Equpment Grounding Conductor

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joemota

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Equipment Grounding 250.122(B)

Where conductors are adjusted in size to compensate for voltage drop, equipment-grounding conductors......shall be adjusted proportionately according to circular mil area.


Question:

We are running 120V 20Amp circuits and are being asked to increase the wire size to #6 on some circuits and #8 on others to compensate for voltage drops. Local code as well as specification requires an equipment-grounding conductor. Can we run a #10 for grounding conductor?
 
Re: Equpment Grounding Conductor

15, 20 and 30 amp circuits require am equipment ground that is the same size as the ungrounded conductor(s).

Be careful if you were considering using a cable wiring method :eek:
 
Re: Equpment Grounding Conductor

Compare the percentage increase in circular mils for the ungrounded conductor, and be sure that compares to the same percentage of the EGC. See Table 8 for circular mils of typical wire sizes.
 
Re: Equpment Grounding Conductor

Ryan your fast, this is one of my 'pet' subjects. :D

I agree with Ryan, for 15, 20 & 30 amp circuits the ratio from ungrounded and grounded conductors to grounding conductors is one to one.

You run 6 AWG ungrounded and grounded conductors the grounding conductor will have to be 6 AWG also.

Also as Ryan said this basically rules out cables.

Bob
 
Re: Equpment Grounding Conductor

250.122(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.
This next part was taken out of the comentary in the 2002 nec handbook.
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. If the ungrounded conductors are increased in size to compensate for voltage drop, the equipment grounding conductors must also be increased proportionately.
Example
A 240-volt, single-phase, 250-ampere load is supplied from a 300-ampere breaker located in a panelboard 500 ft away. The conductors are 250 kcmil copper, installed in rigid nonmetallic conduit, with a 4 AWG copper equipment grounding conductor. If the conductors are increased to 350 kcmil, to what size must the equipment grounding conductor be increased?
Solution
Step 1.
Calculate the size ratio of the new conductors to the existing conductors:

Step 2.
Calculate the cross-sectional area of the new equipment grounding conductor. According to Chapter 9, Table 8, 4 AWG, the size of the existing grounding conductor has a cross-sectional area of 41,740 circular mils.
Step 3.
Determine the size of the new equipment grounding conductor. Again, referring to Chapter 9, Table 8, we find that 58,436 circular mils is larger than 3 AWG. The next larger size is 66,360 circular mils, which converts to a 2 AWG copper equipment grounding conductor.
 
Re: Equpment Grounding Conductor

Originally posted by joemota:
Can we run a #10 for grounding conductor?
Click to expand...
No. You are in limbo land of the NEC. As stated by others; A 15, 20, and 30 amp circuits require the same size EGC as the ungrounded conductors to keep Ryan_618 (Inspector) away. :(

[ March 29, 2004, 04:22 PM: Message edited by: dereckbc ]
 
Re: Equpment Grounding Conductor

250.122(B) can lead to some strange results.

On another forum a person was using 4/0s for 20 amp street lighting circuits.

These 4/0s fed from a 15, 20, or 30 amp breaker need a 4/0 EGC run with them.

Change the breaker to a 100 amp and the EGC run with the 4/0s would only have to be a 1 AWG (actually within 10 cir mils of a 2 AWG)

Bob
 
Re: Equpment Grounding Conductor

EDIT: Forget it, I understand now, after reading 250.122B, it makes cents for long runs that the ground should be increased. Otherwise you will have too much of a voltage drop and your ground could end up not being an adequate ground, but it could act like a resistor, and voltage may desire to look elsewhere's to travel.

I've never heard of these rules before, as far as I'm concerned a #10 ground is fine for up to a #6. Check the back page of Mike Holt's Electrical Formulas with Sample Calculations, Commercial Wire and Raceway Chart and you'll find the same thing. #8 ground is good for up to #3, #6 up to 3/0 etc. What am I missing here?

[ March 29, 2004, 04:49 PM: Message edited by: bonding jumper ]
 
Re: Equpment Grounding Conductor

Originally posted by bonding jumper:
I've never heard of these rules before,.............What am I missing here?
Click to expand...
Your missing 250.122(B)

250.122(B) Increased in Size.
Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.
Click to expand...
That short section is all it takes to change the general requirements of Table 250.122.

You could just use a metal raceway and avoid 250.122(B) altogether. ;)
 
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