# parallel grounds not allowed?



## 1capybara (Feb 27, 2009)

my inspector says parallel grounds arent allowed.
heres the situation:
we run SWA feeder cable from a MDB to a sub-panel, and to
air conditioners.
SWA is a steel wired armored cable rated for
direct burial. [see photo of a SWA cable]
The british use the armored strands for bonding.
Inside are 4 wires: 3 hots and a neutral, or 3 hots and a ground.
My American inspector says we should bond the SWA armor only
on the feed side, the MDB, and cut off the SWA wire on the
load side, at the sub-panels or the air conditioner disconnects.
We do this so as to not create a parallel ground, which he 
says isnt allowed by code. [if we land the SWA on the
load side, the SWA would be a parallel ground with the
grounding conductor to the air conditioners, or parallel to the
the separate grounding conductor for the sub-panels.]
I searched the NEC 2008, I cant
find any referece to "parallel grounds." The conductor size
is 120mm2 = 4/0 approximately. NEC allows parallel conductors
1/0 or greater. 
The same situation exists using an American wire that has 4 cores and a reduced-size ground, if we use the 4th core as a ground,
[to a 3 phase air conditioner]
then the reduced size ground would be a parallel ground, and so according
to our inspector, should be cut short and not landed on its load side.
What do u think ???


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## jwjrw (Jan 14, 2010)

You can only bond at the service or first disconnecting means. Your subpanels have to have the grounds and neutrals seperate to prevent that parallel path. Is it not possible to use conduit and another wire type?


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## HARRY304E (Sep 15, 2010)

1capybara said:


> my inspector says parallel grounds arent allowed.
> heres the situation:
> we run SWA feeder cable from a MDB to a sub-panel, and to
> air conditioners.
> ...


AT the MDP your cable neutral and ECG and at the load the ECG is bonded to the metal parts and the neutral goes to the neutral terminal.
so why is the inspector telling you to cut off the ECG


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## jwjrw (Jan 14, 2010)

It's not parallel grounds. It is creating a parallel path for fault current to take. It would allow objectionable current on the ground if it had more than 1 low resistance path back to the source.


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## 1capybara (Feb 27, 2009)

jwjrw - this is NOT about neutral to ground bond. 
it is parallel grounds in both examples:
1. 3 hots, neutral, separate ground, + SWA run from MDB to sub-panel
OR
2. 3 hots, 4th core used as ground, reduced-size ground 
which is inside the cable [not run separately]
run from MDB to a 3-phase motor.


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## jwjrw (Jan 14, 2010)

1capybara said:


> jwjrw - this is NOT about neutral to ground bond.
> it is parallel grounds in both examples:
> 1. 3 hots, neutral, separate ground, + SWA run from MDB to sub-panel
> OR
> ...



The only thing I know of that he could be talking about relating to grounding is a parallel path for fault current. IDK. Someone here will respond with the correct answer I'm sure.


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## mattsilkwood (Sep 21, 2008)

The OP said air conditioners so I'm guessing the neutral is not an issue here, 3 hots and a ground. 
IMO it would be correct to bond the jacket to the can on both ends. 
It sounds like the inspector is getting this confused with a shielded cable where you would only bod one side.

It would be no different than having to bond a conduit.


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## tates1882 (Sep 3, 2010)

mattsilkwood said:


> It would be no different than having to bond a conduit.


 
I agree.


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## frenchelectrican (Mar 15, 2007)

1capybara.,

Are you using both NEC code and UK edition 18 Regulations ??

There are slighty diffrent way to deal with it.

Merci.
Marc


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## 480sparky (Sep 20, 2007)

If parallel grounding conductors aren't allowed, then someone tell me why 250.122(F) exists?


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## brian john (Mar 11, 2007)

If we are not discussing the neutral, you can have parallel grounds (Equipment Grounding Conductor EGC) ask the inspector what about the building steel, EMT when you pul a EGC, and I could go on and on. The inspector is NOT THINKING.


