power for an oven

[mx842]

I built a powder coat oven several years ago and never could use it but I'm about finished with my new building and I want to hook it up. It has 3) 208 volt 10000 watt heating elements in it. I was going to use 3 phase current when I built it and is why I used those elements. When I finished the build I put a 50 amp 4 wire plug on it just to see if everything worked ok. It got up to 350 degrees in about 20 min and the fan and lights worked. Since then it has been sitting in storage but now I want to hook it up and use it.

My question is what size wire and breaker do I want to use? When I started it up to test it, it seemed to work okay and nothing got hot but I only ran it about an hour then shut it down. This was with all three burners running and with the lights and fan working. I'm not saying this is right just that on the test run it preformed ok. I had a 100 watt entrance service box on the side that fed my controls. The box was fed by a 50 amp cable plugged into a 4 wire 50 amp plug on the wall.

 

[joefromga]

It was probably only using 2 legs. 10kw isn't that much for a 50amp plug with #6 wire.

 

[mx842]

It has 3 10000 watt burners plus the fan and light circuits.

 

[joefromga]

These are heating elements? 10kw x 3 is 30kw. That's pushing it for 50a plug. You probably need to go the next size or two larger.

Check wire amperage ratings . you're definitely going to be in the direct wire range and won't need a plug at that load. If you go 3 phase it changes things a bit because the 208v is going to pull a few more amps than the 240v you tested with as well as the third leg. You should probably be using at least 4ga wire, copper.

 

[ddbackhoe]

I built a powder coat oven several years ago and never could use it but I'm about finished with my new building and I want to hook it up. It has 3) 208 volt 10000 watt heating elements in it. I was going to use 3 phase current when I built it and is why I used those elements. When I finished the build I put a 50 amp 4 wire plug on it just to see if everything worked ok. It got up to 350 degrees in about 20 min and the fan and lights worked. Since then it has been sitting in storage but now I want to hook it up and use it.

My question is what size wire and breaker do I want to use? When I started it up to test it, it seemed to work okay and nothing got hot but I only ran it about an hour then shut it down. This was with all three burners running and with the lights and fan working. I'm not saying this is right just that on the test run it preformed ok. I had a 100 watt entrance service box on the side that fed my controls. The box was fed by a 50 amp cable plugged into a 4 wire 50 amp plug on the wall.

line to neutral would require 28A per leg, for each heater. Cable length would have to be known for sizing.

 

[jenkinsph]

line to neutral would require 28A per leg, for each heater. Cable length would have to be known for sizing.

Can you explain how you came up with 28A/leg?

P/IxE yields 48A @208v

 

[jenkinsph]

It has 3 10000 watt burners plus the fan and light circuits.

Is your new shop set up three phase? If so I would hardwire the oven with a 60 or 70 amp three phase breaker and use #4 thhn wire for the run to the panel. The load should be about 48 amps for each leg running but these elements do pull more current for a short duration while heating up. So while a 50 amp breaker may work moving up to the 60 or 70 amp breaker might eliminate tripping the breaker or over heating it.

 

[CobyRupert]

I built a powder coat oven ..... It has (3)- 208 volt 10000 watt heating elements in it.

My question is what size wire and breaker do I want to use?

I had a 100 watt entrance service box on the side that fed my controls. The box was fed by a 50 amp cable plugged into a 4 wire 50 amp plug on the wall.

You have 30,000 Watts (or 30kW) of load.
The question we need to ask is how are these elements connected?
Are they in a "delta" formation (where element 1 is connected between phases A & B, element 2 is between B & C, and 3 is between A&C?
I assume so, that is, your not using the 4th wire as a neutral and have the elements in a "Y" (wye) formation where element 1 is between phase A & N, element 2 is between phase B & N, and 3 is between C & N.

If elements are wired in "delta" (phase-to-phase), then the current (I) draw is I= 30,000 Watts /(Sqrt(3) x 208V) =83 amps.
You should size the wire and breaker to handle 125% of 83 amps (104A), So basically #2 Awg and a 125A breaker. .

 

[mx842]

You have 30,000 Watts (or 30kW) of load.
The question we need to ask is how are these elements connected?
Are they in a "delta" formation (where element 1 is connected between phases A & B, element 2 is between B & C, and 3 is between A&C?
I assume so, that is, your not using the 4th wire as a neutral and have the elements in a "Y" (wye) formation where element 1 is between phase A & N, element 2 is between phase B & N, and 3 is between C & N.

If elements are wired in "delta" (phase-to-phase), then the current (I) draw is I= 30,000 Watts /(Sqrt(3) x 208V) =83 amps.
You should size the wire and breaker to handle 125% of 83 amps (104A), So basically #2 Awg and a 125A breaker. .

My shop I built isn't 3 phase.

The shop I built the oven in was 3 phase and I originally wired it up for that. I had to move out of that shop and at that point it went into storage. When I tested it There was a 50 amp plug already on the wall where someone had a paint booth plugged in to it. After checking it out I found out they had the plug wired for single phase not 3 phase. I just changed the wiring in my control box for the test just to see if everything worked.

They hooked it up this way so they could say it was portable and not have to have a $60,000 fire suppression system installed on the booth. That was my thinking as well.

This big oven won't get much use, it's only for when I need to do something really big or if I have a bunch of wheels to do. My smaller oven gets most of the use, it's 24'x42''x4' high and most of the stuff i will get will fit in that oven. It also has one of these 3 tube 10000 watt burners in it so running this one off that 50 amp plug wont be a problem. That circuit is a 4 wire circuit with 6 ga wire that is only about 42' from the box with a 50 amp breaker.

