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Old 10-04-2010, 09:59 PM   #1
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Water Heater Replacement


Hello all, I live in a '99 "Skyline" Mobile home, single wide. I just replaced the water heater. The orignal was a 30 gal. 3800 Watt, Single element, 240v on a dbl. 20A breaker & pretty sure it's 12/2 wire.. The new one I installed is a 40 gal 4500 Watt, dual element, 240v. Can I get away with keeping the 12/2 & dual 20A breaker? I haven't hooked up the power yet.. Another note to ponder is that I'll only have the water heater set just above halfway (about 125 degrees) I do know the water heaters amperage is rated at 18,8A . I know this is super close to the 20A breaker rating and a safety factor should be prob around 16A,,,But will this be a safe situation for me to use the existing 12/2 & dual 20A breaker? Thanks very much for any/all advice

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Old 10-04-2010, 10:07 PM   #2
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What do the installation instructions indicate is required for wire & a breaker ?

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Old 10-04-2010, 10:10 PM   #3
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Water heater wiring should be sized at 125% of the load. You need 10-2 wiring on a double pole 30 amp breaker.
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Old 10-04-2010, 10:22 PM   #4
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Thanks for such quick replies! The Installation book does have a chart that "Recommends" 4500 Watts (@240v) to have 25A and 10 gauge. But I'm still curious about a cpl things,,,The book also recommends 12 gauge & 20A for 3k watts and 10 gauge & 25A for 4k watts and considering this "recommendation" It just makes me curious to learn why I would have 12 gauge with a dual 20A and the old heater was 3800 Watts. Thanks again for any info on this so I have a better understanding. Much appreciated
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Old 10-04-2010, 10:25 PM   #5
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Possibly the last person to wire it did not look into what was required
I have #8 wire (had some leftover) & a 30a 240v breaker for my 50g
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Old 10-04-2010, 10:27 PM   #6
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3800/240 = 15.83 amps. 15.83*1.25 = 19.79 amps. A 20 amp rated circuit would work.
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Old 10-04-2010, 11:49 PM   #7
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Thanks again for your answers.
What I'm seeing from all of this is that with my dual element 40 gal @ 4500 watts, is that I should change my wiring & breaker to 10 gauge and 30A?? Sorry I should have been more to the point. I just would like to know if It would be safe to operate the WH on the existing 20A 12/2 set at about 125 degrees. (or does the elements use the whole 4500 Watts when on, which might be taking my chances of a fire?

*Also, the new WH has 12 gauge wires as the hook-up which makes me not understand, or does that even matter? My electrical skills are minimum

Last edited by Mr.Mike; 10-05-2010 at 12:06 AM.
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Old 10-05-2010, 12:21 AM   #8
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id say 27.4 amps using 125% rule,10/2 wire and 30a 2pole is what i would use.
that 12ga tailed out of the elements is only carrying a small percentage of the load which is why its smaller
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Old 10-05-2010, 03:59 AM   #9
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4500/240=18.75. 18.75*1.25=23.44 amps. Yes you need #10 and the 30 amp breaker.

The WH was listed with the correct size conductors inside. They are fine.
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Old 10-05-2010, 07:36 AM   #10
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The current ratings discussed here have to do with heating up of the wiring given the current load in amperes.

The wiring in the heater itself is enclosed in a "fireproof" metal case (the heater shell) and is probably also of a higher temperature rating. The house wiring runs through wood and also other non-nonflammable materials and probably also through insulation as opposed to free air so heating up of the wire is of more concern.
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Old 10-05-2010, 08:32 AM   #11
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Quote:
Originally Posted by Mr.Mike View Post
Thanks again for your answers.
What I'm seeing from all of this is that with my dual element 40 gal @ 4500 watts, is that I should change my wiring & breaker to 10 gauge and 30A?? Sorry I should have been more to the point. I just would like to know if It would be safe to operate the WH on the existing 20A 12/2 set at about 125 degrees. (or does the elements use the whole 4500 Watts when on, which might be taking my chances of a fire?

*Also, the new WH has 12 gauge wires as the hook-up which makes me not understand, or does that even matter? My electrical skills are minimum
What I think you are suggesting is: If you keep the thermostat at 125 degrees, the water heater will draw less than the full rated current.

NOT, the elements will draw the rated current regardless of the T-stat setting. The T-stat only cuts the current off when it senses the water has reached the set point temp.
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Old 10-05-2010, 10:26 PM   #12
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Thanks, That's what I thought but had to make sure. Appreciate your reply!
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Old 10-05-2010, 10:36 PM   #13
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Appreciate that. I also see another issue is that I obviously have to run the new 10/2 (I have some 10 gauge that has 3 wires stamped 10/3) 2 hots and a ground is how I'll use it. My prob. is running it from 1 side of M.Home to the other as it has an insulation bag. I was thinking of drilling a hole in the plastic elec. conduit that comes from the pwr. main in my yard, so I will have a route to get it into the breaker box, Then install a 20' pc of 1" plastic to feed through to other side of home (mounting it with U clamps to the 2 I-Beams under the house (since it will be alot easier than trying to cut the "bag" and stapling along the way) then feeding up through floor to W.H. area. Would anyone object to this? Thanks
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Old 10-06-2010, 05:03 AM   #14
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Do not cut into the service line feed conduit. Instead cut an access panel like this in he wall below the breaker box so you can install a knockout and feed the wire into the box,

http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

Paint the panel to match the wall.
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Old 10-06-2010, 02:15 PM   #15
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Thanks. I'll take that advice as it is common sense for sure! I went to HD & bought an access panel (10x10 up to 15x15) in case I need to get a drill in there to drill through the floor. I have 10/3 UF with no ground (will use the white for ground to panel and at WH. I also got some 1" pvc conduit to put the wire through from 1 side of the house to the other (16') only so I can strap it to the steel beams that run the length of the Mobile home. (I thought the conduit would be better than trying to attach the wire without it because the beams are the only attaching points) Then I have 2 sweeps for the conduit that I'll use to go up through the floor into panel & WH areas. Punch out 1 of the 3/4" knock-outs on the bottom of panel, put in a romex connector, a dbl 30A breaker in the last open slot. I think this will work ok and safely?? This is a 16' x 80' single wide and the panel is on 1 wall and the WH is directly across from it in the same room (closet)16' away...I wanted to give as many details as I could.Thanks

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