What Is Bonding......

Hey Guys,

I was going over my lesson plans and found this image that explains bonding rather nice…in case anyone wanted to refresh their memory…this is an image from Mike Holt…Really does have the best images in the business…


Mike’s Comments: Why is grounding so difficult to understand? One reason is because many do not understand the definition of many important terms. So before we get too deep into this subject, let’s review a few important definitions contained in Articles 100 and 250.Bonding [100]. The permanent joining of metal parts together to form an electrically conductive path that has the capacity to conduct safely any fault current likely to be imposed on it. See Image Above !

Mike’s Comment: Bonding is accomplished by the use of conductors, metallic raceways, connectors, couplings, metallic-sheathed cables with fittings, and other devices recognized for this purpose [250.118].Bonding Jumper [100]. A conductor properly sized in accordance with Article 250 that ensures electrical conductivity between metal parts of the electrical installation.

Effective Ground-Fault Current Path [250.2]. An intentionally constructed, permanent, low-impedance conductive path designed to carry fault current from the point of a ground fault on a wiring system to the electrical supply source.

The effective ground-fault current path is intended to help remove dangerous voltage from a ground fault by opening the circuit overcurrent protective device.

Equipment Grounding Conductor [100]. The low-impedance fault-current path used to bond metal parts of electrical equipment, raceways, and enclosures to the effective ground-fault-current path at service equipment or the source of a separately derived system.

Author’s Comments:
•The purpose of the equipment grounding (bonding) conductor is to provide the low-impedance fault-current path to the electrical supply source to facilitate the operation of circuit overcurrent protection devices in order to remove dangerous ground-fault voltage on conductive parts [250.4(A)(3)]. Fault current returns to the power supply (source), not the earth!

•According to 250.118, the equipment grounding (bonding) conductor must be one or a combination of the following: Figure 250–5

  • Wire Type. A bare or insulated conductor [250.118(1)]
  • Rigid Metal Conduit [250.118(2)]
  • Intermediate Metal Conduit [250.118(3)]
  • Electrical Metallic Tubing [250.118(4)]
  • Listed Flexible Metal Conduit as limited by 250.118(5)
  • Listed Liquidtight Flexible Metal Conduit as limited by 250.118(6)
  • Armor of Type AC cable [250.118(8)]
  • Armor of Type MC cable as limited by 250.118(10)
  • Metallic Cable Trays as limited by 250.118(11) and 392.7
  • Electrically continuous metal raceways listed for grounding [250.118(13)]
  • Surface Metal Raceways listed for grounding [250.118(14)]
    Again courtesy of Mr. Holt…

Wow, and all this time I thought you an d a best friend…

Thanks Paul !!!

Justo…I don’t have friends…:slight_smile:

Wow. Good job paul

I thought “Bonding” referred to the “moment” that you and your girlfriend agree that you both share a special place in each others heart…:wink:

OH Dang… The other bonding!!:smiley:

I-lectrical continuity physically connection to “attach” metal parts to each other to minimize resistance in electrical systems and permit current to travel back to the main panel safely without requiring a different path other then the electrical system… Like YOU and ME… :wink:


Thanks Paul - it’s refreshing to recieve great info from someone who understands what we do.

Hey Bill…thats what I am here for fella…If you ever need anything just ask my friend.


May I note that all of your example posts (excellent, BTW) show metal conduit. Didn’t you say that ROMEX was OK and having the wiring enclosed in EMT was just plain silly? :mrgreen:

Come on over to the ‘Dark’ side, Paul. Join us with the Chicago Codes!


lol…not my images…gotta work with what I got fella…lol…

Yes, Chicago has some strange and expansive AHJ rulings for sure…

Oh…lol…I never said silly…lol…just not for me fella…lol…I dont like pulling wires in conduit and most certainly not in homes…in fact I dont like working with AC either in homes…lol…ME LIKE NM Cable…:slight_smile:


I find the types of posts and info that Paul provides very usefull and informative.

Thanks Paul!

Paul lol’s too much. He obviously has waaaaaaaay too much fun doing what he does. Me? I have to resort to Mr. Cuervo and Mr. Vicodin. :smiley:

" Fault current returns to the power supply (source), not the earth! "

Jeez, this stuff just drives me crazy. Does this mean fault current returns to the pole on the neutral conductor via the grounding or neutral bus bars (depending on the location of the fault)? Doesn’t the neutral conductor then go to a driven rod at the base of the pole?

If fault current goes through the ground bus bar, why doesn’t it wind up going to the ground via the service grounding electrode? -Kent

I ran across this site that explains the difference between grounding and bonding. It helped clear it up for me.



The current must be balanced. “What goes in must come out.” So what ever amount of current is going through the loads via the hot wires from the pole must return to the source (the pole) through the neutral, because this is the path of least resistance.

The ground wires provide a low resistance path back to the neutral bus and then to the pole or transformer. On a fault, this low resistance path will allow a large enough current (current = voltage divided by resistance) to flow through the hot conductor to trip the breaker. But once it has reached the neutral bus, it still goes back to the transformer.

As the link in my previous post explains - the grounding system keeps a person in a parallel path with the grounding system. On parallel circuits, most of the current will travel through the least resistant conductor, thus very little current will flow through the person who happens to come into conduct with something that is grounded but is still live.

So if all the electricity that comes to me eventually goes back to the electric company, why do I continue to get an electric bill each month? I’m confused. If I pay for it, I wanna keep it. Seems to me that we should be putting up a brick wall on the return highway, keep what we’ve paid for, and recycle it. What am I missing?

lol…Mr. Ray…it is because you consumed it…like when you drink those fancy drinks you like…you end up giving the glass back to the table maid right…see…you did not pay for the glass…only what was in it…

Same thing for Electricity…:)…Enjoy It…Voltage ROCKS !

A good analogy is beer. You don’t “keep” that either but Hooters doesn’t give you a rebate for what you leave in the bathroom.

lolololol…If I told you I have never been to a HOOTERS would you believe me Greg…lol

DANG- Your analogy is SOOOO much better than mine…

Now I don’t know if that is a rock band or a drink, but either one sounds good! :smiley:

That might explain why I don’t go to Hooters.
Well, something else might explain it, too. :smiley:

My best friend and I used to go to Hooters in College Station, Texas. When I came out to him, he asked me if I still wanted to go to Hooters. Sure, I said, to his amazement. After a few beers and appetizers, he inquired why I would still want to go there. I said, "Look around you. How many Hooters waitresses do you see. About eight. How many guys do you see? About 88. Case closed. Such places are great Brokeback Mountains.