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| Subject - Need help wiring a custom made oven | |
| TRG | Hi, glad that i found this forum. I run a small powder coating shop and im currently in the process of getting ready to build a 4ftx4ftx6ft walk in oven. I will be heating this oven with (3) 5kw tubular 240volt heating elements. Where i run into trouble is how to wire everything. I have talked to many people all with different suggestions and now im rather confused. I basically need to know how to wire everything. I know as of now i will need (3) 240v 25A solid state relays, the temperature controller, thermocouple, elements, and main feed. How would i go about getting started? ANy tips or suggestions would be GREATLY appreciated. |
| Scott Vickrey | The thermocouple or RTD (resistive temperature device) will hook up to the temperature controller you'll have to get with the manufacturer of the temperature controller to make sure you get a compatible sensor. The controller will act as a control switch for the relays which are hooked up to to the power leads and the elements when the controller calls for heat it will close the relays and allow the power to go through to the elements. Your going to have to use a high temperature wire from the relays to the elements. You'll have to isolate the controller and the relays from the extreme heat by locating it in a separate box and seal the penetrations for the element wires. I'm not sure about the solid state relays. Can they be operated with 120 volts? Or do they need to have a DC control voltage? If you can't find solid state relays that operate on AC then you'll need to use a contactors instead. one leg of the 240 will be 120 to neutral. This can be used as a control voltage. If you have to have DC power then you'll need to add a rectifier and most likely a transformer. The wires to the elements are beyond my area of expertise so I can't you advise you there. The wire feeding the oven will need to be at least #3 awg if the max temperature in the control box and conduit will not exceed 194 degrees Fahrenheit and you use type THHN which is ubiquitous. These wires should be in a metal conduit and fed from an 100 amp 2-Pole breaker. In the control box the power wires will have to be terminated to a terminal block that will allow you to tap off to The control transformer and each relay or contactor. The control transformer should have a fuse on the secondary side protecting the control circuit. I have rattled off some things I hope will help you in your endeavor, but you really need someone to get very involved in the design of the wiring. The devil is in the details. |
| JimmyDee | quote: Solid state relays work on AC just fine. Most can be turned on with a very small voltage and very little current. I have used some that turn on with as little as 3-4 volts and some have a range of say 30-240 volts for turn on. I would think that for the high wattage heater a contacter would work better. Jim |
| TRG | Thanks for the reply Scott. I understand that the thermocouple is wired to the controller, than the controller is wired to the contactors and than to the elements. Do you suggest anyplace to pick up the DP contactors? Also, would the elements need to be wired in parrellel or series? What about the contactors? I have a good clue now how to wire the elements with the controller etc, but where im still a little confused is how the main feed gets brought in and how that gets wired to the "system". I've done my fair share of electrical stuff, but nothing ever this complicated. I contacted a electrician and he wanted about $500 to make me a diagram. Id rather try and figure this out myself, and hopefully not blow myself up! Thanks again. |