Number of duplex recepticals?

[tryinghard]

Design/Calculate or Just Plain USE

Design/Calculate or Just Plain USE

For some sadistic reason I gotta point out a few more facts:
Fact is 215-2(A)(1) ?Feeder conductors shall have an ampacity not less than required to supply the load as CALCULATED in parts II, III, and IV of Article 220?
Fact is 220-10 ?The calculated load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article? which includes 220-14(I) ?receptacle outlets shall be CALCULATED at not less than 180 volt-amperes?
Fact is Annex D3, Noncontinuous Loads, Receptacle Load, 80 receptacles at 180 VA = 14,400 VA. This is a contributing calculation used to determine ?Minimum Size Feeder (or Service) Overcurrent Protection?
Fact is 225-5 ?The ampacity of outdoor branch-circuitry and feeder conductors shall be in accordance with 310-15 based on loads as determined under 220-10 and Part III of Article 220?
Fact is 230-23(A) ?Conductors shall have sufficient ampacity to carry the current for the load as CALCULATED in accordance with Article 220?
And
Fact is 210-11 ?Branch circuits?shall be provided to supply the loads CALCULATED in accordance with 220-10? This is simply telling us to use the 180 VA found in Article 220 just like it does for feeders and services.

The above facts do reveal some commons: branch circuits, feeders, outside branch circuits & feeders, and services all use CALCULATIONS that include 180 VA for receptacles to determine ampacity and overcurrent protection and they all refer to Article 220 for this calculation.

 

[tryinghard]

It may not even be a good minimum for today. Offices have too many computers, printers, etc to follow the minimum.[/I]

We do not circuit general use receptacles for anything other than general use and certainly not heavy or large use! In other words an office printer is too large for general use portable heaters are too large as well. Something is better than nothing and the NEC has established this with the 180 VA per receptacle.

NEC is giving us the 180 VA as a plug number to use for general use receptacle circuits just like we use it to determine feeder and service sizes. Interesting the amperes do not originate at the feeders or services, the amperes are on the branch circuitry first, yet we are supposed to use a plug number of 180 VA per receptacle to size feeders and services and we are NOT supposed to use it to size the branch circuitry?

You see without a benchmark or base one could install an infinite quantity! I?m still wondering how many receptacles would you install on a circuit? How might you account for voltage drop on your receptacle branch circuit?

 

[hmspe]

Has anyone considered asking the NFPA for an interpretation? 62 posts in this thread alone, and there are several other threads on the same topic. We can argue about this forever, but it's quite obvious that there is no consensus. The only valid answer will come from the CMP.

That said, I wonder how designers who are on the "unlimited receptacle" side show the calcs. IMO panel schedules with loads calculated are really feeder calcs which prove the feeder is not overloaded. On the other hand, if I show a load of 3600VA (which would be 20 receptacles at 180VA) on a 20A breaker in a panel schedule I'm guaranteed to have the plans fail in plan check where I live. The same question applies with track lighting. In both cases the requirements for the feeder calc load are (or may be) different than the load that would be used to size the breaker. How do you show both?

Martin

 

[charlie b]

Fact is 210-11 ?Branch circuits?shall be provided to supply the loads CALCULATED in accordance with 220-10?

I agree that this is a statement of fact.

This is simply telling us to use the 180 VA found in Article 220 just like it does for feeders and services.

This is not a statement of fact, but rather an expression of an opinion, an interpretation. I do not agree with that interpretation; I hold a different opinion; I am entitled to do so.

 

[charlie b]

I wonder how designers who are on the "unlimited receptacle" side show the calcs. IMO panel schedules with loads calculated are really feeder calcs which prove the feeder is not overloaded. On the other hand, if I show a load of 3600VA (which would be 20 receptacles at 180VA) on a 20A breaker in a panel schedule I'm guaranteed to have the plans fail in plan check where I live.

I can tell you how I do it. I use the panel schedule to calculate load, just as you describe. I lay out the receptacles, and choose my circuiting pattern. Then I count the receptacles on each circuit. I include, in my panel schedules, a load of 180 VA for each receptacle on any given circuit. If I discover that I had put more than 13 receptacles on one circuit, I go back and change the design.

