2014 change to 250.122(B)

[Smart $]

Does anyone know what edition 250.122(B) was added. I traced it back as far as 1999, where it was changed from regarding increased for voltage drop to increased in size regardless of reason. I want to determine the original premise/substantiation (whimsical, backed by empirical evidence, something else) before proposing a change.

If I do propose a change, I would accept contributions to substantiation and make notes for proper accreditation.

 

[jap]

If I didn't hear of any feedback on the woding of the first sentence of the OP's question, my first thought would be (Increase size of ungrounded conductor means Increase size of Equipment Grounding Conductor) I guess I'm just interpreting this differently somehow.



JAP>

 

[hurk27]

The only time I can see a requirement of upsizing the EGC is when dealing with voltage drop, the extra resistance of the wire can limit the current and cause the OCPD not to operate in the instantaneous area of the trip curve and cause insulation damage by taking longer to trip, up sizing for more then 3 current carrying conductors in a raceway does not cause this problem since the EGC will not have continuous current on it, so by reading 250.122(B)
"Where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation"

The increase is only made if increased after the derating which this would be the intended installation, the 50 amp rating of the breaker would still be the point in table 250.122 to size the EGC from, to me it is saying that there is not increase because the derating was done as part of the intended installation, if we look at the proposal it backs this wording:

The inserted language is simple and clear. It
is pointless and technically incorrect to require an increase in the minimum size
of an equipment grounding conductor, which functions only for a short-time
event and can be insulated or bare, just because some condition of use requires
the ungrounded conductors to increase in size.

That condition of use is the derating for more then 3 current carrying conductors in a raceway.

 

[hurk27]

Look at it this way, in the intended installation the conductors would not have sufficient ampacity before the derating is done, the wording states: "from the minimum size that has sufficient ampacity" so this has to be after the derating, if then we increase the conductors then we must also increase the EGC, not before the derating.

 

[hurk27]

No upsizing the EGC required for that scenario. You did not upsize your conductors to an ampacity greater than the minimum size required.

That said, I'd actually like to see the upsizing changed to being based on the maximum standard OCPD rating that could protect the upsized conductors. For example, say your proposed scenario required you to go with #2 THHN to compensate for voltage drop. Derating for CCC's: 130A ? 70% = 91A. The maximum standard OCPD rating that you could protect this conductor with is 100A. Per Table 250.122, you'd only have to run a #8 EGC... and not a #6.

In calculating your voltage drop going from a #8 to a #2awg for a 46 amp load I came out with about a 500' one way wire run this would give you a resistance path for fault current of .6055 ohms for the #8/#2 awg path, at 208 volts and an infinite buss ahead of this circuit would only provide 343 amps on a bolted fault, from a trip curve from Square D this would put it into the 2-9 second range on time to trip, well out of the instantaneous range, anything above 5 seconds is considered insulation damaging at this current level, add the impedance of the wire path and transformer ahead of this breaker and your well within the range that would easily damage the #8 EGC, I don't think trying to get the code to allow smaller EGC's in this case would be the right answer, the real reason why the NEC requires when you up size the ungrounded conductors for VD you have to up size the EGC proportionately because the added resistance will lower the current to the point the breaker can't protect the wire anymore.

 

[bob]

Look at it this way, in the intended installation the conductors would not have sufficient ampacity before the derating is done, the wording states: "from the minimum size that has sufficient ampacity" so this has to be after the derating, if then we increase the conductors then we must also increase the EGC, not before the derating.

I misread the change and thought it said that has sufficient capacity. This would have covered increases due to VD This is only slightly
better than the existing rule.

 

[hurk27]

What I can't figure is back in the 1999 it only said for voltage drop:

(b) Adjustment for Voltage Drop. Where conductors are adjusted in size to compensate for voltage drop, equipment grounding conductors, where installed, shall be adjusted proportionately according to circular mil area.

the 2002 changed to a more confusing:

(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.

And removed any reference to voltage drop which would be the only reason you would need to increase the EGC,

It stayed with these words until the 2014

in the 2011 hand book it clearly states in the commentary that it does not apply for adjustments or derating:

Where the
ungrounded circuit conductors are increased in size to compensate
for voltage drop or for any other reason related to
proper circuit operation, 250.122(B) requires that the equipment
grounding conductors be increased proportionately.
Increases in ungrounded circuit conductor size for the purposes
of ampacity adjustment, correction, or both are not
required to be considered in applying the provisions of
250.122(B).

So again they try to make it clear that it was not the intent to make this apply to adjustments or derating???

