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Thread: What size wire for a PID

  1. #1
    Boolit Bub
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    What size wire for a PID

    Does it matter what size wire you use to wire up a PID.

  2. #2
    Boolit Master

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    I'm not a PID expert but yes, it matters. The supply wire from the source and the load wire from the SSR need to be big enough for the intended load. Anywhere from #16, #14 or #12 would work. I'm sure some of the guys that build them will be along soon.

  3. #3
    Boolit Master
    georgerkahn's Avatar
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    As a retired electronics tech, the "rule of thumb" we used in the shop was:
    10 gauge wire can safely carry 30 amperes
    12 gauge wire can safely carry 20 amperes
    14 gauge wire can safely carry 15 amperes
    16 gauge wire can safely carry 10 amperes
    18 gauge wire can safely handle 8 amperes

    As writ, this was/is a guide. You need determine the amperage (current) being used -- very simply, the current in amperes may be determined by the voltage divided by the resistance to it. Notated as "Ohms Law" this is I = E/R -- where I is current in amperes, E is voltage, and R is resistance.
    My own corollary -- hopefully preventing either insulation melt-down or fire -- is, "when in doubt go one wire size bigger".
    I have witnessed soooo many devices where builder/designer saved a very few pennies by employing too small for job wires... It DOES matter what size wire you use for any electical device/circuit!

    If I was wiring a PID device "blind", assuming it was 110V (for 220V, the wire sizes would need be 1/2 the size as for 110V), and you were controlling, say, a 1,200 watt pot -- then you can work backwards from another formula: P=AV -- power in watts equals amperes times volts. You know volts is 110, and watts is 1,200; ergo , giving 10.9 amperes. Hence, I'd have no wires in MY ciruit smaller than fourteen gauge.

    Hope this helps, and good luck!
    geo

  4. #4
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    George hit it on the head!
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  5. #5
    Boolit Man
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    Most of use use the term "PID" to refer to the entire device being used to control temperature.

    There are two circuits in a "PID". The control circuits and the power circuits. The control circuits are probably using less than one or two amps total ( I calculate figuring 3 amps). Twenty two (22) ga or larger would be adequate. I like to up size so 18 - 20 ga .

    The power circuit will carry the current that whatever the "PID" is controlling requires. Most lead pots will operate on a 15 amp circuit so as georgerkahn explained you would use 14 ga for the power circuit.

  6. #6
    Boolit Master
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    Yup nothing smaller than 14

  7. #7
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  8. #8
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    Quote Originally Posted by Paper Puncher View Post
    Most of use use the term "PID" to refer to the entire device being used to control temperature.

    There are two circuits in a "PID". The control circuits and the power circuits. The control circuits are probably using less than one or two amps total ( I calculate figuring 3 amps). Twenty two (22) ga or larger would be adequate. I like to up size so 18 - 20 ga .

    The power circuit will carry the current that whatever the "PID" is controlling requires. Most lead pots will operate on a 15 amp circuit so as georgerkahn explained you would use 14 ga for the power circuit.
    This is how I wired my two.

    Only problem I've ever had with mine is it won't come on once. Traced it back to a bad socket(?) when was the last time you heard of a socket going bad?

    well worth the time and minimal cost to have one for your pot.

    Also have one on PC toaster oven
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  9. #9
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    JonB_in_Glencoe's Avatar
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    I used 14

  10. #10
    Boolit Buddy mpkunz's Avatar
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    Excellent info. I would add this. I haven't wired anything up in a long time and all my brewing equipment and melters are based on older model Omega PID's. Some PID's have, or at least had, relays built into them which could handle small loads like 10 A. For those units you must follow the current/wire gauge rules. If you have a module with is designed to have all the load handling done externally by solid state relays, you can wire the PID module itself with #22 hookup wire which even the few existing independently owned and operated Radio Shack stores have, but the the SSR's that handle the actual load need to be sized according to what George listed.
    - Mike

  11. #11
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    To be picky - for 220V you can use half the AREA of the wire you need for 120V, not half the DIAMETER. There are "Ampacity" tables all over the 'Net, those tell you how many amps a given wire can handle if in open air or if in a dense wire bundle or if inside a chassis (i.e. inside your lead pot.) Lots of nice free air flow will cool the wires down, is why there is a difference. And using a bit larger wire diameter isn't a bad idea, unless you're running a 12 mile long cable where wire costs get to be a factor Also I'd suggest avoiding Aluminum cables (sold on that auction site all too often), you want pure copper. Everyone's agreeing here, just fleshing some thoings in a little bit more, here or there

  12. #12
    Boolit Bub
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    This is great thanks for all the reply's. I should have everything I need to start my build next week.

