shared neutral

[iwire]

Re: shared neutral

Originally posted by jbwhite:
Someone tell me if I am wrong, but wouldnt three 20 amp hots all on the same phase need a number 4 neutral?

3 x 20 = 60.

6 AWG is rated 60 amps.

This can not be an NM installation and the terminals involved would probably be listed for at least 75C

 

[physis]

Re: shared neutral



Edit: Is he cheesy? Probably.

[ January 16, 2006, 01:11 AM: Message edited by: physis ]

 

[ramsy]

Re: shared neutral

jbwhite wrote:
Someone tell me if I am wrong, but wouldnt three 20 amp hots all on the same phase need a number 4 neutral?

Maybe, #4 neutral @75^c.
1)Since, (3+1) must be derated to 80%. NEC 310-15b
2)For any constant loads @ 60A * 1.25
3)For any nonlinear loads w/zero-sequence harmonics.
4)For 3-phase 4-wire wye w/hots on same panel phase
5)For copper-clad/Aluminum wire (spec. for hi-cost Cu)
6) For any plan that considers expansion.

 

[augie47]

Re: shared neutral

ramsy, may be too early and the ole brain hasn't kicked in, but I don't follow your point...(excluding #5 and #6), I agree with iwire, this can't be NM so I don't see the 60o consideration. Assuming 75o ratings, I don't see a problem with the #6...enlighten me please.

 

[iwire]

Re: shared neutral

Morning Roger, you like to be precise, thats cool I can be too.

Originally posted by ramsy:
5)For copper-clad/Aluminum wire (spec. for hi-cost Cu)

I think we all know AL has a lower ampacity than CU.

Originally posted by ramsy:
6) For any plan that considers expansion.

Specifications can always change the job.

I can not imagine a specification that allowed the use of one neutral for many circuits but also required room for expansion.

[ January 16, 2006, 07:15 AM: Message edited by: iwire ]

 

[topend]

Re: shared neutral

Thanks, guys. Rich here. I was wondering why I didn't get any responses... (new firewall). I initially figured on 20A circuits (single phase, pipe and wire), then got the spec sheet on the heater and it is rated 20 FLA and the manufacturer recommends #10 wire. Even though 12thhn is rated at 25A, I belive the largest OCPD you can use is 20A, (I thought I could install #12 and a 2P25A breaker). So I bought #10 & 3/4 EMT for the job, only to realize that its capacity is ten #10s, which will make for a pretty tough pull if I use three neutrals and a ground.

 

[ramsy]

Re: shared neutral

iwire wrote:
Morning Roger, you like to be precise, thats cool..

Yes, I try. A college sweetheart once said my writing improved after trying to use fewer words. And, that anal-retentive obsession recently tried some choice slang, precise enough to get sensored on this forum. Reworking two sentences, without that word, required several paragraphs and remained less clear to at least one person. So, precise and stupid may be related.

Re: Maybe, #4 neutral @75^c.
1)Since, (3+1) must be derated to 80%. NEC 310-15b

Augie wrote:
Assuming 75o ratings, I don't see a problem with the #6...enlighten me please.
iwire wrote:
The 80% derated value of 6 AWG CU is typically 60 amps.

Guys, I'm getting 47.5A for 80% derated 6 AWG CU, using 310-15(B)2a & Appendix B Tbl 310-11. Sqrt[(0.5*5)/4]*75*0.8=47.5A high value with EGC.

Re: 3)For any nonlinear loads w/zero-sequence harmonics.

iwire wrote:
Only circuits where the major portion of the load consists of nonlinear loads.

Adding any more current from anywhere exceeds 60A. Using a 60A max for #6 CU, with "three 20A hots", leaves no room for additional current at full load. Me sees three 20A loads, rather than three # 12's.

 

[iwire]

Re: shared neutral

Originally posted by ramsy:

Augie wrote:
Assuming 75o ratings, I don't see a problem with the #6...enlighten me please.
iwire wrote:
The 80% derated value of 6 AWG CU is typically 60 amps.

Guys, I'm getting 47.5A for 80% derated 6 AWG CU, using 310-15(B)2a & Appendix B Tbl 310-11. Sqrt[(0.5*5)/4]*75*0.8=47.5A high value with EGC.

Roger you making this more complicated than it is.

6 AWG @ 90 C is rated 75 amps per table 310.16

75 x .8 = 60 amps.

Done, no reason to go to "Appendix B Tbl 310-11"

 

[LarryFine]

Re: shared neutral

Originally posted by physis:

 

[dlhoule]

Re: shared neutral

Are you referring to white for good guy?

 

[hornetd]

Re: shared neutral

Originally posted by dlhoule:
Are you referring to white for good guy?

I would think he was aluding to the requirement that neutral conductors be white or natural grey.
--
Tom Horne

 

[ramsy]

Re: shared neutral

iwire wrote:
Re: Derating using Sqrt(0.5N/E)*A1
"Roger your making this more complicated than it is. ..no reason to go to Appendix B Tbl 310-11"

Yes I see, 110-14(c), and the Appendix-formula examples don't apply until the # of hots is between 10 - 85.

I'll just stencil my truck, "Expansion-room King"

 

[LarryFine]

Re: shared neutral

Originally posted by hornetd:

Originally posted by dlhoule:
Are you referring to white for good guy?

I would think he was aluding to the requirement that neutral conductors be white or natural grey.

Exactamundo!

Besides, according to Chuck Norris, good guys wear black.

 

[dlhoule]

Re: shared neutral

Darn, I originally thought you were referring to the color of the cape.

 

[LarryFine]

Re: shared neutral

Originally posted by dlhoule:
Darn, I originally thought you were referring to the color of the cape.

Who is Darn?

 

[augie47]

Re: shared neutral

not who, but what.... thats what Sam did when he repaired the cape.... darned it!

 

[dlhoule]

Re: shared neutral

Darn is my polite version of damn. Just like my mistakes are are a polite version of " I f*****up.

Augie, you have to quit this. My stomach is getting too sore.

 

[LarryFine]

Re: shared neutral

Q: What did Delaware?

A: Her New Jersey!