Strange and Interesting GFI Breaker Question

[dzimmanck]

Hi Everyone,

First and foremost, I am an electrical engineer, not an electrician, so forgive my ignorance in some areas. Also, my system is experimental and contained in a power systems lab with no actual grid connection and additional layers of monitoring and protection, so it does not require compliance with NEC. My questions are related to functionality, not compliance.

I have a prototype system that has a tiny generating device on a branch circuit feeding power into a typical load panel on a 20A 2-pole breaker. I need to apply GFI protection to this branch, however, the first GFI breaker I tested (SquareD Homeline) made a strange buzzing sound when tested and only survived 3 self-tests before it malfunctioned and stopped tripping on the self-test.

My thinking is, some aspect of the design wants the service side to stay powered when it trips. In my system, the power is fed from the load side, so the service side drops out when it trips.

My question is, does anyone know any details on the design which could explain this behavior? Are there brands or lines of products which would be OK with this setup?

Thanks!

 

[jim dungar]

My thinking is, some aspect of the design wants the service side to stay powered when it trips. In my system, the power is fed from the load side, so the service side drops out when it trips.

My question is, does anyone know any details on the design which could explain this behavior? Are there brands or lines of products which would be OK with this setup?

For sure the Square D GFCI breaker is not designed for 'backfeeding' as you are doing.

 

[augie47]

You mentioned a 2 pole 20 but to clarify is this a 240/120 volt supply and was the GFCI neutral connected to the supply neutral ?

 

[ron]

Eaton has a good read regarding the issue.

From Page 5
General rule
• Cannot be Reverse-Fed:When a UL Listed circuit breaker is marked showing “Line” and “Load,” the power supply conductors MUST be connected to the end marked “Line.” These devices cannot be reverse-fed.
• Can be Reverse-Fed:If “Line” and “Load” are not marked on the UL Listed circuit breaker, the power supply conductors may be connected to either end. These devices are suitable to be reverse-feed applications.

http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=225828

http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=225829

 

[dzimmanck]

You mentioned a 2 pole 20 but to clarify is this a 240/120 volt supply and was the GFCI neutral connected to the supply neutral ?

Yes, this is 240/120 volt supply with GFCI neutral connected to supply neutral.

 

[dzimmanck]

OK, anyone know a good source for a plug-in style 2-pole, 20A, 240/120V, fault-powered GFCI breaker that allows backfeeding?

 

[mopowr steve]

Why must it be GFCI protected?

​

 

[cpinetree]

Can you just feed from the gfi breaker to another panel, rather than trying to backfeed the GFI.

I converted a small 5x8 trailer into a camper and wanted GFI protection so I feed the 30a 120v from the campground onto one phase of the panel then come out of the GFI breaker (that is attached at the bus bar) to feed the other phase of the panel. This way everything is GFI protected that attaches to that phase.
Sorry if the description may be as clear as mud :weeping:
But basically I have a standard panel that has one phase GFI protected and the other phase not GFI'd. Remeber this is a 120v set up though.

 

[dzimmanck]

I was hoping to do it without an additional panel, but this is the direction I've gotten from a few sources. There just does not seem to be any residential GFCI designed for backfeed operation. I guess there is very little demand.

Can you just feed from the gfi breaker to another panel, rather than trying to backfeed the GFI.

I converted a small 5x8 trailer into a camper and wanted GFI protection so I feed the 30a 120v from the campground onto one phase of the panel then come out of the GFI breaker (that is attached at the bus bar) to feed the other phase of the panel. This way everything is GFI protected that attaches to that phase.
Sorry if the description may be as clear as mud :weeping:
But basically I have a standard panel that has one phase GFI protected and the other phase not GFI'd. Remeber this is a 120v set up though.

 

[tx2step]

I was hoping to do it without an additional panel, but this is the direction I've gotten from a few sources. There just does not seem to be any residential GFCI designed for backfeed operation. I guess there is very little demand.

Why do you need GFCI protection for the input of the panel? Why can't you just feed power into the panel with a standard 20A CB and then feed any loads supplied by the panel with GFCI circuit breakers? The panel itself wouldn't be GFCI protected, but all of your loads and load wiring would be.

 

[newservice]

Is your 'generating device' putting out a stable, undistorted sine wave 60hz frequency?

 

[beefeater]

If your feed is via cord you could use a user attachable in-line GFCI device (like a TRC 25040 101-3 ELCI ) and wire it with your prototype device feeding the line side and the panel on the load side.

 

[winnie]

Is this 'tiny generating device' the only source of power for the panel, or is it intended to be operated in parallel with mains supply?

Is the GFCI protection intended to provide protection for the tiny generating device and its branch circuit, or for the other loads in the panel?

You may need more complex relaying that a GFCI will provide.

-Jon