20a breaker protecting #8 wire

[Little Bill]

I don't see how that answers my question relating to the words highlighted in RED. I understand the calculation , just don't get those words in red. The Code writer should have written "in no case larger than the largest conductor in the Branch circuit" no confusion there. Instead they used "

"but in no case shall they be required to be larger than the circuit conductors
supplying the equipment"

Thus in my interpetation the code writer is leaving a certain condition that this does not apply to.
In my case #12 at the breaker , #6 nm inbetween , and #12 nm at the end.

You're forgetting 250.122(B), you know how the code book is, you can't just pick a section and expect it to cover it all. You have to read the entire article and see if it sends you someplace else. In this case, the ungrounded are upsized for whatever reason, then downsized to terminate, the EGC is required by 250.122(B) to be upsized accordingly. Then the EGC can also be downsized. The EGC is never required to be larger than the ungrounded conductors that serve the equipment. So if #12 serves the equipment, a #12 EGC is all that is required.
If the wires are upsized mid stream they are still serving the equipment. At no point is the EGC required to be larger than the accompanying ungrounded conductors that run with it.

 

[Sierrasparky]

If using #6 NM for voltage drop reasons; Then #12 at each end to make it easier to attach

to breaker, & device & neutral bus. The short lengths of #12 do not figure in to the equation.

The deciding factor is you used #6 for voltage drop.

Nope that is not the question I pose. I feel your interpetation would be just an opinion. No one is stating what the language is reffering to in the code section.

You know if you look at things further if you upsize any NM or SER or any cable above #10 you will have an issue with the ground wire size. What this means is that never anymore can you use what you have in the truck!( over #10), You cannot install a larger size cable above #10 because you do not know what will be needed and must use a breaker sized for the wire.
This is obsurd.


Please tell me what happens when you need to derate NM in an attic and need to go from # 10 to # 8nm , then what!
Please someone tell me how this is reasonable.

 

[Sierrasparky]

How about this for argument sake:

you run #8NM for a A/c Condenser and the plans and specs call for a circuit ampacity of 34 amps. So you comply and install a #8 romex.

Then low and be hold the unit arrives and the ampacity is lower and the MAX HACR breaker is 30 amps. So you need to remove the non-fused pull out and install a fused one and install 30 amp fuses and reduce the size of the whip from the Pull out to the Condenser.

What did we do prior to the code change in 2002!

 

[Sierrasparky]

If using #6 NM for voltage drop reasons; Then #12 at each end to make it easier to attach

to breaker, & device & neutral bus. The short lengths of #12 do not figure in to the equation.

The deciding factor is you used #6 for voltage drop.

Well in the instances I describe are not due to voltage drop.
They could be because that is what you have on the truck- #6 when you only need #8 or
The piece of equipment want a lower breaker than the wire you provided.
How about this one: you place a lower breaker in the main that feeds the breaker panel that you installed the Solar PV backfeed to alleviate the overloading of the buss.
I would think that if you get creative you will find some real issues with the interpetation of this part of the code.
As I see it the problem arises out of long distances resulting in voltage drop. I see no prudent application of this section of the code relating to short distances of say 10 to 40 feet.

 

[ActionDave]

As I see it the problem arises out of long distances resulting in voltage drop. I see no prudent application of this section of the code relating to short distances of say 10 to 40 feet.

I don't see it. Where is the prudent application at any distance?

Voltage drop is not enforceable in the NEC.

You can always use a smaller EGC on a larger breaker no matter how great the distance.

 

[Strathead]

Sorry, it is not against code-- your inspector is talking out his--- you know what. Can he give a code article for it? No- he can't. However it would be wise to write a tag on the wire that states the circuit OCPD.

But why though Dennis? Given the information available from the poster, you could go in and change the breakers to 20 amp and there would be no code violation or problems.

 

[Dennis Alwon]

Sierra I am confused by your question. If you increased the wire even for part of the run then that portion of the run must also have the egc increased. The egc would not be larger than the circuit conductor because that portion has #8 so a #8 EGC would be necessary. Now if you were feeding a panel then you could increase the breaker size to 40 amps and you would not need a #8 EGC- Just a #10 as is normally required.

 

[Dennis Alwon]

But why though Dennis? Given the information available from the poster, you could go in and change the breakers to 20 amp and there would be no code violation or problems.

