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Thread: Will Water Heater Wiring Overheat with External Insulation?

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    DIY Senior Member TJanak's Avatar
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    Default Will Water Heater Wiring Overheat with External Insulation?

    Was reading an article in my local electric co-op magazine. They recommend not setting an electric water heater over 130* if wrapped with an external insulation blanket to avoid overheating the wiring. Is this really a concern? My water heater is set at about 150* and wrapped with a blanket on the sides and top.

    Thanks
    Travis

    When I need a precise measurement of something I often use the highly technical method of eyeballing it.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Guess it would depend on the type of wire that is used...on the jacket of the wiring there is normally a rating. A call to the manufacturer might be in order to see what's internal - it's fairly easy to check the external wiring. And, yes, there is a temperature limit, not so much on the copper in the wire, but on the insulation.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member Runs with bison's Avatar
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    It would have to be a really p*** poor design for the insulation to break down at 130 or 150 F. Those are well within the limits of what any competent engineer would select for the service.

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    I advise not to cover the external thermostat/element access panels with an external insulation blanket.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Wiring can be purchased with heat ratings from as low as 50C on up. One would hope that the thing has sufficient grade of wire, but the thing was designed and tested for NO added insulation, and to save costs, the wire they used may not support the added internal heat if you add insulation. It should be easy to check, as it should be marked on the wire. Then, you'd know. Most WH seem to tell you to not add external insulation. This could be the reason.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member TJanak's Avatar
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    I wonder if they meant the internal wiring on the heater or the wire from the panel to the unit. I looked the other day and it is NM (no B) so technically that is probably under-rated. But I would hope it's not 150* at the top where the splice is made...

    Hackney, why? Adjustment/service issue?
    Travis

    When I need a precise measurement of something I often use the highly technical method of eyeballing it.

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