2014 change to 250.122(B)

[electricalist]

Im only familiar with the buildings ive been in and it seems thst maybe 200' is where there is more oanels xfmrs and panels to that area.. im sure there are many that ate further. But if its the distance that a conduit is no longer a egc. Then couldnt something else be done. That just sounds lije too far. Which means the vd wire will only inxrease insize then the ground then the pipe and the cost and the time. Could it even be inspected correctly. If it doesnt apply to derating then someone will say that run is derated. Uts not for vd.

 

[kwired]

Im only familiar with the buildings ive been in and it seems thst maybe 200' is where there is more oanels xfmrs and panels to that area.. im sure there are many that ate further. But if its the distance that a conduit is no longer a egc. Then couldnt something else be done. That just sounds lije too far. Which means the vd wire will only inxrease insize then the ground then the pipe and the cost and the time. Could it even be inspected correctly. If it doesnt apply to derating then someone will say that run is derated. Uts not for vd.

There is no distance where a raceway is no longer an equipment grounding conductor. As far as adjusting conductor size to compensate for voltage drop - your raceway will also have to become larger which means it will have larger cross sectional area itself. Those that have run the numbers always come up with less resistance in the raceway then they come up with for a 250.122 sized conductor for same application.

 

[Smart $]

That's pretty much saying where a wire-type EGC supplements a rigid, IMC, or EMT wiring method (any others? perhaps cable tray, wireway, ...???), the wire-type EGC does not need to be increased in size.

Still looking for suggestions on how to make a proposal (and thoughts thereabout) for a less than proportionately increased in size EGC. Lacking adequate response, I will simply not submit any.

 

[MasterTheNEC]

When you run the numbers you will find out that steel conduit is suitable for use as an effective EGC in longer lengths than is a code sized EGC of the wire type.

Indeed it is...which is why 250.122(B) now makes sense when dealing with a "wire-type" EGC.

 

[Smart $]

Indeed it is...which is why 250.122(B) now makes sense when dealing with a "wire-type" EGC.

Yes... in cases where the wire-type EGC is the only EGC.

What about where circuits with a wire-type EGC are run in steel conduit? Is there need to upsize the wire-type EGC?

 

[MasterTheNEC]

Yes... in cases where the wire-type EGC is the only EGC.

What about where circuits with a wire-type EGC are run in steel conduit? Is there need to upsize the wire-type EGC?

Well you have to ask yourself WHY the wire-type EGC was run in the first place. If it was due to an engineer spec that specifically calls for the EGC to be of the wire-type installed in the raceway then it is obviously their opinion that the raceway is not reliable....thus the wire-type EGC added and so my opinion would be the Wire-Type EGC has to comply with 250.122(B) where applicable.

Remember most (and I say most for those who do not venture to this forum..) will not question the designer. If they call for 4/0 CU to ground rods and express the need for 4 of them.....if that's on the drawings then that's what they are going to get. Now, I like to argue so game on for the engineer but in reality time is money and if the owners is willing to pay for the engineers design then I will smile and install it.

 

[Smart $]

Well you have to ask yourself WHY the wire-type EGC was run in the first place. If it was due to an engineer spec that specifically calls for the EGC to be of the wire-type installed in the raceway then it is obviously their opinion that the raceway is not reliable....thus the wire-type EGC added and so my opinion would be the Wire-Type EGC has to comply with 250.122(B) where applicable.

And that is somewhat at the heart of many complaints about having to upsize a wire EGC. A lot of times the reason for running a wire-type EGC is not conduit is an unreliable EGC, but rather as a redundant EGC. Where the ungrounded conductors are increased in size, the people that run the redundant EGC are penalized by being required to upsize the wire EGC also.

In short, the wire EGC isn't even required per Code, but yet Code requires it to be upsized if used in these scenarios. So is not running a redundant wire-type EGC better?

Remember most (and I say most for those who do not venture to this forum..) will not question the designer. If they call for 4/0 CU to ground rods and express the need for 4 of them.....if that's on the drawings then that's what they are going to get. Now, I like to argue so game on for the engineer but in reality time is money and if the owners is willing to pay for the engineers design then I will smile and install it.

