DERATING QUESTION

[green2012]

I am a little confused by a different thread I read about derating. When do I count the nuetral as a current carrying conductor?

1. 2 wire circuit? 1 hot 1 nuetral
2. 2 or 3 circuits sharing a nuetral? 2 or 3 hots sharing a nuetral
3. 3 wire circuit (dryer, range, a/c)?

Can anyone explain this clearly.

 

[green2012]

I may have been vague. I am moving 2 panels full of circuits to new locations. I needed to figure out how many pipes it will take to move all the circuits over. Im going to remain under pipe fill(40% fill), but worried about derating. EX: one 3/4 emt will hold 16-12awg wires. 10-20 curent carring conductors in a pipe will derate each wire by 50 percent. 310.15b(5)and(6) is what im asking about. If I put 8hots and 8 nuetrals in each pipe is that 8CCC or 16? The difference means derate by 50% or 70%. so the 3 questions I asked are just to help me understand the 3 scenerios in the panel.

standard circuit 1 hot-1 nuetral
shared nuetral 2 hots sharing a nuetral
3-wire systems a/c, cooktops, dryers

In each of those when do I count the nuetral as a CCC?

 

[Flapjack]

http://forums.mikeholt.com/showthread.php?t=83435&page=4&p=664225#post664225

That is what you want. Scroll down to the bottom. It's in the FAQ section.

Edit: Didn't read your second post.

 

[green2012]

Ok so let me ask it another way. lets say I have 8 pipes comming in a panel, and each has 1 circuit. Thats 16 wires comming in the panel. If I wanted to move the circuits in 1 (3/4)pipe it would derate the wire by 50 percent because I would have 16CCC? What If I grouped them? If I made 8 MWBC's. Then I would have only 8 CCC's (8 hots and 4 nuetrals)? Then I would derate by 70 percent?

 

[infinity]

Ok so let me ask it another way. lets say I have 8 pipes comming in a panel, and each has 1 circuit. Thats 16 wires comming in the panel. If I wanted to move the circuits in 1 (3/4)pipe it would derate the wire by 50 percent because I would have 16CCC? What If I grouped them? If I made 8 MWBC's. Then I would have only 8 CCC's (8 hots and 4 nuetrals)? Then I would derate by 70 percent?

You're correct if it's not from a WYE system. Here this may help:

Neutral Conductors:

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.

 

[Little Bill]

The neutral would count as a CCC in a two wire circuit because it would carry the same amount of current as the ungrounded.

In a MWBC, the neutral would only carry the imbalance between the two ungrounded conductors and would not be a CCC. Well, to clarify, it wouldn't unless there was a lot of imbalance such as lots of fluorescent lighting, lots of computers etc.

A dryer or stove/range neutral would not be a CCC because the 120V part of the circuit would only carry a small amount of current, not enough to cause an imbalance.

There are other definitions depending on your power source, but I doubt you would have that in a residential setting.

Edit: Rob types faster than me!

 

[green2012]

Thanks guys.

A/C circuit is the same right? the nuetral wouldnt carry enough to unbalance. It shouldnt be counted.

 

[infinity]

Thanks guys.

A/C circuit is the same right? the nuetral wouldnt carry enough to unbalance. It shouldnt be counted.

Not sure what you mean about a neutral for an A/C circuit.

 

[green2012]

LOL it was late. I was looking at a picture and I saw the ground as a nuetral. Wasnt thinkin