Hello, group: I have a new oven to install this weekend. The nameplate gives it a rating of 6.4 Kv at 240 volts. By advanced calculus, I get 26.6 amps.
Now my question is, will a 30 amp circuit suffice, or does this thing really use all 6.4Kv? If so, 26.6 amps is more that 80% of the circuit ampacity. Should I run a 40 amp circuit instead? Warren
The installation instructions were not specific. I have decided to run a 40 amp power supply anyway, since I don't want to cut it that close. Thanks to those who responded. Warren
Even when everything is on, the temperature controls will not all be on and drawing current at the same time.
.. And finally 2 and 3 mean that some diversity is allowed for in cooker supply ciruits within the IEE Regulations. It does sound like a rather small cooker though.
Warren, are you sure that it doesn't say Kw and not Kv? It makes a major difference in the interpretation.
If it is Kw, a 6.4 Kw load operating at 240 volts resistive load will draw 26.66 amps as you correctly deduce.
While you could operate it from a 30 amp breaker, you may run into intermittent trip problems with the breaker when the oven is running at full capacity for an extended period of time. I'd personaly go for the next higher capacity breaker, be it 40 or 50 amps, but be sure to size the wire guage accordingly.
For 50 amps, I'd run #8 wire, although #10 may marginally satisfy NEC requirements (I don't have a copy of the NEC handy here at home). Another factor is the distance between your distribution box and the oven, but I'm assuming that it is less than a 50-ft wire run. Realize that the cost of the wire is likely the least expensive thing in the project, because that wire will likely be there to provide service for many years.
Licensed Electricians, please correct me if I'm wrong here, because I don't want to steer the guy in the wrong direction and most of my practical experience here is with 3,000 MCM or larger traction power cables on subways and #24/26 signal and communicatons wiring. I also generally assume that #14 is used for 15 amps, #12 for 20, and #10 for
30 amps, so I'm not entirely sure that #8 is adequate for a 50 amps (but didn't want to suggest #6 which many homeowners have problems working with).
My personal preferance here would be for a 40 amp breaker feeding #8 wire, however I'm not sure if 40 amp breakers are readily availble for domestic distribution panels, but I know that 50 amp breakers are.
Then too, I'm a control system guy, so what do I know! :-)
Your recommendation of #8 Copper and a 40 amp breaker is most likely correct for this installation.
There are many variables the OP didn't share with us. Manufacturer's installation instructions, system supply voltage (not the appliance rated voltage), method of connecting circuit conductors and their temperature rating, etc.
Many installers take the amperage figures of the NEC Tables (i.e. 310.16) under the insulation classifications as the permitted current capacity of a branch circuit wire. While in some cases this could be the case, often there are other non-apparent factors that could limit the current allowed for a specific size conductor. One of many such possibly limiting factors is the temperature rating of terminating devices. If the terminal temperature rating happens to be listed at 60 deg., the amp rating of even 90 deg. wire would be limited to 60 deg.
With the NEC what might appear to be a logically correct choice might be disallowed by other factors.
Louis--
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