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Old 09-22-2011, 09:23 PM   #1
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Electric Water Heater Wiring


Hi, new here but it seems like a knowledgeable site.

Ive been looking into a water heater timer, and upon locating the circuit found out it still has aluminum wiring. Its a fuse panel so there was one 20A fuse on each side used to give 240v. This wiring is 14ga BX at best..though it looks thinner than the 14ga copper conductors. The water heater has 3000w upper and 3000w lower elements, non simultaneous operation, though it says max 4500w...not sure if this is actual or maybe the tank itself isnt fix for an element larger than that.

A friend of mine whos an electrician here in Ontario (canada) told me that code states here that you cannot exceed 75% of current overload device(Im taking this as fuse/breaker). That said, and assuming the wiring is #14, the fuse should be 15A, 75%15A=11.25A. When i clamp meter the hots they're 12A...thus making 15A fuse inadequate, while a 20A fuse on #14 is also wrong.

So, ideally I would need to have 20A fuses with #12 BX? OR am I way off in my calculations LOL

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Old 09-22-2011, 09:44 PM   #2
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Electric Water Heater Wiring


1. Aluminum wire generally must be one size larger than copper wire for a given amperage (breaker rating), for example 15 amps needs 12 gauge aluminum versus 14 gauge copper. The actual criteria involve resistance per foot.

2. The U.S. NEC calls for 80% circuit loading (12 amps maximum draw on 15 amp breakered circuits) for "continuous" usage which means appliances and equipment likely to be on for more than 3 hours at a time. The kinds of appliances are named in the code; I don't recall what water heaters are. Intermittent usage may use the full amperage rating.

3. Wires handle the same number of amperes at 240 volts as they do at 120 volts.

Canadian rules (CEC) may differ.

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Old 09-23-2011, 05:36 AM   #3
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Electric Water Heater Wiring


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Originally Posted by AllanJ View Post

2. The U.S. NEC calls for 80% circuit loading (12 amps maximum draw on 15 amp breakered circuits) for "continuous" usage which means appliances and equipment likely to be on for more than 3 hours at a time. The kinds of appliances are named in the code; I don't recall what water heaters are. Intermittent usage may use the full amperage rating.

422.13 Storage-Type Water Heaters. A fixed storage-type
water heater that has a capacity of 450 L (120 gal) or less shall
be considered a continuous load for the purposes of sizing
branch circuits.
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Old 09-23-2011, 07:08 AM   #4
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Electric Water Heater Wiring


Yikes... time to fix that asap. Is the whole house aluminum or just that line? I just installed a 40 gallon hot water heater. 30 amp dual throw breaker with 10/2 NM. 2 20 amp fuses with 12/2 NM is probably fine but it couldn't hurt to have slightly bigger wiring.
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Old 09-23-2011, 08:23 AM   #5
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Originally Posted by matt151617 View Post
.... I just installed a 40 gallon hot water heater. 30 amp dual throw breaker with 10/2 NM. 2 20 amp fuses with 12/2 NM is probably fine but it couldn't hurt to have slightly bigger wiring.
You will need at least a 25 Amp OCP with a #10 wire if that water heater has 4500 watt elements in it.
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Old 09-23-2011, 02:43 PM   #6
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I plan to fix it this weekend! I just discovered it. The rest of the house is old copper. I plan to run 12/2 bx and surface mount an outlet. In regards to the outlet and the heater cord itself - currently its bx out the top of the water heater with a T slot plug end attached...bx to plug end doesn't seem right to me...? I m wondering if a piece of #12 kavtar with either tslot or 20Atwist is allowable in this case as a permenant solution?

On a side note, I checked things out this morning after a shower and the fuse cartridge was quite warm.. I m assuming this is normal as this has nothing to do with the wiring. the terminal screws and conductors were slightly warm but nothing to be alarmed about.
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Old 09-23-2011, 02:53 PM   #7
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Electric Water Heater Wiring


Do yourself a favor and run 10-2 directly (hard wire) to the WH. Eliminate the plug and cord. Install a disconnect if the WH is out of sight of the fuse pane.

Next project is to install a modern circuit breaker panel.

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