GFI 2 circuits on 3wire w/g problem

[jrmac]

I seem to remember this problem coming up before but can not find the solution, Help.

I split a 3 wire with ground cable into 2 circuits in my garage so every other outlet is a different circuit. I have two 20 amp breakers, one for the black and one for the red wire, the white wire is the common for both circuits. The white and the ground wire are on a common buss in the panel. The breakers are wired one to each side of a 240 volt service. Meaning I measure 240 volts between the red and black wires.

The problem is that one GFI will set and work OK but I can not turn the second one on. I tried putting a standard outlet on the second circuit but it will trip the first circuit GFI when I plug anything into the second circuit. Am I doing something wrong or is this not possible?

 

[physis]

Re: GFI 2 circuits on 3wire w/g problem

These things can seem mysterious but it sounds like it's doing what it's supposed to, detecting a ground fault. I'm hypothisizing a damaged conductor between the first and second receptacles.

I could easily be completely wrong too.

 

[al hildenbrand]

Re: GFI 2 circuits on 3wire w/g problem

Sounds like you are using GFCI breakers, no? If that is the case, a two pole GFCI is required.

Otherwise, if you have GFI receptacles local to the garage and are protecting the downstream receptacles, this sounds like a neutral to neutral connection between the two circuits on the load side.

[ December 30, 2004, 02:30 PM: Message edited by: al hildenbrand ]

 

[physis]

Re: GFI 2 circuits on 3wire w/g problem

Hi Al,

I'm thinking no GFI breakers, but it just occured to me, the second receptacle tripping the first. You could be right, multiwire load sided with one neutral.

Why's there another GFI downstream from the load side?

 

[al hildenbrand]

Re: GFI 2 circuits on 3wire w/g problem

Hey Sam,

Two 120 V circuits. One GFI receptacle on each circuit at the separation of the multiwire homerun. Neutrals downstream of the GFIs in contact with each other.

 

[physis]

Re: GFI 2 circuits on 3wire w/g problem

Or never seperated.

I'm not convinced this was ever wired correctly.

 

[al hildenbrand]

Re: GFI 2 circuits on 3wire w/g problem

Point taken.

What say you jrmac?

 

[jrmac]

Re: GFI 2 circuits on 3wire w/g problem

Al, Thanks for the reply. As to the neutral wire, as I stated in my question, I am using the white as a comon for both circuits. It sounds as though that is not possible with GFI's? The only thing I can do now is put all outlets on one circuit as I have both the red and the black going to each outlet box. The only problem might be that I will have only one circuit with sixteen outlets on it.

 

[peter d]

Re: GFI 2 circuits on 3wire w/g problem

Use a 2 pole GFCI circuit breaker and the problem will be solved.

 

[al hildenbrand]

Re: GFI 2 circuits on 3wire w/g problem

Yep. What Peter says. Be prepared to faint at the price.

 

[jwelectric]

Re: GFI 2 circuits on 3wire w/g problem

A GFCI two pole, single pole or receptacle will trip when there is a difference in current between the phase and grounded (neutral) conductors. This is how they work. If you have pulled one neutral then your only remedy is to install a GFCI receptacle wired line-in and line-out at each outlet. Using a two pole GFCI breaker will only work if both phases carry the same amount of amperage at all times. Don?t take my word for it, try it and see.
Question, Will a GFCI prevent you from being shocked?

 

[jrmac]

Re: GFI 2 circuits on 3wire w/g problem

Thanks for the advice and the warning about cost.
Happy New Year.

 

[physis]

Re: GFI 2 circuits on 3wire w/g problem

You could put a gfi in each of the first 8 and the other 8 could be protected by just one from the load side.

 

[peter d]

Re: GFI 2 circuits on 3wire w/g problem

Originally posted by jwelectric:
If you have pulled one neutral then your only remedy is to install a GFCI receptacle wired line-in and line-out at each outlet.

Huh? It will not trip with imbalanced current on the ungrounded lines since it senses current between all possible paths (L-L, L-N). If what you say is true, why do double pole GFCI breakers have neutral "pigtails" and provisions to connect the load neutral??

[ January 01, 2005, 12:45 AM: Message edited by: peter d ]

 

[al hildenbrand]

Re: GFI 2 circuits on 3wire w/g problem

Jim,

I'm with Peter. For this 120/240 1? multiwire circuit, the 2-pole GFI Breaker will have the two hots and the common neutral running through a single toroid current sensor.

As long as there is no ground fault on the multiwire circuit, the net magnetic field about the multiwire branch circuit conductors will be zero and the breaker current sensor will sense no ground fault for what ever load is plugged into the 120 volt outlets on either or both circuits.

 

[itasca_mn]

Re: GFI 2 circuits on 3wire w/g problem

Yep, a 2-pole 240/120 volt GFCI breaker is perfect for this application. They're designed to supply 240 volt loads, 120 volt loads, or a combination of both. Here is a diagram of one that shows what Al described. Matt