dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
6
share rss forum feed


nunya
LXI 483
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
reply to Zach1

Re: Conduit Size for 6-3 NM

Neutrals are always counted as current carrying conductors.

Zach1
Premium
join:2006-11-26
NW Minnesota
said by nunya:

Neutrals are always counted as current carrying conductors.

Always??? Really???

310.15(5) Neutral Conductor

(a) A neutral conductor that carries only the unbalanced current from the other conductors of the same circuit shall not be counted when applying the provisions of 310.15(B)(3)(a)

--
Zach


nunya
LXI 483
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
That's an exception that's rarely met. We are talking about a single phase or *possibly* two phase system here.
See (b) and (c) right below.
--
If someone refers to herself / himself as a "guru", they probably aren't.

Zach1
Premium
join:2006-11-26
NW Minnesota
My original reply covered that contingency and mentioned (b) specifically. (c) doesn't apply since there are only three insulated conductors in a 6/3 cable making it's (legal) use on a 4-wire 3-phase wye circuit impossible. More than likely the OP's system is a vanilla 120/240 single-phase where the neutral isn't required to be counted for the purpose of current adjustment.
--
Zach


agtle

@teksavvy.com
said by Zach1:

My original reply covered that contingency and mentioned (b) specifically. (c) doesn't apply since there are only three insulated conductors in a 6/3 cable making it's (legal) use on a 4-wire 3-phase wye circuit impossible. More than likely the OP's system is a vanilla 120/240 single-phase where the neutral isn't required to be counted for the purpose of current adjustment.

how will one be sure it is perfectly balanced? this isn't a connected load, it is a sub.


loaded

@myvzw.com
said by agtle :

said by Zach1:

My original reply covered that contingency and mentioned (b) specifically. (c) doesn't apply since there are only three insulated conductors in a 6/3 cable making it's (legal) use on a 4-wire 3-phase wye circuit impossible. More than likely the OP's system is a vanilla 120/240 single-phase where the neutral isn't required to be counted for the purpose of current adjustment.

how will one be sure it is perfectly balanced? this isn't a connected load, it is a sub.

The neutral carries the unbalanced portion of the total circuit load. If the load is balanced across the 240V line, the neutral current approaches zero. As the load becomes more unbalanced, the neutral current is inversely proportional to the that of the lightly loaded phase conductor. Whether the load fed by the 3 wire circuit is static or a sub panel, the circuit theory is the same.

Basic split phase theory and calculations

»www.allaboutcircuits.com/vol_2/c···0/1.html


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast

1 edit
I probably should have been a bit more clear in the scope. This feed will connect to a 60A nonfused disconnect safety switch and be feed by a 60-AMP breaker in the panel.

The panel is in the garage and the conduit will be run along the garage wall to protect the NM until it enters the basement.

Safety switch will be feeding resistance heaters in a 9.6kW electric furnace so it should be pretty balanced with little or no neutral current. In fact, I am not even sure the furnace has a neutral connection, but it probably does for the control transformer. The heater elements are spec'd at 40A load @240VAC so I am well below the rating of the cable.

The pull should not be too difficult - famous last words- as it is 20' straight horizontal, a 90*, 5' up and finally a LB with a short nipple into the side of the panel. I had thought about the "unwillingness" of the 6-3 to bend so stripping the sheath off was a backup plan.

Interesting about the AHJ comment that if the wire is marked, it can be stripped and used for conduit application. In the conduit no one can see the wire markings but it could be disallowed. How is this different than the wire being exposed for 18" or so in the panel and not being labeled? That is legal, but when it is hidden it has to be marked??? I don't see the logic here. Can some one enlighten me?
--
The difference between genius and stupidity is that genius has its limits.

Zach1
Premium
join:2006-11-26
NW Minnesota

1 edit
You might want to verify your furnace but I've not seen an air handler with strip heaters that requires a neutral. The control transformer primary and blower motor are 240V . If this is accurate for yours, you can use 6/2. Have you considered taking the advice of nunya See Profile about running conduit the entire length of the circuit and using THHN/THWN? It would allow smaller conduit, be much easier to pull, eliminate the questions that surround the compliance of cable in conduit and probably be less expensive.

The AHJ here won't allow stripping the sheath off of the cable for use in conduit. Of course, they have to catch it but most local inspectors can tell the difference between a THHN conductor that was manufactured as a single conductor and one that was cabled. Their argument is the cable was approved and listed for a particular use as it was originally manufactured and stripping the sheath for use in conduit is an unauthorized modification and thus renders it unlisted and in violation of 110.3(B)

Of course, YMMV

110.3(B) Installation and Use. Listed and labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
--
Zach