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Old 02-16-2008, 08:44 AM   #1
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Wire size for 300watt trans, 3 way 100ft


Good morning...So I have 100ft of conduit in trench with 14ga thhn/thwn 4 conductors to reach a 3-way switch that is controlling a 300 watt transformer for a 12v pool light, the second switch is close to the transformer. I figure 300watt / 110v = 2.72 amps ( I think) all powered off a 15a gfcib. Given the lenth of the run I am concerened about voltage drop and over heating the wires.

So, am I okay with the 14ga, (I wish I would have bought 12)


Last edited by Al the Diy guy; 02-16-2008 at 10:25 AM.
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Old 02-16-2008, 10:25 AM   #2
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Wire size for 300watt trans, 3 way 100ft


Al

Look at Mike Holts download on pools and 680.23(F)(2). The equipment ground must be an insulated 12 awg. The conductors can be 14 awg if you want. You cannot use the conduit (if metal) for your ground.

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Old 02-16-2008, 10:37 AM   #3
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Wire size for 300watt trans, 3 way 100ft


Quote:
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Al

Look at Mike Holts download on pools and 680.23(F)(2). The equipment ground must be an insulated 12 awg. The conductors can be 14 awg if you want. You cannot use the conduit (if metal) for your ground.

Thanks Stubbie, HEY the box arrived today, pretty spiffy, pretty darn heavy huh? You could have melted it down and made a cannonball. ha ha.

So I need to figure out how to waterproof the line bringing the pool light,
looks like it should work just fine THANKS AGAIN so check your mail box around thursday/friday.


So since I have to replace the ground (not sure how I missed that one, I knew 12g is minimum for equipment ground, guess I didn't associate the light switch as equipment) I think I will just pull all new 12g through. I should be able to fit 7 12g THHN/THWN conductors through 3/4" condiut, what do you think
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Old 02-16-2008, 11:25 AM   #4
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Wire size for 300watt trans, 3 way 100ft


Cool

I'm glad you like it. It was the cadillac of pool jb's in its day. Yes it has some weight to it. You should have seen the look on the face of the mail clerk when she picked it up to go on the scale....

FYI..... Any other conductors in the same raceway with under water light conductors must be gfci protected.

Here is a link to help you with stuff like how many wires will go in a conduit if you are using thhn/thwn conductor insulation. But yes 7 will go in 3/4 easy. You do have to derate the ampacity of the wires according to the loads when over 3 conductors in conduit but in your case you are fine.

http://www.jhlarson.com/ind_tables/ind_table.htm
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Old 02-16-2008, 11:44 AM   #5
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Wire size for 300watt trans, 3 way 100ft


Al

Look at 680.23(F)(3) 1 thru 4 for clarification on the gfci requirements for other conductors in the same raceway with conductors serving underwater luminaires.

Essentially it is saying that if your gfci for the lights is at the pool panel then if you run other conductors in the same raceway leaving that panel with the underwater luminaire conductors they must be gfci protected or if you bring in any conductors load side of the transformer into the same raceway going to the swimming pool jb they must be gfci protected as well as the conductors to the underwater light.
This requirement is because the other conductors have a probability of energizing the conduit or other conductors going to the lights and all metal associated if they fault.

Last edited by Stubbie; 02-16-2008 at 11:57 AM. Reason: fixin my spellin
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Old 02-16-2008, 12:06 PM   #6
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Wire size for 300watt trans, 3 way 100ft


Quote:
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Al

Look at 680.23(F)(3) 1 thru 4 for clarification on the gfci requirements for other conductors in the same raceway with conductors serving underwater luminaires.

