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Old 05-28-2012, 06:09 PM   #1
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Piggy Backing Off GFCI Outlets


I understand there are two ways to wire GFCI outlets.

You can wire a series of GFCI outlets off the same circuit, basically connect to the LINE side of each. Then each of these outlets must be GFCI.

You can save some $ by connecting the first one to the LINE side of an GFCI outlet, then from that outlet, come off the LOAD side and connect to non-GFCI outlets and those would be protected by the first GFCI, right?

My question is whether there is a practical limit of how many I can hang off that first GFCI? In a kitchen where I am wiring one every two feet along the counter around...can I piggy back six non-GFCI outlets or is it too much?

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Old 05-28-2012, 06:18 PM   #2
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Piggy Backing Off GFCI Outlets


There is no NEC limit on the number of downstream receptacles from a GFI.

Any receptacle wired from the LOAD terminals of the GFI would have GFI protection.

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Old 05-28-2012, 06:45 PM   #3
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Piggy Backing Off GFCI Outlets


900' of Romex on the load side of a GFCI will draw 5 mA and will trip the GFCI even with nothing plugged in, due to the capacitance between the three conductors.
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Old 05-28-2012, 06:48 PM   #4
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Piggy Backing Off GFCI Outlets


That distance is not a realistic distance to use, especially considering the usage in one kitchen.
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Old 05-28-2012, 09:50 PM   #5
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Piggy Backing Off GFCI Outlets


option 2 is a circuit breaker gfci

advsantage - last longer, protects whole circuit, less crowded boxes
disadvantage - walk to box to reset, cost ($35 - 55 each), difficult if not impossible to use on circuits that also require AFCI protection
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Old 05-28-2012, 10:02 PM   #6
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Piggy Backing Off GFCI Outlets


Thank you!
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Old 05-28-2012, 10:05 PM   #7
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Piggy Backing Off GFCI Outlets


Both wiring and devices do have some bit of current leakage/resistance. I like to keep it to 4-5 downstream receptacles off a GFI device.
This is my own preference, not a statement of fact.
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Old 05-29-2012, 12:00 AM   #8
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Piggy Backing Off GFCI Outlets


Quote:
Originally Posted by Yoyizit View Post
900' of Romex on the load side of a GFCI will draw 5 mA and will trip the GFCI even with nothing plugged in, due to the capacitance between the three conductors.

How do you arrive at this? At 15pf/ft capacitance per conductor to ground I can see only 1mA flowing at 900'. That won;t trip a GFCI. 15pF/ft is probably a high estimate of the capacitance. Isn't the real issue noise immunity of the GFCI with such a long "antenna" on it.
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Old 05-29-2012, 12:32 AM   #9
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Piggy Backing Off GFCI Outlets


Quote:
Originally Posted by Yoyizit View Post
900' of Romex on the load side of a GFCI will draw 5 mA and will trip the GFCI even with nothing plugged in, due to the capacitance between the three conductors.

Yet another example of a vast amount of knowledge wasted in practical situations.
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Old 05-29-2012, 07:11 AM   #10
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Piggy Backing Off GFCI Outlets


Not that often encountered but, when the circuit has two hot wires sharing a neutral (it's called a multiwire branch circuit) (and each receptacle is pigtailed to the neutral and one of the hots) then continuing protection from a GFCI receptacle requires a separate 2 wire cable to the next location. The continuing MWBC neutral and hots may not be associated with the load terminals of GFCI receptacles.
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Old 05-29-2012, 08:27 AM   #11
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Originally Posted by AllanJ View Post
Not that often encountered but, when the circuit has two hot wires sharing a neutral (it's called a multiwire branch circuit) (and each receptacle is pigtailed to the neutral and one of the hots) then continuing protection from a GFCI receptacle requires a separate 2 wire cable to the next location. The continuing MWBC neutral and hots may not be associated with the load terminals of GFCI receptacles.
Can you elaborate on this?

I don't think this is my case, however, sometimes I cannot be absolutely sure when working in isolation in one or two boxes, thinking the neutral wires are dedicated to specific circuits, when there could have been some box up in the attic where two hot and one neutral branched into two pairs downstream.

If this is the case how would I wire it differently?

