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Outdoor electric instant water heater (outdoor shower) grounding

Outdoor electric instant water heater (outdoor shower) grounding

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  #1  
Old 04-25-11, 07:51 PM
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Outdoor electric instant water heater (outdoor shower) grounding

Hi, I could use some help/advice/opinions.

I'm wiring a 240v electric instant water heater for an outdoor shower in a pool area (got a screaming deal on it). It needs about 40a of service and I've run 2 8ga thhn and a #10 ground in buried pvc conduit (think I buried it to about 2 1/2 ft, but that was a couple of years ago). My water supply is run to this general area (about 18" away, pending hook up) with flexible 1/2" copper.

I'm about to hook this sucker up now, and I'm planning on mounting it on a metal bracket set through a concrete slab underneath a faux rock, about 18" away from the shower area. The shower itself sits over a giant french drain pit about 4 ft deep with about 300 gal capacity.

Anyone see any terrible travesties in this setup or have any recommendations around things to do to enhance safety, or see any code travesties? This unit will likely have a 2 year lifecycle, and it will probably revert to cold water shower at that point. I'm mostly looking for a sanity check, and any recommendations on plumbing in. I could plumb it in via copper or PVC, and I'm leaning toward PVC, just because the fittings on the unit are plastic anyhow, and it seems to offer one less path of conductivity between the unit and shower fixture.
 
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  #2  
Old 04-25-11, 07:55 PM
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Is the water heater going to be in some kind of enclosure? Such as a small shed? I doubt it can get rained on.
 
  #3  
Old 04-25-11, 08:19 PM
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Yes, it is on a concrete slab and under a faux rock - this is Phoenix, so rain isn't that much of a problem, heat will be a more interesting test. But the unit is somewhat disposable because it was so cheap; I'm shooting for two years of use.

Mostly I'm verifying whether grounding back to the panel is correct, and whether anyone has any opinions on the copper versus plastic plumbing. BTW, this unit is about 10ft from a pool area. Pool has no bonding grid of any sorts (1950's pool) but no metal / structures / etc within 20 ft of pool anywhere else.
 
  #4  
Old 04-25-11, 08:23 PM
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If it only uses 1 breaker it must be a real low flow unit. 1 gpm or so. You will need to find a 1 gpm shower head so the flow is restricted, or the unit will not turn on. Most electric tankless I have seen that do any good are the three circuit type. These use three 40-50amp breakers.

It sounds pretty dangerous what your doing. I would seek professional help. A permit probably is whats required by law for this anyway. Permits are for your protection.

copper versus plastic plumbing.
Plastic. Easier and cheaper.

Mike NJ
 
  #5  
Old 04-25-11, 08:48 PM
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Mike, he did say Az. Area counts a lot in how well they work. I had a customer who installed a single 60a unit for a whole house single ocupant. No special flow restrictors or anything. It's been several years and she has been happy with the output.
 
  #6  
Old 04-25-11, 08:48 PM
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I think the unit is rated to about 2gpm on the temp rise I'm after - I only need lukewarm and we start pretty warm in Phoenix as is. Mid-summer, I pretty much don't need the unit, any sun exposed pipe itself is so hot it will warm water for a good 5 to 10 minutes by itself. It is mostly for the late spring/early fall.
 
  #7  
Old 04-25-11, 08:51 PM
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Yes, I'm speaking beyond my education now, but I think we actually have some folks get frustrated with the gas-fired whole house tankless units down here because the temp starts pretty warm and the flow/volume they pull across the unit doesn't fire it fast enough. But that's another thread of speculation I'll be sure to post a link when I someday get to that project, ha.
 
  #8  
Old 04-26-11, 08:54 AM
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The only electrical issue I can think of is that the unit should have a disconnect within line-of-sight. A simple pull-out like the kind you use for an air conditioner would be sufficient. Copper or plastic plumbing doesn't really matter. If you really want to up the safety you could install a 40A double-pole GFCI breaker instead of a standard breaker.
 
  #9  
Old 04-26-11, 02:34 PM
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Hi, thanks for all of the interaction on this thread (by everyone else too). I've been debating a GFCI breaker - am I correct in understanding a double pole GFCI breaker needs some type of neutral? I only have the two hots and ground in the conduit currently.
 
  #10  
Old 04-26-11, 02:37 PM
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The GFCI breaker needs to connect to the neutral bar in the panel where the breaker is installed, but you do not need to install a neutral out to the appliance if the appliance does not require it.
 
  #11  
Old 04-26-11, 04:11 PM
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My only thought would be if a bonding grid would be needed in the standing area of the shower.
 
  #12  
Old 04-26-11, 04:52 PM
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Now that is opening the door for an interesting and complex topic. I'd love some more light shed on that topic. As I understand it the bonding grid is largely about pulling ground to equivalent potential, and in an outdoor shower area, irrespective of the water heater, I'm interested. What I'm a little unclear on is best approach for an area that will be either loose gravel or a few concrete pavers over loose gravel. But let me be clear that there is no grid around the pool area as it is a very old pool - there's no metal or electric within 10 foot of the pool, but I realize this is only one aspect of the reasoning behind a bonding grid, and doesn't address potentials that exist between earth/water, etc. But, the 1953 pool is what it is. So this leads me to a few questions.

