Why Do We Bond at the Service Panel and Not a Subpanel?

An important question was raised by one of our viewers. Why do we bond at the Service Panel and not at the Subpanels? A very valid and super important question that Dustin brings answers to in the latest episode of Electrician U.

CHAPTERS
[00:00] INTRO
[01:07] Merch messages
[01:42] Start of explanation
[03:58] Objectionable Current
[09:21] Example 2
[13:05] Example 3
[18:28] Bonding Wrap up
[19:07] OUTRO

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So, in a typical scenario, we would bring our ungrounded (hots), grounded (neutral) and grounding (ground) conductors into our service. This is at the point that we would bond the grounded and the grounding conductors together. From there, our all the conductors leave and can enter another panel where they are kept separated with no bonding. The primary reason for that grounding conductor is to set an alternate path back to the voltage’s source (breaker or fuse etc.) in case something happens, so there is another path back for the breaker to trip. Without that alternate path, the chances for someone to get shocked are considerably higher.
One of the reasons we separate the conductors past the Service Panel has to do with Objectionable Current. Simply stated, it is current that is going multiple directions at the same time; those directions we DON’T want it to go in! normally, that current leaves the source on the ungrounded wire, travels through the source, and returns to the source on either the grounded conductor or the other ungrounded conductor at the equipment. Objectionable current would be if a wire came off and touched something it wasn’t supposed to and sent the current somewhere else. The neutral conductor is expected to carry current; ground wires are not meant to carry them on anything other than a fault condition. If we didn’t bond the neutral and ground together at some point, we potentially could have objectionable current flowing on BOTH the neutral and ground at the same time and trying to return to source creating a considerable amount of havoc along the way!
If there was an event, say a ground fault where one of the ungrounded conductors touched the case of a dryer, the grounding conductor would carry that objectionable current, momentarily, back to the service panel, where it is bonded to the neutral, thereby completing the circuit. In fact, since the load itself was taken out of the equation (by touching the case and bypassing the load itself) the breaker sees SO MUCH current, that it does exactly what it is supposed to do and will trip. If that grounding wire was not there, and the complete circuit was not made, there would be potential for current to be on ALL the metal downstream from the service point and someone could get severely injured.
So, wouldn’t extra bonding be good by bonding in each panel location? If we were to bond in EVERY panel, then we would leave MULTIPLE paths that the current COULD take on its way back to source to complete the loop, and we would be defeating the purpose of trying to direct the current back to its source. In addition, if the neutral and ground were bonded in EVERY panel, then under the same circumstances, we would be sending potential to EVERYTHING plugged into ALL the circuits. So, we BOND it at the one spot only so we can keep the current corralled along the way WE want it to go and not energize everything along the way!

[johnpetruna]

That is the best explanation of this concept/rule I have ever seen. And I'm almost a boomer!

[turmoilfab]

I’m not even an electrician but this is now the only guy I go to to get an explanation I can try to grasp. Great job!

[john]

I'm a retired IBEW inside wireman. You do a very good job of explaining this. There's so much information that a good electrician needs to know to work in the field and that's why continued training is a must. It's good to be retired.

[neilbarrow]

Hey Dustin. I'm an electrician in the Bahamas and this is the best explanation I've ever heard explaining this. Now I will use this video as a teaching tool when I get in an argument pertaining to bonding. Thanks.

[robertdabicci]

Been wanting an explanation for the multiple sub panel bonding issue and this is the best information I have found. I knew you didn't want to bond except at the main panel but didn't understand why until now. Thank you for a great video. Bob

[nobadmojo]

Man, you've really elevated your teaching game, which is really saying something, your older videos are really good.

This new generation of Electrician U is outstanding! It's very well organized, demonstrated, explained and marketed. Thank you again for all of your efforts and pushing through the challenges. Keep up the excellent work!

[lawbulb]

As a layperson, I didn’t understand any of this until I saw your presentation. I can’t possibly explain it to someone else like you did, but I really get a feel for how this stuff works now. Fascinating stuff!

[williammoyer]

Kudo's from a retired Union Electrician on being able to break it down so well. Keeping the grounds and neutrals separate greatly helps when trouble shooting, GFCI issues especially.

[rossroberts]

This is the only video I have found that actually helps build the concept in your mind. Very nice! The only thing missing is the explanation of "Service Panel" being the first junction past the meter or equivalent as the place needing neutral to ground bonding, be it a service disconnect switch or main breaker panel inside of the structure. Bravo!

[raymond]

Your topics always filled with clarity at its best, and your demonstration is on Q.

[emoryjiles]

This fellow brought up some key points about sub-panel wiring I never really considered. He is a gifted teacher. I’ll be tuning in for more. I’m a humbled 30+ year electrical engineer.

[johnkruton]

Your illustrations and explanations are the excellent educational visual along with Mike Holt’s very technical history and explanation about bonding. Eg: Factory motors, DC pulse (lightning) literally taking 120V line and putting to earth and measuring the current and seeing if a breaker will trip (it doesn’t)….your visuals complete the brain circuit!!!

[memozzy]

I haven't been watching lately but I'm so glad you've grown your channel so much!

[michaeldunn]

1st year apprentice here, thanks for taking the time to make these easy to understand and simplified videos Dustin!

[aaaaaaaaaaaaaa]

I don't think evey8ne knows how much of a help you are!! Your such an amazing content creator appreciate your time man !!

[johnlieber]

In your example you have multiple subpanels all flowing through each other. In the case of a single subpanel, say in a garage, in my mind it seems like having the neutral and ground bonded in the subpanel means that during everyday operation, neutral current can flow back on either the neutral or ground wire or both! This does not seem like a good idea, and I would be very curious to know why anyone EVER thought bonding these in a subpanel was a good idea. Maybe I am misunderstanding something. Thank you and love your channel, very clear and to the point!

[spruce_goose]

16:18 I believe objectionable current is more in reference to neutral current (i.e. normal operating conditions) rather than ground fault. In other words, the issue is less ground fault current traveling on a neutral conductor and more normal operating current that should be solely on the neutral traveling on the ground (EGC).

[s.mendez]

Most excellent explanation, especially since it was done in color for us visual learners. Thank you for your teachings.

[BrandonCarrillo-pw]

I do a lot of diy wiring, I've always followed this as a rule but never fully understood why. This is the best visual explanation anyone could ask for, Thank you so much!

[elBusDriverKC]

Great topic. I actually already knew all of this, but wanted to make sure there wasn't any gaps I needed filled in. You do a good job of explaining! On that note, please do a video on portable gas generators in relation to grounding, neutral, back feed dangers etc...