Essentially it is saying that if your gfci for the lights is at the pool panel then if you run other conductors in the same raceway leaving that panel with the underwater luminaire conductors they must be gfci protected or if you bring in any conductors load side of the transformer into the same raceway going to the swimming pool jb they must be gfci protected as well as the conductors to the underwater light.
This requirement is because the other conductors have a probability of energizing the conduit or other conductors going to the lights and all metal associated if they fault.
Stubbie, Thanks, I am okay on that one, the only thing going into that JB is the three conductors coming from the transformer and the three coming in from the light. The transformer is powered by 15a GFCIB. I have a seperate conduit that carries seven conductors, 4 for the 3-way switch and three for a receptacle which are powered by another 15a GFCIB.
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Old 02-16-2008, 12:34 PM   #7
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Wire size for 300watt trans, 3 way 100ft


Good deal

Here is the general idea. The pool pump if hardwired does not need gfci unless its conductors share the same conduit with the underwater lights.
Also I'm showing the gfci breaker as that is your case.... it is not required for 15 volts or under. Darn good idea though and an above code installation in my opinion....
Attached Thumbnails
Wire size for 300watt trans, 3 way 100ft-swimming-pool-gfci-lights.jpg  

Last edited by Stubbie; 02-16-2008 at 09:05 PM.
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Old 02-16-2008, 05:05 PM   #8
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Wire size for 300watt trans, 3 way 100ft


Quote:
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Good deal

Here is the general idea. The pool pump if hardwired does not need gfci unless its conductors share the same conduit with the underwater lights.

Thanks Stubbie, yes, I am okay, I am GFCIB on lights and receptacles, not sharing raceway with pump. I remember seeing a post by you with regard to equiopotential bonding that really makes me wonder "WHY" my niche is a classic example it is PVC, low voltage light, but yet when I "Bond" it to the Equiopotential Grid, I will have also tied it into my grounding system as the lug on the outside of the niche for bonding is itself bonded to the "ground" lug on the inside of the niche. So if something goes wrong and goes to ground, the whole Equiopotential grid and everything connected to it could go live right? doesn't make sense. I know its code, and I am doing it, but I wish the niche wasn't bonded to the grounding lug.

Side note, I ran a 3/4" nipple through on of the holes you tapped and now I will be able to put a watertight compression fitting on it, so far so good. I'll take a picture of it when done. Thanks again
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Old 02-16-2008, 05:21 PM   #9
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Wire size for 300watt trans, 3 way 100ft


Speaking of Equiopotential bonding....I would imagine I would also have to bond the Junction Box to the grid as well
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Old 02-16-2008, 07:58 PM   #10
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Wire size for 300watt trans, 3 way 100ft


Quote:
I remember seeing a post by you with regard to equiopotential bonding that really makes me wonder "WHY" my niche is a classic example it is PVC, low voltage light, but yet when I "Bond" it to the Equiopotential Grid, I will have also tied it into my grounding system as the lug on the outside of the niche for bonding is itself bonded to the "ground" lug on the inside of the niche. So if something goes wrong and goes to ground, the whole Equipotential grid and everything connected to it could go live right? doesn't make sense. I know its code, and I am doing it, but I wish the niche wasn't bonded to the grounding lug.
First you must follow the manufacturers instructions for installing the forming shell . Second there are some PVC wet niche forming shells that do not require the #8 bond wire or bonding to the grid. These are generally sold as matching pair with the LOW VOLTAGE light. Which is also listed as non grounding and has a locking PVC face plate exposed to the pool water. Also PVC conduit from the jb to the forming shell. And also a pvc junction box not a metal one. Other wise the bonding lug on the pvc forming shell is used to bond the metal junction box to the grid. See diagram in next long winded post after this one.

Your forming shell and luminaire should look something like the one at the end of my long dissertation......so grab a beer....

Start thinking bonding lug (a place to connect to in order to bond or join metal together as one) ) and not ground lug (a place to connect metal to a facilitate a fault current path). Not a 100% perfect comparison but I think looking at it this way will make things more understandable since you have a PVC forming shell.

Also at the end of this is a excerpt from NFPA 70 and the UL 676 governing pools documenting the part about some situations not requiring the #8 bonding wire so you don't think I pulled that one out of my ***. Take note it says "low voltage system" meaning junction box is pvc, forming shell is pvc and light is a non grounding type.The only change to that language is they now are calling it a bonding wire instead of an equipment grounding conductor. Calling it the later was misrepresenting the purpose of the #8 which is to bond the forming shell and the junction box to the grid...especially if a line voltage light and PVC conduit to a metal forming shell. So the primary purpose is bonding with other possible duties as described below. The connection of the #8 to the equipment ground coming from the wet niche light cord and transformer at the junction box is only incindental and not intentional. A result of bonding the metal of the junction box to the equipotential grid via the #8.

