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1. Cooktop

Hello,

I am replacing a cooktop that is wired with AWG 10 3 insulated wires. My question is what size wire and breaker do I use on the new one. The sticker on it says 7.0kw 120/240v and to the right says 5.3kw 120/208v. Should the wire be copper or aluminum? On the new unit there are 4 wires, red, black, white and green.

Thanks,

David

2. Most instructions will give you the wire size required along with a disclaimer that the given wire size is in copper. They will also give wiring diagrams for 3 wire to 4 wire.

What's the model and brand?

3. If it is rated at 7 kw, it is just over 29 amps at 240v. If it were me, I would run 8/3 with ground romex and put it on a 40a breaker.

4. Model

It is a Jenn-Air JED8430BDB, serial number 16252549NR.

5. Originally Posted by condor
\ The sticker on it says 7.0kw 120/240v and to the right says 5.3kw 120/208v.
240²/7 kw = ~8.2 Ω
208²/5.3 kw = ~8.2 Ω
I guess it makes sense.

What is the distance back to the panel?

6. Its about 37 feet to the panel.

7. Originally Posted by condor
Its about 37 feet to the panel.
OK so if you want a max 5% drop at 240v at 29A you want no more than 12v/29A = 0.4 Ω for 74' loop distance = 5.4 Ω/1000' so you need larger than #16 AWG, copper, for voltage drop.

For ampacity, it looks like #10 AWG copper would just do it at 29A at 60°C insulation. With 90°C insulation you could even go to #12.
http://www.jhlarson.com/ind_tables/c...able310-16.htm

So it's #10 or #12, copper. For aluminum you need #10 with min. 75°C insulation.

Wood slowly chars at 120°C so you can pick your own factor of safety.

8. Originally Posted by Thatguy
OK so if you want a max 5% drop at 240v at 29A you want no more than 12v/29A = 0.4 Ω for 74' loop distance = 5.4 Ω/1000' so you need larger than #16 AWG, copper, for voltage drop.

For ampacity, it looks like #10 AWG copper would just do it at 29A at 60°C insulation. With 90°C insulation you could even go to #12.
http://www.jhlarson.com/ind_tables/c...able310-16.htm

So it's #10 or #12, copper. For aluminum you need #10 with min. 75°C insulation.

Wood slowly chars at 120°C so you can pick your own factor of safety.
Wow, that's hard. Let a guy pick his poison.....

9. Originally Posted by Thatguy
OK so if you want a max 5% drop at 240v at 29A you want no more than 12v/29A = 0.4 Ω for 74' loop distance = 5.4 Ω/1000' so you need larger than #16 AWG, copper, for voltage drop.

For ampacity, it looks like #10 AWG copper would just do it at 29A at 60°C insulation. With 90°C insulation you could even go to #12.
http://www.jhlarson.com/ind_tables/c...able310-16.htm

So it's #10 or #12, copper. For aluminum you need #10 with min. 75°C insulation.

Wood slowly chars at 120°C so you can pick your own factor of safety.
I really don't know what to say about some of this.
The fact that you are doing a VD calculation for a 37' run, or the fact that you are suggesting #12 for a 29A circuit, or that you are suggesting using the 90 deg C column for ampacity.

Matt is right. This new unit requires a new run of 8/3 w/g and a 40A breaker.

10. I should have sized the breaker first?
Back to the books (that I already have)

11. Well, I'll just say that 310.16 is fine, but there are many other sections that alter how we use it.
For instance, pretty much the only thing we can use the 90 deg column for is derating.
You also have to be aware of 240.4(D), what it applies to, and what exceptions there are to it.

The code is not something you get from a chart on a single web page.

12. It'll be a while before I live this one down.
What's the written equivalent of

Open mouth, insert foot

?

13. Thank you all for your answers. I will go with 8/3 and a 40A breaker.

14. One more question, does this romex 8/3 with ground sound ok?

Conductors:

* Solid conductors: Soft, uncoated
* Copper Stranded conductors: Uncoated copper per ASTM-B3 and ASTM-B8

Conductor Insulation and Jacket:

* Color coded PVC (polyvinyl chloride), rated 90°C dry
* Insulated conductors also jacketed with clear nylon (polyamide)

Grounding Conductor:

* Soft, uncoated copper per ASTM-B3

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