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## tates1882 (Sep 3, 2010)

1capybara said:


> my inspector says parallel grounds arent allowed.
> heres the situation:
> we run SWA feeder cable from a MDB to a sub-panel, and to
> air conditioners.
> ...


 
I don't see the differnce in your situation and having a emt run with a ecg inside if it. I would have asked for the code ref from your inspector. Is the armor jacket rated for use as an egc? As far as bonding on the feed side only, I would do both ends. If say you had a line to ground short on the swa feeder to the subpanel about 4 ft back from the lugs. I would think the fault current would have a better path back to the ocpd by going to the sub then down the feeder egc to ocpd. 

just my 2 cents. tw


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## Jlarson (Jun 28, 2009)

The inspector is dumb. :yes:


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## frenchelectrican (Mar 15, 2007)

Jlarson said:


> The inspector is dumb. :yes:


 
Maybe so .,,

I do know in France for SWA cable if used with feeder useage we have to bond both end of SWA cable that why I am waiting if the OP answer which code he is using either NEC or UK codes if latter it have to be bonded both ends { If I recalled right with UK codes}

Merci.
Marc


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## Jlarson (Jun 28, 2009)

frenchelectrican said:


> Maybe so .,,
> 
> I do know in France for SWA cable if used with feeder useage we have to bond both end of SWA cable that why I am waiting if the OP answer which code he is using either NEC or UK codes if latter it have to be bonded both ends { If I recalled right with UK codes}
> 
> ...


I assume NEC since he mentioned NEC parallel conductor rules.


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## frenchelectrican (Mar 15, 2007)

Jlarson said:


> I assume NEC since he mentioned NEC parallel conductor rules.


 
Yeah ., I have to reread the OP comment very carefull and sort it out and I know the inspector will NOT like my answer .,

Bond both end of SWA amour strands and be done with it basically it the same idea with ridge conduit with full boat with EGC in there.

Merci.
Marc


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## Jlarson (Jun 28, 2009)

frenchelectrican said:


> Yeah ., I have to reread the OP comment very carefull and sort it out and I know the inspector will NOT like my answer .,
> 
> Bond both end of SWA amour strands and be done with it basically it the same idea with ridge conduit with full boat with EGC in there.
> 
> ...


We use a lot of shielded TC cable and if it's not instrumentation/data I bond the shield on both ends and no one ever said boo about it. I agree with the metal conduit comparison too.


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## erics37 (May 7, 2009)

480sparky said:


> If parallel grounding conductors aren't allowed, then someone tell me why 250.122(F) exists?


250.122(F) is permitting us to parallel our EGCs, but each one needs to be sized in accordance with 250.122.

So going back to 250.122(A), that tells us to size EGCs from Table 250.122, which is based on the OCPD. So I could technically have a _calculated_ EGC in each run that was larger than one of the paralled circuit conductors in that same run. Right?

But back to 250.122(A), it says that in no case shall EGCs be required to be larger than the circuit conductors supplying the equipment. Which makes my question thus: in this case, would "circuit conductors" be referring to the wire size in each parallel run? Or would it be referring to the total sum circular mil area of each whole set of paralleled phases?

I've never been clear on this. I have arguments and counter-arguments both in my head at the same time as to whether it makes sense to have a huge EGC in each run with comparatively smaller circuit conductors.


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## frenchelectrican (Mar 15, 2007)

I going to post the photo what I am talking about the SWA bonding clamp look like.

And I used them pretty often.










Here the second photo how the crosscut view of SWA cable being termatied.










Merci.
Marc


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## 1capybara (Feb 27, 2009)

mattsilkwood said:


> .....
> It sounds like the inspector is getting this confused with a shielded cable where you would only bond one side.


Mattsilkwood, this is EXACTLY the reason the inspector gave!
Is this in the NEC ???


