Derating question.

Status
Not open for further replies.
D

darekelec

Senior Member
Location
nyc
If I have 4 electric ovens fed with 2 hots and 1 neutral each from 3 phase 208 V wye system how many CCCs do I have in one conduit? 8 or 12?
 
I was wondering why ovens even have neutral wire connection? electronics and blower? then on neutral should not be more than 0.5A but per NEC it has to be counted as CCC. Heating elements are off 208V and without connection to neutral probably.
 
darekelec said:
I was wondering why ovens even have neutral wire connection? electronics and blower? then on neutral should not be more than 0.5A but per NEC it has to be counted as CCC. Heating elements are off 208V and without connection to neutral probably.
Click to expand...

Don't forget the light(s) in the oven. Cooking in the dark is so frustrating. :)
 
I'm curious even more. If it was 240V single phase system would neutral still have to be counted as CCC?
The resulting 0.5A is not imbalance of the load therefore neutral has to be counted. Am I right?


Sent from my iPhone using Tapatalk
 
I agree, when it comes to how much heat that conductor will create in the raceway, the load on that neutral is probably pretty insignificant and in some instances the appliance may have a place to land an incoming neutral but has no neutral load to connect to it. But the way NEC is worded you can not take that into consideration.
 
This is a copy of a post written by Rob/Infinity that explains when a neutral is counted as a CCC.

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 conductors so the neutral is not counted as a CCC.
Click to expand...
 
Te above is true but none of the conditions are met by my oven circuit. Neutral in my circuit does not carry the imbalance but rather actual small load of electronics, blower and bulb(s) so it has to counted per nec as CCC.
It's silly cause this 0.5A on neutral ruins my derating.


dura lex sed lex[the] law [is] harsh, but [it is the] law
 
darekelec said:
Te above is true but none of the conditions are met by my oven circuit. Neutral in my circuit does not carry the imbalance but rather actual small load of electronics, blower and bulb(s) so it has to counted per nec as CCC.
It's silly cause this 0.5A on neutral ruins my derating.


dura lex sed lex[the] law [is] harsh, but [it is the] law
Click to expand...
Correct, on a 208/120 system it is not imbalanced current unless all three phases are part of the circuit. However the neutral conductor doesn't necessarily need be same size as ungrounded conductors if it is not going to see the load - but I believe there is a 70% rule that may kick in for a range.

This gets more complicated by the fact these ranges are typically cord and plug connected and are easily changed out possibly by a unit that does have more significant neutral load.
 
darekelec said:
If I have 4 electric ovens fed with 2 hots and 1 neutral each from 3 phase 208 V wye system how many CCCs do I have in one conduit? 8 or 12?
Click to expand...

Dennis Alwon said:
IMO you have 12 current carrying conductor's based on 310.15(B)(5)(b)
Click to expand...

Darek,

Read the section that Dennis referred to:

(b) In a 3-wire circuit consisting of two phase conductors
and the neutral conductor of a 4-wire, 3-phase, wyeconnected
system, a common conductor carries approximately
the same current as the line-to-neutral load currents
of the other conductors and shall be counted when applying
the provisions of 310.15(B)(3)(a).
Click to expand...

You must count the neutral as a CCC. No, if, and or buts.

Despite any arguments that the neutral may carry less amps at some point, the neutral has the potential to carry the full load also. Even if were to somehow come up with a reduced neutral as kwired referred to, it is still a CCC.
 
jumper said:
Your oven circuits are shown as (B) above. You have 3 CCCs per circuit.
Click to expand...
Agreed. But that does not mean that all three conductors will have the same, large current. Please see the attached sketch.
 

Attachments

  • Range circuit.pdf
    86.4 KB · Views: 1
I agree I have to threat my neutral as CCC but not because of 310.15 (B)(4)(b).
There is a difference in diagram I am posting now and Charlie just did.
And yes, I have 2 hots and 1 neutral in a circuit.

I used 4 cables and 4 conduits.
 

Attachments

  • image.jpg
    image.jpg
    83.2 KB · Views: 0
Status
Not open for further replies.
Top