Derating for ccc's

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Coreyp08

Member
Location
Cleveland,ohio
I feel rather stupid asking this, but I just started at a new company that is telling me I must run 6 hots and 6 neutrals(12 thhn) in my 3/4 emts. I was always under the impression I am only allowed 6ccc's in a conduit before I need to derate them. I have always ran 4 hots and 4 neutrals with ground max in any size conduit. (12 ga on 20a breaker) to keep under 9 ccc's. Also I would always run 9 hots with 3 neutrals and not count the neutral as ccc because the load would balance out. Am I wrong? In this specific application I am wiring in a hotel so the circuits would be for kitchen/bath outlets and what you would generally expect. My company claims the minimal load on the circuit would allow me to derate my wires based on the load and not the breaker ampacity.
 

kwired

Electron manager
Location
NE Nebraska
I feel rather stupid asking this, but I just started at a new company that is telling me I must run 6 hots and 6 neutrals(12 thhn) in my 3/4 emts. I was always under the impression I am only allowed 6ccc's in a conduit before I need to derate them. I have always ran 4 hots and 4 neutrals with ground max in any size conduit. (12 ga on 20a breaker) to keep under 9 ccc's. Also I would always run 9 hots with 3 neutrals and not count the neutral as ccc because the load would balance out. Am I wrong? In this specific application I am wiring in a hotel so the circuits would be for kitchen/bath outlets and what you would generally expect. My company claims the minimal load on the circuit would allow me to derate my wires based on the load and not the breaker ampacity.
Actually you must start derating at 4CCC's, but smaller 90C conductors generally need more then 9 CCC's before adjustments will require a larger conductor, I think you have the right thing in mind but didn't quite say a couple things quite right in there.

As far as derating or the actual load on the conductors - that is allowed for permanently connected loads, what gets you into trouble is receptacle outlets and 210.19(A)(2), which says conductor ampacity supplying multiple receptacles on a branch circuit must not be less then the rating of the branch circuit.

So 20 amp circuit feeding multiple receptacle outlets - must have 20 amp conductor even if you normally only have 1 amp of load connected.
 

Coreyp08

Member
Location
Cleveland,ohio
Actually you must start derating at 4CCC's, but smaller 90C conductors generally need more then 9 CCC's before adjustments will require a larger conductor, I think you have the right thing in mind but didn't quite say a couple things quite right in there.

As far as derating or the actual load on the conductors - that is allowed for permanently connected loads, what gets you into trouble is receptacle outlets and 210.19(A)(2), which says conductor ampacity supplying multiple receptacles on a branch circuit must not be less then the rating of the branch circuit.

So 20 amp circuit feeding multiple receptacle outlets - must have 20 amp conductor even if you normally only have 1 amp of load connected.


I understand what you are saying about permanently connect loads, but would a refrigerator or dishwasher count if it has a dedicated duplex receptacle? Thanks for the reply also.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Here is something written by Trevor -a mod here- wrote
Here's some examples of when to count the neutral as a CCC:


208Y/120 volt system-different circuit types:


A)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C)- 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*


Notes:
A)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B)- In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C)- In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.


120/240 volt system-different circuit types:


D)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's


Notes:
D)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E)- In this circuit the neutral will only carry the imbalance between the two ungrounded condcutors so the neutral is not counted as a CCC.
 

kwired

Electron manager
Location
NE Nebraska
I understand what you are saying about permanently connect loads, but would a refrigerator or dishwasher count if it has a dedicated duplex receptacle? Thanks for the reply also.
Reality tells me it probably is not loaded any more then the appliance nameplate, but as is written I have to say that it is a multiple receptacle outlet circuit.
 

J.P.

Senior Member
Location
United States
I always stop at 8 ccc plus a ground in 3/4. By the time you derate your pipe ends up being 1".

As far as de-rating less because the load is light on the receps? Who can say what the load on the receps may be 10 years from now.

It's just easier to run more 3/4" instead of messing around with 1" boxes and fittings.

Your in a tough spot with a new company. Are you the guy getting nailed if this gets spotted?
 

kenman215

Senior Member
Location
albany, ny
I always stop at 8 ccc plus a ground in 3/4. By the time you derate your pipe ends up being 1".

As far as de-rating less because the load is light on the receps? Who can say what the load on the receps may be 10 years from now.

It's just easier to run more 3/4" instead of messing around with 1" boxes and fittings.

Your in a tough spot with a new company. Are you the guy getting nailed if this gets spotted?

Same thing here. I don't bother running #12 in anything over 3/4" anymore. I stop at eight with a ground, typically 3 hits sharing a neutral, and I also count the neutral as a ccc, because there is the imbalance current running back on it.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
When it comes to 15 and 20A branch circuits the magic number is nine. If you don't go over nine CCCs you don't have to upsize your wire or conduit. For three phase you get stuck at eight if you are pulling full boats, but you get six circuits single phase or three phase either way. I have wondered if that was done on purpose when they set up the derating table.

I can't see any sense in using 3/4" conduit for 20A circuits unless specs say it has to be, otherwise it's just a waste of material and effort. It gets you nothing. I've pulled full boats into 1/2" conduit since I started. It's not that hard.
 

kenman215

Senior Member
Location
albany, ny
When it comes to 15 and 20A branch circuits the magic number is nine. If you don't go over nine CCCs you don't have to upsize your wire or conduit. For three phase you get stuck at eight if you are pulling full boats, but you get six circuits single phase or three phase either way. I have wondered if that was done on purpose when they set up the derating table.

I can't see any sense in using 3/4" conduit for 20A circuits unless specs say it has to be, otherwise it's just a waste of material and effort. It gets you nothing. I've pulled full boats into 1/2" conduit since I started. It's not that hard.