I guess I won't be using this circuit for the big oven after all. I'm thinking now that I'll run another circuit maybe three (one for each burner) so I can keep it portable. I have just enough room in my box for three more 50 amp circuits and I think I have enough wire on hand. Do you think that would work?

 

[CobyRupert]

Now I'm even more confused on what you have.

(1)- 10,000 Watt burner (3 tube) or (3) - 10,000 Watt burners? That is, 10,000 or 30,000 Watts of load?
By burners, I think you mean elements?
If 3 elements, do all 3 come after the re-wire? Sounds like only 1 does, so your load is 10,000 watts?

Even then, it really wouldn't be 10,000W, I mean:
Are you running these (208V) elements on 240V single phase? (i.e. people rarely have 208V single phase and not 208V 3 phase). That is a 10,000 watt/208V element will output a lot more wattage if run at 240V, and a lot less if wired line-to neutral (120V). Current draw is also dramatically effected.

Are the element(s) wired line-to-line, or line to neutral?

 

[mx842]

Now I'm even more confused on what you have.

(1)- 10,000 Watt burner (3 tube) or (3) - 10,000 Watt burners? That is, 10,000 or 30,000 Watts of load?
By burners, I think you mean elements?
If 3 elements, do all 3 come after the re-wire? Sounds like only 1 does, so your load is 10,000 watts?

Even then, it really wouldn't be 10,000W, I mean:
Are you running these (208V) elements on 240V single phase? (i.e. people rarely have 208V single phase and not 208V 3 phase). That is a 10,000 watt/208V element will output a lot more wattage if run at 240V, and a lot less if wired line-to neutral (120V). Current draw is also dramatically effected.

Are the element(s) wired line-to-line, or line to neutral?

Yeah I can do that sometimes.:laughing: 1 burner = 3) 3500 watt tubes rated at 10000 watts total. Each burner has 6 stud connectors for one in and one out. Basically each burner has 3 separate tubes with wire connectors on each end that are connected together with a bracket.

I'll see if I can find some pics if not I'll take some and post them.

The way I wired it is each tube, (9 in all, 3 each burner) has 1, 10 ga wire coming into the tube and 1, 10 ga wire going back to the control box. Each 3 tube burner has it's own terminal board in the control box and each burner has it's own contactor relay. I had a 125 Amp service panel over top of the control box that fed the control. I had it set up where every relay was on it own 40 amp breaker in the service box.

When I did the test run I fed the service panel with a 10' long, 4 conductor 8 ga cord, that had a 50a 4 pin plug. The plug was plugged into the existing 50 amp pug that fed the old paint booth.

I don't know if this helps you understand this mess I have any better but if not I'll try again.

 

[CobyRupert]

Lots of variables/ And we know none.

What feeds the 4 wire plug? 240V, a neutral, and a ground?
You have 3500 watt tubes, I assume that is their 208V rating?
How are the 4 wires from the receptacle distributed among the tubes? If it was previously 3 phase, 1/3 of the tubes may be running at 240V, and the other 2/3 may be running at 120V.

(A 3500 Watt tube rated for 208V is a 4660 Watt tube when run at 240V, and it's a 1165Watt tube when running at 120V.

Bottom line: Given that nobody knows much; for safety's sake, I'd suggest that the ampacity of any wire that you use is greater than the ampacity of any breaker you use. That way you hopefully won't melt the wire.

 

[mx842]

Lots of variables/ And we know none.

What feeds the 4 wire plug? 240V, a neutral, and a ground?
You have 3500 watt tubes, I assume that is their 208V rating?
How are the 4 wires from the receptacle distributed among the tubes? If it was previously 3 phase, 1/3 of the tubes may be running at 240V, and the other 2/3 may be running at 120V.

(A 3500 Watt tube rated for 208V is a 4660 Watt tube when run at 240V, and it's a 1165Watt tube when running at 120V.

Bottom line: Given that nobody knows much; for safety's sake, I'd suggest that the ampacity of any wire that you use is greater than the ampacity of any breaker you use. That way you hopefully won't melt the wire.

Four 6 ga wires, 240 with ground and neutral.

The tubes I bought had a 208v/240v rating.

Each contactor is fed by a terminal strip, with it's own thermostat. Thermostat calls for heat and sets off the contactor which sends current out of the bottom terminals on the contactor to, two other terminal strips one for the red wire one for the black. Well it's one strip that has two sections, one for the red wire one for the black. Each burner has 6 wires going to it from these strips, current goes in one end of the tube and out the other end back to the terminal strip. same for the other two tubes in this one, three tube heater kit.

There are three, 3 tube burners in all, each has it's own contactor, thermostat, terminal boards in the oven. Basically three different circuits that work together. I set it up so that once the oven got up to temp one of the burners would drop off and not come back on unless needed.

I don't want to melt any wires but when I tested this thing I ran it off one single 50a plug in circuit and it worked just fine. Not saying that this is the right way to do it I'm just saying that's how it went. I knew when I tried it that it seemed to me to be too much to ask of this one 50 amp plug. I fired off one burner at a time until they were all working then kicked on the lights and fan unit until it got up to temp. What's strange is that nothing seemed to get hot or warm even the whole time I was running it for the test.

 

[ddbackhoe]

Can you explain how you came up with 28A/leg?

P/IxE yields 48A @208v

Simple...3 phase of 208Volts, assumption was measuring one leg to neutral (RMS)