Thread: Equipment Grounding conductor size

Here is a simple electrical question to all. Lets say EC ran 2/0 AA8000 compact AL ungrounded feeders with a #10 EGC. However, they "mac adapt" down at 50 amp (fused) OCPD in the MDP. EC say's #10 is fine due to OCPD...I say no way and gave him or her the NEC section number...thoughts? What size should it be?


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Originally Posted by Roland Miller

Here is a simple electrical question to all. Lets say EC ran 2/0 AA8000 compact AL ungrounded feeders with a #10 EGC. However, they "mac adapt" down at 50 amp (fused) OCPD in the MDP. EC say's #10 is fine due to OCPD...I say no way and gave him or her the NEC section number...thoughts? What size should it be?

Roland: Are you serious?

This is an actual write up from an actual electrical inspection. So YES--I am serious

Not enough information to make a determination.

Need to verify industry source for compact aluminum and determine the size needed based on the ampacity required. Is this for a motor? Q's like that.

Cannot find AA8000 in the code book for insulation type so either give us the manufacturer so we can look it up or provide it.

Once we know what size wire for the ungrounded conductors (including circular mils) then we can upsize the EGC proportionally.

Table 5A in chapter 9 will help but not for ampacity of the compact aluminum.

I can ballpark it but codes are not about ballparking.

Also, terminal ratings would be nice too.

Thanks for the great question Roland!

I think based on the 2/0 conductor size terminated on the 50 amp OCD along with the #10 EGC. We would have to use the 60 degree column and 50 amp ampacity conductors. Then just a straight ratio. I don't find the other information useful in the question. Am I missing something?

When the wires are upsized for VD the grounding conductor size must also be increased. It is not based on the OCPD when this is done but the wire cross sectional area.

Originally Posted by Roland Miller

I think based on the 2/0 conductor size terminated on the 50 amp OCD along with the #10 EGC.

I will happily admit I don't know what you're talking about, but it might help if you wrote in complete sentences.

Originally Posted by Roland Miller

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Am I missing something?

.
....
.

The fact that the conductor is compact does not alter its ampacity. Insulation data seems to be missing.

Compact conductor size comes into play with raceway sizing.

Like Jeff says, more data is needed.

I think based on this information-- 2/0 conductor size terminated on the 50 amp OCD along with the #10 EGC you can find the answer..

Originally Posted by John Arnold

I will happily admit I don't know what you're talking about, but it might help if you wrote in complete sentences.

Roland said this:

Originally Posted by Roland Miller

Here is a simple electrical question to all. Lets say EC ran 2/0 AA8000 compact AL ungrounded feeders with a #10 EGC. However, they "mac adapt" down at 50 amp (fused) OCPD in the MDP. EC say's #10 is fine due to OCPD...I say no way and gave him or her the NEC section number...thoughts? What size should it be?

Roland should have said it as this:
-> Here is a simple electrical question to all.
-> Let's say an Electrical Contractor ran 2/0 AA-8000 series alloy compact aluminum underground feeders with a #10 AWG Equipment Grounding Conductor.
-> However, they adapted the conductors down to a 50 amp fused OverCurrent Protection Device in the Main Distribution Panel.
-> Electrical Contractor say's the #10 AWG equipment grounding conductor is fine due to the 50 amp rating of the overcurrent protection device.
-> Roland says no way and gave him or her the NEC section number. What are our thoughts?
-> What size should the equipment grounding conductor be?

From the 2008 NEC. (underlining is mine)
- 250.122 Size of Equipment Grounding Conductors.
- - (A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment. Where a cable tray, a raceway, or a cable armor or sheath is used as the equipment grounding conductor, as provided in 250.118 and 250.134(A), it shall comply with 250.4(A)(5) or (B)(4).
- - (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.

Table 250.122 says that when the overcurrent protection device is rated at 40 through 60 amps, and the conductors are aluminum, the equipment grounding conductor shall be a minimum size of #8 AWG aluminum.

However, (B) above states that if the ungrounded conductors are increased in size (no reason given, but there could be several reasons for them to be increased in size), then the equipment grounding conductor shall be increased in size proportionately according to the circular mil area of the ungrounded conductors.

