Electric wall heater - continuous load

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Sierrasparky

Senior Member
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USA
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Electrician ,contractor
Is a properly sized electric wall heater a continuous load? I don't see how as they generally cycle on and off. Many EC over the years say yes.

Same question for a A/C condenser. I have A/C and even in a 100+ degree summer heat I have never seen that thing run longer than 20 - 30 minutes at a time.
 

JFletcher

Senior Member
Location
Williamsburg, VA
Is a properly sized electric wall heater a continuous load? I don't see how as they generally cycle on and off. Many EC over the years say yes.

Same question for a A/C condenser. I have A/C and even in a 100+ degree summer heat I have never seen that thing run longer than 20 - 30 minutes at a time.

Fixed space heating is considered a continuous load per 424.3(B).
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Is a properly sized electric wall heater a continuous load? I don't see how as they generally cycle on and off. Many EC over the years say yes.

Same question for a A/C condenser. I have A/C and even in a 100+ degree summer heat I have never seen that thing run longer than 20 - 30 minutes at a time.


Many parts of article 440 talk about continuous current etc however it is irrelevant when it comes to sizing conductors because of 440.32

440.32 Single Motor-Compressor. Branch-circuit conductors
supplying a single motor-compressor shall have
an ampacity not less than 125 percent of either the
motor-compressor rated-load current or the branchcircuit
selection current, whichever is greater.


424.3 Branch Circuits.
(B) Branch-Circuit Sizing. Fixed electric space-heating
equipment and motors shall be considered continuous load.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Ok That being said. If there is a heating load of 4000 watts at 240v will #12 work on with a 20 amp breaker.

I get 20.83 circuit ampacity.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
20.4amps and you would be compliant with #12

BTW-- 4000 watts must be on a 25 amp breaker not 30 amps

I guess you can divide by 240 and round up and then multiply by 150% but I am not sure that is the intent
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
20.4amps and you would be compliant with #12

BTW-- 4000 watts must be on a 25 amp breaker not 30 amps

I guess you can divide by 240 and round up and then multiply by 150% but I am not sure that is the intent

Thanks Dennis,
I guess the question now is why Must the breaker be 25?

I thought and has been said here before that you can use a lower trip breaker as long as the circuit wiring is correct?

Please forgive me for being nit picky. I just want to get it straight so I can explain it to my GC properly.
 

kwired

Electron manager
Location
NE Nebraska
Thanks, Can you give me a little more to go on?
The mentioning that it will work comes from similar experience - but it is still breaking some code rules.

Start with 210.19 - a minimum of 20.83 ampacity is needed. 12 AWG 75C conductor is fine with that, but we are not done yet.

Then go to 210.20 and a minimum of 20.83 amps overcurrent protection is needed, we are allowed to go to next standard size of 25 amps.

Then 240.4(D) limits 12 AWG to 20 amps protection, with no exceptions for this particular application.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
The mentioning that it will work comes from similar experience - but it is still breaking some code rules.

Start with 210.19 - a minimum of 20.83 ampacity is needed. 12 AWG 75C conductor is fine with that, but we are not done yet.

Then go to 210.20 and a minimum of 20.83 amps overcurrent protection is needed, we are allowed to go to next standard size of 25 amps.

Then 240.4(D) limits 12 AWG to 20 amps protection, with no exceptions for this particular application.

so 240.4 trumps it all?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The mentioning that it will work comes from similar experience - but it is still breaking some code rules.

Start with 210.19 - a minimum of 20.83 ampacity is needed. 12 AWG 75C conductor is fine with that, but we are not done yet.

Then go to 210.20 and a minimum of 20.83 amps overcurrent protection is needed, we are allowed to go to next standard size of 25 amps.

Then 240.4(D) limits 12 AWG to 20 amps protection, with no exceptions for this particular application.


Not what I was looking at--- or maybe you were talking about conductor ampacity

422.11(E) Single Non–Motor-Operated Appliance. If the branch
circuit supplies a single non–motor-operated appliance,
the rating of overcurrent protection shall comply with
the following:
(1) Not exceed that marked on the appliance.
(2) Not exceed 20 amperes if the overcurrent protection rating
is not marked and the appliance is rated 13.3 amperes
or less; or
(3) Not exceed 150 percent of the appliance rated current if
the overcurrent protection rating is not marked and the
appliance is rated over 13.3 amperes. Where 150 percent
of the appliance rating does not correspond to a
standard overcurrent device ampere rating, the next
higher standard rating shall be permitted
.
 
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Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Not what I was looking at--- or maybe you were talking about conductor ampacity

Boy now I am confused.
There appears to be two contradicting code sections.
I don't know about the NEC version but the California version states the more restrictive code prevails. So I would think that you cannot use #12 CU and a 20 amp breaker for a 4000 watt heater on 240v volts.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Boy now I am confused.
There appears to be two contradicting code sections.
I don't know about the NEC version but the California version states the more restrictive code prevails. So I would think that you cannot use #12 CU and a 20 amp breaker for a 4000 watt heater on 240v volts.


That is correct...you cannot use #12 nor a 20 amp breaker. #10 with a 25 amp breaker would be the setup

Conductor size based on 125% of 4000 watts
4000 / 240 = 16.67
16.67 x 125% = 20.83 amps..... based on what kwired stated a #12 awg is not allowed. Based on 150% of the amps--- 16.67 X 150% = 25 amps -- the largest overcurrent protective.

My point was you cannot use a 30 amp breaker with the #10 wire
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
That is correct...you cannot use #12 nor a 20 amp breaker. #10 with a 25 amp breaker would be the setup

Conductor size based on 125% of 4000 watts
4000 / 240 = 16.67
16.67 x 125% = 20.83 amps..... based on what kwired stated a #12 awg is not allowed. Based on 150% of the amps--- 16.67 X 150% = 25 amps -- the largest overcurrent protective.

My point was you cannot use a 30 amp breaker with the #10 wire

No 30 amp breaker on #10 CU for a 4000 watt heater?
If I was confused before I am now worse.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
No 30 amp breaker on #10 CU for a 4000 watt heater?
If I was confused before I am now worse.


This is because article 422.11(E) states that we can not exceed 150% of the appliance rated current. Appliance is 4000 watts x 150% = 25 amps for the overcurrent protective device. Here you are protecting the appliance as well as the wire.

Think of an a/c unit-- you may pull a number 10 awg to the unit but the unit may limit the overcurrent protective device to 25 amps. That's similar to what I stated above.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
So the manufactures are wrong when some call for a 30 amp circuit breaker for a 4000 watt heater?
 

JFletcher

Senior Member
Location
Williamsburg, VA
Lets further muddy the waters, even tho this heater is probably hardwired...say this is cord and plug, and the factory plug is a 6-20. Can you put a 6-20R on a 25A circuit? They arent listed in 210.21.

They do make cord and plug (6-20p) 4000W 240V heaters, tho the two Ive installed receptacles for were portable units.

So the manufactures are wrong when some call for a 30 amp circuit breaker for a 4000 watt heater?

Nope. If the 4000W is at 208V, continuous load would exceed 80% of a 25A breaker, so 30 it is. and 110.3(B) means they are never wrong. :roll:
 
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