  13. #13
    Boolit Master
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    RAK2018 -- happy that I (and others, I am sure, here ) were/are able to offer you some good information. However (don't you, too, always hate that "but..."?) -- I was remiss on one extremely important component most necessary, imho. To wit: FUSING! Most residences have FDR's (Female Duplex Receptacles -- aka, "outlets") which are rated and protected at 15 Amperes -- either by fuses or circuit breakers. All the fuse or breaker does is melt or trip when the amperage exceeds the current carrying ability of, guess what? The WIRE SIZE -- to which I again refer to the numbers I wrote in first post (#3) here above. Yes, some houses have special appliance circuits rated at 30Amps, using 10-gauge wire -- but most modern residential circuits are fused at 20 amps.
    Here is the "however" -- in that I highly recommend that, at the closest electrical point where your supply line enters your PID box -- generally immediately past the on-off switch -- you wire in a fuse. My personal favorites are the Buss 3AG -- the glass fuses roughly 1/4" or so in diameter and roughly 1 1/4" long. Name:  fuse.JPG
Views: 123
Size:  8.3 KB Holder may be readily obtained, and you can use a fuse to better protect your circuitry; the fuse/circuit breaker protects your house wiring.
    I do not wish to enable this thread going off on tangents -- just hopefully providing a bit of info to add a tad more safety to you and your project. As an example of "why", think of an aquarium filter which only draws 1.5 amps, which is plugged into a 15 amp outlet in a 20 amp protected circuit. The filter uses 18 gauge wire. Here's the danger: If the 18 gauge wire (aka zip cord) imsulation cracks, and arcs -- I've seen this demonstrated, and have done it myself -- it will be shooting sparks like a highway fusee on roadside -- drawing only 8.3 amps! Your circuit breaker is "happy" -- less current than, say, a large electric coffee maker or a clothes iron -- while your house is burning down!
    A fourteen amp 3AG would be as big as I would go -- and all should be protected.
    Again, BEST!
    geo

  14. #14
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    Ceramic fuses aka "high rupture capacity" or HRC are actually superior for a fuse where an arc could strike as the fuse fails, usually used when you could have a huge surge current. The sand filling inside them quenches the arc so your fuse doesn't explode in flames etc.; down side is that you can't see if its blown or not. PID shouldn't need a ceramic fuse so long as the Line and Neutral wires are kept a respectable distance apart & not run so threy touch anything that will become extremely hot.

  15. #15
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    A Lee pot only draws 8A. I fused my PID for 10A (going in and out).

    The probe should use the same wire as used with the probe.
    A deplorable that votes!

  16. #16
    Boolit Bub
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    Yeah, thermocouple wires uses a different kinds of metal alloy for each wire, k type is allumel and chromel. The TC works by reading the resistance of the circut, resistance changes as the temp increases/decreases

  17. #17
    Boolit Buddy
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    I used 12ga wire. I have 20 amp circuits in garage

  18. #18
    Boolit Master
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    Quote Originally Posted by wjham77 View Post
    Yeah, thermocouple wires uses a different kinds of metal alloy for each wire, k type is allumel and chromel. The TC works by reading the resistance of the circut, resistance changes as the temp increases/decreases
    Not quite resistance. A RTD works with resistance, the TC works from voltage. The TC wire (depending on type, K, etc) creates a small mV range depending on temperature. You actually read the temperature by measuring the voltage created across the tip where the two different types of metal are joined. That's why you don't extend TC wire with plain copper wire. Ideally you would also use a special terminal strip, but it works with standard strip.

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BR Bench Rest M Magnum RN Round Nose
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