Akin to "20A breaker protecting #8 wire"

[Little Bill]

I ran into a situation today that was sort of like the other thread "20A breaker protecting #8 wire". I didn't want to confuse the other thread anymore than it already is for some, so I started a new one.

I was asked to help wire a commercial kitchen. Well actually a donut, coffee, and ice cream shop.

They have two commercial ovens. They are 3? ovens. The name plate on the ovens says the amperage/current is 54-57-59. Also states the supply conductors should be 4 AWG-75 deg. With the current for each phase listed you would think you would need a 60A breaker.
With a 60A breaker normally you could run #6 AWG.

My question is since the conductor size is listed on the name plate as #4 and #6 would be rated for 65A and what would be "normal", would this be considered upsizing the conductors as in 250.122(B)? Would you need to also upsize the EGC proportionally from a #10, which would be what a 60A breaker would call for, if it is considered upsizing?

Also, and to back up a little. Do you think a 60A breaker would suffice for the currents that are listed on the name plate?
The name plate didn't mention the OCPD size.

 

[Dennis Alwon]

Well looking at 422.11(E)(3) states that if the appliance OCPD is not marked then you can go 150% of the units marked current. Basically you could use a 90 amp breaker on the unit. I would probably use a 70 amp breaker which would require a #8 EGC and there would be no issues using a #4 CCC

 

[Little Bill]

Well looking at 422.11(E)(3) states that if the appliance OCPD is not marked then you can go 150% of the units marked current. Basically you could use a 90 amp breaker on the unit. I would probably use a 70 amp breaker which would require a #8 EGC and there would be no issues using a #4 CCC

Since 422.11(E)(3) says "single non-motor-operated appliance" I don't know if this would apply since there are motors in the ovens. I assume for fans, I didn't open the doors to see if they had any type of rotissorie or conveyor, but I did see a motor, maybe 2 in the back. I also think the nameplate said the motor part used 5A at 208V, which I think is single ?.

What about the upsizing, would it be considered upsizing since the nameplate calls for #4?

 

[Fulthrotl]

Also, and to back up a little. Do you think a 60A breaker would suffice for the currents that are listed on the name plate?
The name plate didn't mention the OCPD size.

no.

now, it's a resistive load, so it's not gonna inverse on you if you get a voltage sag...
a motor will draw more on reduced voltage, but a radient load will draw less....

and when you get a voltage surge, it will draw more, and you are an amp away from
the nominal setpoint on the breaker. you get a 5% surge, you'll trip the breaker, most likely.

the way i was taught to circuit for continuous loads was not to exceed 80% of the
OCPD. the inverse of that is 125% of the working load, so that comes to 73.75 amps.

THWN #6 is good for 65 amps, #4 is good for 85 amps.

a 70~80 amp breaker would be what i'd use, with a #8 ground, and three #4 THWN, for
a 33% fill in a 1" emt conduit.... bigger tube if it's gonna be a hard pull.

 

[Sierrasparky]

Take a look at this draft language for 2014 nec 250.122 Increase in size
:

(B) Increased in Size.​

​

​

​

​

Where ungrounded conductors areincreased in size from the minimum size that has sufficientampacity for the intended installation, wire type equipmentgrounding conductors, where installed, shall be increased insize proportionately according to the circular mil area of​

the ungrounded conductors. [ROP 5?199]

 

[Little Bill]

Take a look at this draft language for 2014 nec 250.122 Increase in size
:

(B) Increased in Size.​

Where ungrounded conductors areincreased in size from the minimum size that has sufficientampacity for the intended installation, wire type equipmentgrounding conductors, where installed, shall be increased insize proportionately according to the circular mil area of​

the ungrounded conductors. [ROP 5?199]

Maybe a bit clearer!

 

[kingpb]

no.

now, it's a resistive load, so it's not gonna inverse on you if you get a voltage sag...
a motor will draw more on reduced voltage, but a radient load will draw less....

and when you get a voltage surge, it will draw more, and you are an amp away from
the nominal setpoint on the breaker. you get a 5% surge, you'll trip the breaker, most likely.

the way i was taught to circuit for continuous loads was not to exceed 80% of the
OCPD. the inverse of that is 125% of the working load, so that comes to 73.75 amps.

THWN #6 is good for 65 amps, #4 is good for 85 amps.

a 70~80 amp breaker would be what i'd use, with a #8 ground, and three #4 THWN, for
a 33% fill in a 1" emt conduit.... bigger tube if it's gonna be a hard pull.

This is the approach I would take also.

 

[realolman]

Take a look at this draft language for 2014 nec 250.122 Increase in size
:

(B) Increased in Size.​

Where ungrounded conductors areincreased in size from the minimum size that has sufficientampacity for the intended installation, wire type equipmentgrounding conductors, where installed, shall be increased insize proportionately according to the circular mil area of
​

the ungrounded conductors. [ROP 5?199]

I think I have a better idea:

Where ungrounded conductors are increased in size for the purpose of limiting voltage drop, wire type equipment grounding conductors, where installed, shall be increased in size proportionately according to the circular mil area of
​

the ungrounded conductors.

If somebody wants to use larger wire than is necessary because the circuit already exists or whatever, (not because of voltage drop), why should they get caught by the reduced neutral trick, where a 40 amp breaker could be used on a cable but not a 20... that's just dumb.

 

[infinity]

They have two commercial ovens. They are 3? ovens. The name plate on the ovens says the amperage/current is 54-57-59. Also states the supply conductors should be 4 AWG-75 deg. With the current for each phase listed you would think you would need a 60A breaker.
With a 60A breaker normally you could run #6 AWG.

If this is part of the listing of the equipment then this is your minimum size conductor. So unless you install a larger conductor you would not need to increase the size of the EGC.

 

[Little Bill]

If this is part of the listing of the equipment then this is your minimum size conductor. So unless you install a larger conductor you would not need to increase the size of the EGC.

Thanks Rob, that's what I was looking for. No one else seemed to know about what the base size of the conductors would be. I thought they ought to be what the nameplate said but wasn't sure.

I did up size the conductors to 2AWG because the customer had it already and wanted it used. I also upsized the EGC to 4AWG.

 

[charlie b]

I did up size the conductors to 2AWG because the customer had it already and wanted it used. I also upsized the EGC to 4AWG.

The #4 EGC was a bit of overkill, I believe. My calculations tell me that a #8 would have been adequate. That is based on upsizing the ungrounded conductors from #4 to #2, not from #6 to #2. Therein, of course, lies my long-standing problem with 250.122(B): what do you use as the starting point, when you calculate how much you have upsized the ungrounded?

 

[ActionDave]

.... what do you use as the starting point, when you calculate how much you have upsized the ungrounded?

The one that gives you the smallest EGC.

 

[ZZDoug]

It is not upsizing from #6 because #6 isn't legal for two reasons - the manufacturer says #4 and so does code because a commercial oven is a continuous load.

 

[Little Bill]

It is not upsizing from #6 because #6 isn't legal for two reasons - the manufacturer says #4 and so does code because a commercial oven is a continuous load.

You'll have to show proof of this for me to believe it. Anything with a thermostat cuts on and off, therefore no continuous load.