Lots of options to wire an electric hot water booster

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  #1  
Old 11-15-10, 05:34 PM
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Lots of options to wire an electric hot water booster

Hi there, I have an electric hot water heater that I need to wire. It requires 2 seperate 40 amp 220 breakers and a ground.

I have several options and am looking for the best one as to time and money:

1) in the same room (unfinished) as the heater is a 100amp sub panel. Much of the kitchen runs out of it, and I am a bit concerned about overloading it. (I have not measured amp draw). Also, there is not enough room in that sub panel for 2 more 220 breakers. There is room for 1.

2) in a room above (partially finished) is another 100 amp subpanel. This is running has 2 bedrooms, 2 bath's, 2 jacuzzi tub's, 2 in floor heaters, and a 220 V dryer. There is enouh room in this breaker for 2 more.

3) I could go all the way back to the main panel (55' or so)

4) I could install another subpanel just for this, and wire the subpanel back to the main panel.

Looking for ideas, and I have some questions:

A) Does it matter if the 2 seperate 220 40amp breakers are in the same panel (each runs a different heating element)

B) Does the ground need to go all the way back to the main panel, or can I connect it to a subpanel? Does this answer change based on how I wire the breakers?

C) What size wire?

Thanks much to all.

P.S. I went to a big box home improvement store and the dude told me that they were not allowed to advise on electrical. Really? Has our litigous society so screwed up it impacts customer service?
 

Last edited by rdhamm; 11-15-10 at 05:36 PM. Reason: typos
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  #2  
Old 11-15-10, 05:46 PM
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Go with plan #3/4.
Run a 100 amp sub panel from the main panel to the room with the water heater.

This will cover question A: It does not matter where the circuits originate. You would have to install a disconnect next to the heater for each of the 40 amp circuits anyway. The sub panel mentioned above would cover that requirement.

B) The ground will connect to the sub panel's ground bar. (NOT the neutral bar) When you pull your feeder from the main panel you need at least 2 wires and a ground. Since this heater will take just about all the capacity of the panel I see no reason to bring a neutral other then it might be a good idea to do so anyway. You never know what the future holds.

C) You will need to run #2 NM-B or #4 THHN

P.S.) That doesn't surprise me. However likely you might have to go to a supply house for the cable.
 
  #3  
Old 11-15-10, 05:49 PM
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Thanks All Around Swell Guy

That is kindof the direction I was heading..until I saw the cost. The additional box and 100A breaker will double the cost won't it?
 
  #4  
Old 11-15-10, 05:53 PM
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P.S. I went to a big box home improvement store and the dude told me that they were not allowed to advise on electrical. Really? Has our litigous society so screwed up it impacts customer service?
There is a good reason why some of the big box store will not advise on electrical side due there are safety and code issue it have to be dealt with it.

The other reason why some big box store personals are not qualifed to answer that question unless they hold that trade liscense.

For the rest of details I am with Toyln go with subpanel route that is the safest and wise set up.

Merci.
Marc
 
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Old 11-15-10, 05:58 PM
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I think I would go back to the main panel and run two new circuits from there. 4 #8 conductors and one #10 ground should be sufficient for the two circuits. Split the circuits in a 4" box and feed two 60 amp non-fusible disconnect switches and then feed the heater. You could get by with a 3/4" conduit, but I'd probably use a 1" conduit to make the pull easier. As an alternate, use two 8-2/G NM-B cables (romex). Rather than the two disconnect switches, you could also use two 40 amp 2 pole breakers in NEMA1 enclosures as a disconnecting means for each circuit.
 
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Old 11-15-10, 06:00 PM
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Thanks guys... Have a great Week.
 
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Old 11-15-10, 06:14 PM
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You can pick up a 100 amp sub panel, with or without a main, for about $50
 
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Old 11-15-10, 06:20 PM
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Before i tried to add that kind of load I would have a demand load calculation performed. Sounds likes there is already potential for lots of usage by everything that is already installed.
 
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Old 11-15-10, 06:48 PM
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I agree with PCboss I think it will be wise to run the load demand to make sure you are in safe zone I have see few issue with tankless electrique waterheater and from my experince the minuim service size you will have is 200 amp or larger { it pretty common for me go with class 320 service (basically a resdentail 400 amp service )}.

Merci.
Marc


{ Our electrique tankless waterheaters in France are wired for 415 volts either single or triphase supply }
 
  #10  
Old 11-15-10, 09:03 PM
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200 Amp service now

The whole house was remodeled and I upgraded to a 200 Amp service. The home is now 3 floors, and I had 2 subpanels installed, to end up with one set of breakers on each floor.

Not all of the equiment is installed yet, for example one bathroom is not yet completed, so I cannot do a test at this time. I do need to wire this though, in order to install the tub and finish the bath.

Thanks again for all the feedback. I'll go back to the main panel (lots of room in there) and figure out what works best price wise (2 runs or one with yet another subpanel).

-Roger
 
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Old 11-15-10, 09:49 PM
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I'll go back to the main panel (lots of room in there)
It isn't dependent so much on number of open slots as much as estimated load. A three story all electric house certainly would need a demand calc done. You can Google that. Here is one based on the NEC. Free NEC Electrical Load Calculation Software
 

Last edited by ray2047; 11-15-10 at 10:06 PM.
  #12  
Old 11-15-10, 10:22 PM
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Originally Posted by rdhamm View Post
P.S. I went to a big box home improvement store and the dude told me that they were not allowed to advise on electrical. Really? Has our litigous society so screwed up it impacts customer service?
It's very good to hear that. It really has nothing to do with a litigious society as it is more people tend to take what the guy in aisle 4 says as gospel, even when he has no clue what he's talking about. It is actually BETTER customer service for them to not give you advice, because 99 times out of 100, they wouldn't know their nut from a wirenut. It's cringeworthy to hear some of the crap they tell people. I hope it becomes company-wide policy.
 
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Old 11-16-10, 09:24 AM
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Originally Posted by rdhamm View Post
P.S. I went to a big box home improvement store and the dude told me that they were not allowed to advise on electrical. Really? Has our litigous society so screwed up it impacts customer service?
Be thankful they didn't give you advice, because it's almost always wrong. Even that big chart they have up on the wall, printed by the corporate office, that shows wire gauge to amps is always wrong. I have been in the store on several different occasions where I overheard really unsafe advice from the store employees and had to interrupt. I'm glad to hear the store you went to has this policy.

I have heard that some Home Depot stores now have a licensed plumber and electrician on staff for questions, but the stores in my area don't have this yet.
 
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Old 11-16-10, 09:54 AM
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I have heard that some Home Depot stores now have a licensed plumber and electrician on staff for questions, but the stores in my area don't have this yet.
And there may only be one so who you get is a toss up. The HD I worked at often started sending "volunteers" home at 9am if early sales predictions were lower then Corp predicted daily total and some shifts there might not be anyone assigned. That could mean someone from gardening or flooring helping in electrical.
 
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