Making a presumption that the conductor insulation is THHN-2.

Using the 50 amp fuse overcurrent device as the base for sizing, the conductor size which 'would most likely have been used' would have been #6 THHN-2 aluminum.

Okay, let's compare the circular mils size for the following:
- Using the conductors rated for the 50 amp fuse overcurrent device: #6 aluminum (26240 circular mils) ungrounded conductors with a #8 aluminum (16510 circular mils) equipment ground.
- And using the installed 2/0 compact aluminum (?133100? circular mils) to determine its proportionally sized equipment ground.

I have the circular mils of the 2/0 compact aluminum marked with ?? as I could not find it listed, and do not know if the circular mils is based on its conductor size originally and therefore the circular mils does not change simply because the conductor is compact aluminum. Maybe, maybe not.

*IF* the circular mils of the compact aluminum are rated as "equivalent circular mils", then I should not be too far off.

2/0 compact aluminum (?133100? circular mils)
#6 aluminum (26240 circular mils)
= 133100 / 26240 = 5.7 proportional factor

to determine its proportionally sized equipment ground
#8 aluminum (16510 circular mils) equipment ground
= y / 16510 or y = 16510 X 5.7 = 94104 circular mils proportional

94104 circular mils = 1/0 AWG equipment ground conductor (105600 circular mils, a #1 is too small at 83690 circular mils)

Have not done that in so many years that I do not know how close I am, but, have no fear ... I am sure that Roland will lambaste me regardless how close or how far I am to/from the correct answer ... so be it, there are some "presumptions" in there anyway.

So, Fred or Roland, how close am I to the answer and were my presumptions close enough?

Fred, I am sure you will give a reasonable and thought out answer for educational purposes.

Roland, I expect nothing more from you than you have given continuously so far.

My answer is the EGC would have to be upsized to 6-awg copper based on a proportional increase using the 60 deg column of the aluminum side.

Before I can be of much help, assuming, of course, that I can be of help, I will need to know if the conductors are direct-buried, or if they're in conduit above ground, etc. Are they subject to single family dwelling rules,etc. You know, a little more paint in the scene.

Originally Posted by Fred Warner

You know, a little more paint in the scene.

Fred,

Understood, I was connecting the dots in the best manner in which I could, I connected dot 4 to dot 12 to dot 31 to dot 36 because the others were missing. I got a zig-zag line. Maybe if the other dots were there it would make a pretty picture?

Jeff's answer would be correct. It actually falls midway between #6 and #4 so it would be up to the AHJ to determine where in the system this installation fell and evaluate the available fault current to determine whether #6 would work or it would have to be #4 copper.

We know several things the rest of you are missing (it is the background paint). You need to be working in the 60 C column based on the 50 amps and 110.14(C). and the equipment grounding conductor the EC installed was copper based on 250.122(table)..

The more thorough the question, the more thorough the answer. Sorry I didn't get a chance to play. But, at least I got to make up a saying: "The more thorough the question, the more thorough the answer."

I'll take credit for posting this here. It actually came from a friend that is in DC. And since there was enough information to make a logical attempt with the calculation I decided it was good enough to post. Jerry came up with a different size but based on his math and the conditions he saw in the problem--his was correct also.

And the answer is #3 copper.. With the termination temperature rating at 75 degrees. You do your ratio in the 75 degree column with aluminum. then multiply that ratio time the CM area of #10 copper and you would get # 3 copper...

Originally Posted by Roland Miller

And the answer is #3 copper.. With the termination temperature rating at 75 degrees. You do your ratio in the 75 degree column with aluminum. then multiply that ratio time the CM area of #10 copper and you would get # 3 copper...

Thank you for the clarification on the conditions, or as Fred might say ... Thank you for finishing the painting of the picture.

Regardless, though, any way you looked at it, and just as you said: the #10 AWG was wrong.

Originally Posted by Jerry Peck

Thank you for the clarification on the conditions, or as Fred might say ... Thank you for finishing the painting of the picture.

Regardless, though, any way you looked at it, and just as you said: the #10 AWG was wrong.

JP: I have read this entire thread, thrice now and . . . nothing. I just don't follow any of it. But, as it happens, I am due back on Earth soon, and must go quickly.