Table 250.122 or Table 250.66?

[JasonCo]

[FONT=&quot]A 120/240-volt, 1-ph, 3-wire, 100-A main breaker load center is installed for the service on a barber shop. The “green grounding screw” for this panel was lost so you will have to use a piece of wire instead. The service-entrance conductors are 3 AWG. The minimum size conductor you will install in place of the green screw is ___ AWG.

This is a homework question. I am just trying to seek some help on understanding the terminology of this question. For starters, I'm confused about the scenario of this question. If the ground screw goes missing in a panel, how are you going to use a piece of wire to replace it? Do they mean using a mechanical lug to replace the screw? I don't understand what they are saying to be honest... But I'm assuming this is going to be answered off tables 250.122 or table 250.66.

Table 250.66 is Grounding Electrode conductors and Table 250.122 is Equipment Grounding Conductors for Grounding Raceway and Equipment.

Unsure what "wire" they are referring to... Personally I have never used a green screw in a panel, so I have no personal experience with this question.
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[GoldDigger]

This could be a reference to a grounding screw for the enclosure itself, in which case the question does not make a lot of sense,
or a reference to a bonding screw whose purpose is connect the ground (EGC) bar to the neutral bar when the panel is used as a service disconnect point.
In the latter case, a factory supplied screw is considered to be an adequate bonding means regardless of what the calculated current for the panel is.
But when the screw cannot be used or was not part of the design, a wire from one bar to the other must be sized according to the rules for a main bonding jumper.

 

[don_resqcapt19]

Since this is a homework question, you have to do some work. What is that missing green screw called by the code? One you know that, you can find that term in Article 250 and it will tell you how to size it.

 

[Dennis Alwon]

The main bonding would be size by the grounding electrode conductor. The equipment grounding conductor is the ground found in raceway, cables etc, that ground all electrically parts--from the book

The conductive path(s) that provides a ground-fault current path and connectsnormally non–current-carrying metal parts of equipment together and to the system grounded conductor or to the
grounding electrode conductor, or both.

 

[JasonCo]

Thanks for your help! To answer Golddiggers question

If I look bellow table 250.122, it reads "terminal screw" with a hexagonal head. Or A green, hexagonal, not readily removable "terminal nut".

Edit: So answer would be number 8 wire? I have to use the 100 amp Overcurrent protection breaker for sizing it off table 250.122.

 

[don_resqcapt19]

You do not size the green screw per the rules in 250.122. It is not an equipment grounding conductor. I know you know what it is, as you have recently asked other questions about it.

 

[don_resqcapt19]

The main bonding would be size by the grounding electrode conductor. ...

I don't understand how it has anything to do with the grounding electrode conductor.

 

[infinity]

A 120/240-volt, 1-ph, 3-wire, 100-A main breaker load center is installed for the service on a barber shop. The “green grounding screw” for this panel was lost so you will have to use a piece of wire instead. The service-entrance conductors are 3 AWG. The minimum size conductor you will install in place of the green screw is ___ AWG.

This is a homework question. I am just trying to seek some help on understanding the terminology of this question. For starters, I'm confused about the scenario of this question. If the ground screw goes missing in a panel, how are you going to use a piece of wire to replace it? Do they mean using a mechanical lug to replace the screw? I don't understand what they are saying to be honest... But I'm assuming this is going to be answered off tables 250.122 or table 250.66.

Table 250.66 is Grounding Electrode conductors and Table 250.122 is Equipment Grounding Conductors for Grounding Raceway and Equipment.

Unsure what "wire" they are referring to... Personally I have never used a green screw in a panel, so I have no personal experience with this question.

You're close but neither of those tables are what you would use. Take a look at 250.102(C)(1) and then go back to the question and pick out the relevant information to find the answer.

 

[Mouser]

The question is worded to leave a secondary key word out but your looking for a bonding jumper at the service panel so...

Do this.

Subject index "bonding Jumpers" which tells you to see "Jumpers Bonding".

Sub index "Service Equipment" The first code section listed is were you want to carefully read.

 

[JasonCo]

You're close but neither of those tables are what you would use. Take a look at 250.102(C)(1) and then go back to the question and pick out the relevant information to find the answer.

I'm not gonna lie, this is a pretty confusing question holly crap! So, they are saying the ground screw went missing so instead I need to use a bonding jumper to jump wire from the service equipment to my panel? I mean I'm all sorts of lost. A piece of wire will go from where to where in my panel? The ground bar?

 

[rcarroll]

The ground bar is fine.

 

[infinity]

I'm not gonna lie, this is a pretty confusing question holly crap! So, they are saying the ground screw went missing so instead I need to use a bonding jumper to jump wire from the service equipment to my panel? I mean I'm all sorts of lost. A piece of wire will go from where to where in my panel? The ground bar?

First you need to understand what the green screw that goes through the neutral bar into the metal enclosure is. It's the main bonding jumper (MBJ). If you loose the screw you can make your own MBJ with a piece of properly sized wire, this will take the place of the screw which connects the metallic cabinet (panel enclosure) to the neutral. If the panel has a separate EGC bar then you can use the MBJ to connect it to the neutral bar.

 

[texie]

I'm not gonna lie, this is a pretty confusing question holly crap! So, they are saying the ground screw went missing so instead I need to use a bonding jumper to jump wire from the service equipment to my panel? I mean I'm all sorts of lost. A piece of wire will go from where to where in my panel? The ground bar?

I get a sense that maybe you are confusing the so called missing "ground screw" with a green grounding screw that is used as a terminal, for say, connecting an EGC to a box. In the context of your question, the missing green screw is the main bonding jumper-not a terminal. Take a look at 250.28 and see if that helps. Also see the definition of Bonding Jumper, Main to see what it connects between.

 

[texie]

The ground bar is fine.

Off topic, but aren't we about do for a meeting?

 

[Dennis Alwon]

I don't understand how it has anything to do with the grounding electrode conductor.

Huh.. the main bonding and grounding electrode conductor are sized almost identically. I would just saying he could use 250.66 for the bonding unless he has a newer code then it would be T250.102(C)(1). He didn't mention that table. That table and 250.66 were the same at one time

 

[texie]

Huh.. the main bonding and grounding electrode conductor are sized almost identically. I would just saying he could use 250.66 for the bonding unless he has a newer code then it would be T250.102(C)(1). He didn't mention that table. That table and 250.66 were the same at one time

Yes, 250.66 used to be used for both GEC and all the other things now in 250.102(C)(1). But you had to use the table correctly and apply the notes if you were using for other than a GEC. The problem was that some people did not understand that while a GEC maxed out at 3/0 CU, all other items that are now in the new table do not max out like a GEC does.

 

[don_resqcapt19]

Huh.. the main bonding and grounding electrode conductor are sized almost identically. I would just saying he could use 250.66 for the bonding unless he has a newer code then it would be T250.102(C)(1). He didn't mention that table. That table and 250.66 were the same at one time

That is just not how your post read to me...to me it says that the sizing of the main bonding jumper is based on the size of the GEC.

 

[augie47]

Start with what you are doing. You are grounding an AC service so you go to 250.24 where (B) tells you you need a main bonding jumper and refers you to 250.28.. follow the leads from there.......