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## Jlarson (Jun 28, 2009)

1capybara said:


> Mattsilkwood, this is EXACTLY the reason the inspector gave!
> Is this in the NEC ???


As far as I know, it's not, never really looked or cared, I just always did it as common and good practice to prevent ground loops in instrumentation/data systems.


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## John Valdes (May 17, 2007)

1capybara said:


> Mattsilkwood, this is EXACTLY the reason the inspector gave!
> Is this in the NEC ???


I also agree. The inspector is confused between a drain and grounding conductor or braided grounding conductor.
In electronics most applications that use shielded cable with a drain wire, the drain wire is only connected at one end.
Tell him he is over thinking this and this is not the inside of a television set.
On the cable you show, the braided outer skin is the EGC. There is no insulated EGC in that cable.


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## 1capybara (Feb 27, 2009)

brian john said:


> If we are not discussing the neutral, you can have parallel grounds (Equipment Grounding Conductor EGC) ask the inspector what about the building steel, EMT when you pul a EGC, and I could go on and on. The inspector is NOT THINKING.


I agree 100%
:thumbsup:


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## abellm (Oct 4, 2009)

You might ask Mr. Inspector (AHJ) the specific reference so that you can study up on it! He probably will not find anything for you though....I would not suggest leaving a circuit 'cut short' on proper bonding and grounding. The most critical path for our electrons is the "return" path for proper facilitation of the O.C.D.


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## RIVETER (Sep 26, 2009)

jwjrw said:


> The only thing I know of that he could be talking about relating to grounding is a parallel path for fault current. IDK. Someone here will respond with the correct answer I'm sure.


If you bond one end of the braided outer and had an inside conductor used as an egc, would it not, in the case of a fault, set up an inductive choke at the the unattached end and create an extra impedance to the fault current?


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## abellm (Oct 4, 2009)

Even if the braided outer is only bonded on ONE end, the internal EGC - which should be landed on both ends would be sufficient to facilitate operation of your O.C.D. (This senario suggests that the system is otherwise properly bonded) Standard circuit breaker design of the 'time inverse type' will normally TRIP as quickly as it sees that LOW potential (fault to ground).


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## 1capybara (Feb 27, 2009)

frenchelectrican said:


> Maybe so .,,
> 
> I do know in France for SWA cable if used with feeder useage we have to bond both end of SWA cable that why I am waiting if the OP answer which code he is using either NEC or UK codes if latter it have to be bonded both ends { If I recalled right with UK codes}
> 
> ...


the intention is to make everything to NEC, but this cable doesnt exist
in America XLPE/ SWA/ PVC/ CU.
Both me and the inspector are American electricians.
A British electrician also told us, he bonds both sides of the SWA.


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## ibuzzard (Dec 28, 2008)

David,we also followed the procedure of bonding only one end of the SWA cable in Iraq, as a directive,clarification,deviation - whatever you want to term it.The sole intent was to have only one fault path,to facilitate faster tripping of the breaker,supposedly.There ,the armor was never used as the sole grounding path, but only as a means of physical protection for the conductors.One of the core conductors was used as the EGC.The UK sparky's indicated that using only the armor as the EGC is considered poor design,though legal under the 18th edition of the British Standard.

There is a problem,as you know,of using European materials,and making them compliant to our NEC,causing real problems .I hated terminating that SWA.The company I was with,who shall remain nameless(o.k.,it was KBR)never failed to come up with one of their allowable "deviations" which was supposed to give us permission to violate the NEC.Most of the "slave-state" electricians,who formed a majority of the U.S. ex-pat electricians - particularly those from Louisiana and Texas,were either untrained and/or under-educated, and never failed to fall into lockstep with their dept.leads,and blindly followed the blind.If you didn't, you might go home to no job.

