Product Manual vs. NEC

cdillman7

Member
Location
Wisconsin
Occupation
Electrician Apprentice
My friend bought a 10kw Comfort Zone Electric Heater

(see: https://www.amazon.com/Comfort-Zone...er+cz269er+10000+watts&qid=1615526178&sr=8-13)

And I'm trying to figure out conductor size and overcurrent protection for him.

With Ohms law I get 10kw at 240v = load size of 41.67 amps.

According to NEC Article 424 Fixed Electric Space Heating Equipment, this ceiling mounted electric heater is a continuous load. And must be multiplied 125 % of the load = 52.0875 amps. I emailed the manufacturer what amps the blow motor is rated at but haven't gotten a response yet. Regardless - 6/2 Romex is rated at 55 amps and the next closest Overcurrent Protection Device (Curcuit Breaker and separate Disconnect) would then theoretically be at 60 amps.

I read the manual and it doesn't mention continuous loads (seems to ignor it completely). Can't figure out how to upload pictures of manual but it only say that the device is at 10kw, 240V 69 Hz, Phase1, 41.67 amps and BTU/Hour: 32, 122. Wire should.be copper at a rating of 75C, fuse size 50amps and min copper wire size at: 6AWG.

So which Breaker Size should I side with? The 50 amp according to the manual or should I use a 60 amp breaker as I calculated via the NEC?

Thanks for the help!
 

kwired

Electron manager
Location
NE Nebraska
My friend bought a 10kw Comfort Zone Electric Heater

(see: https://www.amazon.com/Comfort-Zone...er+cz269er+10000+watts&qid=1615526178&sr=8-13)

And I'm trying to figure out conductor size and overcurrent protection for him.

With Ohms law I get 10kw at 240v = load size of 41.67 amps.

According to NEC Article 424 Fixed Electric Space Heating Equipment, this ceiling mounted electric heater is a continuous load. And must be multiplied 125 % of the load = 52.0875 amps. I emailed the manufacturer what amps the blow motor is rated at but haven't gotten a response yet. Regardless - 6/2 Romex is rated at 55 amps and the next closest Overcurrent Protection Device (Curcuit Breaker and separate Disconnect) would then theoretically be at 60 amps.

I read the manual and it doesn't mention continuous loads (seems to ignor it completely). Can't figure out how to upload pictures of manual but it only say that the device is at 10kw, 240V 69 Hz, Phase1, 41.67 amps and BTU/Hour: 32, 122. Wire should.be copper at a rating of 75C, fuse size 50amps and min copper wire size at: 6AWG.

So which Breaker Size should I side with? The 50 amp according to the manual or should I use a 60 amp breaker as I calculated via the NEC?

Thanks for the help!
I'll tell you that the 50 amp breaker likely doesn't ever trip, But NEC would actually require the 60 amp breaker.

Be careful the motor doesn't add enough to put you over 55 amps with the 125% factor - if so you need to increase to 4 AWG or use a wiring method that can apply the 75 C ampacity table.
 

cdillman7

Member
Location
Wisconsin
Occupation
Electrician Apprentice
I'll tell you that the 50 amp breaker likely doesn't ever trip, But NEC would actually require the 60 amp breaker.

Be careful the motor doesn't add enough to put you over 55 amps with the 125% factor - if so you need to increase to 4 AWG or use a wiring method that can apply the 75 C ampacity table.
so maybe # 6 THHN would be better than 6-2 Romex?
 

kwired

Electron manager
Location
NE Nebraska
so maybe # 6 THHN would be better than 6-2 Romex?
Yes, same amount of copper same voltage drop, but because you are not limited to 60C ampacity table you have 65 ampacity instead of 55.

You are still fine with NM cable as long as the load doesn't go above 44. (you mentioned 10 kW heat but was not certain what the blower motor load was - which is what possibly could put you over 44.

