REDUNDANT GFCI

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domnic

Senior Member
Occupation
Electrical Contractor
I looker at a job for boat dock and swim platform on small lake. he wants a 15 amp 120 volt gfci outlet on land next to the dock and wants it fed from a 20 amp gfci breaker in the barn . I know it will work . this sounds like a good idea . I never thought of this. what is your input ?
 

topgone

Senior Member
Sounds good, the breaker protects the wiring to the receptable, but the recteptacle need not be a GFCI.

Good catch! Just you wire the GFCI at the barn properly, so a non-GFCI receptacle at the dock gets protected from ground aults.
 

Ingenieur

Senior Member
Location
Earth
I think he is saying from a life safety perspective redundant is good

in mining we use 5 layers
a neut gnd resistor, as low as 100 mA

Secondary on the main cb, small td of 0.1 to 0.2 sec
a pt across it to trip at 50%
a ct on it to trip at 40%
both trip the main

Primary on the branch ckt
gf relay tripping branch cb at 30%
a ground monitor, if continuity >3 ohm trip branch cb
 

user 100

Senior Member
Location
texas
+1

$15 is pretty cheap life insurance.

x2

Its inexpensive, hurts nothing and of all examples of electrical overkill this is one that is not entirely unreasonable or "out there"- what if the gfci breaker gets moved or replaced w/ a standard for some reason (can you say trunkslammer)? Considering the location and circumstances, this 2nd layer of gfci is perfectly acceptable.
 
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topgone

Senior Member
x2

Its inexpensive, hurts nothing and of all examples of electrical overkill this is one that is not entirely unreasonable or "out there"- what if the gfci breaker gets moved or replaced w/ a standard for some reason (can you say trunkslammer)? Considering the location and circumstances, this 2nd layer of gfci is perfectly acceptable.

Why spend some more when those loads are on the same feed? Knowing how to wire things is important. Do it like this:
2014-10-22_032339_gfci_receptacle.jpg
 

user 100

Senior Member
Location
texas
Why spend some more when those loads are on the same feed? Knowing how to wire things is important. Do it like this:
View attachment 15104

Yes, I am aware of feeding reg recs with/thru gfci- but if the ho gets this explained to him and still wants it done his way w/ the redundant protection, then imo, just let it be- ​he's paying for it.:)
 

iwire

Moderator
Staff member
Location
Massachusetts
Why spend some more when those loads are on the same feed? Knowing how to wire things is important. Do it like this:
View attachment 15104

Did you honestly just explain to a forum of electrians how to wire a GFCI?

Your faith in our abilities is a bit lacking. :D

Yes, you can wire them that way and sometimes we do. But in the OPs case the customer asked for redundancy, a GFCI breaker feeding a GFCI receptacle. Given the failure rate of GFCIs and the number of electrical accidents that happen around the waterfront it does not sound like a bad waste of $15.00.

Beyond the OP many of our commercial kitchen customers will not accept what your diagram shows, they want a GFCI receptacle at each point of use.
 

Ingenieur

Senior Member
Location
Earth
Is good practice in an application around water like this
very small cost increase for exponentially increased reliability and the ability to show due dilligence in the event of an accident that ends up in court
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
There is more than just redundancy here. The receptacle will offer higher sensitivity to cord connected loads. A good idea IMO.
I thought that 6ma was 6ma at every point in the series circuit.
More of a concern to me is that a fault will trip either one or both, making resetting more frustrating.
 

Ingenieur

Senior Member
Location
Earth
I thought that 6ma was 6ma at every point in the series circuit.
More of a concern to me is that a fault will trip either one or both, making resetting more frustrating.

the person saved by the back-up really won't care about that
nor should they

If the fault is between the first and second will both trip?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I agree that a backup makes sense, especially given the failure rate of receptacle GFCIs and the lack of testing.
I do not agree that one type is more sensitive than the other.
 

kwired

Electron manager
Location
NE Nebraska
How long of a run between the two GFCI's?

The longer the run the more capacitive leakage you may have causing undesired tripping.

If you want "double protection" that is fine but don't put one of them at the beginning of a long run.
 

kwired

Electron manager
Location
NE Nebraska
NO, GFCI's only look downstream.
Sort of. Only thing they really care about is that current that goes out comes back on another monitored conductor, then there is also a signal injected that allows them to instantly trip on a neutral to ground fault even if no load current is otherwise present.
 
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