Equipment Grounding Conductor 250.122 (D)

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NEC 2008 section 250.122 (D) (2) now requires a different calculation when sizing the grounding conductor when using an MCP (motor circuit protector). this new calculation invalidates the standard size grounding conductor now supplied in type TC cables and Armored 600V power cables. When you go to 100HP and above motors the standard ground wire in these cables are undersized by one. Does any one know if the cable manufactures are going to upgrade their cables to meet the new code requirement or are we going to be forced to upsize feeder cables or run individual conductors.
 
I don't believe taht should be the case. The ungrounded conductors are not being increase to accomodate voltage drop or any other reason for proper circuit operation. So hopefully it won't become a circle.
 

iwire

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edgutah said:
I don't believe taht should be the case. The ungrounded conductors are not being increase to accomodate voltage drop or any other reason for proper circuit operation.

250.122(B) is not limited to voltage drop, if the circuit conductors increase in size for any reason at all then the EGC must increase.
 

don_resqcapt19

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Bob,
The change in the 2008 code no longer lets you size the EGC, for a motor circuit that has an MCP as the ground fault and short circuit protection, based on the size of the motor overload protection. You are now required based on the maximum permitted rating of a dual element fuse. This change will increase the required size of the EGC for motor circuits that use a MCP. I think there will also be an issue with motor circuits that use other types of OCPs, but have never checked as I don't use any cables.
 

LarryFine

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iwire said:
250.122(B) is not limited to voltage drop, if the circuit conductors increase in size for any reason at all then the EGC must increase.
Bob, if I only need an 8ga. NM cable for a load, but happen to only have a piece of 6ga. handy, you're saying it's non-NEC-compliant to use it?

That happened to me today. If it makes a difference, two of these cables went from the panel to a junction box, making two #10 EGC's in parallel.
 

Dennis Alwon

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LarryFine said:
Bob, if I only need an 8ga. NM cable for a load, but happen to only have a piece of 6ga. handy, you're saying it's non-NEC-compliant to use it?

That happened to me today. If it makes a difference, two of these cables went from the panel to a junction box, making two #10 EGC's in parallel.

I think that is correct. If you upsize for any reason your need to upsize the egc. Crazy--- The new change could be very interesting in a residential setting.
 

iwire

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don_resqcapt19 said:
Bob,
The change in the 2008 code no longer lets you size the EGC, for a motor circuit that has an MCP as the ground fault and short circuit protection, based on the size of the motor overload protection. You are now required based on the maximum permitted rating of a dual element fuse. This change will increase the required size of the EGC for motor circuits that use a MCP. I think there will also be an issue with motor circuits that use other types of OCPs, but have never checked as I don't use any cables.

Don, I am not following you.

The OP notes that the cable he uses does not have a large enough EGC to meet the new rules of .122(D) and asks if he can simply use the next size cable to get the EGC large enough.

My feeling once he does that he runs right into .122(B)
 

iwire

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LarryFine said:
Bob, if I only need an 8ga. NM cable for a load, but happen to only have a piece of 6ga. handy, you're saying it's non-NEC-compliant to use it?

It depends on the circuit rating and the EGC size.

But yes it could be a violation.
 

don_resqcapt19

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iwire said:
Don, I am not following you.

The OP notes that the cable he uses does not have a large enough EGC to meet the new rules of .122(D) and asks if he can simply use the next size cable to get the EGC large enough.

My feeling once he does that he runs right into .122(B)
Bob,
I guess I didn't read you post close enough...you are correct that 250.122(B) becomes an issue when you use a conductor larger than what is required by the code.
 
Just so everyone know where I'm coming from. All of my work is done on the industrial side. When my understanding of the code need clarifying I pull out the NEC Handbook. I realize the commentary is not part of the code but you have to start somewhere. So to quote the Handbook for 250.122 (B) ?Equipment grounding conductors on the load side of the service disconnecting means and overcurrent devices are sized based on the size of the feeder or branch-circuit overcurrent devices ahead of them. Where the ungrounded circuit conductors are increased in size to compensate for voltage drop or for any other reason related to proper circuit operation, the equipment grounding conductors must be increased proportionately.?
So increasing the ungrounded conductor size just because I want to waste money does not have anything to do with the ?proper circuit operation?
Does anyone know who authored the comment in the Handbook? Maybe they could give some insight.
 

roger

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The commentary simply backs up the actual code wording.