So why didn't they just put the 1999 wording back in as it was good enough and was clear that it only applied to voltage drop???

I think some people tend to over think things to try to show just how smart they are but most of the time they come out on the dumb end.

 

[hurk27]

I misread the change and thought it said that has sufficient capacity. This would have covered increases due to VD This is only slightly
better than the existing rule.

I saw it but didn't commit on it, if it did say capacity it would have removed any requirement to upsize the EGC, VD included, because the circuit would not have had the capacity for the load on the long run, and if your only required to upsize after the capacity is met when you wouldn't be no longer upsizing after this point.

Them little words get us all the time

 

[Smart $]

In calculating your voltage drop going from a #8 to a #2awg for a 46 amp load I came out with about a 500' one way wire run this would give you a resistance path for fault current of .6055 ohms for the #8/#2 awg path, at 208 volts and an infinite buss ahead of this circuit would only provide 343 amps on a bolted fault, from a trip curve from Square D this would put it into the 2-9 second range on time to trip, well out of the instantaneous range, anything above 5 seconds is considered insulation damaging at this current level, add the impedance of the wire path and transformer ahead of this breaker and your well within the range that would easily damage the #8 EGC, I don't think trying to get the code to allow smaller EGC's in this case would be the right answer, the real reason why the NEC requires when you up size the ungrounded conductors for VD you have to up size the EGC proportionately because the added resistance will lower the current to the point the breaker can't protect the wire anymore.

Appreciate the effort you put into that analysis... but only being provided with basic results and not actual calculations with the variables and constants used, I'm going to surmise there is fault in your premise. Don't be despondent about it, for it is the same fault in premise I see in a lot of Vd calculations... and I'll reiterate I am only surmising fault at this point.

The fault centers on an assumed conductor temperature. Consider that when you determine the circuit will have insufficient voltage for the load using the minimum size circuit conductors required by Code: 46A load on #6 w/#10 EGC. Because of more than 3 conductors are in the raceway, the minimum 'normal' ampacity is upped by a factor of 143% (the inverse of derating 70%). The temperature of the other conductors has no bearing on this increase... it is only assumed that they will operate at the same temperature.. so let's revise the scenario, to make it easier to understand, to not more than 3 conductors in raceway, so we don't have to derate... and go with: 46A load on #8 w/#10 EGC, ungrounded upsized to #4... because of voltage drop using #8...

Now, say you do the voltage drop calculation using the IEEE exact voltage drop formula (link). Note the value for R is from Chapter 9, Table 9. Proceed to that table and tell me at what temperature that value of R is given at....?

Next, tell me how much current has to be carried by the circuit conductor for it to be at that temperature [it's okay to make assumptions; hint: Table 310.15(B)(16) 75?C column ]. Now tell me if the conductor will be at that temperature while conducting 46A of current. If not, why not? Without calculating or having to provide empirical evidence, make an assumption and tell me will it be higher or lower?

....

If you've arrive at the same conclusion I always do, you'll be starting to get the gist of why I surmise fault in the premise.

Let me give you a simpler approach. If our concern is voltage drop, draw up an 'on-paper' circuit with 3 resistors in series across a voltage supply. Let the middle resistor represent the load, and the two resistors to each side represent the voltage drop of the conductors. The load resistor's value is (E-3%E)/I, where I = 46A, which would make the 'wire' resistors 1.5%E/I. These values represent the limit no matter what size, ampacity, or length of conductors you use. You can also determine I?R values, and these will also be the limit.

When you use a larger, longer conductor for voltage drop reasons, you will be spreading the same or less I?R loss over a greater distance, which result in a lower point temperature of the circuit conductors. In comparison, the temperature of the #10 EGC will be: a) higher, b) the same, or c) lower?

 

[Smart $]

Does anyone know what edition 250.122(B) was added. I traced it back as far as 1999, where it was changed from regarding increased for voltage drop to increased in size regardless of reason. I want to determine the original premise/substantiation (whimsical, backed by empirical evidence, something else) before proposing a change.

...

As best I can tell, this upsizing requirement first appeared in the 1974 NEC edition. Archived information on the NFPA website only provides Technical Committee Reports, and does not provide information on submission or substantiation. At that point of NEC evolution, it was:

250-95. Size of Equipment Grounding Conductors. The size of copper, aluminum, or copper-clad aluminum equipment grounding conductors shall not be less than given in Table 250-95.

Where conductors are run in parallel in multiple raceways, as per­mitted in Section 310-4, the equipment grounding conductor, where used, shall be run in parallel. Each parallel equipment grounding con­ductor shall be sized on the basis of the ampere rating of the overcurrent device protecting the circuit conductors in the raceway in accord­ance with Table 250-95.

