Branch circuits in Subpanels [RE-wrenches]

[Darryl Thayer]

the currents must be balanced...  If the load and
supply currents pass through the nipple in opsite
directions this is met.  I have ofter run 240 volt
single phase in a conduit without the neutral. 
likewise the power from the main panel to the subpanel
should run through the same conduit as the load
conductors.  
Darryl

--- Dan Rice <danrice at scinternet.net> wrote:

> 
> Ray,
> 
> The issue with passing only the line conductors
> through the conduit nipple
> between panels is induced eddy currents within the
> conduit nipple. The
> changing magnetic field(s) in the conductor(s)
> passing through the conduit
> nipple induces an electric current within the
> surrounding metallic conduit.
> If both line and neutral of the given circuit pass
> through the conduit, then
> the opposite effects of each wire's changing
> magnetic fields cancel one
> another out, and there is no net effect on the
> surrounding conduit. This is
> why all current carrying conductors of a particular
> circuit must remain
> together inside metallic raceways. The problem is,
> the induced eddy currents
> in the surrounding conduit can result in the conduit
> heating up, which I
> believe is due to the conduit material's internal
> resistance to these eddy
> currents, which can be rather high. I am sure that
> there are engineering
> calcs that can be performed to ascertain how
> significant this heating effect
> may be based upon the wire size, AC frequency,
> amperage, conduit size,
> material type, length, phase of the moon and which
> side you part your hair
> on.
> 
> I'm not sure how you feel about them, but there are
> new connectors that take
> the place of wire nuts. Similar to "backstab"
> push-in connections to AC
> light switches and receptacles, these connectors are
> small-ish blocks that
> you push the stripped ends of solid conductor wire
> into. I think these
> connectors can be purchased with different numbers
> of holes to accept two to
> several conductors. They may help you to save room
> in the primary load
> center as you splice on extensions. I've not used
> them in place of wire
> nuts, and I never back stab receptacles when wiring
> AC circuits, so I can't
> vouch for this approach, but it may be worth
> considering. It's an
> alternative to crimp butt splices, and these
> connectors are listed for this
> type of purpose anyway...
> 
> I hope that helps.
> 
> Dan Rice
> Abundant Sun, LLC
> 
> ----- Original Message -----
> From: "Ray Walters" <walters at taosnet.com>
> To: <RE-wrenches at topica.com>
> Sent: Friday, October 20, 2006 6:54 PM
> Subject: Branch circuits in Subpanels [RE-wrenches]
> 
> 
> |
> | Hi All;
> |
> | I have a question related to the grid/tie back up
> question. When we add
> | a sub panel for circuits to be powered by the
> inverter, we install a
> | short 1" to 3 " by 2 " diam nipple to connect the
> sub panel to the
> | existing load center. In many cases the existing
> branch circuit wiring
> | is too short to run directly over to the sub
> panel, so we wire nut
> | extensions to make the run over to the new sub
> panel. To avoid too many
> | wire nutted connections, we have considered just
> running the hots over
> | to the adjacent sub panel, and leave the neutrals
> and grounds connected
> | (as before) to the existing main load center. We
> run #6 or #4 over to
> | connect the subpanel's ground and nuetral bars to
> the main load center.
> | (yes, we observe the "nuetral bonded to ground in
> only one place" rule)
> | Now, I realise code specifies that hots, neutrals,
> and grounds on branch
> | circuits have to be run in the same raceway, and I
> wouldn't consider
> | this, if the load centers were not side by side.
> What are the potential
> | problems here? Basically we're trying to observe
> another section of the
> | code that specifies "professional, workmanship
> like manner": and wire
> | nutting all the hots, neutrals, and grounds to
> jump 2 ft over to an
> | adjacent box looks like a real mess, not to
> mention the potential
> | dangers of all those extra connections crammed
> into the sides of the
> | existing load center.
> | Obviously, if its new construction, we can get the
> branch wires left
> | long enough to do this right. However, this is an
> existing service
> | situation. What do you all think or do in these
> situations? (I've also
> | considered crimped butt splices, but IMHO, they
> are not reliable on
> | solid core wire.)
> |
> | Thanks very much,
> |
> | Ray Walters
> 
> 
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