Heat Treat Oven Wiring Schematic

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by jtdesigns, Aug 22, 2012.

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  1. jtdesigns

    jtdesigns

    181
    May 2, 2011
    Thanks to Jim and Stacy's input I have used my Autocad to create a wiring schematic for a heat treat oven that has the following features.

    240VAC
    Auber Instruments PID
    Dual SSR
    Fused Line Leads
    Fused PID
    Power On Switch
    Power On LED
    Heat On Switch
    Heat On LED

    I did this because I have to everything laid out for me so I don't screw things up. For those in the know, please double check my schematic and maybe the powers that be will include this as a sticky so others like me that need it spelled out to the letter can take on this project and lmit the chances of getting zapped.

    Jeff

    Click image below:

    View attachment Heat Treat Oven.pdf
     
    Last edited by a moderator: Oct 23, 2012
  2. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Well laid out. I'll put it in the stickies with the HT oven info. Thanks
     
  3. SteelSlaver

    SteelSlaver

    Feb 17, 2007
    Yes much better presentation than the one I drew up. As mentioned in our phone call the main power led is a little redundant as when the main switch is on the PID lights up. Like the addition of LED on the feed to the SSR that tells you power should be going to the elements.
     
  4. ddushane

    ddushane

    174
    Apr 19, 2001
    I hate to show my ignorance but why to you need two relays?

    Dwayne
     
  5. stevomiller

    stevomiller

    May 4, 2001
    Two relays are used because both legs of 208/220 are "hot". A single relay would turn the element on/off, but if anything conductive that was grounded touched the elements it would a) turn the element on and b) become a shock hazaed.
     
  6. ddushane

    ddushane

    174
    Apr 19, 2001
    Thanks, Stevo!
     
  7. ddushane

    ddushane

    174
    Apr 19, 2001
    The schematic shows a fuse in each power leg of the 220 before the switch and one between the switch and the PID, What size breaker needs to be used for this circuit, what size fuses should be used in the 220 power input before the switch, what size fuse between the switch & the PID? Thanks for any help.

    Dwayne
     
  8. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Those values will depend on the calculated current draw of the coils.
    The two fuses should be rated around 25% above the coil draw per leg. They should be slow-blow type fuses.
    The PID fuse should be slightly above the PID max current draw...usually you just use a 1 amp fuse here. It should be a fast acting fuse.
    The breaker feeding the oven should be at least 50% bigger than the oven draw. The wiring to the oven socket needs to be up to the task,too. It would not hurt for it to be larger than the required code size. Long continuous high current draw is more of a wire over-heating problem than short time draw devices like grinder motors.

    For instance, if the coil draws 10 amps per leg, use 15 amp slow blow fuses in the mains, a 1 amp fast acting fuse on the PID, and feed the oven from a 20 amp 240VAC breaker. 10/3cG ( 10 gauge, three wire, with ground) wire would be good for the feed to the socket.
     
  9. ddushane

    ddushane

    174
    Apr 19, 2001
    Stacy, You said the two fuses should be rated around 25% above the coil draw per leg, are you talking about the SSR's, the ones I put in mine are rated at 40 amp load current. Is this what your calling the coil draw? The main breaker is 30 amp, I went exactly according to the schematic that Jeff shows above. Same size wire & everything. The only problem was the fuses. He didn't list the size of them, I hope I didn't ruin anything, I put 10 amp fuses in all three places & plugged it up & flipped the power switch, something popped & I unplugged it. I haven't had the chance to take it apart to see what blew yet. I hope it was just the fuses. The fuse block I used for the power input was heavy duty and the fuses are probably 1 1/2" long & 1/2" diameter but they're still just 10amp. The fuse for the PID is a 10 amp, small glass fuse. I appreciate any help.

    Dwayne
     
  10. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    No, the SSRs are just an electronic switch. They only carry the current the coil draws. The 40 amp number is the max current they can handle with a heat sink ( before they burn up). I usually figure the SSR at half the rating. The heating coil will probably draw a total current of around 20 amps ( or less), which is about 10 amps per leg ( or less). The breakers will protect the house wiring if there is a complete short. The fuses will protect the coils if there is a temporary short. The PID fuse will protect the PID if there is a SSR failure, or other control circuit short.
     
  11. ddushane

    ddushane

    174
    Apr 19, 2001
    Thank you for your reply Stacy. I'm seeing it now, when you said coils I was lost, I don't know why I couldn't see you were talking about the heating elements. Thanks again for your help. God bless you & yours,

    Dwayne
     
  12. reedje777

    reedje777

    33
    Sep 27, 2011
    On the Auber PID, should I get the PID with SSR output or Relay output?
     
  13. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    SSR output ( most have both). You want a DC voltage sufficient to actuate the SSR coming from the PID. Most SSRs use 3-15VDC as the activation voltage. Most PIDs have 0-10VDC output.
     
  14. slysterry

    slysterry

    1
    Apr 3, 2014
    Pardon my ignorance, L1 and Ld are the black and red 220v wires? What happens with the third (white) wire? I am re-wiring an old oven with updated controls, we use the oven to heat foam for thermal molding, and I shorted out my old analog controller, I'd like to replace the old system and drive the old oven with these controllers.
     
  15. Kieran Klein

    Kieran Klein

    266
    Feb 21, 2014
    I have the exact same question. I am very interested in finding out since I am building a 220 oven
     
  16. Don Nguyen

    Don Nguyen

    Oct 4, 2011
    In the schematic, it has a toggle switch wired with the door switch. What exactly am I looking for?
     
  17. John Katt

    John Katt

    Mar 19, 2012
    The white wire is neutral, you would use it to ground the metal casing and to wire 120volt devices in the oven, in my case the pid and the dc converter to run the cooling fan are ran off L1 and the white wire, all wires are connected to a mini bus so there is no possible way for any wire to come lose and short circuit the whole thing
     
  18. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    The toggle switch in the line that goes through the door switch is a plain 1amp SPST toggle switch. It will carry no real current, as the voltage and current through it are the control voltage to the SSR. It is the "HEAT ON" switch. The SPST door switch is a momentary contact switch of some type. These are often called limit switches or micro switches. It breaks the control circuit if the door opens....thus shutting off power to the coils.
     
  19. Kieran Klein

    Kieran Klein

    266
    Feb 21, 2014
    Ok that makes sense. I am sure I will come back to this thread about 30 more times before the whole project is done. Thanks!
     
  20. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    The simple way to describe the 220VAC circuit for the heater coils is:
    L1 goes to SSR1, through the coils, back to SSR2, and back to L2. If the path is any different you have something wrong. All other wiring is control circuits. They carry no large amount of current.

    Make sure all circuits are right and someone who knows his/her stuff takes a look before plugging it in.
     
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