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Default Electrical question: a gfci AND a lighting circuit

Hey gang,

I have two circuits serving the "south 40"

"A" is a security lighting circuit currently switched from three locations
with a 3-way switch at the final common work box. Power is GFCI protected
at the panel

"B" is an unswitched dedicated 20A circuit with a GFCI outlet at the final
common work box.

I decided after the fact (after conduit was covered) that I needed to have
GFCI protected unswitched power at the light pole A. Since I had already
run 12/3 WG to the light pole, and had an "extra" unused red wire, I thought
that I could get a GFCI protected hot lead by connecting my "extra" red wire
to the load side of my B circuit GFCI, then wired the common and ground back
through the lighting circuit A.

I did it but as soon as I apply a load I throw the breaker or the GFCI (I
can't remember which)

Is there a way to rewire to make this work without more wire/conduit?

That is, can I retain my switched lighting circuit "A" without creating a
new branch circuit? (concerned about too much load on the circuit because I
will have to walk up a steep hill to the panel in the house if the GFCI
interupts or the circuit breaker throws )

If NOT, can I create an always HOT branch circuit by taking the HOT from my
switched lighting circuit? (currently switched from three locations,
including at the final work box)

Wouldn't that mean taking power feed from BOTH the black AND the red
(traveller) at my 3-way switch at "A". I think that means the hot supply
wire would change from being the black wire to the red wire every time a
lighting switch was operated on circuit "A". That means the HOT would
consist of a black and red cross connected. Don't think I can do that....

Any other ways to skin this cat?

TIA!

MT


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Chris Lewis
 
Posts: n/a
Default Electrical question: a gfci AND a lighting circuit

According to :
Hey gang,

I have two circuits serving the "south 40"

"A" is a security lighting circuit currently switched from three locations
with a 3-way switch at the final common work box. Power is GFCI protected
at the panel

"B" is an unswitched dedicated 20A circuit with a GFCI outlet at the final
common work box.

I decided after the fact (after conduit was covered) that I needed to have
GFCI protected unswitched power at the light pole A. Since I had already
run 12/3 WG to the light pole, and had an "extra" unused red wire, I thought
that I could get a GFCI protected hot lead by connecting my "extra" red wire
to the load side of my B circuit GFCI, then wired the common and ground back
through the lighting circuit A.

I did it but as soon as I apply a load I throw the breaker or the GFCI (I
can't remember which)

Is there a way to rewire to make this work without more wire/conduit?


No.

GFCI's work by comparing the current on the hot and neutral wire, and
tripping if the current differs by more than about 3ma.

You're pairing the neutral on "A" with the downstream GFCI'd hot from "B"
to produce your outlet on pole "A". As soon as you pull 3ma or more from
that outlet, _both_ GFCI's will see the exact same imbalance between their
respective neutrals and hots. It's a matter of luck as to which one will
trip first - might even both trip.

Secondly, since these two circuits share the same neutral, it's a no-no.

If the circuits are off the same main leg of the panel, you
could fry the neutral without tripping either breaker (assuming you
got around the GFCI issue).

If the circuits are off opposing legs, you won't overload the neutral,
but code will not permit "haywire routing" like this (usually expressed
in terms of "all conductors for a circuit need to be in the same cable").
This has to do with a notion that circuits should have "predictable
behaviour" (vis-a-vis subsequent rework) without having to know what
wierd way it was wired.

If you originally pulled individual wires, you _might_ get away with it
code-wise, but I really don't like it - requires some additional care
in connections (pigtailing) etc. But you still have the GFCI's not liking it.

While you _could_ get this to operate by converting "A" to a regular breaker
(perhaps putting a outlet-less GFCI in pole "A" right on the lamp), and
taking your B "hot" from the line side of the outlet (and using a GFCI outlet
for "A"), you still have to contend with the shared neutral issue above,
and you're not GFCI'ing anywhere near as much of the circuits as you originally
were.

Your other suggestions give me a headache, so I'll let someone else answer ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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Default Electrical question: a gfci AND a lighting circuit

Thanks Chris. Haywired is right! I'll just tap into the lighting circuit
to get power now, then I'll run more wire/conduit in the spring.

Thanks for your help.

MT

"Chris Lewis" wrote in message
...
According to :
Hey gang,

I have two circuits serving the "south 40"

"A" is a security lighting circuit currently switched from three
locations
with a 3-way switch at the final common work box. Power is GFCI
protected
at the panel

"B" is an unswitched dedicated 20A circuit with a GFCI outlet at the
final
common work box.

I decided after the fact (after conduit was covered) that I needed to
have
GFCI protected unswitched power at the light pole A. Since I had
already
run 12/3 WG to the light pole, and had an "extra" unused red wire, I
thought
that I could get a GFCI protected hot lead by connecting my "extra" red
wire
to the load side of my B circuit GFCI, then wired the common and ground
back
through the lighting circuit A.

I did it but as soon as I apply a load I throw the breaker or the GFCI (I
can't remember which)

Is there a way to rewire to make this work without more wire/conduit?


No.

