Why Are GROUNDING Conductors Smaller Than GROUNDED Conductors???

The conductors we use as electricians come in many different sizes, colors, and compositions of the metallic portion as well as the insulation portion. Most of us electricians know that the Size of the conductors we use are based upon the ampacity they will be carrying (for the most part anyway). So why then, are the “Grounding” conductors for any particular installation smaller than the “Grounded conductors”? In the latest episode of Electrician U, Dustin dives into this question from one of our followers.

[0:20] - Intro
[0:34] - Article 100
[2:00] - Neutral examples
[5:30] - Article 250.122
[7:30] - 220.61 Feeder or service neutral
[8:30] - Outro

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Let’s define the two different conductors first. Article 100 of the NEC defines the Grounded conductor (neutral) as a system or circuit conductor that is INTENTIONALLY grounded. An Equipment Grounding Conductor is a conductive path(s) that is part of an effective ground fault current path that connects normally non-current-carrying metal parts of equipment together and to the system grounded (neutral) conductor or to the grounding electrode conductor or both. Now, the neutral conductor is designed to be a current-carrying conductor under normal circumstances, whereas the grounding conductor is not meant to carry current under normal conditions.
If an electrical system is Perfectly balanced, which almost every single system is not PERFECTLY balanced, the neutral conductors MAY not have much (or any) current on it. The neutral conductor is designed to carry the imbalance of current on a circuit all the time, so it must be sized like it would be carrying current. There are some instances where you can have a reduced neutral size (for instance a dwelling unit) and your grounded conductor can actually be smaller than your ungrounded (hot or phase) conductors. There are also situations where you may have an excess of three phase nonlinear loads where you must Increase the size of your neutral, and the Grounded conductor is actually LARGER than its associated Ungrounded (hot) conductors.
So, on to the Grounding conductor. This conductor is not meant to carry current on it under normal circumstances. Only if something goes wrong, and only for long enough for the circuit to be completed and the breaker to trip. This is the reason that the grounding conductor can be smaller than the grounded conductor of a system. So only under fault conditions, should the grounding conductor have current on it. And, by a small amount of time, I mean fractions of seconds! Just long enough for the circuit loop to be completed (as electrical circuits must be to work!), for the breaker or fuse to recognize that there is far more amperage on the circuit than it is designed to carry, and to trip the breaker (or blow the fuse) and stop current from flowing.
This brings up another potential question. If it is only meant to carry current under fault conditions and only for a split second, then why are there any size restrictions at all for the grounding conductors? The longer the run, the longer it is going to take for the current to travel back to its source. So, the potential current that may be required to travel on the grounding conductor COULD be on there long enough to melt insulation (or even the metal conductor portion), therefore, we have to size it to be able to carry that offensive current for long enough and not be adversely affected.
Article 250 of the NEC concerns Grounding and Bonding and if you have questions about the installation you are working on, is the most likely place you will start your research. Table 250.66 covers sizing of the grounding electrode conductor (ground wire) for alternating current systems. Article 250.102 (C)(1) covers sizing of the Grounded Conductor (along with several bonding

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