8-2 uf nmcb 100'

[Aceman]

I understand about this upsize requirement Ace but what about when its included in the cable?

There are no exceptions for cables, it applies to everything.

 

[walrus]

I wonder what the reason for the code is, beyond upsizing for voltage drop or for derating which I can understand. When neither apply it makes no sense

 

[hidollartoys]

If one uses 8/2 NM or UF on a 40A breaker or 6/2 NM or UF on a 50A breaker, all is well, as soon as you decrease the rating of the fuse / circuit breaker on those cables then the rule kicks in, because the ungrounded conductor was "increased in size". Just one of those rules that can be baffling at times.

You are disregarding 250.122(F)(1).

 

[JBurgess]

You are disregarding 250.122(F)(1).

What year code are looking at? In 2008 this section deals conductors in parallel and would not apply.

(F) Conductors in Parallel. Where conductors are run in
parallel in multiple raceways or cables as permitted in
310.4, the equipment grounding conductors, where used,
shall be run in parallel in each raceway or cable.
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 or
cable in accordance with Table 250.122.

 

[sberry]

6 & 8 AWG NM & UF cable has a 10 AWG equipment grounding conductor & because of the above code section disallows the use of either size or type for 30A, because one cannot put a larger EGC in the cable assembly
I dont see how this disallows 6 wire for 30A ocpd, 250.122 says for overcurrent not exceeding x Amps and 122.B uses the wording proportionately. Still hasnt changed the proportions and is well under the ocpd which inherently makes it a safer install. Limiting overcurrent is always a good thing when it comes to short circuit protection.
Seems like an application of code issue, does it apply?

 

[sberry]

Apparently I am wrong on this, just never occured to me that using a smaller breaker would be an issue.

 

[oleguy]

well,the way i read table 250.122 is,6-2 # 10 ground will be good.#10 copper is good for 60 amps.there fore a 30 amp over current device is code as the 6-2 is good for 55 amps.he is
useing romex.the table reads grd size for over current device.

 

[Norcal]

well,the way i read table 250.122 is,6-2 # 10 ground will be good.#10 copper is good for 60 amps.there fore a 30 amp over current device is code as the 6-2 is good for 55 amps.he is
useing romex.the table reads grd size for over current device.

250.122(B) supersedes all that when using larger conductors, one has to follow the most restrictive, not the least.

 

[oleguy]

well,in my opinion if the increase went from #6 to #4 then yes but there is no increase in ungrounded conductors.they are still #6 there fore #10 ground because #6 romex is only good for 55 amps.i might go along if you put 75*c wire in the ckt but not as it stands.show me in the code that where it says you can,t use a lower value breaker.if this is the case then we know who has stock in the copper mines...lol

 

[Norcal]

well,in my opinion if the increase went from #6 to #4 then yes but there is no increase in ungrounded conductors.they are still #6 there fore #10 ground because #6 romex is only good for 55 amps.i might go along if you put 75*c wire in the ckt but not as it stands.show me in the code that where it says you can,t use a lower value breaker.if this is the case then we know who has stock in the copper mines...lol

We keep coming back to 250.122(B)

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.

Bold & Italics by me.

6 AWG is a increase of the minimum 10 AWG required for a 30A circuit. This is a not a problem if using a conduit, simple matter to increase the grounding conductor & comply w/ code.

 

[oleguy]

if this were in conduit what size ground would i need?

 

[walrus]

if this were in conduit what size ground would i need?

Depends on the breaker, 40 amp breaker and you can stay with the #10, 30 amp breaker and you need a #8, makes a lot of sense doesn't it?.

 

[oleguy]

yeah,#8 is what i came up with.you are right,makes no sence.

 

[Aceman]

What I was told a while back when we were wiring a Home Depot, and we all were asking ourselves the same question, was that they needed a rule to cover the oversized cables used for voltage drop. Home Depots are built with a couple of electrical rooms with a ton of circuits ran across the store, so there were quite a few #8 20 amp circuits.

I was told contractors used to tell inspectors they ran large cables just for derating purposes just so they wouldn't have to pay for oversized/more expensive ground wires. Well, if you run a mile out to a load and need to upsize the cable for voltage drop, you shouldn't certainly upsize the ground also to help clear the fault quickly. Right?

Since the code making panel didn't want to start arguments between electricians and inspectors debating whether or not the oversized cables were installed for derating OR voltage drop reasons, they just made one rule to cover it all. That's why the rule makes more sense for voltage drop but makes no sense at all when you simply use #2 AL on a 40 amp breaker just because that was the breaker you had.

 

[sberry]

What intrigues me is that we are not changing the relationship between the 2 wires by lowering the ocpd, I understand the need if it goes beyond 60A or if the conductors are bigger than a 6. If the fault rating of the ground wire is adequate at 40 or 60 @ 100 ft doesn't it make some sense it would be adequate for 30?
I know you guys are more well schooled and current than I am and after all the discussion the subject is clear so I get that I was mistaken as to WTF but does this mean every time you use less than the max allowable breaker you need to match conductor size? Says proportionate to, whats that mean? Equal to?

 

[yotarover]

my thread keeps getting bigger and bigger

i said the hell with it and just ran the 8-2 with a 60amp breaker and a 50amp outlet on the end of it. right dead smack across my building and then curved 12ft inward and ended up with 135ft. yes i did have 6/3 cost me 400$ that i didnt have to spend on 1 item. talked to the big man at the local welding shop. and the 8/2 is fine for my power arc 200 since i have a 60a breaker. even a old retired vetren of duke power said it was fine.

keep it coming