400 amp service grounding

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rojay

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I came across a 120/240 volt single phase 400 amp service at a residential job yesterday. It was a typical back to back installation with a 320 amp meter and two 2” RMC 90’s terminating at 2 separate 200 amp MB panel boards via 3-3/0 service entrance conductors.

Along with the service entrance conductors in each raceway a supply side bonding jumper was pulled and terminated at bonding bushings at both ends of each raceway.

While an NEC allowed parallel path for neutral current already exists between the meter can and the service disconnects via the 2” RGC’s - is the addition of another parallel path via #4 SSBJ’s pulled with the service conductors technically a code violation or just a waste of money?
 
rojay said:
I came across a 120/240 volt single phase 400 amp service at a residential job yesterday. It was a typical back to back installation with a 320 amp meter and two 2” RMC 90’s terminating at 2 separate 200 amp MB panel boards via 3-3/0 service entrance conductors.

Along with the service entrance conductors in each raceway a supply side bonding jumper was pulled and terminated at bonding bushings at both ends of each raceway.

While an NEC allowed parallel path for neutral current already exists between the meter can and the service disconnects via the 2” RGC’s - is the addition of another parallel path via #4 SSBJ’s pulled with the service conductors technically a code violation or just a waste of money?
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The rule on metal service raceways is you need more then just standard locknuts to assure the raceway is bonded. It only needs such bonding at one point.
 
kwired said:
The rule on metal service raceways is you need more then just standard locknuts to assure the raceway is bonded. It only needs such bonding at one point.
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So then the only time the NEC would require bonding at both ends of a service raceway would be in the case of concentric/eccentric ko’s at both ends?
 
rojay said:
So then the only time the NEC would require bonding at both ends of a service raceway would be in the case of concentric/eccentric ko’s at both ends?
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Nope, it's still only required at one end. You're are not trying to maintain the continuity between the two pieces of equipment you are only trying to ensure that the service raceway is bonded with a means better than standard locknuts.
 
Thanks for the clarification guys! Great point- the service raceway is no less bonded to the service equipment by using only one grounding bushing (w/ jumper if necessary) vs. using two.
 
rojay said:
So then the only time the NEC would require bonding at both ends of a service raceway would be in the case of concentric/eccentric ko’s at both ends?
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rojay said:
Thanks for the clarification guys! Great point- the service raceway is no less bonded to the service equipment by using only one grounding bushing (w/ jumper if necessary) vs. using two.
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Others answered your question, I will add the time you will need say a bonding bushing at both ends of a raceway is if using the raceway as an EGC and you have concentric/eccentric KO's at both ends and a requirement to bond around said KO's. This of course would be non service raceway for what I am describing.
 
kwired said:
Others answered your question, I will add the time you will need say a bonding bushing at both ends of a raceway is if using the raceway as an EGC and you have concentric/eccentric KO's at both ends and a requirement to bond around said KO's. This of course would be non service raceway for what I am describing.
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But what if things were arranged such that a service raceway was the sole fault path? Then I believe we would need a BB at both ends.
 
electrofelon said:
But what if things were arranged such that a service raceway was the sole fault path? Then I believe we would need a BB at both ends.
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Can you name a scenario where that would be possible? All of the equipment on the line side of the service disconnect should be bonded to the neutral and not really on the metal raceway for any return path. Same scenario with a PVC service raceway.
 
infinity said:
Can you name a scenario where that would be possible? All of the equipment on the line side of the service disconnect should be bonded to the neutral and not really on the metal raceway for any return path. Same scenario with a PVC service raceway.
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Why can't I use an approved raceway as the fault path at a service? Bonding to the neutral is one option but I believe bonding jumpers or raceways are acceptable as well. Consider a metal pull box, them RGS raceway, then bonded panelboard. Couldn't the RGS bond the box?
 
electrofelon said:
Why can't I use an approved raceway as the fault path at a service? Bonding to the neutral is one option but I believe bonding jumpers or raceways are acceptable as well. Consider a metal pull box, them RGS raceway, then bonded panelboard. Couldn't the RGS bond the box?
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On supply side of service disconnect, every enclosure will have a bond to the grounded conductor - any raceways between them just need something more then standard locknut to assure they are bonded, and only need bonded in one place. You could even put a pipe bonding clamp on it outside the box and bond it via that if you wanted - many seem to think bonding bushings are the only way to do this.
 
electrofelon said:
But not necessarily "directly" to the grounded conductor
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Service equipment has to have a direct connection to the grounded conductor.
Wire binding Jumpers and raceways are allowed. If I use a raceway, I need service bonding on both ends, IMO.
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That is not correct, one end of the raceway is all that needs an extra connection beyond a lock ring.
 
rojay said:
So then the only time the NEC would require bonding at both ends of a service raceway would be in the case of concentric/eccentric ko’s at both ends?
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Only required if the service raceway contains a grounding electrode conductor, to be bonded at each end.
For con/ecc KOs only one end of the raceway is bonded, to provide a fault current return path to the source.
 
electrofelon said:
I think what you are thinking of has to do with equipment where there is a service disconnect which would require a MBJ, grounded conductor brought to service equipment, etc. Consider a metal pull box or wireway.
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I have always bonded them to the grounded conductor when it is service conductors - but I suppose you could rely on a metal raceway as long as it isn't solely depending on a standard locknut for that bonding path.
 
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