Unless you have a PM who pretty much only buys solid THHN (after all it is a whopping 2 cents/ft cheaper). Not nearly as easy pulling max fill through 1/2" with that...
 

iwire

Moderator
Staff member
Location
Massachusetts
Unless you have a PM who pretty much only buys solid THHN (after all it is a whopping 2 cents/ft cheaper). Not nearly as easy pulling max fill through 1/2" with that...

Solid is not as much of a problem as pulling max fill in any conduit.

I only run 1/2" for three conductors of less.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
. . . and I also count the neutral as a ccc, because there is the imbalance current running back on it.
That is the one time that you don't have to count the neutral as a CCC. It is when the neutral carries more than just the imbalance between the other phases that the neutral must be counted.

 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
When it comes to 15 and 20A branch circuits the magic number is nine.
And here is the basis for that "magic number":

  • 9 CCCs gives a derating factor of 70%.
  • The 90C column tells us that a #12 THHN has an ampacity of 30 amps.
  • 70% of 30 is 21 amps.
  • 21 is larger than 20 (i.e., the ampacity of #12 THHN at 75C), so we assign an ampacity of 20 amps.
  • This allows us to still use a 20 amp circuit breaker with #12 THHN wires and with 9 CCCs.
  • If there were 10 or more CCCs, then the derating factor of 50%, multiplied by the 90C ampacity of 30 amps, would put you below 20. Thus, you can't still use a 20 amp breaker with #12 THHN wires and with 10 or more CCCs.

It is worth noting that this reasoning does not work if the wire does not have a 90C rating. So if you are using THWN wire (that does not also have a THHN designation), then the process shown above would tell us that the magic number is 6 CCCs.

And now I must disagree with Action Dave, with regard to the 15 amp branch circuits. For #14 THHN wire and a 15 amp circuit breaker, the magic number is 6, not 9. As a homework assignment, use the process shown above to confirm, or refute, my claim. As another homework assignment, find the magic number for 30 amp circuits and #10 wire.


 

kenman215

Senior Member
Location
albany, ny
That is the one time that you don't have to count the neutral as a CCC. It is when the neutral carries more than just the imbalance between the other phases that the neutral must be counted.

I realize that, and don't count it on three phase loads, but if I'm sharing a neutral between three receptacle circuits in a 120/208 situation, I really have no idea how big the imbalance is going to be, so I'd rather just count it...

Sent from my SCH-I545 using Tapatalk
 

Frank DuVal

Senior Member
Location
Fredericksburg, VA 21 Hours from Winged Horses wi
Occupation
Electrical Contractor, Electrical Engineer
Um, that's the point. On a three phase conduit feeding three circuits of single phase receptacles with 4 wires, the neutral just carries the imbalance (unless harmonics are there, that's another story which might involve LARGER neutral than #12), so the total current for all 4 wires is the same as 3 CCCs. i.e. for the neutral to carry ANY current, at least one of the phase wires needs to be carrying less than the other two phase wires.

Of course, there is NO harm in counting it as 4 CCCs. Just conservative.
 

Carultch

Senior Member
Location
Massachusetts
I feel rather stupid asking this, but I just started at a new company that is telling me I must run 6 hots and 6 neutrals(12 thhn) in my 3/4 emts. I was always under the impression I am only allowed 6ccc's in a conduit before I need to derate them. I have always ran 4 hots and 4 neutrals with ground max in any size conduit. (12 ga on 20a breaker) to keep under 9 ccc's. Also I would always run 9 hots with 3 neutrals and not count the neutral as ccc because the load would balance out. Am I wrong? In this specific application I am wiring in a hotel so the circuits would be for kitchen/bath outlets and what you would generally expect. My company claims the minimal load on the circuit would allow me to derate my wires based on the load and not the breaker ampacity.

If the neutrals HAVE TO carry the load, because there is no other option than for them to be part of the return path of the current, then the neutral counts as a CCC. Example would be a phase+neutral single phase circuit.

If the neutral is just carrying the return for the imbalance of the load (linear loads), then it doesn't have to count, regardless of the balancing.
 

Smart $

Esteemed Member
Location
Ohio
....

If the neutral is just carrying the return for the imbalance of the load (linear loads), then it doesn't have to count, regardless of the balancing.
We have to be careful how we word this type of circuiting. What you stated is not true for 3-wire with neutral circuit of a 208Y/120V 3Ø 4W, or simply a 120/208V 1Ø 3W circuit, or this part of a MWBC. The neutral is always counted as a CCC in this case, even though it is only carrying the imbalance of line-to-neutral loads.
 

fmtjfw

Senior Member
And here is the basis for that "magic number":
  • 9 CCCs gives a derating factor of 70%.
  • The 90C column tells us that a #12 THHN has an ampacity of 30 amps.
  • 70% of 30 is 21 amps.
  • 21 is larger than 20 (i.e., the ampacity of #12 THHN at 75C), so we assign an ampacity of 20 amps.
  • This allows us to still use a 20 amp circuit breaker with #12 THHN wires and with 9 CCCs.
  • If there were 10 or more CCCs, then the derating factor of 50%, multiplied by the 90C ampacity of 30 amps, would put you below 20. Thus, you can't still use a 20 amp breaker with #12 THHN wires and with 10 or more CCCs.

It is worth noting that this reasoning does not work if the wire does not have a 90C rating. So if you are using THWN wire (that does not also have a THHN designation), then the process shown above would tell us that the magic number is 6 CCCs.

And now I must disagree with Action Dave, with regard to the 15 amp branch circuits. For #14 THHN wire and a 15 amp circuit breaker, the magic number is 6, not 9. As a homework assignment, use the process shown above to confirm, or refute, my claim. As another homework assignment, find the magic number for 30 amp circuits and #10 wire.



What is the standard OCPD size below 15A?
 
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