Who makes more money should not influence the issue. Financial gain is not the purpose of the NEC. Yet it has been influenced by those standing to gain financially as a result of changes.

 

[MasterTheNEC]

And that is somewhat at the heart of many complaints about having to upsize a wire EGC. A lot of times the reason for running a wire-type EGC is not conduit is an unreliable EGC, but rather as a redundant EGC. Where the ungrounded conductors are increased in size, the people that run the redundant EGC are penalized by being required to upsize the wire EGC also.

In short, the wire EGC isn't even required per Code, but yet Code requires it to be upsized if used in these scenarios. So is not running a redundant wire-type EGC better?


Who makes more money should not influence the issue. Financial gain is not the purpose of the NEC. Yet it has been influenced by those standing to gain financially as a result of changes.

Ironically I do not see it as about the financial gain...I see it as an Engineer who possibly (hypothetical here) graduated with little or no knowledge of the National Electrical Code [NEC] and simply creates a design that is excessive. While it is excessive it is still code compliant if done properly....and Excessive...:angel:

 

[Smart $]

Ironically I do not see it as about the financial gain...I see it as an Engineer who possibly (hypothetical here) graduated with little or no knowledge of the National Electrical Code [NEC] and simply creates a design that is excessive. While it is excessive it is still code compliant if done properly....and Excessive...:angel:

Not objecting to that scenario. It's not the only scenario subject to the requirement though.

 

[iceworm]

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. Not true. I would have questioned the presenter as well. There is no known physics to support this. As noted by plenty, it is the reduction of available fault current that is the issue.

... The increase is size [given by conditions of 250.122(B)] are based on a reliable return of fault current for the given OCPD. ...

True. Fits my understanding of the physics behind clearing faults.

But you do agree that the resistance [impedance] will change based on the length of the run?

Well, one really only understands if it can be quantified. I highly suspect most understand the physics behind NEC Table 9 - which does discuss the impedance/length/pf equations. So, yes, it is impedance reducing the available fault current.

Considering the code attempts to tie the EGC increase to conductor increase for VD reduction, one might think the code panels also understand that long runs reduce the available fault current.

And kwired pointed out an excellent example

... I have seen many circumstances with long runs on irrigation equipment where overcurrent protection fails to open - most of the time the length of the circuit is likely the reason why, as the same fuse with same fault would open on shorter circuit lengths. ...

Still looking for suggestions on how to make a proposal (and thoughts thereabout) for a less than proportionately increased in size EGC. Lacking adequate response, I will simply not submit any.

• The code attempt to tie EGC upsize to VD didn't work - although I don't know why not.
• The code attempt to paint all with the same brush (upsize conductors for any reason - upsize EGC) didn't work. Too many cases of condut fill/temperature derate where the impedance did not go up.
• And the current one is, what? - too sloppy?

How about just a circuit length table?
120V - - increase EGC one wire size per 100'
240V - - increase EGC one wire size per 200'
480V - - increase EGC one wire size per 400'

1000V - - increase EGC one wire size per 1000'

over 1000V -- not to worry

Or engineering supervision (Include TCC chart showing trip curves and cable damage curves) I see this on industrial 480V distribution.

It is simple and addresses the length/impedance issue.

just a thought

ice

 

[Smart $]

...

How about just a circuit length table?
120V - - increase EGC one wire size per 100'
240V - - increase EGC one wire size per 200'
480V - - increase EGC one wire size per 400'

1000V - - increase EGC one wire size per 1000'

over 1000V -- not to worry

Or engineering supervision (Include TCC chart showing trip curves and cable damage curves) I see this on industrial 480V distribution.

It is simple and addresses the length/impedance issue.

just a thought

ice

If I submit a table based on distance, substantiation is the problem. Upsizing the ungrounded conductors for voltage drop compensation uses distance as its basis. It'd likely get rejected vene if I could substantiate it. :huh:

If for a reason other than voltage drop (or adjustment and correction), there's no physics to support upsizing, but currently required. I have no idea how that ever managed to be accepted... so I'd still be wondering how to substantiate it.

