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I need to install a GFI breaker on a Baptistry.

Its feeding from A 90 amp double pole breaker, then it feeds into a 60 amp and 2 20 amp sub feed panel that powers the heater, pump and timer. Where should I install the GFI or GFI's to get the proper protection.

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  • Anonymous Mar 24, 2009

    How do I determine WHICH neutral wire is the one in the circuit I want to protect with a GFCI? There are 20 or 30 white neutral wires in the panel.


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You could install a standard GFCI in line at each component ( heater, pump & timer) or you could install AFCI breakers similar to what are required in many residential codes (provide the same protection at the panel not at the location...

The AFCI breakers will need to match your panel type (siemens, GE or Square-D) and the amperage/configuration.

I would install them at the lowest level (closest to the components) in the system to reduce possibility of fire in the wiring between the components and the afci breaker.

Posted on Jan 04, 2009

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If you have (90) 50w lamps = 4500 watts total. Assuming a 120/240 panel, if you put 1/2 on one "side" of the panel and the other 1/2 on the other "side" of the panel, that would be 2250 watts on each half. The generator should be rated *at least* 125% of the load; 4500w x 1.25 = 5625W. Using a 4500W generator on this load will cause it to overheat and shorten its life as it is running at 100% of capacity all the time..

One half of the panel is 120V to neutral, and the other is 120V to neutral - or 240V between both circuit breaker terminals. Ohms law for DC circuits and purely resistive AC circuits says Volts x Amps = Watts; or Watts / Volts = Amps. So, 2250W / 120V = 18.75A on each pole of a 2 pole circuit breaker that feeds the sub panel. A #12 copper wire is rated for 20 amps; but as per National Electrical Code - must be de-rated to 80% of rating which means it is good up to 16 amps maximum. A #10 copper wire is rated for 30 amps, but it too must be derated to 80%, making it good for 24 amps maximum. So, if you are going to feed a sub panel supplying (90) 50watt lamps, you will need to run a #10/3 copper cable from a two pole 30 amp circuit breaker at the generator to a 120/240 volt "main lug only" sub panel rated for at least 30 amps.

Divide your load evenly across the sub panel - (4) 15 amps circuits via (2) two pole 15 amp circuit breakers on each "side" of the panel if you run (2) 14/3 cables out to the lights - or (4) single pole 15 amp circuit breakers if you run (4) 14/2 cables out to the lights. No circuit breaker terminal should have more than 23 lamps that means you have (2) w/ 22 lamps and (2) with 23 lamps. The circuit w/ 23 lamps will draw 23 lamps x 50w = 1150W. 1150W / 120V = 9.6A. The 22 lamp load will be 22 x 50w = 1100W. 110W / 120V = 9.2A. Which is well within the 12A maximum allowed (after derating as required by code) by a #14 copper wire rated for 15A.

Good luck!

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1) Match wire and breaker:

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No, i have a 50 amp GFCI in my main panel and i am trying to feed a sub panel in my garage. i have power to everything until i plug anything in or turn on the lights.

GFCI's are really temperamental. They are this way for a reason. It seems like you have something that is tripping this. I would try using a regular 50 amp breaker, and then see what happens. You can also try process of elimination. Shut everything down, then bring power up - one item/circuit, appliance, etc. at a time. This will narrow down your problem. Also, if you have a refrig/freezer on this GFCI, this could be tripping it too. Any appliance, etc. that has a motor - usually leaks to ground just enough for the GFCI breaker to sense, and trip it. I hope some of these solution's will help you...Good Luck!

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