Expert: Master Bob - 1/2/2005

Question
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Followup To
Question -
I have read some of the prior questions in this category and these provided some help but I would like clarification.
I am installing a Built-in oven and it lists the electrical requirements at 3.0 KW, 60 Hz and 120/240.  I currently have a regular range that is running from a 3-wire #6gauge to 50amp breaker.  
Question 1. Is this 50amp to large for the new oven?  
The existing wiring does not have a dedicated ground and the directions with the new oven indicate that I could run the three wires to the new oven by hooking the oven ground and neutral to the neutral wire from the incoming line.  Question #2. Should I attempt to run all new wires so there is a dedicated ground. Or can I run a separate ground wire?
Question #3 If I keep the existing wire and it is not long enough to get to the new oven location I was planning on using a junction box to extend the line is this okay?
Thank you for your help.
Answer -
Hi Cory,

  Most regular residential ovens typically draw from 11 - 15 kW and are on 50 or 60 amp breakers and #6 copper. Based on your description...you are replacing a standard oven with a built-in which has a much lower power requirement.

  This 3 kW oven can be ran with 10/3 with ground...on a 2 pole 30 amp breaker. If you attempt to use the existing wiring and breaker....not only will you be over-sized - you will not have the proper protection and serious damage could result in the event of a problem with the unit (the 50 amp breaker would not trip).

 Based on the electrical data you supplied - I'd recomend replacing the wire with 10/3 w/ground.....and installing a 2 pole 30 amp breaker (unless the oven's manual specs a 2 pole 20 amp is adequate)

 I do not recommend splicing at a junction box to add length to the wire with loads of this size. If all new 10/3 w/gr wire is ran - you should buy sufficent length so that splicing is not necessary. Under the new Codes....all ovens (and dryers)installed in new construction now require a seperate ground....the bonding of the ground to neutral is no longer permitted. (NOTE - this applies only to NEW construction....existing homes are grand-fathered. But - where you will need to run new wire - it is adviseable to install it to meet the current Code requirements)

 With this in mind - the answers to your questions are:

1). Yes....the 50 amp circuit is too large.
2). Yes....new 10/3 w/gr. wire should be ran and a 2 pole 30 amp breaker used (unless specs suggest a 2 pole 20)
3). the existing wiring should be removed or disconnected at both ends.(in case you go back to a standard oven in the future)

 Hope this helps....if you need more details, please follow up.

Best Wishes and Happy New Year,

Bob Osgood
Master Electrician

RKO ELECTRIC

www.rkoelectric.com


Thank you for your response. I tried to follow-up sooner but you were maxed out.  I tried to find more information out about the oven that I am installing and have confirmed that it is 3.0 KW but could not find any documentation on the correct breaker amperage.  So I have ran 10/3 w/gr wiring and was curious about the breaker.  It appears that it may only require the 2 pole 20 amp breaker.  I assume it would be safer to try the 20 amp breaker first and see if the oven works properly and if it starts tripping the breaker than I could install a 2 pole 30 amp.  I thought if I went with the 30 amp breaker first that it may not trip if there is any issues with the oven.  Or should I just go with the 30 amp?  If you could clarify that would be great.  Thank you again for your assistance.

Answer
Hi Cory,

  Thanks for following up. Due to the high volume of questions I receive (here and at other expert sites I belong to)...I'm often maxed out. Between running a small electrical company and family/social needs...I don't have a whole lot of spare volunteer time....I just do the best I can. I always include my company website URL at the end of every answer so that there will be several ways to contact me...please feel free to contact me by e-mail if you see me "maxed out" in the future at either:

rkoelectric@verizon.net

or:

info@rkoelectric.com

 I suggested either the 20 amp or 30 amp breaker becuase of the odd rating of the oven. 3000 watts at 240 volts will draw about 12.5 amps....so a 20 amp 2 pole breaker would be sufficient....and I would stay with the #10 wire (which is good for up to 30 amps) that you have already run.

  Always use the minimum size breaker first....you can oversize the wire a little...but you never want to oversize the breaker. Based on the spec's you quoted....the 20 amp 2 pole breaker and #10 wire should be fine for this installation. Swap to a 30 amp 2 pole ONLY if the 20 amp 2 pole shows it can not handle the load. The wiring you've run is good for up to 30 amps....so you'll be all set if you find you eventually need the 30 amp breaker.

 Hope this clarification helps...if you need more details -
please follow-up here or at the above e-mails if maxed out.

Happy 2005

Bob

rkoelectric.com