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Discussion Starter · #1 ·
I just had a question on the 12 AWG coming out of my two ovens and water heater. I know they need to be ran with 10 AWG because of the wattage. The 12 AWG handles 30 amps when it has over 90 degree rating. The conductors do have over 90 degree temperature rating. So 110.14(C)(1)(a)(3) states that you can use 75 degree and 90 degree insulation and it has to be taken from the 75 degree column. That would make the termination at the water heater only able to handle 25 amps. The water heater is 4500. 4500/240. 18.75x.125=23.4375. So does a 90 degree 12 AWG termination at the water heater work with nm-b 10/2 and 30 amp breaker? Following the codes, it does not seem to work.
Another side note is the two homeruns to the kitchen appliances. no lights on those but you can buy cabinet lighting that plugs into them. Just erases all the code work.
 

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Im a little unclear on where the wire is that you are talking about here, but INSIDE a UL listed piece of equipment, a manufacturer can do whatever they want to as long as it is approved by the UL and carries a sticker. As long as the wiring you bring into the equipment is legit per code and nothing you do voids the UL listing (modifying wiring, adding components inside the equipment) you should be fine.


I just had a question on the 12 AWG coming out of my two ovens and water heater. I know they need to be ran with 10 AWG because of the wattage. The 12 AWG handles 30 amps when it has over 90 degree rating. The conductors do have over 90 degree temperature rating. So 110.14(C)(1)(a)(3) states that you can use 75 degree and 90 degree insulation and it has to be taken from the 75 degree column. That would make the termination at the water heater only able to handle 25 amps. The water heater is 4500. 4500/240. 18.75x.125=23.4375. So does a 90 degree 12 AWG termination at the water heater work with nm-b 10/2 and 30 amp breaker? Following the codes, it does not seem to work.
Another side note is the two homeruns to the kitchen appliances. no lights on those but you can buy cabinet lighting that plugs into them. Just erases all the code work.
 

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which brings to mind my welder. i have a 'buzz box' stick welder. on that welder is a #12 cord. feeding it is a #10. required is a 50a breaker. i have run this for 20 years with no problem. what math am i missing?
 

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which brings to mind my welder. i have a 'buzz box' stick welder. on that welder is a #12 cord. feeding it is a #10. required is a 50a breaker. i have run this for 20 years with no problem. what math am i missing?
Insulation.

With conductors, it's not that the AWG of copper that maxes out, it's the insulation that maxes out on the heat. If you use a higher rated insulation, you can crank the amps up.
 

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Discussion Starter · #5 ·
Similar to papaotis's situation is where I am trying to get at. Can you Splice smaller AWG wire with larger wire? Papaotis is running 50 amps on a 12 AWG and it is working because his welder is designed only to draw enough amps that are safe on 12 awg. Is this safe and common to do? It seems that if Papaotis welder drew more amps then suppose to then it could possibly pull 50 amps on the 12 and short circuit.

Running the circuit for my water heater, that has 12/2 terminals with higher insulation rating on it, with a 10 AWG does not seem to much of an issue. I will run that homerun with out to much worry, but this issue still haunts me on another homerun.

The Nec permits two ovens and a cooktop on one circuit. Add up the nameplates of all of them, use the oven table and you can usually splice all three off a 8/3 or 6/3 circuit. You bring that to a junction box next to the stove and make your connections with the flexible conduit from the ovens. That is where I get confused. The 8/3 or 6/3 will be spliced to two 12/3's for the ovens(Each oven is 3600 watts). The 8/3 or 6/3 will also be spliced to the cooktop with something larger then a 12/3. Have not bought the cooktop yet. Is this how it is done? Is it safe to wire 12 AWG to 8 AWG?

I will probably just make it easier on my mind, not my hands, if I just bring a separate circuit to each oven and cook-top.
3600 convection oven 12/3 home run
3600 oven 12/3 home run
8000 cook-top 8/3 home run
 

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Yeah that's the idea.. you can run smaller awg with a higher insulation temperature.. then splice to a larger awg with a lower insulation temperature. You just gotta make sure your breaker will protect the weakest link in that chain.
 

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Discussion Starter · #7 ·
I know that the insulation can let you get more amps out of it. I was trying to get at how splicing larger wires to smaller ones without higher temp insulation works. If a person hooks up two ovens and a cooktop most likely you will run 8/3 or 6/3. That 8/3 or 6/3 will be spliced to the two ovens that are only 12/3 and then spliced to the cooktop that probaly has 10/3 or 8/3. This one circuit supplying the two ovens and cooktop will be on a 40 or 50 amp circuit so that means that the two 12/3's will be on a 40 or 50 circuit. If those ovens pull more then suppose to than the breaker will not pop until it hits 40 or 50 which is double that of what 12/3 can handle. This method seems to count on the equipment functioning properly all the time instead of protecting it with a circuit breaker in case it does malfunction. I ended up just wiring each oven and cook top with a separate circuit but it definitely would of been nice to just run one.
 

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I think taps like that are permitted if smaller gauge wire , in this situation 12/3 , if the wire doesn't exceed a certain length
 

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...With conductors, it's not that the AWG of copper that maxes out, it's the insulation that maxes out on the heat. If you use a higher rated insulation, you can crank the amps up.
Bingo.

Check out some of the the temperature ratings for Teflon coated conductors. I could pass 54A through a #12.

NEC is worst-case-scenario field wiring and is often very conservative. Equipment is much more carefully engineered to work and still be cost effective, hence the smaller conductors.
 
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