Under engineering supervision seems to be the only way to proceed and yet be vague enough to easily provide substantiation.

 

[iceworm]

.... Upsizing the ungrounded conductors for voltage drop compensation uses distance as its basis. ...

This concept comes from a guy named Corwin (as I recall) - An electrician that was getting close to retirement maybe 35 - 40 years ago when I met him. I recall him telling me he had license #10.

The Corwin Theory was to upsize the conductors for voltage drop based on:

Distance divided by Voltage = number of wire sizes to jump

Multiples of 120V for voltage >>> match up with multiples of 100 feet.

So for 120V, 20A circuit, over 300 feet, under 400 feet is stepped up 3 wires sizes. So 12, 10, use #8.
For a 480V, 50A circuit, say a 30hp motor, over 400 feet, under 800 feet, bump one wire size. So, 8, use #6
For 240V, 200A, over 1000 feet, under 1200 feet, bump 5 wire sizes. So 2/0, 3/0, 4/0, 250, 300, use 350kcmil​

Put up a spread sheet, Use the table 8 resistances. Have it calculate the VD. See what the percentages are. If they are as I recall, they will be in the 3% - 5% range. You would apply the number of steps the current carrying conductors would be sized up to the EGC.

If this ever got accepted, just think where it will be in a 100 years. You will be in the same class as the guy that came up with the 25ohm ground rod number - etched in historical stone.

So why don't you do this he asked? Well, this is about as close as I can get to the process - I'm getting a bit queasy already. Better somebody that cares.

ice

 

[GoldDigger]

Ice,
A refreshing approach.
Among other things it addresses, at least in part, the situation in which the load is low compared to the breaker size and wire ampacity, and so no conductor upsize was done for voltage drop.
The fault current will still be limited by the resistance of the ungrounded conductor, but at least your formula will provide for a lower resistance EGC.

 

[Smart $]

This concept comes from a guy named Corwin (as I recall) - An electrician that was getting close to retirement maybe 35 - 40 years ago when I met him. I recall him telling me he had license #10.

The Corwin Theory was to upsize the conductors for voltage drop based on:

Distance divided by Voltage = number of wire sizes to jump

Multiples of 120V for voltage >>> match up with multiples of 100 feet.

So for 120V, 20A circuit, over 300 feet, under 400 feet is stepped up 3 wires sizes. So 12, 10, use #8.
For a 480V, 50A circuit, say a 30hp motor, over 400 feet, under 800 feet, bump one wire size. So, 8, use #6
For 240V, 200A, over 1000 feet, under 1200 feet, bump 5 wire sizes. So 2/0, 3/0, 4/0, 250, 300, use 350kcmil​

Put up a spread sheet, Use the table 8 resistances. Have it calculate the VD. See what the percentages are. If they are as I recall, they will be in the 3% - 5% range. You would apply the number of steps the current carrying conductors would be sized up to the EGC.

If this ever got accepted, just think where it will be in a 100 years. You will be in the same class as the guy that came up with the 25ohm ground rod number - etched in historical stone.

So why don't you do this he asked? Well, this is about as close as I can get to the process - I'm getting a bit queasy already. Better somebody that cares.

ice

Are we talking about upsizing for [possible] voltage drop, or upsizing the EGC when ungrounded cobductors are upsized??? Seems to me this is just one method for upsizing the ungrounded conductors and the EGC upsizing just follows suit. I think I like my 'based on highest OCPD rating' method better.

 

[MasterTheNEC]

If I submit a table based on distance, substantiation is the problem. Upsizing the ungrounded conductors for voltage drop compensation uses distance as its basis. It'd likely get rejected vene if I could substantiate it. :huh:

If for a reason other than voltage drop (or adjustment and correction), there's no physics to support upsizing, but currently required. I have no idea how that ever managed to be accepted... so I'd still be wondering how to substantiate it.