So assuming that your forming shell is pvc and has a bonding lug and is not a listed combination with a non-grounding wet niche light I'll try to explain as it is common for people to have a difficult time with this concept. I'm going to para phrase from some of my literature to make it faster for me to explain this bonding in the forming shell. First thing to understand is that any faults in the supply conductors to themselves or metal out to the metal junction box will cause the gfci breaker to trip out since you have one on the low voltage light circuit. Even though gfci isn't required for this low voltage light of yours it is an excellent idea. However from the JB to the forming shell its a different story. So see if the below helps you understand if not I'll give it another try.

The equipment grounding conductor in the flexible cord of the wet-niche luminaire may be relatively small (as little as 16 AWG in accordance with the NEC), and may have a length of one hundred feet or more. The relatively small AWG and long length will result in increased impedance through the flexible cord equipment grounding conductor.
If the electrical bond between the luminaire and the metal forming shell is poor or absent, in an electrical fault condition within the luminaire this increased flexible cord impedance causes a relatively greater voltage potential between the dead metal of the luminaire and other dead metal connected to the premises’ equipment grounding conductor.
The supplemental equipment grounding conductor in the form of corrosion resistant metallic conduit connected to the forming shell or the 8 AWG copper conductor routed with the flexible cord in nonmetallic conduit provides a second, more conductive, path for fault current originating in the luminaire. If the luminaire securement does not provide an effective electrical bond to the forming shell, there is an equally ineffective electrical bond to the supplemental equipment grounding conductor.
Section 680.26 of the NEC requires essentially all of the dead metal within 1.5 m (5 ft) horizontally from the pool wall and the dead metal of equipment associated with the pool water circulating system to be connected to a low-impedance common bonding grid, using a solid copper conductor not smaller than 8 AWG. Likewise, the electrical impedance of the electrical bond from the dead metal parts of the wet-niche luminaire to the pool bonding grid must be low. UL 676 requires the impedance between dead metal parts of a luminaire and the 8 AWG pool bonding grid conductor connected to the applicable terminal on the forming shell not to be more than 0.020 ohm. For perspective, this is approximately the DC resistance of 10 m of solid 8 AWG uncoated copper conductor at 25C, a relatively low value. So in the case of a metal forming shell the #8 plays double duty as a redundant equipment ground for fault current in the event of a fault with the lunimaire that cannot be sufficiently handled by it's equipment ground wire in the cord for what ever reason. So look at it as the metal of the forming shell is providing an alternate path for a fault at the light to get to the bonding lug and utilize the #8 for a alternate fault path fault back up to the equipment grounds in the junction box so a breaker will trip. All this is primarily directed at line voltage lights (120v) and metal forming shells.

With a PVC forming shell and a low voltage light like you have this all is rather irrelevant. In which case the lug provided on the forming shell is just a means to bond the metal of the junction box (deck box) to the equipotential grid via the #8 bond wire. You may also have a metal trim ring for the lamp which will bond to that lug with a metal strap....see the diagram.

Lets take a break...Cheers..

The equipotential grid is primarily concerned with voltage gradients that occur from external means other than the pool electrical equipment and supply conductors. By this I mean underground utilities or service laterals that are breached or failing causing current to leak into the soil in the vicinty of the pool. These voltage gradients cause touch potential of metal parts to become elevated to the point you may get electrocuted if you come in contact with a piece of metal at a different potential than the other metal around the pool as the result of a voltage gradient in or around the pool. The bonding of all the metal brings all metal to the SAME potential and then by defintion current cannot flow if touched by you as there is no difference of potential on that metal in respect to the other metal. Whew....the end.
Attached Thumbnails
Wire size for 300watt trans, 3 way 100ft-wet-niche-forming-shell.jpg   Wire size for 300watt trans, 3 way 100ft-pool-lights.jpg  

Last edited by Stubbie; 02-17-2008 at 12:52 PM.
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Old 02-16-2008, 08:21 PM   #11
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Wire size for 300watt trans, 3 way 100ft


Quote:
Speaking of Equipotential bonding....I would imagine I would also have to bond the Junction Box to the grid as well
The lug in the forming shell is not a ground lug it is a bonding lug... the junction box will be bonded to the grid with that number #8 coming up through the pvc conduit from the forming shell bonding lug. Remember the forming shell bonding lug has an inside connection and an outside connection. From the outside connection you run your bond wire to the grid. So you essentially get two for the price of one in that the forming shell and the jb are bonded by the one wire to the grid.