When conductors are adjusted in size to compensate for voltage drop, grounding conductors, where required, shall be adjusted proportionately in size.

Exception No. 1: An equipment grounding conductor not smaller than No. 18 copper and not smaller than the circuit conductors if -an integral part of a listed flexible cord assembly shall be permitted for grounding cord-connected equipment where the equipment is protected by overcurrent devices not exceeding 20-ampere rating.

Exception No. 2: The equipment grounding conductor shall not be required to be larger than the circuit conductors supplying the equip­ment.

Exception No. 3: Where a raceway or a cable armor or sheath is Used as the equipment grounding conductor, as provided in Sections 250-57(a) and 250-91 (b).

 

[infinity]

As best I can tell, this upsizing requirement first appeared in the 1974 NEC edition. Archived information on the NFPA website only provides Technical Committee Reports, and does not provide information on submission or substantiation. At that point of NEC evolution, it was:

The wording that you've posted first appeared in the 1975 edition, the 1971 edition has no such wording.

 

[augie47]

What I can't figure is back in the 1999 it only said for voltage drop:



the 2002 changed to a more confusing:



And removed any reference to voltage drop which would be the only reason you would need to increase the EGC,

It stayed with these words until the 2014

in the 2011 hand book it clearly states in the commentary that it does not apply for adjustments or derating:



So again they try to make it clear that it was not the intent to make this apply to adjustments or derating???

So why didn't they just put the 1999 wording back in as it was good enough and was clear that it only applied to voltage drop???

I think some people tend to over think things to try to show just how smart they are but most of the time they come out on the dumb end.

I read what the Handbook states but that's an opinion. The actual wording of the NEC does not state "except for adjustments or derating".
At one of the IAEI seminars I attended it was stated that the increase in wire size for any reason increased the current avialable in the event of a fault and the EGC had to be increased to compensate for that.
I want to go along with the Handbook but on what premises do they make that statement ?

 

[Smart $]

...
At one of the IAEI seminars I attended it was stated that the increase in wire size for any reason increased the current avialable in the event of a fault and the EGC had to be increased to compensate for that. ...

Then ask that person(s) to explain why in many cases you can protect those same circuit conductors with a greater rated ocpd and not have to use a larger EGC, and be 100% compliant...???

 

[kwired]

At one of the IAEI seminars I attended it was stated that the increase in wire size for any reason increased the current avialable in the event of a fault and the EGC had to be increased to compensate for that.

True but not entirely true. Take two installations with identical size and length of conductors from the source to a fault location, but make one supply a small transformer and the other one a large transformer and guess which one has higher fault current. There is more to this then conductor sizes alone, but your average electrician in the field is not supposed to be smart enough to calculate that kind of thing, yet he needs to mark equipment with the maximum available fault current now:roll:

 

[electricalist]

I may be off track but I was at a bldg today. There is a 225 amp mb panel in space A with 4/0 to back of bldg about 150 ' to a jbox where it is nsi connected # 3 to a 200a mb panel where it is breakered at 100 amps. Other than finding the jacka $$ that built it. Would the ecg be required to be sized for 225 wire . Which sounds like a gec and if so could you go to bldg steel from nearest point of tap. Thinking will suplemental grounding for the increased wire size being the problem point of that code... I think ocp should determine egc but I get improper knowledge of afc and irc means alot services are possible problems

 

[electricalist]

I hope this code doesnt apply to houses. I remember olenty of 6/2 runs between lv lighting on a 20 amp breaker. Good luck getting that ground to comply

 

[kwired]

I hope this code doesnt apply to houses. I remember olenty of 6/2 runs between lv lighting on a 20 amp breaker. Good luck getting that ground to comply

Is the LV source even grounded? I haven't seen one that is and and two wire cable is all that is needed- but if you need 6AWG you probably will not find a two wire cable very easily.

 

[electricalist]

They were usually lv can lights so I think they needed 3wire. First can is 12 2 jumpers 6/2 egc to the can but a upsized ground connected to a smaller size ground compliant to that point makes no sense unless #6 s ground size makde it back to primary bonding

 

[kwired]

250.20(A) only gives us three conditions where a system of less then 50 volts needs to be grounded:

where the supply transformer is supplied with over 150 volts to ground

where the supply to the transformer is ungrounded

where installed outside as overhead conductors

 

[electricalist]

I gotcha. Dont have a 2014 yet. Ty sir