Gronding

Status
Not open for further replies.
I

istechjr

Member
I work at a company in Wisconsin and am taking the Journeymen's class of yours
and have a question of bonding and grounding a new Pnael that was installed.

The Contractor that installed a new panel for us has no ground wire coming to
the panel and the Transformer as far as I know is not Bonded to the Building.
to each outlet there are no ground wires pulled and the outlets have no ground
pigtails to the boxes. When we called him on it he sent a article over from the
code book that stated that conduit is a acceptable ground. He refered to the
following article 250.118 Items 2, 3, & 4.and he states that this is a
acceptable equipment grounding conductor using the conduit.

I beleive that the proper way of doing it is to pull a ground wire.

Would you please advise your stand. I have been reading your articles and
beleive that you would say to pull the ground wire however I beleive this
contractor does not want to occur the cost of the ground conductor and pulling
of it.

Thank you for your time.
 
The raceways in the code section given, correctly installed, are recognized equipment grounding conductors. A separate equipment grounding conductor (wire) would augment the raceway but the NEC does not require it if you are using a raceway recognized as an equipment grounding path.

Reference 90.1(B).

Pete
 
Istechjr,

I personally will always pull a grounding conductor. I did find the following interesting. Of course it applies to properly installed conduit. I have read something about a limit in length for conduit as a grounding conductor. Unfortunately I can find it for the life of me.


Electrical grounding by Ronald P. O'Riley page 135:
"Question: How do the various metal raceways used for equipment grounding conductors compare with a copper conductor in their ability to conduct the electron flow


Answer: An accurate comparison cannot be made because of the unknown length of the raceway, conductors enclosed, or the ambient temperature in which the raceway might be installed. Figure 10-22 uses approximate values for a simplified comparison illustration. It shows the resistance per 1000 ft (300 m) of various metal conduit-type raceways and the copper wire size with a comparable resistance per 1000 ft (300 m) Aluminum is often used for an electrical circuit conductor. Note how the resistance of ? in. (13 mm) aluminum conduit is approximately as low as the resistance of a 2/0 AWG copper conductor.
The IMC has approximately 62 percent as much cross-sectional area as rigid steel conduit. EMT has approximately 22 percent of the cross sectional area of rigid steel. As the size of the conduit increases, the cross-sectional area of the metal in the conduit increases.



Reason: The resistance of a conductor is inversely proportional to its cross-sectional area. This means the resistance of the conductor will decrease as the cross sectional area of the conductor increase.”

Fig. 10-22 Comparison of metal raceways resistance to copper-conductor resistance.

Equipment Grounding Conductor Raceway Material Comparison.

(Type Conduit) (Size) (Dc Res. Per m ft) (Copper wire size)

Rigid steel ? .320 4 AWG


IMC ? .490 6 AWG


EMT ? .970 10 AWG


Aluminum ? .080 2/0 AWG


Justin J. Walecka
 
Last edited:
You can download a free program from the Steel Tube Institute that calculates the maximum length of conduit or copper conductors for use as an equipment grounding conductor here.
Don
 
The key to using a metallic raceway as the equipment ground and effective fault path is to make sure all fittings and parts are installed properly. A single loose coupling or terminal adaptor renders the installation useless. The same can be said for a poorly spliced or poorly terminated conductor, but I feel it is more likely to occur with conduit or tubing.
 
Has anyone as an inspector turned down, or anyone as a contractor been turned down for using a recognized raceway as an equipment grounding conductor based on the length of the raceway? 250.4(5), for example, gives us the performance requirements for a grounded system. Does it then become the responsibility of the inspector and/or installer to assure that these performance criteria have been met? How does one go about assuring that they have given that there are numerous variables that come into play?

Pete
 
That is the problem of the design professional. It is their responsibility to ensure installations will perform intended function. The inspector’s job is to ensure compliance with the approved plans and NEC requirements.

There are times where the actual circumstances of the installation will cause question into the performance of the installation. At that time, the inspector may choose to perform a calculation or request the installer/design professional to provide that documentation.

Most of time however, this can be determined at time of plan review.
 
istechjr, Article 250.146 requires an equipment bonding jumper unless direct metal to metal contact is made such as utility boxes, or if self grounding devices are used.

(A) Surface Mounted Box Where the box is mounted on the surface, direct metal-to-metal contact between the device yoke and the box or a contact yoke or device that complies with 250.146(B) shall be permitted to ground the receptacle to the box. At least one of the insulating washers shall be removed from receptacles that do not have a contact yoke or device that complies with 250.146(B) to ensure direct metal-to-metal contact. This provision shall not apply to cover-mounted receptacles unless the box and cover combination are listed as providing satisfactory ground continuity between the box and the receptacle.

(B) Contact Devices or Yokes Contact devices or yokes designed and listed as self-grounding shall be permitted in conjunction with the supporting screws to establish the grounding circuit between the device yoke and flush-type boxes.
Rick
 
I am from the metro Chicago area and the only type of installation used is metalic tubing. We do not allow the use of NM. As far as the ground wire for devices, there are some communities that require receps to be self grounding or have a ground jumper installed between the box and the device. However, unless it is spec. we generally do not pull a grounding conductor. This is not limited to commercial, the same is true for residential.
 
scott moran said:
As far as the ground wire for devices, there are some communities that require receps to be self grounding or have a ground jumper installed between the box and the device.
Click to expand...


You would have to do at least one or the other to comply with the NEC unless you meet the requirement of RUWired (A) post.
 
Status
Not open for further replies.
Top