1500 W Water Heater

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DBuchanan's picture
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Joined: 2013-10-28

Have a 12 gal. 1500 W water heater. Sticker on top says to use no smaller than #10 wire. Why? Thanks.

shamsdebout's picture
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Joined: 2014-02-10

Good question. I am not aware of any technical or code reason for this. I don't think voltage drop would play a major issue for a water heater.

I would contact the manufacturer and share what you find.

W A Werning's picture
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Joined: 2014-02-12

Short answer is 110.3(B), that is the manufacturer's instruction(s).

Also, see 210.23(A)(2) for utilization equipment fastened in place, like your water heater is. If lighting units and other cord and plug connected utilization equipment not fastened in place or both are also supplied. This is the permissible load per Table 210.24

DBuchanan's picture
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Joined: 2013-10-28

[quote=shamsdebout]Good question. I am not aware of any technical or code reason for this. I don't think voltage drop would play a major issue for a water heater.

I would contact the manufacturer and share what you find.[/quote]

Thanks shamsdebout.
Manufacturer said #12 wire on a 15 amp breaker. Couldn't explain sticker.

DBuchanan's picture
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Joined: 2013-10-28

[quote=W A Werning]Short answer is 110.3(B), that is the manufacturer's instruction(s).

Also, see 210.23(A)(2) for utilization equipment fastened in place, like your water heater is. If lighting units and other cord and plug connected utilization equipment not fastened in place or both are also supplied. This is the permissible load per Table 210.24[/quote]

Thanks Mr. Werning. I hear you on 110.3(B), "because we said!", I was just wondering why. This will be a dedicated circuit so I don't think it would be limited to the 50% called out in 210.13(A)(2).

Kadeselfer's picture
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Joined: 2014-03-20

The manufacturer's instructions say its 110.3(B. That's what I have read as well.

W A Werning's picture
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Joined: 2014-02-12

In addition to my previous comments, your electric water heater is a continuous load per 422.13 for sizing the branch circuit conductors. Ohm's Law says: 1,500W / 120V = 12.5A. 422.13 requires 125% for sizing conductors: 12.5A x 125% = 15.62A or 16A.

For overcurrent protection see 422.11(E) (1) (2) (3). What size OCPD do you have? Check out 422.11(E) (1) (2).

mdshunk's picture
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Joined: 2014-03-14

Could also be as simple as the "standard" sticker from the water heater manufacturing line got inadvertently applied to this little wee water heater.

W A Werning's picture
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Joined: 2014-02-12

To Buchanan, water heater question: Voltage drop formula based on 120V, 13A, 125 ft. run, 12.9 K factor for copper. Use 12 AWG, 20A conductor for individual branch circuit.
VD= 2 x 12.9 K x 13A. x 125 ft. divided by 6,530 Cm for 12 AWG.
(Chapter 9, T.8 ) = 6.42V drop.
That is a voltage drop of 5.35%, which is a violation of 210.19(A)(1) In.4 and 215.2(A (3), Note 2.
Could be the Mfg. just trying to protect his product and maintain your warranty and eliminate any voltage drop caused by a smaller conductor than 10 AWG.

mdshunk's picture
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Joined: 2014-03-14

voltage drop is not an enforceable requirement.

mdshunk's picture
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Joined: 2014-03-14

besides, voltage drop will make a resistive load, like a little under counter water heater, last much longer.

mc5w's picture
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Joined: 2013-10-09

There are a number of instances where the manufacturer requires oversized wire such as the #10 copper for your water heater. This is enforceable under NEC 110.3(B). One issue is that a water heater as small as 2 gallons can be refitted with a 2,000W, 120V element without overloading the controls.

Another instance was a CAT scanner we installed. Here are the manufacturer's specifications:
Voltage: 208V, 3-wire, 3-phase, no neutral
Full Load current: 120A, no neutral
Circuit breaker: 175A
Phase conductors: 4/0 copper, no neutral
Redundant Equipment Ground: 4/0 copper
Redundant grounding electrode conductor from local fusible switch to building steel so that the electrical system has 2 grounding connections to the building steel: 4/0 copper

Their directions stated that for larger CAT scanners the wire sizes and circuit breaker sizes are proportionally larger.

Similarly, EVERY gasoline and diesel fuel dispenser manufacturer specifies that the underground wiring must be both explosionproof and to have hospital grade redundant equipment grounding No. 12 insulated copper minimum redundant ground wire in the galvanize rigid conduit. PVC underground is not allowed by the manufacturer. This applies even if the conduit only has a 5V RS-485 data line in it.

If you do not comply with these requirements, the manufacturer **WILL NOT** provide startup services, will not provide technical services, and will disavow any warranty!

Mike Cole mc5w at earthlink dot net
OCILB Lic. No. EL45,008
Columbus, Ohio
Cellular: two one six-eight three two- seven zero two four

Kris687748's picture
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Joined: 2014-05-19

mdshrunk: "Could also be as simple as the "standard" sticker from the water heater manufacturing line got inadvertently applied to this little wee water heater."

This is what I was thinking also. Sometimes the most simple answers may actually be right. Strange that they would not be more careful for something like this though.

tmegger's picture
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Joined: 2014-04-09

I AGREE with mc5w concerning mfgs installation instructions. Just to expound a bit, none of us here are "Design Professionals" so you are asking the wrong people for an answer to a question that only the mfg can answer.

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