The OP #1 post has a 20 amp breaker with #8 wire attached. In that case the egc must be increase to #8

 

[Dennis Alwon]

If you had a #12 egc with #8 circuit conduits on a 20 amp breaker then it is possible that in some case the #12 would have too much impedance to trip. Remember 250.122(B) says in no case shall the EGC be larger than the circuit conductors NOT theconductors that could be connected to the circuit breaker.

 

[kwired]

Because 14 awg uses a 14 egc
12 awg uses 12 EGC
10 awg uses a 10 egc

All other sizes use a smaller size than the conductors in the circuit. A 40 amp breaker with #8 wire would have a #10 egc. That would calculate differently-

A 10awg conductor upsized to #8 would be the same for the EGC since the egc starts at 10 awg also. Look at the link and do the math for a 14,12, or 10 wire and you will see.

below 30 amps is where there is a lot of problems with this - especially when using cable assemblies where you can not always easily obtain a cable with a larger equipment ground installed in it. Raceways not so much of a problem- you generally can pull whatever you need through it.

The question is does anyone know why the NEC chooses 14, 12, and 10 for 15 thru 30 amps for EGC sizes in 250.122 but once you go larger than a 30 amp overcurrent device we can start using smaller EGC's than what the ungrounded conductors typically will be?

Is it because reduced EGC's can not carry enough fault current in some cases (which I find a little hard to believe) or is it more for just mechanical protection because of physical size of the EGC, with the smaller conductors?

 

[Dennis Alwon]

below 30 amps is where there is a lot of problems with this - especially when using cable assemblies where you can not always easily obtain a cable with a larger equipment ground installed in it. Raceways not so much of a problem- you generally can pull whatever you need through it.

The question is does anyone know why the NEC chooses 14, 12, and 10 for 15 thru 30 amps for EGC sizes in 250.122 but once you go larger than a 30 amp overcurrent device we can start using smaller EGC's than what the ungrounded conductors typically will be?

Is it because reduced EGC's can not carry enough fault current in some cases (which I find a little hard to believe) or is it more for just mechanical protection because of physical size of the EGC, with the smaller conductors?

That's for the smart guys, the engineers, to answer. I know that #12 used to have a #14 wire for an egc and they felt that it did not always clear the fault.

 

[Sierrasparky]

Sierra I am confused by your question. If you increased the wire even for part of the run then that portion of the run must also have the egc increased. The egc would not be larger than the circuit conductor because that portion has #8 so a #8 EGC would be necessary. Now if you were feeding a panel then you could increase the breaker size to 40 amps and you would not need a #8 EGC- Just a #10 as is normally required.

I do not see why you are confused. I have issue with this rule and obviously knew very little about they way others interpet it. To simply state increase the breaker to 40 amps means you did not fully read my rant.
No doubt in my mind you , me and others will run into an issue where the breaker may need to be downsized because of unforseen circumstances and using cables greater in size than #10. No longer can the contractor throw in a larger wire because he has it on the truck , other consequences will prevail with this interpetation.

I will empisize the other forum posts where it is claimed that Voltage drop upsizing is not required. So better to use #8 NM breaker at 40 amps when you only need 20amps on a long run .

If you folks want to interpet it this way then I think there should be an added caviot regarding distance , impedence or something because this as written is non-sense. This rule has a place but not as broadly defined as many of you have opined.

 

[kwired]

That's for the smart guys, the engineers, to answer. I know that #12 used to have a #14 wire for an egc and they felt that it did not always clear the fault.

I do not see why you are confused. I have issue with this rule and obviously knew very little about they way others interpet it. To simply state increase the breaker to 40 amps means you did not fully read my rant.
No doubt in my mind you , me and others will run into an issue where the breaker may need to be downsized because of unforseen circumstances and using cables greater in size than #10. No longer can the contractor throw in a larger wire because he has it on the truck , other consequences will prevail with this interpetation.

I will empisize the other forum posts where it is claimed that Voltage drop upsizing is not required. So better to use #8 NM breaker at 40 amps when you only need 20amps on a long run .

If you folks want to interpet it this way then I think there should be an added caviot regarding distance , impedence or something because this as written is non-sense. This rule has a place but not as broadly defined as many of you have opined.

The problem is the rule is written to cover all installations, yet not all installations have the same conditions.

