#6 is usually code-proper up to a 200A service at least. But I recommend
consulting your inspector before buying anything. The other wires you
mention are brutally expensive, and it's best to nail it all down exactly
with the guy who gets to say yea or nay before shelling out the bucks.
Furthermore, it's cheaper (plus legal and safe if done properly) to use
aluminum conductors for big feeds. If the wires are longer
than a few feet, I recommend considering it. It's MUCH cheaper.
Going to aluminum saved me about $400 on my subpanel feed.
Ask the inspector about aluminum too.
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
The size of the Equipment Grounding Conductor (EGC) is based on the
rating of the Over Current Protective Device (OCPD) rather than on the
size of the conductors. What size OCPD were you planning to use to
protect the feeder?
For a one hundred ampere breaker a number eight copper or number six
aluminum Equipment Grounding Conductor (EGC) is required. If you do use
number three copper for the feeder conductors you must use number six
copper or number four aluminum for the EGC. This last is because the
code requires that the size of the EGC be increased in proportion to the
increase in size of the current carrying conductors.
While what you say is true, I'm curious at what point you determine a wire
is oversized. If using table 310.15(b)(6), then #4 cu is all that is
required. If using 75C wire in table 310.16, then you need #3 cu. If using
60C wire (or NM cable), then you need #2 cu. I can't see how the equipment
grounding would care about what insulation heat rating the wire has. So at
what point must you begin to increase the EGC size?
Thanks. I was hoping #6 would be OK.
Now I have another problem.
In my main panel, which is 200A, the neutral buss bar is full. Actually it's
the ground bus bar. I can see the entrance service cable attached to the lug
on the neurtal bar. The ground bar is only about 1" away and an inch in
front of the neutral bar. It appears the neutral bar wasn't even used. The
white wire & bare ground from each circuit attach to the same screw on the
ground bar. (easier access for whoever wired the house years ago. The rear
bar is really inaccessable. And I assume they are bonded together
anyway)..... I can't double up any of the wires because they're already
Well, I could double up 1 of them and install a 2-pronged lug adaptor for my
#3 conductor. That would solve the problem for my new neutral conductor. But
where to attach my new ground wire? Can I attach another ground bus bar
directly to the main panel sheet metal? I could them attach a couple of the
ground wires to this to free up room on the neutral bar. (Opps, I mean the
Your panel was improperly wired during installation. Since the white
coded neutral conductors carry current during normal operations they
must be terminated singly with only one under each clamp or screw.
The label in your panel may indicate that the neutral bar can accept
more than one wire per terminal but that is only permissible when the
wires in question are Equipment Grounding Conductors only. Since EGCs
do not carry current during normal operations there is little
possibility that the unequal loading of the multiple conductors will
cause the terminal to loosen. With neutral conductors this is an
issue so each neutral wire must be the only one in each terminal.
What are you planning to use the number six wire for?
>>> For a one hundred ampere breaker a number eight copper or number six
>>> aluminum Equipment Grounding Conductor (EGC) is required. If you
>>> number three copper for the feeder conductors you must use number six
>>> copper or number four aluminum for the EGC. This last is because the
>>> code requires that the size of the EGC be increased in proportion
>>> increase in size of the current carrying conductors.
> While what you say is true, I'm curious at what point you determine a
> is oversized. If using table 310.15(b)(6), then #4 cu is all that is
> required. If using 75C wire in table 310.16, then you need #3 cu. If
> 60C wire (or NM cable), then you need #2 cu. I can't see how the
> grounding would care about what insulation heat rating the wire has.
> what point must you begin to increase the EGC size?
> Kent, WA
I made a bad assumption that the reason for the #3 conductors was to
compensate for voltage drop. 310.15 (b) (6) only applies to service
conductors and to feeders that supply the entire supply to a dwelling
unit so it would not apply to the situation as outlined in the original
posting. I would use the smallest wire size that the code would permit
for the OCPD in question as the starting point. If the wire selected is
larger than that minimum then the only rational reason is to avoid
voltage drop. In any case if you increase the wire size to avoid
voltage drop you must increase the size of the equipment grounding
conductor proportionately. I don't have an NEC here so I can't check
the wire size for the one hundred ampere feeder. If the number three is
the minimum that the code would allow for the 100 ampere feeder then a
number eight EGC would be all that is needed.
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