Under engineering supervision seems to be the only way to proceed and yet be vague enough to easily provide substantiation.

Ok, now you will be doing the research on that concept now in order to substantiate your submission to the CMP right?

 

[charlie b]

The Corwin Theory was to upsize the conductors for voltage drop based on: Distance divided by Voltage = number of wire sizes to jump

Here's my problem with that approach. As the design engineer, I see it as my role to select the wire sizes. But it is not my role to dictate, to the installer, the path by which the conduit is to be run. So I am not going to know the final circuit length. I won't know if the run will be 80 feet, or 90 feet, or 110 feet. I can use the CAD program to estimate the distances, but the installer may well choose to run the conduit a different way, for what are very good reasons that I am not going to know.

 

[iceworm]

.... As the design engineer, I see it as my role to select the wire sizes. But it is not my role to dictate, to the installer, the path by which the conduit is to be run. So I am not going to know the final circuit length. ...

Hummm - only resolution I see is to make failure to upsize the EGC a felony. Prosecute under a RICO type statue, a conspiracy - get the PE, EC, installing journeyman.

Or, use the same criteria used for judging parallel conductor lengths. Never heard of anyone tagged for that.


Then again,

.... As the design engineer, I see it as my role to select the wire sizes. But it is not my role to dictate, to the installer, the path by which the conduit is to be run. So I am not going to know the final circuit length. ...

Truely, I'll agree. Personally I liked the previous get-em-all approach:

If the CCC are upsized - for any reason - then upsize the EGC.​

However, for some unfathomable reason - that didn't work. Best I can tell, is that approach may install an extra $0.5 of copper on a few occasions, which according to some ECs could easily push the job into the red.

So, your turn - you pick one.

• Easy to apply in the field, by the installing journeyman (no engineering/TCC/cable damage calc required)
• minimizes any un-needed copper.
• eliminates inconsistant application (ie a 60A circuit takes a smaller EGC than a 20A circuit)
• account for not upsizing if CCC are upsized for conduit fill/temperature.

ice

 

[iceworm]

Are we talking about upsizing for [possible] voltage drop, or upsizing the EGC when ungrounded cobductors are upsized???

The original Corwin Theory upsized the CCC for VD on length.

The collary Worm Theory is based on the Corwin Theory reasoning, but only upsizes the EGC - doesn't matter if the PE/EC/JM upsizes the CCC or or not. GoldDigger refered to this in his post.

. I think I like my 'based on highest OCPD rating' method better.

absolutely - no question - excellent method. Possibly the best yet. (assuming you are discussing post 63, 67?)

But that only covers the case of conductive raceway**. And it puts the NEC even farther into the design guide. And isn't a redundant EGC a design issue? And the issue isn't personnel safety but is rather a save the structure issue

Still looking for suggestions on how to make a proposal (and thoughts thereabout) for a less than proportionately increased in size EGC. Lacking adequate response, I will simply not submit any

** Which maybe is the only case you wish to cover.

ice

 

[iceworm]

That's pretty much saying where a wire-type EGC supplements a rigid, IMC, or EMT wiring method (any others? perhaps cable tray, wireway, ...???), the wire-type EGC does not need to be increased in size.

Still looking for suggestions on how to make a proposal (and thoughts thereabout) for a less than proportionately increased in size EGC. Lacking adequate response, I will simply not submit any.

Okay here is another one.

Where a wire-type EGC supplements a rigid, IMC, or EMT wiring method (any others? perhaps cable tray, wireway, ...???), the wire-type EGC size is a design issue - art 250.122 does not apply.

Informational Note:
Example: For a 1200A CB, feeding a 1000 foot feeder, the NEC equally allows a #14 as well as a 250kcmil.​

ice

 

[Smart $]

Ok, now you will be doing the research on that concept now in order to substantiate your submission to the CMP right?

If I had a grant-type scenario which covered all costs plus a living allowance, no problem.

Even if that were to happen (I'm leaning toward not likely at present ), it'd never be done in time to make the current deadline for submission.