I think most of us would agree if you had a circuit only 100 feet long and you increased your conductor sizes by just one size or maybe two because of voltage drop that leaving the EGC the same size would likely result in fairly reliable enough low impedance for ground fault protection. There will be increased impedance and slower response time from the OCD but you are still fairly well protected. Take that same size circuit and increase it to 1500, 2500, even 3200 feet and now you not only have the voltage drop issue requiring larger circuit conductors, but you also have a significant amount of impedance in the EGC if you don't also increase it in size. But there is likely many more 100 foot circuits installed than there is 3200 foot circuits, yet the rule is written so it applies to all.

I see this in some of the irrigation work I get involved in. Many long circuits involved in some of this work. I have seen many line to line faults that occur at the far end of a circuit that end up burning open a termination, or switch contacts or something else before opening overcurrent devices. Impedance over the distance of the lines limiting the amount of current that flows is the main reason. Less impedance means more current flows which means overcurrent device responds to the condition quicker.

We have the opposite problem at the source end when determining if the gear has high enough interrupt rating, and if not high enough, sometimes just making conductors longer adds enough impedance to lower the available fault current to a level below the interrupt rating of the gear.

What works for you in one place can work against you in another.

 

[Sierrasparky]

Kwired,
You seem to contracdict yourself. You claim that in a 100 foot circuit the issue of not upsizing the EGC seems ok and is the norm. The code should be making rules for the norm not what ifs. Certainly I think the code panel could add " for long distances over XXX"

The instances I see as reduiculous is the one I cited for a A/C condenser where the wire was accidentally oversized, or replaced with a more efficient unit that required less power. How many installers would know to remove a non-fused pullout and install a fused one to reduce the over-current device instead of putting a smaller breaker in the panel feeding that branch circuit. Heck you can't even get most EC to realize that placing a SQ D homeline in a Murray panel is a no no.

These code panels need to be reasonable and safe at the same time.

 

[kwired]

Kwired,
You seem to contracdict yourself. You claim that in a 100 foot circuit the issue of not upsizing the EGC seems ok and is the norm. The code should be making rules for the norm not what ifs. Certainly I think the code panel could add " for long distances over XXX"

The instances I see as reduiculous is the one I cited for a A/C condenser where the wire was accidentally oversized, or replaced with a more efficient unit that required less power. How many installers would know to remove a non-fused pullout and install a fused one to reduce the over-current device instead of putting a smaller breaker in the panel feeding that branch circuit. Heck you can't even get most EC to realize that placing a SQ D homeline in a Murray panel is a no no.

These code panels need to be reasonable and safe at the same time.

I don't think so. Like I said the rule is written for one fits all. I have seen upsized long conductors with upsized EGC's that will carry fault currents for what seems like an eternity before something clears - whether it is an overcurrent device or a termination. The whole key to successful operation of overcurrent devices in short circuits or ground faults is low impedance - which results in high current - which results in faster operation of the overcurrent device, minimizing other effects from possible overheating of something or stray current creating shock hazards, and things of that nature. Bottom line is the longer the circuit the more impedance it will have, increase conductor size will lower impedance, but we size conductors for voltage drop based on normal load conditions and not according to fault current conditions. A really long run with a larger conductor often will have more impedance @ fault levels than a very short run at minimum normal load ampacity.

 

[ActionDave]

Like I said the rule is written for one fits all.....

Are you certain? A 10AWG EGC is allowed to be run with a circuit 5280' long or longer, but only if it is on a 60A breaker. On a 20A breaker it may not be allowed.

 

[kwired]

Are you certain? A 10AWG EGC is allowed to be run with a circuit 5280' long or longer, but only if it is on a 60A breaker. On a 20A breaker it may not be allowed.

Exactly one scenario I was getting at. In either instance the resistance of that long conductor may not allow for quick operation of the OCPD.
Any time you start getting a lot of length to a circuit you are going to have this issue. When determine the size of ungrounded conductors you do not use available fault current to determine voltage drop, you use the expected load. Increasing the size of EGC because you increased the ungrounded conductors is a step in the right direction but does not assure that the ground fault that would result in 5000 amps of current on a short run will still be 5000 amps if the fault happens 1000 feet from the source.


One fits all may not be the right thing to say but is best I could come up with.