Your forming shell is pvc it doesnt need bonding (considering it as a single unit) to the grid but the bonding lug on it will facilitate bonding the metal junction box to the grid.

If anything goes to ground like a phase to ground fault your overcurrent protection and or gfci will trip. For instance if the cord shorts to ground at the light fixture the equipment ground in the cord will carry the fault current back to the source (utility transformer) and the breaker will trip. So actually anything that would energize the grid, as remote as that would be, will cause a circuit breaker to trip as this would occur with the system wiring and the equipment grounds would facilitate the tripping of the circuit breaker on the branch circuit where the fault occurs.

Also remember that the #8 is an insulated wire from the JB to the forming shell further protecting it from being energized by any fault in the lamp cord that is in parallel with it. Everywhere else there is little contact with the equipotential grid with anything that would likely energize it as far as the pool electrical equipment and branch circuit conductors. Voltage gradients provide for a much more likely source of energizing pool metal than the pool electrical system. Therefore we bond this metal around the pool to a common grid to eliminate or greatly reduce shock hazards.

I'm glad that junction box is working out because it is a real top of the line product. Your doing a darn good job with this project and shows by your diligence to detail, you should congratulate yourself on doing your home work.

Forming shell and jb bonded by #8 bonding wire to grid
Attached Thumbnails
Wire size for 300watt trans, 3 way 100ft-wet-niche-bonding.jpg   Wire size for 300watt trans, 3 way 100ft-pool-pump-pool-panel.jpg  

Last edited by Stubbie; 02-17-2008 at 12:43 PM.
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Old 02-17-2008, 10:31 PM   #12
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Wire size for 300watt trans, 3 way 100ft


For those interested a new alternative for the bonding grid under the deck walk is in the new 2008 though I haven't verified when this alternative can be used. It is showing up as an accepted change for 2008 on Mike Holt. If your jurisdiction is under 2008 there are several important changes to Art. 680.


Last edited by Stubbie; 02-19-2008 at 01:45 AM.
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Old 02-18-2008, 08:33 AM   #13
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Wire size for 300watt trans, 3 way 100ft


Stubbie, so as you know there are two grounding lugs in the JB, can I put three in there? 1 for the lamp cord ground, one for the ground in the run to the transformer, and then on for the #8 Bond? Al
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Old 02-18-2008, 10:26 AM   #14
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Yes you can. But all you really need to do is put the #8 under one of the lugs and then connect the two equipment grounds (transformer and lamp cord) in a wirenut with a pigtail of solid #12 and run the pigtail to the 2nd lug. Or you can buy a 2 hole lug and replace one of the lugs if you like . Or you can stack another lug like what is in there....might need a longer grounding screw. If I remember right one of the screws is not wanting to be removed... Can't remember which one cause I was going to stick another lug in there for you. But decided it wasn't necessary.

The idea on the equipment ground from the transformer and lamp cord is to bond them so that fault current can get all the way back to the pool panel and from there to the main panel and out to the center tap of the transformer over the service neutral so a breaker will trip if you have a fault at the lamp. So you just want to get the metal of the box bonded to those equipment grounds in case a hot would come loose in the jb and short to the metal of the box. See below
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Old 03-22-2008, 07:24 PM   #15
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I finally had my electrical inspection on my inground pool project

The inspector said it was obivious that I had done my homework

Passed without any problems whatsoever, and just as important EVERYTHING works as it should and is SAFE. THANKS TO Stubbie, Chris, inphase and the rest of you that helped me through the hardest (mentally) part of my pool project.

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