I'm sure he is probably forbidden from discussing it,but I'd be curious to hear from Joe Tedesco on the justification of KBR's vast number of deviations from NEC.I was constantly having to maintain my ground with untrained supervisors over issues such as pencil-whipping paperwork,refusing to use unsafe work practices/methods,etc. Joe can attest to this,as I provided him with photos and copy of an infraction I "wrote-up" of a group of unnamed knuckleheads(o.k.,they were Bosnians/Albanians,and Serbs),who,having no jobs to return home to,and not knowing any better,anyway - would do anything asked of them.I ran into Joe while I was radioing in a completed work order.He was KBRs' main consultant for all of Iraq.

Hope all is well with you,I'm swamped with work,and really glad to be home with my family.Glad you are out of Afghanistan, when will you return to Cali?Steve


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## frenchelectrican (Mar 15, 2007)

1capybara said:


> the intention is to make everything to NEC, but this cable doesnt exist
> in America XLPE/ SWA/ PVC/ CU.
> Both me and the inspector are American electricians.
> A British electrician also told us, he bonds both sides of the SWA.


They do exist in North Americia area but it super limited to get them { pretty hard to get them } 

And I do understand you are try to stay with NEC code that is not a issue with it I can see where it goes and it very common to bond both side of SWA cables { it is a SOP in France } It is simauir to with steel conduit runs.

Merci.
Marc


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## 1capybara (Feb 27, 2009)

frenchelectrican said:


> And I do understand you are try to stay with NEC code that is not a issue with it I can see where it goes and it very common to bond both side of SWA cables { it is a SOP in France } It is simauir to with steel conduit runs. Merci.
> Marc


Marc, exactly right. For example, we run an emt from one panel to feed another. inside the emt are 3 hots a neutral and a ground. the emt
is bonded by its connector to the feed side. would you try to prevent the
emt from making metal to metal contact [bond] on its load side???
Of course NOT!!!

ibuzzard wrote:
"David,we also followed the procedure of bonding only one end of the SWA cable in Iraq, as a directive,clarification,deviation - whatever you want to term it.The sole intent was to have only one fault path,to facilitate faster tripping of the breaker,supposedly."
yes, this is the identical situation here in Afghanistan. It is a
directive from TF Power.


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## Mike D (Sep 16, 2008)

I can understand only hooking one end of the SWA up, if it is in a 3 phase -4 wire feeder. (no EGC)

If the cable has another EGC and the SWA, it would be fine to hook both ends up.


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## brian john (Mar 11, 2007)

ibuzzard said:


> David,we also followed the procedure of bonding only one end of the SWA cable in Iraq, as a directive,clarification,deviation - whatever you want to term it.The sole intent was to have only one fault path,to facilitate faster tripping of the breaker,supposedly..


 
From a logical stand point this makes no sense. If you have more conductor area you should have lower impedance and this should facilitate a faster trip.


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## JimGavin (Oct 12, 2010)

*Master Electrician,*

For American Electricians we must understand that in Europe they use SWA cable and rarely use Conduit with separate conductors. BS7176 allows the SWA to be used up to 16mm conductors or about #6 awg. Above 16mm (6awg) then a separate ground conductor shall be routed with the SWA. Typical general rule is 1/2 the size of the current carrying conductor inside the SWA.

It doesn't matter if the facilities are inspected to NFPA 70 (NEC) or BS7671. They both require ground conductors to be installed.

How are you connnecting the SWA to a cabinet? SWA cable manufactures require the installation of cable glands on each end of the cable. The purpose of the gland is two fold, it provides a grounded path but more important it protects the conductors from being improperly installed. 

A majority of the deficiencies noted during inspections involve grounding of distribution systems. There appears to be a commonly held misconception that driving a ground rod and attaching a grounding electrode conductor to metal or the grounding bar of a piece of equipment will provide an adequate ground fault current path, guaranteeing timely disconnection of circuit protective devices (fuses, circuit breakers, etc.) under all conditions. Given the generally high resistivity of the local soils (sand), this is rarely a valid assumption. The only practical method of ensuring adequate ground fault protection in this region is to provide a continuous low impedance current path from a circuit’s fault point back to the neutral of its power source (transformer or generator) utilizing the appropriate conducting materials (copper, aluminum, etc.). 