GFCI's work by comparing the current on the hot and neutral wire, and
tripping if the current differs by more than about 3ma.

You're pairing the neutral on "A" with the downstream GFCI'd hot from "B"
to produce your outlet on pole "A". As soon as you pull 3ma or more from
that outlet, _both_ GFCI's will see the exact same imbalance between their
respective neutrals and hots. It's a matter of luck as to which one will
trip first - might even both trip.

Secondly, since these two circuits share the same neutral, it's a no-no.

If the circuits are off the same main leg of the panel, you
could fry the neutral without tripping either breaker (assuming you
got around the GFCI issue).

If the circuits are off opposing legs, you won't overload the neutral,
but code will not permit "haywire routing" like this (usually expressed
in terms of "all conductors for a circuit need to be in the same cable").
This has to do with a notion that circuits should have "predictable
behaviour" (vis-a-vis subsequent rework) without having to know what
wierd way it was wired.

If you originally pulled individual wires, you _might_ get away with it
code-wise, but I really don't like it - requires some additional care
in connections (pigtailing) etc. But you still have the GFCI's not liking
it.

While you _could_ get this to operate by converting "A" to a regular
breaker
(perhaps putting a outlet-less GFCI in pole "A" right on the lamp), and
taking your B "hot" from the line side of the outlet (and using a GFCI
outlet
for "A"), you still have to contend with the shared neutral issue above,
and you're not GFCI'ing anywhere near as much of the circuits as you
originally
were.

Your other suggestions give me a headache, so I'll let someone else answer
;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.



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Posted to alt.home.repair
 
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Default Electrical question: a gfci AND a lighting circuit

Great suggestion, but I don't think I can do it.

I never "planned" on adding the additional circuit, so I used 3/4" conduit.
There are also three 90 degree bends. I'd never get the 12/3 WG out and two
12/2 WG back in. New conduit will be easier. Yesterday I capped the red I
took from the load side of GFCI "B" and connected my receptacle to black
from the switched hot "A". So now I have a working switched receptacle and
security light on "A". Come springtime I'll run new conduit and wire for
constant power at "B"

Reading my GFCI packet would have answered my question. I thought I could
use any neutral to complete the circuit, since they were all interconnected
at the bus on the panel. Chris Lewis explained that the GFCI works by
sensing the current difference between hot and neutral. That answered my
question. I was thrown off when my GFCI tester worked and showed OK, but
when I applied a real load, it threw the GFCI. Tester draws almost no
current.

No way to do it right without more wires. I never knew/thought about the
future repercussions as Chris/Code discussed, and I like doing it "by the
book". If my memory failed me on the "haywiring", I'd end up electrocuting
myself servicing the circuit years from now...

Thanks!

Matt



wrote in message
...
On Thu, 8 Dec 2005 13:12:08 -0800,
wrote:

Hey gang,

I have two circuits serving the "south 40"

"A" is a security lighting circuit currently switched from three
locations
with a 3-way switch at the final common work box. Power is GFCI
protected
at the panel

"B" is an unswitched dedicated 20A circuit with a GFCI outlet at the final
common work box.

I decided after the fact (after conduit was covered) that I needed to
have
GFCI protected unswitched power at the light pole A. Since I had already
run 12/3 WG to the light pole, and had an "extra" unused red wire, I
thought
that I could get a GFCI protected hot lead by connecting my "extra" red
wire
to the load side of my B circuit GFCI, then wired the common and ground
back
through the lighting circuit A.

I did it but as soon as I apply a load I throw the breaker or the GFCI (I
can't remember which)

Is there a way to rewire to make this work without more wire/conduit?

That is, can I retain my switched lighting circuit "A" without creating a
new branch circuit? (concerned about too much load on the circuit because
I
will have to walk up a steep hill to the panel in the house if the GFCI
interupts or the circuit breaker throws )

If NOT, can I create an always HOT branch circuit by taking the HOT from
my
switched lighting circuit? (currently switched from three locations,
including at the final work box)

Wouldn't that mean taking power feed from BOTH the black AND the red
(traveller) at my 3-way switch at "A". I think that means the hot supply
wire would change from being the black wire to the red wire every time a
lighting switch was operated on circuit "A". That means the HOT would
consist of a black and red cross connected. Don't think I can do that....

Any other ways to skin this cat?

TIA!

MT


Can you get another wire in the conduit? Raceway systems are supposed
to be installed such that wires can be installed after the conduit was
installed. You may need to pull all the wire out, mate the new wires
and pull it back.




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Chris Lewis
 
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Default Electrical question: a gfci AND a lighting circuit

According to :
No way to do it right without more wires. I never knew/thought about the
future repercussions as Chris/Code discussed, and I like doing it "by the
book". If my memory failed me on the "haywiring", I'd end up electrocuting
myself servicing the circuit years from now...


There is precisely one way to do it without more wire - but you lose
the "unswitched" attribute on pole "A" ;-)

In short, wire the new "A" outlet in parallel with the lightbulb. You'll
have a switched duplex outlet which is GFCI'd at the panel.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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