Wall Oven Wiring - Is a Plug/Socket Permitted

[Baumgrenze]

For most of 20 years we cooked and baked in our kitchen using the 1950's 40 inch GE Liberator 2-oven range that came with the house when we purchased it. That range had a 3-prong plug on a heavy cord and there was a matching socket mounted on the junction box wired at 220V. If the stove needed to be moved, it could be unplugged and reconnected easily. During the months of construction our remodel involved this was a daily ritual performed by the construction crew.

When remodeled our kitchen 'it was time' to discard the old and install a new, modern wall oven. Its power cord required that it be 'hard wired' to the wiring in the junction box.

Is this wiring arrangement for the convenience of the manufacturer, or is it required by changes in the uniform electrical code?

I ask because it is clear to me that modern wall ovens need maintenance. Oven maintenance frequently requires that the oven be disconnected and pulled at least part way out of the wall. I know enough about the metallurgy of copper wiring to know that it work hardens easily. This means that every disconnection/reconnection makes the following one more difficult as the terminal ends of the wires harden. The wires are also harder to stuff back into the junction box.

Does the current code permit the use of the plug/socket arrangement of the 1950's? If it does, it makes sense to me that it would be wise to implement it.

thanks,

baumgrenze

 

[WorthFlorida]

It’s best to call your building department and ask. Local codes could be different than elsewhere but usually the inspector want’s it done according to the manufacturers instructions. If you do go with a plug it must be a four pin plug and wire fed from the electric panel. You're in a remodel mode, not a replacement so everything needs to be to current code. Not sure why you think a modern wall over needs to be pulled out for maintenance?

 

[Sponsor]

 

[Baumgrenze]

It’s best to call your building department and ask. Local codes could be different than elsewhere but usually the inspector want ps it done according to the manufacturers instructions. If you do go with a plug it must be a four pin plug and wire fed from the electric panel. You're in a remodel mode, not a replacement so everything needs to be to current code. Not sure why you think a modern wall over needs to be pulled out for maintenance?

Thank you for your interest.

I realize I need to supply some more information.

The remodel I described was performed during the summer of 2010.

Earlier this fall, the oven failed spectacularly (sizzle, pop, and smoke) and support calls suggested failure of the 'out of sight' oven heater element. A service call revealed several things.

1) The control board on the oven failed, most likely because of a poor solder joint between the oven element relay and the board.

2) The oven element that was replaced appears to be undamaged. The replacement was declared 'mine' because I suggested that it had failed.

3) In today's world, parts for an appliance like this modern oven are made available by the manufacturer for 5 years. By the end of year 10, the supply of those parts most likely to fail has all but disappeared. If you want one replaced, you, the customer are responsible for sourcing one. In some cases, for a premium fee, you can find a rebuilt circuit board; there are apparently 'craftsmen' who specialize in replacing failed components and restoring failed boards.

4) If a built in oven is properly installed, its power source or connection point is located as near as possible to the point on the oven where the power cable enters it. This allows a 50" armored cable to be long enough for the oven to be pulled to the front of the cabinet bay holding it. (Our architect, general contractor, electrician was unfamiliar with this concept and the cable was connected some inches into the back of an adjacent storage cupboard.) The result is that replacement of many components in oven will require disconnecting the oven cable from the junction box where it is connected because the oven cable is too short.
Breaking and remaking the connection is not as 'simple' as it sounds because the original wiring in the box gets work hardened each time a connection is broken and/or made. Also, unstuffing and restuffing the box works the wire each time and hardens it. This is my reason for concern regarding having to break the connection each time.

Extending the junction box to behind the oven is 'non-trivial' because much of the wall behind the oven is occupied with built-in bookcases. I've included 2 images.

 

[Jadnashua]

Many, not all, devices like this require a neutral. If yours does, anything new you add must have a 4-wire cable from the panel and a 4-pin cable (and plug, if used) to make the connection. Depending on the rated current, the plug and receptacle must be the right type. The 120vac available when neutral is available lets you use a standard light bulb, and sometimes, they'll use that for a circuit board versus feeding it the 240vac. I think, but do not know for sure, that this would fall into the same category as an electric dryer, which is usually connected with a plug versus hard-wiring it.

If it does not specify neutral in the installation manual, you can use a 3-wire setup, otherwise, you are required to have both the neutral and the safety ground wire, not just the neutral.

 

[Baumgrenze]

I woke up this morning with a wiring question. I realized that the wire size in the hookup whip on the oven appeared much smaller than that in the junction box supplying the power. I regretted not getting a good image or measurement on the wire size when the power was off and access was at a maximum, so I do not know the gauge.

What troubled me is that this oven, HBL3450UC/08, requires a 220V/30 A circuit and it is connected to 50 A breakers at the service entrance.

Isn't it true that the whip wiring becomes part of the circuit to be protected by the service entrance breakers?

If so, isn't it improper to wire such an oven to a breaker that requires a much larger current to trip? Put another way, if a short developed between the junction box and the oven parts wouldn't it be possible that the whip wiring would overheat and burn before the breaker would trip?

Thanks
baumgrenze

 

[Reach4]

House wire rules have a large margin built in. The wiring inside the appliance can be much lighter than the house wiring delivering the power to the appliance.

 

[hj]

Often the appliance wiring has a more "durable" insulation. In addition, a short small wire can carry a heavier load than a long small one of the same gauge.

 

[Baumgrenze]

Thanks for the reassurance. The same electrician who installed my new service entrance also overfilled a junction box because he 'knew better than' the UEC rules, i.e., that some of the connections would 'never' carry a significant load. I learned about limits on bundling nm cables after his work was done and behind wall board. He liked 'order' and worked accordingly. He also left some studs with overlarge holes for the same reason. I don't have accurate measurements, just snapshots of the work in progress.
Hence my tendency to question his judgement when something does not make sense to me.

thanks,
baumgrenze

 

[Stuff]

What troubled me is that this oven, HBL3450UC/08, requires a 220V/30 A circuit and it is connected to 50 A breakers at the service entrance.

If it specs a 30 amp circuit you need to change the breaker to 30 amp. Exception is if it is spit with a cooktop (tap rules).

 

[Jadnashua]

Generally, the breaker is there to protect the house wiring, not the actual device it's connected to which may have its own, internal protection. Maybe I'm wrong, but I look at it this way...a typical 15A circuit might have a 60W light bulb in a lamp plugged in...the wiring to the lamp doesn't have to be suitable for 15A, nor will the breaker protect the lamp, but it will protect the wiring in the house. OFten, they call for a "minimum of" x supply for an appliance, but more is okay.

Yes, you can replace the breaker with a lower amperage one, but it might not be required.

What does the code say about this?

 

[Stuff]

Yes, breaker is to protect wires.

Code says manufacturer's instructions overrule. That oven states 30 amp circuit. Doesn't say minimum 30 amp circuit but could argue it is implied.

 

[WorthFlorida]

I woke up this morning with a wiring question. I realized that the wire size in the hookup whip on the oven appeared much smaller than that in the junction box supplying the power. ...

Internal appliance wiring is covered by the UL certificate, not NEC. Most of the time the wiring in an appliance is smaller than the feed and sometimes it does looks unnerving.