conflicting statements I received from a code inspector as well as two different licensed electrical contractors is stemming from the definition of a feeder/ branch circuit vs. single branch circuit or multi wire branch circuit.

 

[kwired]

Thank you all for the help. The first code inspector was correct. The sad thing is the other inspector was standing along side two commercial electrical contractors and they were all in agreement that ground rods were not needed in this scenario. Thanks again.

Ground rods are never required, a grounding electrode system however is. If no other electrodes are otherwise present then ground rods are usually the most economical way to add an electrode where there is none.

 

[mwm1752]

Thank you all for the help. The first code inspector was correct. The sad thing is the other inspector was standing along side two commercial electrical contractors and they were all in agreement that ground rods were not needed in this scenario. Thanks again.

Seems to reason that" if " this is a new garage with a foundation then the UFER would be installed and is a stand alone GE. In that case no ground rods are needed. Agreee with Kwired comments otherwise.

 

[kwired]

Seems to reason that" if " this is a new garage with a foundation then the UFER would be installed and is a stand alone GE. In that case no ground rods are needed. Agreee with Kwired comments otherwise.

That "if" is still based on "if" there is qualifying electrode present. NEC doesn't make us put rebar in footings, it just requires us to use them if they are present and meet the electrode requirements. Other building codes are what may require rebar to be present for structural purposes.

That said most of the time if there is a building inspector there is likely a reinforcement requirement, may or may not be bare steel bars though.

 

[mwm1752]

That "if" is still based on "if" there is qualifying electrode present. NEC doesn't make us put rebar in footings, it just requires us to use them if they are present and meet the electrode requirements. Other building codes are what may require rebar to be present for structural purposes.

That said most of the time if there is a building inspector there is likely a reinforcement requirement, may or may not be bare steel bars though.

You are aboslutely correct in catching my assumption. I mean not all footers require steel, but I have not seen any that are like that -- So, when the steel is inserted in the footer then by code a UFER electrode is present and shall be used. FYI tying 20" of 4# bar in a footer can be so much easier than driving a ground rod sometimes & results in a better Electrode.
Your assumption of no footer steel is a big IF also. How many footers have you seen with our steel reinforcement?

 

[kwired]

You are aboslutely correct in catching my assumption. I mean not all footers require steel, but I have not seen any that are like that -- So, when the steel is inserted in the footer then by code a UFER electrode is present and shall be used. FYI tying 20" of 4# bar in a footer can be so much easier than driving a ground rod sometimes & results in a better Electrode.
Your assumption of no footer steel is a big IF also. How many footers have you seen with our steel reinforcement?

For small outbuildings in areas with no building code enforcement (which is most of where I work) - used to be quite a few, but lately they still put reinforcement even in places it maybe doesn't need to be.

 

[eprice]

Yes, the bus bar is floating. Would I be safe in assuming that a sub panel in a detached garage if supplied power through a feeder/branch circuit ( wire between two o.c.p.d) that the sub panel has its own grounding system; hence grounding rods electrodes. I believe that the conflicting statements I received from a code inspector as well as two different licensed electrical contractors is stemming from the definition of a feeder/ branch circuit vs. single branch circuit or multi wire branch circuit.

If the bus bar where the neutral and grounds land is isolated from the panel enclosure and a fault occurs between an ungrounded conductor and the enclosure, there is no path for that fault current to travel back to the source via the feeder neutral or the feeder equipment grounding conductor and the fault will not be cleared until something or someone becomes that path. The grounding electrode system cannot perform that function since the resistance of that path will most likely be too high to allow enough current to flow to trip a breaker.

If, because of the age of the installation, the neutral and equipment grounds are allowed to land on one bus, that bus needs to be bonded to the enclosure in order to provide a reliable fault current return path.