Installing electric water heater in garage attic

[lep]

I am finishing out the second story of an essentially new garage. The plumber installed lines to an electric water heater in the attic, just above the bathroom. The plan is to finish all wiring for the upstairs, get the inspection, have the sheetrocking and trim done, and then call the plumber back to finalize hookups in the bathroom and kitchenette.

I am now looking over details for wiring the water heater. This is essentially new construction, since I can run wiring freely through the framing form the service box.

The unit is a 30 gallon 240V system with a black and red wires emerging from the top of the unit next to a green ground screw. The plan is to use two 30 amp breakers (GE) for the hot and red respectively, and then run the ground to the green screw. Now here comes the question: do I need a 10/2 or 10/3 Nymex cable to do this? If a 10/2 has a black, red and ground, then I believe I am ok using 10/2, since i only need the two alternating 120V hot lines and a signle ground. I believe a 10/3 is not needed since I don't need two hots, a neutral and a ground(?). I know 12/2 has 3 wires in it: hot, neutral, and ground, so I am assuming 10/2 has either a black, red, and ground, or black, white, and ground -- probably doesn't matter.

Here's my checklist:

1. First, nail a metal junction box to the joist just above (but not directly over) the water heater.
2. Run the Nymex cable from the service box to the attic (inside of course) across the roof joists to the junction box.

(there is 5/8" plywood covering the entire floor of the attic, but I don't think I want to run the cable across the attic floor -- unless it's enclosed in conduit -- doubt I want to do this)

3. At the service box, attach the red and black hots to two 30 AMP breakers in the service box.
4. At the junction box nailed into the attic joist(over the heater), secure the the ground wire with a screw threaded into the side of the box. Punch out a 1/2" knock out in the side of the junction box and run 10/2 flexible metal conduit to the cover plate of the water heater, secure the conduit to the plate. Connect the cables at the heater, and at the junction box.
5. Don't set the breakers to "On" until there's water in the heater.
6. For that matter, maybe run the wiring an don't make the final connections at the heater until water is in the heater(?).

Last, what will an inspector expect to see for the 10/2 that runs from the service box to the heater? Do I need metal conduit (pipe) when running accross the roof joists? (the light in the attic made code apparently and didn't need metal conduit -- its powered from a 14/2 simply running across the joists).

[lep]

Change spelling of nymex to nomex.

[HayZee518]

ok, your feeder will be a 10/2 with ground romex. Tape the white wire with a red colored "phase" tape. tape both ends at the appliance and at the panel. something about nomenclature here. romex cable is designated by the number of conductors it carries [minus] the bare ground which is a given. so.....12/2 is two current carying conductors with a bare ground. 10/3 will be two hots, a neutral and a bare ground. FOR YOUR BREAKER for the hot water tank. Purchase a two pole 30 circuit breaker. DON'T get two single pole units. The two single pole units require a tie-bar to be installed on the breaker's handles. Romex can be stapled to the existing joists, but if stapled between the joist surface must be run on running boards. you don't require emt tubing for the installation. the feeder doesn't require a junction box next to the heater. run the cable directly inside the unit. the bare connects to the green screw. a junction box is just another reason for a failure, should any of the splices loosen up. the bare at the panelbox goes to the neutral bar.

[lep]

HayZee - thanks a million! Very clear and informative. Any problem using a 1/2" cable clamp in the wiring cover plate to fasten down the 10/2 cable?

thx - lep

[HayZee518]

conduit devices and wiring devices of the half inch variety actually have a 1/2 inch straight pipe thread. they go into a seven-eighths inch hole [ID] no problems witht the romex clamp. just install it in the KO for the wire, in or next to the wiring cover. leave enough of slack to wire to - six inches is a good length. when you wire nut them fold them easily into the access box, just don't cram them in there. I know for fact #10 wire solid is not the easiest thing to work with.

[Kidd6488]

Originally Posted by HayZee518

the bare at the panelbox goes to the neutral bar.

Can I nit-pick and point out that the bare conductor ("ground") should go to the Equipment Ground bus bar in the panel? Just in case (like my panel), the Neutral and Ground bars are already separated...

to the OP: In most cases, the neutral and ground bus bars are one and the same. (this common bar is the system bonding point, where the neutral to ground connection is made).

[LazyPup]

There are a couple more points you should be aware of when installing a water heater in an attic space.

When a water heater is installed in an attic space, the physical location of the water heater may be no more than 20' from the attic access door.

The attic access door or hatch must be large enough to pass the water heater through it. (under the IRC the minimum hatch or door size is 22"x30"; Under the UPC the minimum is 30"x30")

An electric water heater is required to have an "electrical service disconnect" in the near proximity and in direct line of sight from the water heater. (Exception, the breaker may be used as the service disconnect if it is in direct line of sight from the water heater location).

In your situation the correct placement would be to install the service disconnect where you are presently planning the junction box.

Code requires a minimum of one light fixture in the near proximity of the water heater and the switch to control that light must be within 6' of the access door to the attic space.

Code requires a 120v duplex receptacle in the near proximity of the water heater.

The water heater is required to have a drip pan & the drip pan must have a 3/4" drain line that terminates into an approved waste receptor or it must terminate outside the structure. Under the IRC the point of termination must be not more than 6" above average terrain. The UPC permits the line to terminate ata point greater than 6" but not more than 24" above average terrain.

The T&P valve must also have a full bore line the same size as the T&P discharge port and it must terminate the same as the pan drain.

The T&P MAY NOT terminate into the pan and the pan & T&P drain lines MAY NOT be combined into a single line.

[HayZee518]

Kidd6488 - a bare ground is connected to the auxillary ground bar ONLY if it is in a sub panel -or- if there is one installed in the main panel. Normally in a main panel the neutral bus is bonded to the equipment ground through a heavy duty jumper wire or a bonding screw,
Lazypup - the only place I've seen a manual disconnect and servicing receptacle is in a refrigeration location remote from a panel disconnect. Can you or would you quote me the NEC section and sub section?

[normel]

For the required disconnect, see Section 422.31(B).
For the required lighting, see Section 210.70 (A)(3).
The receptacle is only required for HVAC equipment, but is a nice thing to do if the WH is in a space not normally served by a receptacle (like a crawlspace).

BTW, those code sections are from the 2005 version.

[LazyPup]

I don't know whether it's in the NEC or not, but its in both of the national model plumbing codes.

"Electric water heaters require an insight or lockable electrical disconnect"

International Residential Code IRC-1307.5 & T4001.5
Uniform Plumbing Code UPC-309.0-6


Attic installation requires a light & receptacle near Water Heater

IRC-305.1.3.1 & 3803.4
UPC-511.5


Light switch required at the entrance to the attic
IRC-3803.4
UPC511.5