1. Rebar in the ground in this wet area seems less than optimal. Is there any type of rolled wire grid on the market that would be compliant over a 7ft by 9ft area (1M beyond area of shower). I see references to 8 AWG in code, but that's not actually the spec for grid is it, just the spec for attachment to grid, right?

2. What would be a realistic depth for this metal bonding grid? Am I missing this in NEC?

3. From a functional perspective rather than a code perspective, what is the implication between a localized shower bonding grid and transition to the ground and pool areas around away from this bonding grid? This doesn't seem terrible since pool deck is a good 10 ft from shower area, and there's no electric in those other areas, but showerers are still likely to be wet and transient power could be a paranoia (albeit one that is already there).
 
  #13  
Old 04-27-11, 06:13 AM
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You ask very good followup questions. The bond grid and pavers are mentioned in Article 680. I do not remember a burial depth requirement.

The grid used to be specified as a copper grid, then it changed to a single conductor near the walk path. Without looking I don't remember the latest. It would also depend on with code cycle your area has adopted.
 
  #14  
Old 04-27-11, 09:34 AM
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Equipotential bonding is covered in 680.26, and I'm not sure it would be required for an outdoor shower that is not specifically part of the pool. As PCboss said, it might be a consideration but I wouldn't go so far as to say it's absolutely required. After all, we don't do a bonding grid in a normal bathroom shower, locker room shower stalls, garden hose the kids play in, etc.

Originally Posted by bojimbo View Post
1. Rebar
Steel ties are allowed when embedded in concrete, when not in concrete the bonding grid should be #8 solid copper. I don't know if anyone makes a prefab #8 copper grid, but I think you could do a plenty good-enough job by just snaking out a length of bare #8 copper wire into a grid shape. The code specifies the grid should be 12" squares, welded at the corners*, "below-grade under the deck media". No exact burial depth is specified, so probably just under the soil or paver base is fine.

* I would probably fudge this by using some bare #12 copper wire to wrap/tie the corners. If you're really interested in going the extra mile you could check at some electrical suppliers and specialty pool installers to see if they actually sell a grounding mat but I would bet the cost is based on ordering several pallets of it to do a water park sized pool and would basically be unavailable in the quantity you need.

From a functional perspective rather than a code perspective, what is the implication between a localized shower bonding grid and transition to the ground and pool areas around away from this bonding grid?
Probably none. It's also worth considering that you live in an area with very dry (and therefore non-conductive) soil so ground currents near the surface are not likely.
 
  #15  
Old 04-27-11, 06:10 PM
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Now that creates another interesting angle. Again from a functional rather than a code perspective, do you believe a single #8 copper line run around the perimeter of the shower would supply a reasonable semblance of a bonding grid? The ground is exceptionally dry here and short of a torrential flood that happens no more than once a year and could create momentary exposures elsewhere, I can directly identify my only 2 possible nearby sources of electrical current - one is the heater being discussed, and one is pool equipment on the opposite side, and really too far away to be touched by wet conditions short of a torrential downpour. Do you think a single conductor surrounding the shower area would deal effectively with those possible potentials? To enhance the conversation, perhaps we can consider the case in which somebody is showering, somebody else has cut through the circuit conductors for the heater and left them exposed in the ground, and there is currently a downpour. Would a single conductor loop suffice to bring the potential to ground?

Thanks for the comments, you folks have supplied some excellent feedback and food for thought. I'll consider the bonding grid approach further, and for now I've introduced the GFCI breaker and an exposed shutoff switch in line of sight of shower. I'm also taking a bit more care to further isolate the electrical heater unit from potential paths of conductivity, switching to a wood post mounting in concrete instead of metal bracket. Speculating a bit further about the bonding grid, 150 or so feet of #8 is not an inconsequential cost, so I'll be considering a bit further, but I'll make sure to complete my consideration before pouring any concrete post footings. Thanks for the comments on dry ground, they are appreciated, and it is quite dry around here.
 
  #16  
Old 04-27-11, 09:06 PM
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Originally Posted by bojimbo View Post
...whether anyone has any opinions on the copper versus plastic plumbing.
You might want to ask about that in a plbg. forum. Usually it's a matter of preference, but sometimes water chemistry makes copper a bad idea. I've done a fair amount of copper work and find it easy to work with. If you are using plastic you need to use proper transitions from any copper, and avoid threaded female plastic fittings like the plague.

Nominal 1/2" copper I think has a larger ID than 1/2" PEX or CPVC. At your flow rates that may not be an issue, however.

Also, local code often determines the type of acceptable shower valve (pressure balanced or thermostatic).

There may be other plumbing code issues, and again, you should find a forum frequented by plumbers, and preferably plumbers in AZ. I seem to recall some discussions about ridiculous pool shower requirements somewhere warm, but I don't recall if that was CA or AZ or FL.
 
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