250.66 vs 250.122?

[JasonCo]

I'm an apprentice in school, just getting a bit confused on which table to go to when trying to understand grounding conductors. So I understand if you have a grounding conductor that goes from the panel grounding bar to the ground rod, this is considered a grounding electrode conductor. But... Lets say you have to size a conductor that goes from your ground bar in your service panel to the metal housing in a 3 phase motor. Wouldn't this fall under a equipment grounding conductor that falls under 250.122? I'm just confused with all this, any help to better understand this would be amazing! Thank you

Edit: Another example I'd also be confused about is a grounding conductor going from your panel ground bar to a ground bar in a pull box. Would that be a bonding jumper, equipment grounding conductor or grounding electrode conductor? Wouldn't that be a bonding jumper...?

 

[Smart $]

There are three types of grounding conductors

Grounding electrode conductors... with no surprise here, these go to grounding electrodes and sized per 250.66.

Equipment grounding conductors... these are required to be run with the circuit conductors. Wire type are sized per 250.122.

Bonding conductors and jumpers are all other wire type grounding conductors and are sized per 250.102.

 

[Ponchik]

The way that I try to remember this is:

Grounding Electrode Conductor (GEC) Generally you install the "Electrode" in the ground. So GEC is the wire that connects the electrical system to the ground because it has the word "electrode" in it. 250.66

Equipment Grounding Conductor (EGC) it is the wire type that connects the "Equipment" to the grounding system. 250.122

Bonding jumper, It is the wire that bonds, jumps two pieces together.

BTW, metallic raceways do count as an equipment grounding conductor. However, they are not sized based on 250.122

 

[GLSA]

All three of your scenarios fall under three different parts in article 250. Spend some time in your code book to understand the differences. Also check out the free stuff Mike provides on his website it should clear up some of the confusion for you.

 

[steve66]

Table 250.66 is always used for sizing conductors to grounding electrodes and grounding electrode systems.

But 250.122 is generally used for any feeders or branch circuits, AFTER a circuit breaker or fuse.

If you have a transformer that is a separately derived system (like a 3 phase delta to wye), on the secondary of a transformer, before the secondary fuse or breaker, you must use 250.66.

Then, once the feeder has ran through the fuse or circuit breaker, you switch to using 250.122.

For both of your questions about running to a motor or to a pull box, the ground would be ran with feeders or branch circuits. So it would be using 250.122 based on the largest fuse or breaker supplying a circuit to that motor or pull box.

 

[augie47]

I alwsy go back to the rule Steve66 just cited. If the accompanying conductors are protected by an overcurrent device such as the circuit going to your motor, its 250.122. If there is no overcuurent device ahead of what is being grounded such as a service panel or transformer then 250.66

 

[Smart $]

...
If you have a transformer that is a separately derived system (like a 3 phase delta to wye), on the secondary of a transformer, before the secondary fuse or breaker, you must use 250.66.
...

Between transformer secondary and the system disconnecting means, if in a separate enclosure, you run a supply-side bonding jumper (SSBJ) of the wire type sized per 250.102(C). The required GEC is sized per 250.66. You will have both for an SDS over 1,000VA.

• Jumpers before disconnecting means - 250.102
• Jumpers after disconnecting means - 250.122

 

[Smart $]

I alwsy go back to the rule Steve66 just cited. If the accompanying conductors are protected by an overcurrent device such as the circuit going to your motor, its 250.122. If there is no overcuurent device ahead of what is being grounded such as a service panel or transformer then 250.66

Forgetting 250.102.

 

[steve66]

Forgetting 250.102.

Which I believe for most cases just refers back to 250.66 and 250.122. Except that if you have feeders or service conductors larger than those listed in 250.66, you also have to make sure the grounding conductor stays at least 12.5% of the feeder or service conductor size.

 

[Smart $]

Forgetting 250.102.

Which I believe for most cases just refers back to 250.66 and 250.122. ...

He's just learning and I don't want to get him in trouble on a technicality. The types in the table's title—Grounded Conductor, Main Bonding Jumper, System Bonding Jumper, and Supply-Side Bonding Jumper—do not get kicked back to 250.66. They do exist and new ones are installed every day. I want to teach him to do it the right way from the get go. Please do not interfere with that process again.

 

[ggunn]

There are three types of grounding conductors

Grounding electrode conductors... with no surprise here, these go to grounding electrodes and sized per 250.66.

Equipment grounding conductors... these are required to be run with the circuit conductors. Wire type are sized per 250.122.

Bonding conductors and jumpers are all other wire type grounding conductors and are sized per 250.102.

There is a fourth type in PV systems; the combination EGC/GEC, sized to the larger of the two determined by 250.122 and 250.66.