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Old 05-29-2012, 10:34 AM   #12
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Piggy Backing Off GFCI Outlets


Quote:
Originally Posted by curiousB View Post
How do you arrive at this? At 15pf/ft capacitance per conductor to ground I can see only 1mA flowing at 900'. That won;t trip a GFCI. 15pF/ft is probably a high estimate of the capacitance. Isn't the real issue noise immunity of the GFCI with such a long "antenna" on it.
When I measured a chunk of Romex it came in 100 pF/ft and now I figure the correct length for a 5 mA current difference in the GFCI toroid is more like 2200'. The equiv. circuit is 3 caps in a delta config.

The datasheets for GFCI integrated circuits may address the noise immunity issue. National Semiconductor makes one.

IIRC some GFCI manufacturer recommended no more than 400' or so. I don't know how much of the 4 to 6 mA budget you can use up before you get an excessive number of nuisance trips. 2 mA?

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Old 05-29-2012, 10:43 AM   #13
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Piggy Backing Off GFCI Outlets


Quote:
Originally Posted by miamicuse View Post
Can you elaborate on this?

I don't think this is my case, however, some I cannot be absolutely sure when working in isolation in one or two boxes, thinking the neutral wires are dedicated to specific circuits, when there could have been some box up in the attic where two hot and one neutral branched into two pairs downstream.

If this is the case how would I wire it differently?
If two hots and one neutral branched into two pairs (separate neutral for each hot) then no special consideration is needed.You treat each hot/neutral pair as a separate circuit to feed a GFCI receptacle and optionally continue on from the GFCI load terminals with another 2 wire cable.

You would see just one or two 2-wire cables entering a particular outlet box where you might install a GFCI receptacle, if two cables then one is the feed and the other is the continuation.

When two hot wires share a neutral, usually one of the hot wires is red and the other is black.
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Old 05-29-2012, 01:17 PM   #14
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Piggy Backing Off GFCI Outlets


Quote:
Originally Posted by AllanJ View Post
If two hots and one neutral branched into two pairs (separate neutral for each hot) then no special consideration is needed.You treat each hot/neutral pair as a separate circuit to feed a GFCI receptacle and optionally continue on from the GFCI load terminals with another 2 wire cable.

You would see just one or two 2-wire cables entering a particular outlet box where you might install a GFCI receptacle, if two cables then one is the feed and the other is the continuation.

When two hot wires share a neutral, usually one of the hot wires is red and the other is black.
OK may be my description is not sufficient, let me try an example.

In one of my junction boxes in the attic, right next to a access hatch, I have a 3/4" conduit coming from the panel. It has 4 hot wires (I think the colors were brown, black, red, orange) from 4 circuits, let's say circuits 1, 2, 3, 4, but only two neutral white wires.

Inside this junction box there is a splice where each neutral wire splits into two, and there are four conduits leaving this box, each of them have their own neutral going to the downstream junction box. One neutral wire was split to pair with circuits 1 & 2, the other with 3 & 4. That makes 1, 2 a multi-branch circuit right?

If I am not aware of this and working on the box downstream, I would see two wires coming into this box from circuit 1 and a neutral, and would assume that neutral is dedicated right? And if I were to wire A GFCI outlet off it and a few other non-GFCI from the LOAD side of the GFCI would this be a problem?

In that particular junction box, what they did was they had outside eave soffit lights controlled by two circuits, probably because there are too many of them. Going all around the eave of the house there are 16 soffit lights, and they had circuit 1 controlling lights 1, 3, 5, 7, 9... and circuit 2 controlling 2, 4, 6 , 8, 10...

The curious thing is why they didn't just use one neutral all the way, why run two neutrals in parallel through all these lights but only wire them up on alternate ones.
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Old 06-05-2012, 09:00 PM   #15
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Piggy Backing Off GFCI Outlets


One more question about this topic.

Let's say I have four boxes all in the bathroom, the conduit runs from Box 1 to 2 to 3 to 4. They are actually fairly close to each other, but due to framing and piping in the way, the conduits run up to the attic and back down as it hops from box to box.

Box 1 - Sconce switch and GFCI outlet.

Box 2 - Sconce 1

Box 3 - Sconce 2

Box 4 - Outlet, end of run

I have a neutral wire that runs from box 1 to 2 to 3 for the sconces.

However, since I am piggybacking the outlet in Box 4 on the GFCI outlet in Box 1, I need to run a special neutral wire coming out of the LOAD side of the GFCI outlet in Box 1, all the way to Box 4 for that outlet right? I can't just splice off the neutral for the sconce in Box 3, I don't think.

Just wanted to make sure. Thanks.

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Last edited by miamicuse; 06-05-2012 at 09:03 PM.
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