44 x 1.25 =55. can still protect that with next size up rule @ 60 amps.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
My friend bought a 10kw Comfort Zone Electric Heater

(see: https://www.amazon.com/Comfort-Zone...er+cz269er+10000+watts&qid=1615526178&sr=8-13)

And I'm trying to figure out conductor size and overcurrent protection for him.

With Ohms law I get 10kw at 240v = load size of 41.67 amps.

According to NEC Article 424 Fixed Electric Space Heating Equipment, this ceiling mounted electric heater is a continuous load. And must be multiplied 125 % of the load = 52.0875 amps. I emailed the manufacturer what amps the blow motor is rated at but haven't gotten a response yet. Regardless - 6/2 Romex is rated at 55 amps and the next closest Overcurrent Protection Device (Curcuit Breaker and separate Disconnect) would then theoretically be at 60 amps.

I read the manual and it doesn't mention continuous loads (seems to ignor it completely). Can't figure out how to upload pictures of manual but it only say that the device is at 10kw, 240V 69 Hz, Phase1, 41.67 amps and BTU/Hour: 32, 122. Wire should.be copper at a rating of 75C, fuse size 50amps and min copper wire size at: 6AWG.

So which Breaker Size should I side with? The 50 amp according to the manual or should I use a 60 amp breaker as I calculated via the NEC?

Thanks for the help!
You must have read a different manual than I did...
cz260.JPG
 

cdillman7

Member
Location
Wisconsin
Occupation
Electrician Apprentice
? those are same values OP mentioned. The million dollar question is why isn't the OCPD 125% of the 41.67 then increased to next standard size which would be 60? This should be a continuous load application.
exactly - I eventually called the manufacturer and found out too what that the fan motor only used .15 amps; the manufacturer is only showing in the manual what the fuse is for a non-continous load; you have to reclasify the OCP with the 125% to get 41.67 X 1.25 = 52.08 ; then add the .15 amps = 52.24 amps; closest CB for that load size is a 2 pole 60 amp breaker. I"m sure the 50 amp CB would likely not trip, but if it was my license on the line; I'd rather follow the code book that cite the manual which gives itself an out clause where it states; make sure to follow the NEC.
 

mwm1752

Senior Member
Location
Aspen, Colo
does the NEC require the breaker to carry the load or to protect the conductor? protect conductor
or does the NEC require feeders to carry the load with option of oversizing the breaker protection? yes
it may not be practical to undersize the OCPD but it does not make it non compliant. In this case the continuous load calcs are for the conductor.
440.4(B)
 
Last edited:

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
does the NEC require the breaker to carry the load or to protect the conductor? protect conductor
or does the NEC require feeders to carry the load with option of oversizing the breaker protection? yes
it may not be practical to undersize the OCPD but it does not make it non compliant. In this case the continuous load calcs are for the conductor.
The NEC requires the breaker to be sized at not less than 125% of the continuous load. Undersizing it would be non-compliant.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
Also curious why the nameplate requires #6 copper at 75C. If the continuous load was 50A, then #8 cu should be OK. The #6 would be more inline with a 60A load than a 50A one, but that looks like what this should have really been anyways.
 

kwired

Electron manager
Location
NE Nebraska
Also curious why the nameplate requires #6 copper at 75C. If the continuous load was 50A, then #8 cu should be OK. The #6 would be more inline with a 60A load than a 50A one, but that looks like what this should have really been anyways.
IF continuous load were 50 amps you would need a minimum conductor ampacity AND minimum overcurrent protection at 125% of the continuous load which would mean you need minimum conductor ampacity of 62.5 and next standard size OCPD would be 70 amps.

#8 @ 75C could only be used on a 40 amp max continuous load and be on a 50 amp OCPD, over 40 amp continuous load puts you over 50 amps when you increase by 125% - #8 is too small and next standard OCPD is 60.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
By 50A continuous load, I meant 50A after the 125% factor was applied. But nameplate is just over 40 so the continuous factor is a bit over 50 making #8 too small. But usually the wire size matches the fuse size in a heater.
 
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