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Joined: Jan 2008
Posts: 1
S
New Member
Can anyone shed any light on 250.122(B)? Thank you in advance.

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Joined: Jan 2003
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Sure, what do you want to know?


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Jul 2004
Posts: 9,745
Likes: 13
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Member
Short answer. If you upsize the conductors for something like voltage drop you also have to upsize the EGC.


Greg Fretwell
Joined: Mar 2005
Posts: 1,213
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Member
They want to you increase the EGC by the same ratio you increase the current conductors. These #s are availible in Table 8

For example, lets say you have a 125A circuit (Normally #2 Cu w/#8 EGC) but have to increase the conductors to 1/0 to allow for derating:

#2 = 66kcmil
1/0 = 106kcmil
Increase is 60%.

#8 = 16.5kcmil.
16.5kcmil * 160% = 26.4kcmil

Looking through the table, #6 = 26.2kcmil, and would be the proper ground wire to use.

Joined: Nov 2000
Posts: 2,148
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The interesting part is where you have a circuit protected at 30 amps or less....the EGC must be the same size as the circuit conductors. This often comes into play for parking lot lighting where you may be using a #4 or 6 on a 20 amp circuit.
Don


Don(resqcapt19)
Joined: Mar 2008
Posts: 9
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New Member
This is like many parts of the NEC which has been around from the early nightteen 30s when large pipe organ was popular

Now we have keyboardsand large amp systems or sound systems which make some of the old way of doing things of date , remember knob and tube, worked well in its day

Just food for thought thank you

Joined: Apr 2003
Posts: 139
B
Member
The conflict described by Don also occurs on equipment such as motors and air conditioning equipment that may have conductors that are permitted to be sized smaller than the branch circuit overcurrent device.

In many cases, the contractor will install conductors sized based on the max overcurrent device instead of the minimum branch circuit size and NOT increase the EGC in proportion.

The contractor doesn't understand why the EGC has to be increase when a smaller EGC is normally permitted for that circuit rating.

There were a couple proposals submitted this past code cycle that tried to clear up this issue, but none were accepted.

I have tried to come up with a good rewrite of 250.122(B) myself without much luck.


Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter

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