Feeder for Heat Loads

[david]

The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Exception No. 1: Where the assembly, including the overcurrent devices protecting the feeder(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the feeder conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

The commentary that I look at in relationship to this discussion is comparing the statement to the exception. Sizing the feeder min if equipment (over current devices) are rated not at 100% then the load plus 125% of the continuous load must be consider in the general rule. Compared to the exception when the equipment is rated at 100% then the ampacity of the ungrounded feeder conductor is based on the continuous loads plus the non-continuous loads without the 125% multiplier

 

[Dennis Alwon]

It was brought to my attention by Cadpoint that 215.2 has changed a bit in the 2014. See if you think this helps

(A) Feeders Not More Than 600 Volts.
(1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. Conductors shall be sized to carry not less than the larger of 215.2(A)(1)(a) or (b).

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


(b) The minimum feeder 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.

 

[david]

In both cases 215.2 (A) directs us to 220 parts 111 IV and V not including parts I and II the statement seems simplistic in saying the feeders conductors and overcurrent sizes are based on 220. parts III, IV and V

 

[Dennis Alwon]

In both cases 215.2 (A) directs us to 220 parts 111 IV and V not including parts I and II the statement seems simplistic in saying the feeders conductors and overcurrent sizes are based on 220. parts III, IV and V

So again we ignore the rest of 215.2(A). Why is the second half of the article there if it is ignored or not necessary-- I see it as contradictory statements.

Maybe it would help if someone explained what the second part of 215.2 is in reference to.

 

[texie]

It was brought to my attention by Cadpoint that 215.2 has changed a bit in the 2014. See if you think this helps

This seems to be more confusing. My IAEI 2014 Code Change Analysis is at the office. Would like to see what the commentary says about this. Or even the 2014 Handbook. Can someone take a look?

 

[david]

Doesn?t article 220 part III already take into consideration if the loads are continuous or not.

The commentary is simply saying that you must size the feeder min at a 125% of the continuous (calculated load ) if the equipment is not 100% rated to dissipate the heat.
In other words the statement coupled with the exception is a reminder that conductor sizes must be increased from the calculated load for the reasons addressed in the rule and the exceptions

 

[Dennis Alwon]

Okay here is how I see it.

(A) Feeders Not More Than 600 Volts.
(1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220.

This means only that the conductors must have an ampacity not less than the 100% stated in 220.51 however,

Conductors shall be sized

to carry not less than the larger of 215.2(A)(1)(a) or (b).

I see this as how the feeder must be sized- stated below

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


(b) The minimum feeder 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.

 

[Dennis Alwon]

Doesn?t article 220 part III already take into consideration if the loads are continuous or not.

The commentary is simply saying that you must size the feeder min at a 125% of the continuous (calculated load ) if the equipment is not 100% rated to dissipate the heat.
In other words the statement coupled with the exception is a reminder that conductor sizes must be increased from the calculated load for the reasons addressed in the rule and the exceptions

I think some of you may have missed this post of mine http://forums.mikeholt.com/showthread.php?t=159695&page=2&p=1548261#post1548261

 

[Smart $]

I don't understand-- Do you not consider these branch circuits loads to the heaters to be continuous??? I say this because you call them noncontinuous. As I see it the heaters are continuous based on 424.3(B).

Let's try this another way...

What would be the difference in implementation between the following fictitious section...

424.3 General. Fixed electric space-heating equipment
and motors shall be considered continuous load.

...and the real one (hints)...

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

---

If the entire panel is feeding what I call continuous loads then IMO the feeder must be based on 125% of the heaters.

Non maybe we are saying the same thing-- I am not saying to calculate the heater loads at 125% and then use 125% again for the feeder. I am saying if you calculate the load for each heater at 125% then you don't need to multiply that by 125% again. I am saying calculate the wattage as is and then for the feeder add 125%. For example-- 5- 3000 watt heaters= 15000. The feeder for these loads must be based 1500*1.25=18750 watts

And I'm saying the Code reads like this for your example:

3000W heater on individual branch circuit. Branch circuit sized for 3000W ? 125% = 3750W.

5 noncontinuous heaters on feeder. Feeder circuit is sized for 3000W ? 5 = 15,000W.

If your premise is correct, it should be a simple task to cite section reference which points out my violation.

 

[Dennis Alwon]

Why do you say 5 non continuous heaters on the feeder-- that is what I don't get. The NEC says they are continuous branch circuit loads so it would follow through in 215.2(A) that the feeder must be sized 125% of the continuous loads so in that scenario I would use the 3750 amps *5 to calculate the feeder. I am not sure why I am are seeing this so differently. I would not continue this discussion but I truly respect your knowledge here and I am dumbfounded and cannot see it.

