OCPD for heating equipment

[timm333]

Just want to clarify the overcurrent protection for heating equipment. In Canadian electrical code section 62-114(7), we size the OCPD of the heating equipment for 100% FLC. But NEC 424.22 is not clear. Can we size the OCPD for heating equipment (and furnace) for 100% FLC in NEC?

 

[bphgravity]

The NEC requires the branch circuit to be sized and protected at 125% of the continuous load. Per the 2014 edition:

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

To help the installer comply with 424.28(A) and 424.29, the manufacturer will provide a nameplate that clearly indicates branch circuit ratings, minimum and maximum overcurrent devices, etc...

 

[iwire]

To help the installer comply with 424.28(A) and 424.29, the manufacturer will provide a nameplate that clearly indicates branch circuit ratings, minimum and maximum overcurrent devices, etc...

I have never seem those markings on fixed electric space heaters.

Just voltage, phase and KW.

 

[timm333]

Thanks. Is electric furnace also sized for 125%?

 

[Dennis Alwon]

Thanks. Is electric furnace also sized for 125%?

All electric heating is sized at 125% for the conductor size & ocpd. Generally on a furnace there is minimum circuit ampacity & minimum overcurrent protective device (heat pump).

 

[Little Bill]

All electric heating is sized at 125% for the conductor size & ocpd. Generally on a furnace there is minimum circuit ampacity & minimum overcurrent protective device (heat pump).

I think you meant to say

MCA = minimum circuit ampacity

&

Maximum overcurrent protective device

Although I have seen "minimum breaker or fuse" on some equipment. But most say "MCA & Max breaker/fuse"

@ the OP - the 125% is already figured in on the nameplate for HVAC

 

[timm333]

There are 2 types of breakers, one which are rated for 80% and the others which are rated for 100%. Are all NEC rules applicable to 100% breakers only?

 

[kwired]

There are 2 types of breakers, one which are rated for 80% and the others which are rated for 100%. Are all NEC rules applicable to 100% breakers only?

There are 2 types of breakers but more accurate description would be those rated for 100% continuous loading and those that are not. The ones you find in a typical "loadcenter" are not the ones rated for 100% continuous loading. Most anything you find rated 100% continuous will be a type designed to be individually mounted and not one that plugs onto a common bus in a panelboard.

 

[timm333]

Do the rules in NEC apply only to the breakers which are "not" rated for continuous duty, or do the rules in NEC also apply to breakers which are rated for continuous duty?

 

[kwired]

Do the rules in NEC apply only to the breakers which are "not" rated for continuous duty, or do the rules in NEC also apply to breakers which are rated for continuous duty?

Maybe you need to specify which rules you are asking about. There are different rules for each breaker type - kind of sort of.

How about we start with basics of determining conductor ampacity and go to 210.19(A)(1):

(1) General.


Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Conductors shall be sized to carry not less than the larger of 210.19(A)(1)(a) or (b).


Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.


The minimum branch-circuit conductor size shall have an allowable ampacity not less than the maximum load to be served after the application of any adjustment or correction factors.


Exception: If the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the branch-circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

There is similar wording in 215 for feeders.

What it is describing here is that we need to use 100% of the load in all cases, and add another 25% to any continuous portion of the load. So a single load that is continuous add on another 25%, for combinations of continuous and non continuous you only need to add additional 25% to the continuous portion.

That is the general rule for Standard overcurrent devices.

The exception kicks in when you do have a device listed for operation continuously at 100 percent of it's rating. Then you can disregard the added 25% and ignore whether or not it is continuous load or not. Those devices are not something many of us see often or even at all, so be sure what you have before even thinking about using the 100% in the exception.