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  1. #1

    Electric Reheat box

    I have a question about a high limit temp on a duct heater I am working on.

    The high limit switch has 105 on it do you think it cuts out a 105F or 105C. I

    put a temp probe just past the heat coils in the duct and it goes up to 140F

    and cuts out. Its a REDD-I unit. I called the so call tech support with this

    company and they say 105F but when I pulled the fuse link it was rated for

    104C. What do you think? Any input would be helpful.

  2. #2
    Join Date
    Dec 2006
    Location
    phoenix
    Posts
    106
    If you read 104C then it's centigrade, which make sense. You can Google fusible links for electric heaters and they'll give you their temperature ratings. Fusible links normally are a one time safety. They're not a resetting snap disc Klinkon. Just making sure that we're talking about the same thing. You can get a lot of info searching this forum (electric heaters) too.

  3. #3
    Yea I understand the fuse link its the high limit switch. It says 105 on it would you think its 105C or 105F for a duct heater.

  4. #4
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    456
    I would think it resets at 105F, that is too low for a hi-limit to open.

  5. #5
    Join Date
    Dec 2006
    Location
    phoenix
    Posts
    106
    The high limit has to be higher than 105F. Does the safety say 105C or just 105? I don't want to quote a range of temperatures because it varies from unit to unit. That's why I suggested that you Google for the info. I'm not trying to be evasive, I just don't your level of experience.

    There are different types of high temperature limits, some are auto resetting and some are a one time fuse, such as a fusible link. It depends on the location of the high limit, the heater element material, and other factors which determine the high limit temperature rating.
    Electric heaters can be dangerous. If you're not a contractor, maybe it would be wise to call a professional. Again, I don't know you. You may be qualified but it's hard to tell with a new member. No animosities intended.

  6. #6
    No no offense taken I understand what your saying. I have been doing this for several years. The auto reseting high limit switch just says 105 on it with no indication of F or C. On the other hand the fuse link has 104C on it. I appreciate the help. I took the switch to my local supply house and they looked it up but nothing. I just can't imagine that it opens at 105F and not 105C. Now the other post saying that could be the reset temp does make sence to me.

    thanks

  7. #7
    Join Date
    Dec 2006
    Location
    phoenix
    Posts
    106
    Ok Since you have been doing this for a few years, check your airflow too. The supply temperature sounds very high, but I don't know your return air temperature or what you mean by "just past the heat coils". Each OEM has a minimum airflow for each heater.

    You can easily and accurately check your CFM if you know your TD and wattage. Google or search this forum for formulas. You don't want to be close to the minimum airflow or you'll have problems. I'm assuming that this a constant volume airflow system. I hope this points you in the right direction.

  8. #8
    The Manufacturer clarified that it is 105 F.

  9. #9
    Join Date
    Dec 2007
    Posts
    26

    Confused

    seperate heat pump? vav off of trunk line?

  10. #10
    The system has a roof top unit that feeds about ten rooms and a nurses station. Each room has its own tstat and electric reheat box. Only three rooms are doing this. I am going to check the air flow today and the temps the other units are putting out. Thanks for all the replys.

  11. #11
    Join Date
    Jul 2007
    Location
    Delta BC Canada
    Posts
    87
    Does this system have a zoning system.When there is a call for heat a damper reduces airflow to 50% for heating.It may require you to increase airflow across the heaters on a call for heat.
    In the ductwork where the duct heaters are installed ,do have sufficent distance past the heaters to ensure proper air flow through the duct heaters (the installers guide should give you that info)as you say it is hapening on more than 1 system

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