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Thread: RTD Terminal Block Recommendation

  1. #1
    Join Date
    Oct 2006
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    345

    RTD Terminal Block Recommendation

    Looking for recommendations for connecting a 3-wire RTD (24ga wire) to RTD extension wire (22ga) at a terminal block. Terminal block will need to fit inside a FS box. Area is a marine environment - salty - corrosive.

  2. #2
    Join Date
    Feb 2003
    Location
    Illinois
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    23,657
    I would be really tempted to use Scotchlok UR "button" splices for that application. I know that is not a terminal block, but they have gel in them and keep moisture out. They are good for 19-26 gauge.
    Don, Illinois
    Ego is the anesthesia that deadens the pain of stupidity. Dr. Rick Rigsby
    (All code citations are 2017 unless otherwise noted)

  3. #3
    Join Date
    Feb 2003
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    Bremerton, Washington
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    7,915
    Or, what I use is King DryCon wire nuts...Its a wire nut with "goo" inside, and can be undone, the UR connectors have to be cut off.
    Moderator-Washington State
    Ancora Imparo

  4. #4
    Join Date
    Jul 2013
    Location
    Moab, UT USA
    Posts
    222

    RTD's

    Quote Originally Posted by tom baker View Post
    Or, what I use is King DryCon wire nuts...Its a wire nut with "goo" inside, and can be undone, the UR connectors have to be cut off.
    The main thing with RTD's is a tight connection, especially if your distance back to your readout control is longer.
    I have used wirenuts successfully,
    Microwave Radiation Dangers should be openly discussed

  5. #5
    Join Date
    Aug 2004
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    Northern illinois
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    16,859
    I might be inclined to just get some barrier block type terminals.
    Bob

  6. #6
    Join Date
    Oct 2006
    Posts
    345
    Project specs call for stainless steel. I'm thinking that may be a conflict with the copper based RTD and extension materials....can rtd terminals be stainless steel?
    Last edited by Natfuelbilll; 08-19-18 at 06:20 PM.

  7. #7
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
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    6,937
    180819-1955 EDT

    You want the lowest possible resistance in the connections. That meas twisting the wires together, then wire nutting with internal goo as described above.

    .

  8. #8
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,937
    180819-2124 EDT

    In an ideal RTD system you would use 4 wires, a 4 wire resistor, two wires to supply a known current to the sensing element, and two voltage sensing wires to report back the voltage directly across the sensing element to the measuring instrument.

    To save wire this can be reduced to three wires by eliminating one voltage sensing wire, and assuming that each of the current wires and any connections in each current path are equal in resistance.

    At the measuring instrument the current is measured. Two voltage drops are measured using the single voltage sensing wire. The first voltage drop is the sum of one current wire resistance plus the RTD element resistance. The second drop is the voltage across the other current wire. This second voltage is subtracted from the first drop to get the voltage across the sensing element. Thus, there can be no significant added resistance in either current wire vs the other current wire. Resistance in the voltage sensing line is of no great importance , if not large, because little current flows in the voltage sense wire.

    You need to understand fundamentals to know why certain procedures need to be employed.

    .

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