20a breaker protecting #8 wire

[stickboy1375]

Ummmm, what about a simple switch leg? Cant we do those any more? Gonna make life pretty hard if that's true

You'll get used to it.

 

[jerrywilson]

derating

derating

it is the size of the overcurrent device that limits the size of the circuit not the wire size.....derating wire is required due to vd,in tucson az we are required to derate the wire if for example,a service upgrade is done and the new panel was moved to a new location.if you have to install a jbox to refeed ckts into house.derating the wire is required.

 

[480sparky]

Ummmm, what about a simple switch leg? Cant we do those any more? Gonna make life pretty hard if that's true

Running 14/3 instead of 14/2 isn't all that hard.

 

[stickboy1375]

Running 14/3 instead of 14/2 isn't all that hard.

Or expensive... or just simple fact of changing wiring habits... :angel:

 

[jerrywilson]

Im pretty sure that a 20amp ckt only requires a #12 egc...no matter what size the wire happens to be..its still a 20amp ckt.the gec is sized by the largest ungrounded service ent conducter.the egc is sized by the ocd.

Explain o to me then:

Using a #6 wire fed from a 60 Amp breaker only requires a #10 EGC.

Take that SAME #6 wire, and feed it from a 20 Amp breaker, now the EGC is required to be a #6!

How is the ground wire any safer being a #10 on a 60 Amp circuit?

 

[kwired]

Or expensive... or just simple fact of changing wiring habits... :angel:

Start running power to switch first instead of to light first:happyyes:

Explain this scenario to me then:

Using a #6 wire fed from a 60 Amp breaker only requires a #10 EGC.

Take that SAME #6 wire, and feed it from a 20 Amp breaker, now the EGC is required to be a #6!

How is the ground wire any safer being a #10 on a 60 Amp circuit?

It makes sense in some cases and in others it doesn't make sense. If you increase a 20 amp circuit to 6AWG conductors, it makes perfect sense to increase EGC by same amount and you end up with 6 AWG EGC also.

Where it is more confusing is if you increase a required 40 amp conductor to 6 AWG for voltage drop reasons. 10 AWG is acceptable for EGC for overcurrent protection of 40 amps, but you increased the ungrounded conductors so therefore you are supposed to also increase EGC proportionally, if I calculated correctly you should need 8AWG for the EGC. Yet if you have same 6 AWG on a 60 amp breaker 10 AWG is acceptable. That is a case where it doesn't make as much sense.

 

[jerrywilson]

Start running power to switch first instead of to light first:happyyes:



It makes sense in some cases and in others it doesn't make sense. If you increase a 20 amp circuit to 6AWG conductors, it makes perfect sense to increase EGC by same amount and you end up with 6 AWG EGC also.

Where it is more confusing is if you increase a required 40 amp conductor to 6 AWG for voltage drop reasons. 10 AWG is acceptable for EGC for overcurrent protection of 40 amps, but you increased the ungrounded conductors so therefore you are supposed to also increase EGC proportionally, if I calculated correctly you should need 8AWG for the EGC. Yet if you have same 6 AWG on a 60 amp breaker 10 AWG is acceptable. That is a case where it doesn't make as much sense.

you are not required to increase the size of the EGC.its still a 40amp circuit! EGC is sized to OCPD not the largest ungrounded conducter...that would be the grounding electrode conducter...also your talking about short circuit protection.not overcurrent protection

 

[Little Bill]

you are not required to increase the size of the EGC.its still a 40amp circuit! EGC is sized to OCPD not the largest ungrounded conducter...that would be the grounding electrode conducter...also your talking about short circuit protection.not overcurrent protection

I believe you need to read 250.122(B) then come back with what you read.

 

[jerrywilson]

you are correct...I guess i should read a little further next time.....I have always used table 250.122 to size my egc.if i do have to derate,than i size my egc to the conducter size.I do stand corrected.thankyou

I believe you need to read 250.122(B) then come back with what you read.

 

[Little Bill]

you are correct...I guess i should read a little further next time.....I have always used table 250.122 to size my egc.if i do have to derate,than i size my egc to the conducter size.I do stand corrected.thankyou

No problem. I'm usually on the other end!

 

[Dennis Alwon]

Im pretty sure that a 20amp ckt only requires a #12 egc...no matter what size the wire happens to be..its still a 20amp ckt.the gec is sized by the largest ungrounded service ent conducter.the egc is sized by the ocd.