(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to the circular mil area of the ungrounded conductors.

Notice there is no reason given as to why the ungrounded conductors may be increased in size, but for what ever reason, even if it's just a desire to waste money, it's mandatory that the EGC get's to waste it's share too.

Roger
 
Causes alot of work but hope it's OK

Causes alot of work but hope it's OK

So lets take an example. A 100HP motor 124FLA*1.25=155A required ungrounded conductor would be #2/0 per T310.116 for 3/C in a cable. Per 250.122 (D)(2) the ECG would need to be a #4 because using the fuse rating of 225 amps and table 250.122. TC cable manufacture standard is 3/C #2/0 with #6 Ground and a 3/C #3/0 with a #4 Ground. A #2/0 is .137 in sq and a #3/0 is .173 in sq so the ratio is .173/.137=1.263. If I used this ratio for the increase on the ECG of a #6 it would be .027 in sq*1.263=.034 in sq. A #4 = .042 in sq. which is grater than .034 sq in. So have I met both 250.122 (B) and 250.122 (D) (2)?
 
Equipmt Grounding Conductor 250.122

Equipmt Grounding Conductor 250.122

This is going to seem lon winded but I posted this under Electrical Cal/Eng. These are only my comments. still need help.

NEC 2008 section 250.122 (D) (2) now requires a different calculation when sizing the grounding conductor when using an MCP (motor circuit protector). this new calculation invalidates the standard size grounding conductor now supplied in type TC cables and Armored 600V power cables. When you go to 100HP and above motors the standard ground wire in these cables are undersized by one. Does any one know if the cable manufactures are going to upgrade their cables to meet the new code requirement or are we going to be forced to upsize feeder cables or run individual conductors.

Just so everyone know where I'm coming from. All of my work is done on the industrial side. When my understanding of the code need clarifying I pull out the NEC Handbook. I realize the commentary is not part of the code but you have to start somewhere. So to quote the Handbook for 250.122 (B) “Equipment grounding conductors on the load side of the service disconnecting means and overcurrent devices are sized based on the size of the feeder or branch-circuit overcurrent devices ahead of them. Where the ungrounded circuit conductors are increased in size to compensate for voltage drop or for any other reason related to proper circuit operation, the equipment grounding conductors must be increased proportionately.”
So increasing the ungrounded conductor size just because I want to waste money does not have anything to do with the “proper circuit operation”
Does anyone know who authored the comment in the Handbook? Maybe they could give some insight.

So lets take an example. A 100HP motor 124FLA*1.25=155A required ungrounded conductor would be #2/0 per T310.116 for 3/C in a cable. Per 250.122 (D)(2) the ECG would need to be a #4 because using the fuse rating of 225 amps and table 250.122. TC cable manufacture standard is 3/C #2/0 with #6 Ground and a 3/C #3/0 with a #4 Ground. A #2/0 is .137 in sq and a #3/0 is .173 in sq so the ratio is .173/.137=1.263. If I used this ratio for the increase on the ECG of a #6 it would be .027 in sq*1.263=.034 in sq. A #4 = .042 in sq. which is grater than .034 sq in. So have I met both 250.122 (B) and 250.122 (D) (2)?

Since this is actually a continuation of this thread, I attached this thread (post) to this one to maintain continuity. Charlie
 
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don_resqcapt19

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First, I think this has always been a problem when the motor starter used an inverse time breaker or fuses as the code requires the EGC to be sized based on the rating of that device. Under the 2005 code when the stater used an motor circuit protector the EGC was permitted to be sized based on the rating of the overload device. This was changed in the 2008 code creating the problem you have encountered.
As far as your calculations, they work out ok in this case, but the rule requires them to be based on the circular mil area of the wire and that is normally done using the values in Chapter 9, Table 8. This would be 211,600/167,800 or a ratio of 1.261 (for all practical purposes the same as your number). The area of a #6 is 26240 circular mils and the increased size would have to be at least 33,089 circular mils...a #4 is 41,740 so you are good to go.
 
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