In what scenario for a stove would using a 50a breaker for #8awg be permitted?

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JohnDS said:
In what scenario for a stove would using a 50a breaker for #8awg be permitted?

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In the scenario wherein the stove is actually a 5HP 230V single phase motor and has a starter with OL heaters that will not allow more than 32A perhaps?

#8 is rated for 40A. You have to size wire for 125% of the continuous load, so 32 x 1.25 = 40A.

You can't put a 50A breaker as the only OCPD on a conductor rated for 40A.
 
Thanks for the replies. I may have read into this wrong but I was under the impression that a stove is not considered a continuous load. Can you confirm this? Or were you refering to the hypothetical situation of the stove having a motor?

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JohnDS said:
In what scenario for a stove would using a 50a breaker for #8awg be permitted?

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In the scenario where both the wire and the terminations on both sides, are rated for 75C or greater. You cannot do this with ROMEX, as Romex (NM cable) has a specific rule to require 60C termination considerations, 334.80. You'd likely be using conduit and THHN/THWN/THWN-2 wire.
 
JohnDS said:
Thanks for the replies. I may have read into this wrong but I was under the impression that a stove is not considered a continuous load. Can you confirm this? Or were you refering to the hypothetical situation of the stove having a motor?

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A stove is not a continuous load. It cycles on/off via a thermostat so it's not on (full) for the required 3 hours that defines continuous loads.
 
If you used MC cable with 75° C terminals on both ends you could use a 50 OCPD with the #8 conductors.
 
ActionDave said:
If you are using conduit and THHN.

I believe there was a short time in the 1990's when romex got upgraded insulation that guys were using the 75 degree scale in 310.15.
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I could be wrong, but that was about the time they developed "NM-B" which is all you can get now and I believe is even required in NEC to use type NM-B for all new wiring.

AFAIK you were always required to size NM cable per 60degree ampacity table as minimum size, but could use higher temp table for ampacity adjustments if the cable were rated higher temp. NM-B is rated 90C.
 
kwired said:
I could be wrong, but that was about the time they developed "NM-B" which is all you can get now and I believe is even required in NEC to use type NM-B for all new wiring.

AFAIK you were always required to size NM cable per 60degree ampacity table as minimum size, but could use higher temp table for ampacity adjustments if the cable were rated higher temp. NM-B is rated 90C.
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So, still no good on 8/3 romex with 50a breaker?

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JohnDS said:
So, still no good on 8/3 romex with 50a breaker?

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For the range, no. For a motor or air conditioning circuit, generally would be allowed, but motor full load (times 1.25) or MCA still needs to be 40 or less.
 
JohnDS said:
So, still no good on 8/3 romex with 50a breaker?

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For a stove no but it might be possible that the stove can use a 40 amp OCPD which would work with the #8 NM cable. How many KW?
 
infinity said:
For a stove no but it might be possible that the stove can use a 40 amp OCPD which would work with the #8 NM cable. How many KW?
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I dont have specs, it was just a question that popped up in general that I was curious about because i had overheard someone suggesting a 50 can be used.

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JohnDS said:
I dont have specs, it was just a question that popped up in general that I was curious about because i had overheard someone suggesting a 50 can be used.

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A 50 can be used where the 8 AWG is allowed to be sized per 75C ampacity table. If you have NM cable you must use 60C ampacity table.
 
mbrooke said:
Was this in the code?
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I couldn't find it. I looked back as far as the 1975 NEC and that had the 60° C limitation. The 1984 required NM cable to contain 90° C conductors and the 60 ° limitation remained.
 
infinity said:
I couldn't find it. I looked back as far as the 1975 NEC and that had the 60° C limitation. The 1984 required NM cable to contain 90° C conductors and the 60 ° limitation remained.
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Guess it was simply be accident in ActionDave's case. I remember chating with MasterTheNec with him saying SE had a 75*C outer jacket and NM having a 60*C outer jacket. Which would explain why NM is still restricted to 60*C.
 
I think the issue gets a bit more complicated in that Note 4 to Table 220.55 would allow you to power a Household range up to 13kw on a 40 amp circuit.
 
mbrooke said:
Guess it was simply be accident in ActionDave's case.
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Some places probably did/do allow the 8/3 for a 50 amp range- the nec is not set in stone when it comes to many ahjs. Perfectly reasonable to see that many would allow such an exception for a dedicated circuit.
 
user 100 said:
Some places probably did/do allow the 8/3 for a 50 amp range- the nec is not set in stone when it comes to many ahjs. Perfectly reasonable to see that many would allow such an exception for a dedicated circuit.
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In theory it makes sense as the load is very diverse and transient.

FWIW in Canada 8/3 has been allowed for some time on 50 amp range circuits.
 
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