424.3 is only regarding branch circuit sizing and says nothing about feeder or service sizing.
220.3 indicates 424.3 is "special", but 125% factoring for continuous load(s) is not implemented under Article 220.
Feeder for Heat Loads
- Thread starter augie47
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220.3 indicates 424.3 is "special", but 125% factoring for continuous load(s) is not implemented under Article 220.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Are we not talking about a feeders here-- I am not sure why 424.3 has anything to do what Gus has mentioned. I am still uncertain why 215.2 is ignored by you. Are you saying it doesn't say what I think it says or are you saying that we ignore it? :?
texie
Senior Member
- Location
- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
One of the things that bothers me is the seeming conflict between 215.2 and 220.51.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yep.. there seems to be a contradiction there.
kwired
Electron manager
- Location
- NE Nebraska
May take a little research, but perhaps a look at ROP/ROC's back to whenever the sections in question were written/changed will help determine why it is what it is.
I am not ignoring it. I'm simply discussing the root of the misunderstanding. 215.2 says you have to size at 125% continuous load. 424.3 says the heaters must be considered continuous AND only for sizing the branch circuits. Nothing says the heater load(s) shall be considered continuous for feeder and service sizing. Now if it outright said heater load(s) shall be considered continuous, without mention of branch circuit sizing, then I would think that would carry up through feeder and service sizing... but it does not say that!!!
That's how I see it.
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.
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Sure art. 215.2 takes us to T.220.3 indirectly but it means nothing in my opinion if that has nothing to do with feeders. Why is it even brought into this discussion?
So art. 215.2 takes us to Parts III, IV, and V of art 220 where we find 220.51 which states fixed electric heat to be calculated at 100%. So then what does the last part of 215.2 mean if it is to be ignored for heaters and possibly other piece of equipment.
I don't understand how we extract from 424.3 when in fact I am ignoring it as I don't see what part a branch circuit plays in this discussion. Please enlighten me as you are seeing something I am not.
Stormwires
Member
- Location
- Lakeland,fl. USA
The NEC enforces the bare minimum requirement, I personally would add my heaters together then factor in the 125% for my feeder then you don't have to worry about it.
220.51 states heater load is calculated at 100%. It is saying there is no demand factor for heating. It has nothing to do with whether the heater load is continuous or noncontinuous.
I have a question for you: Do you know of any typical fixed space heating systems which are designed and installed to be continuous loads? In my mind, they are all designed to be thermostatically controlled and thus noncontinuous loads.
Stormwires
Member
- Location
- Lakeland,fl. USA
In the case where a thermostat malfunctions, turning it into a continuous load.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Well most water heaters are continuous because the NEC says so so why, when 424.3(B) that states branch cir. sizing must be for continuous load, should we ignore it.
It also makes no sense that a branch circuit would be required to be 125% but the feeder feeding all these continuous loads-- whether they are or are not consider that way in our minds- doesn't need to be continuous.
All I'm saying is where a noncontinuous load is required to be considered continuous for the purpose of branch circuit sizing there is nothing which says that consideration must carry through feeder and service sizing. I am not saying ignore it at the branch circuit level... as it is required.
From my perspective, where these loads that are to be considered continuous for branch circuit sizing are in fact noncontinuous loads, it stands to reason that they do not have to be considered continuous for feeder and service sizing. Now if they are in fact continuous loads, feeder and service sizing should be impacted as such.
I believe the reason these loads are to be considered continuous at the branch circuit level is to account for the perhaps rare occasion where demand is at full current for 3 or more hours.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Smart I responded to this
My point is we install all heater to be continuous, baseboard heat as well as electric heating systems. I don't believe they generally run for 3 hours especially in new homes but the code still requires it.
I still don't see how you avoid 215.2 which is about feeders saying the minimum size must be sized to 100% of noncontinuous loads plus 125% of continuous loads. If we have all continuous loads then how do we avoid that-- I know you stated 220.51 says to calculate at 100%. This is where I believe a few of us may be confused. Maybe just me. IDK. This is where you keep saying there is nowhere in the code that requires the feeder to be 125% but you don't address it-- maybe if you explain that to me. I totally understand where you are coming from but this discrepancy has me but you say there is none.
I will add if the heaters are t-stat controlled it seems obvious the feeder would not need to be 125%. I don't even know why they are considered continuous at all even for the branch circuit. I am sure there are instances where a heater may be in a well house where there is little to no insulation and will run constantly so perhaps that is where it is coming from.
Please forgive me for dragging this out as I am sure you are tired of it..
My point is we install all heater to be continuous, baseboard heat as well as electric heating systems. I don't believe they generally run for 3 hours especially in new homes but the code still requires it.
I still don't see how you avoid 215.2 which is about feeders saying the minimum size must be sized to 100% of noncontinuous loads plus 125% of continuous loads. If we have all continuous loads then how do we avoid that-- I know you stated 220.51 says to calculate at 100%. This is where I believe a few of us may be confused. Maybe just me. IDK. This is where you keep saying there is nowhere in the code that requires the feeder to be 125% but you don't address it-- maybe if you explain that to me. I totally understand where you are coming from but this discrepancy has me but you say there is none.
I will add if the heaters are t-stat controlled it seems obvious the feeder would not need to be 125%. I don't even know why they are considered continuous at all even for the branch circuit. I am sure there are instances where a heater may be in a well house where there is little to no insulation and will run constantly so perhaps that is where it is coming from.
Please forgive me for dragging this out as I am sure you are tired of it..
Well I'd certainly like to get it straightened out... not just for your sake, but for others and myself as well.
What I see we have here is three areas of Code interpretation: 1) practiced, 2) intended, and 3) literal. All three can be one and the same. From my perspective, in this case, the literal interpretation (mine et al) does not jive with practiced (yours et al).
If the Code said outright, [these] loads shall be considered continuous, there would be no conflict between yours and mine interpretations. However, the Code does not outright say that. It says [they] shall be considered continuous for branch circuit sizing... period. Just the mere fact Code says to consider [these] loads continuous lends to the fact they typically are not continuous loads.
So where does the Code say [they] shall be considered continuous for feeder and service sizing? It does not... at least not literally AFAIK.
Do some consider it to be implied? Appears so.
Is it the intent of the Code? IDK!!!
Please cite references to any Code section which directly or indirectly states we must consider [these] loads continuous for feeder and service sizing.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Smart that what I keep saying 215.2-- we are not in calculations but in what is required for a feeder
If the branch circuit is continuous as required in 424 then does that 125% mentioned above state we must use it at 125%?
If the branch circuit is continuous as required in 424 then does that 125% mentioned above state we must use it at 125%?
Not contending that.
Being considered continuous for branch circuit sizing involves 210.19(A)(1). How are these noncontinuous loads considered continuous under 215.2(A)(1)?
david
Senior Member
- Location
- Pennsylvania
220.1 Scope.
This article provides requirements for calculating branch-circuit, feeder, and service loads. Part I provides for general requirements for calculation methods. Part II provides calculation methods for branch-circuit loads. Parts III and IV provide calculation methods for feeders and services. Part V provides calculation methods for farms.
215.2 Minimum Rating and Size.
(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. 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.
This article provides requirements for calculating branch-circuit, feeder, and service loads. Part I provides for general requirements for calculation methods. Part II provides calculation methods for branch-circuit loads. Parts III and IV provide calculation methods for feeders and services. Part V provides calculation methods for farms.
215.2 Minimum Rating and Size.
(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. 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.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
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). 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
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
David I am not sure what you are saying when you just quote the articles. Can you add something to it.
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