 

[Smart $]

It was brought to my attention by Cadpoint that 215.2 has changed a bit in the 2014. See if you think this helps

(A) Feeders Not More Than 600 Volts.

(1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. Conductors shall be sized to carry not less than the larger of 215.2(A)(1)(a) or (b).


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


(b) The minimum feeder 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.

The only real difference is the requirement was separated into sub-paragraphs. Still says the same requirement as previous editions.

(a) is for minimum sizing the conductor for implementation of 110.14(C). Sizing per this requirement pads the continuous loads an extra 25% so the termination temperature will always be less than their rating during operation.

(b) is for the ampacity of the conductor, under the conditions of use beyond the terminations, to be able to carry the full load. Note there is no factoring of the continuous loads at 125% for this determination.

 

[GoldDigger]

From my view on the sidelines, it seems clear that your fundamental difference is whether "shall be treated as continuous loads for the purpose of A" has the same effect in this case as "shall be treated as continuous loads" when you are looking at B rather than A.
I can see the logic behind both arguments, but I am not willing to make a call between them except that clarification of the code would be nice.
However I suspect that the CMP would vote that the meaning is already obvious even though they are split 50-50 on what the meaning is.
:angel:

Tapatalk!

 

[Smart $]

Why do you say 5 non continuous heaters on the feeder-- that is what I don't get. The NEC says they are continuous branch circuit loads so it would follow through in 215.2(A) that the feeder must be sized 125% of the continuous loads so in that scenario I would use the 3750 amps *5 to calculate the feeder. I am not sure why I am are seeing this so differently. I would not continue this discussion but I truly respect your knowledge here and I am dumbfounded and cannot see it.

The heading of 424.3(B) is Branch-circuit Sizing. You consider the load continuous for branch-circuit sizing... and that's it. It doesn't say loads are to be considered continuous for any other purpose... anywhere.

 

[Smart $]

...
However I suspect that the CMP would vote that the meaning is already obvious even though they are split 50-50 on what the meaning is. :angel:

Their version of plausible deniability...

 

[Dennis Alwon]

The heading of 424.3(B) is Branch-circuit Sizing. You consider the load continuous for branch-circuit sizing... and that's it. It doesn't say loads are to be considered continuous for any other purpose... anywhere.

Sure that is what it says but the heading is not for feeders. Again I go back to 215 for feeders

I have this written up for our Raleigh meeting in April with 7 cmp members as the forum. Hopefully they will address it.

 

[david]

I agree. The 125% rating for branch circuit is not carried through to the calculation for a feeder. This is even true if one heater load is all the feeder serves... but would seem strange having a feeder of a smaller size than the branch circuit wiring... :blink:

220.51 Fixed Electric Space Heating.
Fixed electric space-heating loads shall be calculated at 100 percent of the total connected load. However, in no case shall a feeder or service load current rating be less than the rating of the largest branch circuit supplied.

 

[david]

There is no contradiction between the two. 215.2 says nothing about fixed space heating specifically. You guys are extracting an interpretation based on how you read 424.3. As mentioned throughout, 424.3 says nothing about feeder and service sizing. 220.51 further substantiates my viewpoint.

PS: See post#4... 220.51 prevents a feeder being lesser rated than a branch circuit.

doesn't this support your position

 

[Smart $]

doesn't this support your position

I think it does. If the "considered continuous" of 424.3(B) passed to feeder and service sizing, it would be impossible for their load current rating to be less than any branch circuit. That stipulation would be redundant.

 

[GoldDigger]

If the feeder supplies only a single branch circuit and that circuit has only heating loads, then the effect is to apply the 125% to the feeder also. But if there is more than one branch circuit, it is very easy to have the feeder smaller than the calculation of the heater loads as continuous for the feeder ampacity calculation would require.

Tapatalk!

 

[Smart $]

Sure that is what it says but the heading is not for feeders. Again I go back to 215 for feeders

Correct. The heading is not for feeders.

And when we go to 215 for feeders we size according to the calculated load of 220 and add 25% for continuous load... but the heater(s) are noncontinuous loads by definition (at least the one we are discussing].

424.3(B) by way of its heading says the heater load(s) are considered continuous... but only for branch circuit sizing. Considering the heater loads as continuous for feeder and service sizing is not stated.

I have this written up for our Raleigh meeting in April with 7 cmp members as the forum. Hopefully they will address it.

Looks like we'll have to wait until then to get some resolve...