Unfortunately some of the steel wire armored cables (SWA) have been installed improperly. Some are installed with a termination gland but are missing the bonding jumper from the gland to the ground bar. The majority have been installed with no gland and the armor either disconnected or partially installed by braiding a few strands and connecting to the ground bar. Again, this results in NO low impedance ground fault current path from a point of ground fault on a wiring system through normally non-current carrying conductors, to the electrical supply that will guarantee timely disconnection of circuit protective devices (fuses, circuit breakers, etc.) under all conditions.

Regardless of any other unknown design issues, based on the observed conditions regarding improper grounding, corrective action should be made to reduce the possibility of electrical hazards by installing a separate properly sized grounding conductor throughout each distribution system and verifying that a bonding connection is made to each of the SWA cables that have not been terminated correctly. Completing the grounding connection will reduce the potential for electrical shock hazard which may be caused by accidental contact of normally non-current-carrying conductive materials to energized parts. The proper size grounding conductors (British Code “protective conductor”) can be sized by referencing the NEC Table 250.122 or British Electrical Code BS 7671 Table 54.7.

If using SWA cables and 50Hz systems then AHJ should be using BS7671 because there are conflicts in voltage ranges when using NFPA 70 NEC. Just personal note I would say the BS7671 is actually more stringent than the NFPA 70 NEC

Jim


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## ibuzzard (Dec 28, 2008)

Brian,I agree with you.I can't figure the basis behind that directive,asking "how come?"only muddled things, i.e. ask four people,get four different responses.In the end,we complied with it,and I felt I didn't have any exposure ,liability-wise,so that's one I wasn't going to argue.

JimGavin-The majority of the SWA strands I saw were made up badly,that is to say either loose, and/or pulled out of the gland, and/or no "banjo fitting"/jumper to ground bus.In many cases,perhaps most,there was an over-sized gland, I even saw plastic glands,or NO glands.That path would have been useless anyway,so removing the strands of armor from one end probably made no difference.The camp I was in in Iraq was a mess.


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## 1capybara (Feb 27, 2009)

ibuzzard said:


> Brian,I agree with you.I can't figure the basis behind that directive,asking "how come?"only muddled things, i.e. ask four people,get four different responses. In the end,we complied with it,and I felt I didn't have any exposure ,liability-wise, so that's one I wasn't going to argue.
> 
> Thats what we did too. Because we didnt have SWA glands,
> we landed 100% of the SWA stands [on the line side] on lugs,
> ...


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## frenchelectrican (Mar 15, 2007)

ibuzzard said:


> Brian,I agree with you.I can't figure the basis behind that directive,asking "how come?"only muddled things, i.e. ask four people,get four different responses.In the end,we complied with it,and I felt I didn't have any exposure ,liability-wise,so that's one I wasn't going to argue.
> 
> JimGavin-The majority of the SWA strands I saw were made up badly,that is to say either loose, and/or pulled out of the gland, and/or no "banjo fitting"/jumper to ground bus.In many cases,perhaps most,there was an over-sized gland, I even saw plastic glands,or NO glands.That path would have been useless anyway,so removing the strands of armor from one end probably made no difference.The camp I was in in Iraq was a mess.


 
Ibuzzard .,
Speaking of SWA cable I have fair share of dolts mess up with the SWA termatation I have few of them I did see they were made up really bad or pulled out that one reason why I have to use both SWA strands plus the EGC in the main cable assambly for safety reason.

Merci,
Marc


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## abellm (Oct 4, 2009)

This is yet another case of an Inpsector blurting out a "violation" without sharing his/her great knowledge!!! M.A. (show me the .....facts!)


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## BIGRED (Jan 22, 2007)

Capybara you are a large rodent.:laughing:


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