Jerry look at 250.122(B). If the wire is upsized then the egc must be proportionally upsized. With 14-10 wire sizes the ratio is 1-1. So if a #8 circuit conductor is used on a 20 amp OCPD, then a #8 egc is required


Sorry I see little Bill got there-- I should have finished the thread before responding

George Stolz did a great post on this issue. Read it here

 

[Sierrasparky]

Jerry look at 250.122(B). If the wire is upsized then the egc must be proportionally upsized. With 14-10 wire sizes the ratio is 1-1. So if a #8 circuit conductor is used on a 20 amp OCPD, then a #8 egc is required


Sorry I see little Bill got there-- I should have finished the thread before responding

George Stolz did a great post on this issue. Read it here

I am still confused on this subject.
Why is the ratio used on conductors 14-10 of 1:1 used instead of the percentage increase of the current carrying conductors being increased.

In other words if you upsize from 6 to #2 what is the ratio of increase. Why shoud that differ for a # 12 or #10 being upsized to #6?

 

[Dennis Alwon]

I am still confused on this subject.
Why is the ratio used on conductors 14-10 of 1:1 used instead of the percentage increase of the current carrying conductors being increased.

In other words if you upsize from 6 to #2 what is the ratio of increase. Why shoud that differ for a # 12 or #10 being upsized to #6?

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.

 

[Little Bill]

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.

To add to what Dennis said about 1:1 ratio. You never have to run an EGC larger than the ungrounded conductors. If you do the math on some of the ratios, it will give you a larger value than what the ungrounded conductor was resized to, then you would just use the same size EGC as the ungrounded.

 

[Sierrasparky]

so how do the words : "but in no case
shall they be required to be larger than the circuit conductors
supplying the equipment"
fit into the subject?

250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum
equipment grounding conductors of the wire type shall not
be smaller than shown in Table 250.122, but in no case
shall they be required to be larger than the circuit conductors
supplying the equipment. Where a cable tray, a raceway,
or a cable armor or sheath is used as the equipment
grounding conductor, as provided in 250.118 and
250.134(A), it shall comply with 250.4(A)(5) or (B)(4).

 

[Little Bill]

so how do the words : "but in no case
shall they be required to be larger than the circuit conductors
supplying the equipment"
fit into the subject?

250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum
equipment grounding conductors of the wire type shall not
be smaller than shown in Table 250.122, but in no case
shall they be required to be larger than the circuit conductors
supplying the equipment. Where a cable tray, a raceway,
or a cable armor or sheath is used as the equipment
grounding conductor, as provided in 250.118 and
250.134(A), it shall comply with 250.4(A)(5) or (B)(4).

Just what I wrote in post #54.
I don't know what you are asking that I didn't cover.:?

 

[Sierrasparky]

Just what I wrote in post #54.
I don't know what you are asking that I didn't cover.:?

Well you have a 20 amp breaker, to # 12 wire NM to ,# 6NM wire, # 12 nm to the equipment! The #12's are last and the conductors supplying the equipment.

I ask where does the words "but in no case
shall they be required to be larger than the circuit conductors
supplying the equipment"

Just saying , I know it may be a game or play on words.

 

[Dennis Alwon]

so how do the words : "but in no case
shall they be required to be larger than the circuit conductors
supplying the equipment"
fit into the subject?

250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum
equipment grounding conductors of the wire type shall not
be smaller than shown in Table 250.122, but in no case
shall they be required to be larger than the circuit conductors
supplying the equipment. Where a cable tray, a raceway,
or a cable armor or sheath is used as the equipment
grounding conductor, as provided in 250.118 and
250.134(A), it shall comply with 250.4(A)(5) or (B)(4).

Lets say you have a wire that has a #4 ccc and a #8 EGC in a normal situation. Now because of the long distance you want to use a 1/0 conductor rather than a #4. This is fine to do but if the breaker is still an 80 amp breaker as a #4 might have then the egc must be proportionally enlarged also. You go to Table 8 in Chapter 9 and look up the cm of the #4 =41740 but now you went up to a 1/0 which is 105600cm. If you divide 105600/41740 = 2.5. That means the 1/0 is 2,5 times larger than the #4. Now we have to look up the egc and do the same. #8 = 16510 but now we must increase it by the same 2.5 which gives us 41275cm Look up in the tables and we must use a number equal to or greater than 41275 for the egc-- That would mean we need a #4 egc

 

[Sierrasparky]

Lets say you have a wire that has a #4 ccc and a #8 EGC in a normal situation. Now because of the long distance you want to use a 1/0 conductor rather than a #4. This is fine to do but if the breaker is still an 80 amp breaker as a #4 might have then the egc must be proportionally enlarged also. You go to Table 8 in Chapter 9 and look up the cm of the #4 =41740 but now you went up to a 1/0 which is 105600cm. If you divide 105600/41740 = 2.5. That means the 1/0 is 2,5 times larger than the #4. Now we have to look up the egc and do the same. #8 = 16510 but now we must increase it by the same 2.5 which gives us 41275cm Look up in the tables and we must use a number equal to or greater than 41275 for the egc-- That would mean we need a #4 egc

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.

 

[John120/240]

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.[/COLOR]

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.