Can a bond bushing replace an EGC in an electrical update?

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dgraham

New User
Location
Austin Texas
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Electrician
I am doing a renovation for a municipal client and most of the conduit is 40+ years old so they used the raceway as a ground. The client and engineer want to know if it is possible for us to use bond bushings in each box instead of pulling in a new EGC.
 
The raceway is permitted as the EGC. Bonding bushings can be used but are probably not required depending on a few factors like concentric or eccentric KOs and above 250 volts to ground.
 
LarryFine said:
Welcome to the forum.

For the most part, conduit that is properly connected to metallic boxes and enclosures can act as the EGC without additional bonding.
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FWIW, I always specify a wire EGC. Every joint/connection in a conduit run is a potential point of failure.
 
ggunn said:
FWIW, I always specify a wire EGC. Every joint/connection in a conduit run is a potential point of failure.
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And so is every wire nut and screw.
In most commercial construction with metal framing you could leave every raceway joint loose and still have a better EGC than a wire can offer. This is the reason in 517.13 the metallic raceway is the primary EGC and the wire is secondary.
 
A note about terminology: GEC vs. EGC.
IF you're referring to the green wire that's run with circuits, the pipe itself is quite a good conductor. I've witnessed the UL research tests, where the sloppiest EMT assembly you could ever imagine was able to handle enormous amounts of fault current.
HOWEVER, I've also witnessed (and fixed) a 1963 multi-panel commercial service, where the power company main fed a cluster of three large panels, all grouped together. The extremely competent original contractor - the very man who brought the "Ufer" into the NEC - had counted on the conduit stubs connecting the three panels to 'create' one panel. Alas, nearly half a century later age and corrosion had combined to degrade that ground / neutral bond, resulting in massive power quality problems and voltage surges. Simply isolating the ground from the neutral in two of the panels, and running a green wire to the first panel eliminated the problem.
LIKEWISE, I have discovered that in an ungrounded system (480 3-phase, no neutral), using the pipe alone WILL result in all manner of problems if there are ANY single phase (480 volt 2-wire) circuits. Even a failing light bulb will introduce all manner of transients - and finding that fault is extremely difficult.
 
roger said:
And so is every wire nut and screw.
In most commercial construction with metal framing you could leave every raceway joint loose and still have a better EGC than a wire can offer. This is the reason in 517.13 the metallic raceway is the primary EGC and the wire is secondary.
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I have no problem with redundancy.
 
roger said:
And so is every wire nut and screw.
In most commercial construction with metal framing you could leave every raceway joint loose and still have a better EGC than a wire can offer. This is the reason in 517.13 the metallic raceway is the primary EGC and the wire is secondary.
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100% on the mark, and the fault current should remain somewhere in the direct path of the faulted conductors to the source or OCP.
 
dgraham said:
I am doing a renovation for a municipal client and most of the conduit is 40+ years old so they used the raceway as a ground. The client and engineer want to know if it is possible for us to use bond bushings in each box instead of pulling in a new EGC.
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Would not the engineer make that decision if he designing the job- why else is he there—-
 
Long thread on this on another forum. I use the pipe if its legal. Double so in steel buildings.
 
I was doing a machine install in a box factory and they were fussing over static cling. Someone got the idea they were going to drill holes in the floor for rods to have "independant" ground. It was a tuff sell to point out we were in a steel building with huge rebar mat and was real contentious regarding the fact they should not disconnect egc and replace with the rods. I said,,, you can pound all the rods you want but you cannot unhook this wire.
 
I still remember it, they called their preferred EC when we said that we want something signed that we provided the machine wired correctly. EC came by later and said,, we straightened that out.
 
ggunn said:
I have no problem with redundancy.
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The problem is the wire EGC debate has become pratically to the level of a cult. Why does no one use two OCPD's or GFCI's in series for redundancy? What if you just have one and it fails? What I like to see is some critical thinking about whether a wire EGC should be used rather than a blanket statment. Say I have a dozen pipes all strapped to strut that are bolted to building steel. Why on earth would a wire EGC be needed? On the other side, say A single, maybe smaller diameter pipe strapped to a non conductive surface. Maybe the wire EGC is prudent in that case.
 
electrofelon said:
Say I have a dozen pipes all strapped to strut that are bolted to building steel. Why on earth would a wire EGC be needed? On the other side, say A single, maybe smaller diameter pipe strapped to a non conductive surface. Maybe the wire EGC is prudent in that case.
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Certainly in a steel frame building there are hundreds of parallel paths with the EGC so your point is valid. In 40 years in the trade I have seen an evolution in the thinking about this.

When I started in the 80's you never saw a green wire in any raceway. Even with 3/4" FMC we never installed a wire type EGC (old NYC electrical code). Then in the late 90's-2010's we were pulling in EGC's and IG's everywhere, often a separate EGC for every branch circuit even in a common raceway. Fast forward to 2015 and beyond we stopped pulling them in because someone started to realize (per electro's point) that they were a waste of money in steel framed construction or where you had large racks of conduits all connected together every 6' with a piece of strut. The last big high rise building I worked in they had an odd idea where they specified that only raceways for emergency circuits got a wire type EGC.
 
Yes, hundreds of pathways. I am not sure what a snapshot of a fault thru the pipe would look like but despite the building being one unit similar to say an appliance they still want ground to run with the curren conductors, with steel the boxes the pipes and bolted to the frame in most places that a loose nut isnt such a concern. Found one of my own the other day in the ceiling was missing he nut. I might have even ran another clip next to it but it was wedged tight. 20 ft in the air for light.
 
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