This is my design practice, my design decision. But if I were to chose instead to design the circuits in some other way, if for example I were to chose to put 26 receptacles on one circuit, I submit that I will not have violated any article in the NEC. Bottom line: IMHO there are no words in the NEC, as that book is presently written, that would forbid that practice. I just don?t chose to practice that way.

 

[hmspe]

I can tell you how I do it. ... If I discover that I had put more than 13 receptacles on one circuit, I go back and change the design.

That's what I do, too, although I seldom go over 6. I'd rather have extra circuits with no complaints of nuisance trips. No one has ever accused me of under-designing.

On track lighting I have occasionally put actual load in the panel schedule then added an adjustment factor at the bottom of the panel, but that's easy to explain to the reviewer because everyone agrees on the rules for track.

Martin

 

[~Shado~]

Hello,
1st, I want to thank everyone for their comments. I have followed the forums for quite some time and it has made me a better electrician in general. No matter how hotly debated a subject becomes, it has broadened and opened my thoughts, ideas to areas I may never have considered.

On to subject at hand..... and this is just my opinion.
The NEC is minimun accepted standards. No one has listed 90.1(b) or(c) in any of their comments.
(b) - states that compliance results in an installation that is essentially free from hazard but not necessarily effecient, convienent, or adaquate for good service or future expansion of electrical use.
(c) - states " This CODE is not intended as a design specification......"

Also, while discussion on art 220, no one has brought up the fact that it is used for 3 seperate calc potentials - 1 residential and 2 commercial calcs. One calc is for Bank/Office buildings, the other is for rest of commercial, ie...wharehouses, retail, service industry, etc...

I havent found where it definatively states minimum or max number recepts, just a guide line for calculating the potential load on a circuit. ART 220 gives us that guide line by mandating that the load calc for ckt be based on 180 va per yoke in commercial installs. This in effect allows us to arrive at the number of devices in that ckt. This is where we design and install correctly.

 

[SmithBuilt]

I’m still wondering how many receptacles would you install on a circuit?

I now realize this is a waste of time, at least for me, to be arguing. I've never to my knowledge put over 10 or 13. So please don't question my integrity as I'm just debating the code, it has little to do with my methods.

How might you account for voltage drop on your receptacle branch circuit?

I don't really see how this would be relevant to the number of receptacles on a branch circuit.


I'm throwing in the towel. Have fun!

Tim

Welcome to the forum Shado.

 

[tryinghard]

I see some parallels and with these as example it appears NEC directs us to use 180 VA per receptacle to size branch circuitry.

Is this why we size a feeder from Article 220?
215-2(A)(1) ?Feeder conductors shall have an ampacity not less than required to supply the load as CALCULATED in parts II, III, and IV of Article 220
If not where does the NEC tell us?

Is this why we size a service from Article 220?
230-23(A) ?Conductors shall have sufficient ampacity to carry the current for the load as CALCULATED in accordance with Article 220
If not where does the NEC tell us?

Is this why we size branch-circuitry from Article 220?
210-11 ?Branch circuits?shall be provided to supply the loads CALCULATED in accordance with 220-10?

If not how is the meaning different than 215-2 & 230-23?. Please do not be intimidated just explain your points.

 

[charlie b]

? 215-2(A)(1) ?Feeder conductors shall have an ampacity not less than required to supply the load as CALCULATED in parts II, III, and IV of Article 220

? 230-23(A) ?Conductors shall have sufficient ampacity to carry the current for the load as CALCULATED in accordance with Article 220

? 210-11 ?Branch circuits?shall be provided to supply the loads CALCULATED in accordance with 220-10?

I see a big difference in the three cases, specifically in the words that I highlighted. ?Shall have an ampacity? is a directive that is related to the design choices for the amount of load and the size of the wire. ?Shall be provided to supply the loads? is not. The only thing that ?Shall be provided to supply the loads? tells us is that everything that you counted, when you calculated the load, has to get a branch circuit to feed it.

 

[tryinghard]

? The only thing that ?Shall be provided to supply the loads? tells us is that everything that you counted, when you calculated the load, has to get a branch circuit to feed it.

Does this actually happen on purpose, in such a way that code is required to be written? I wonder if electricians intentionally leave out branch circuitry when wiring receptacles?
I'm not seeing it and I'm really trying hard!

 

[tryinghard]

Also 210-11 and 220-10 are integral for feeder size (215-2(A)(1)) and service size (230-23(A)), in other words you cannot have feeder size or service size without the 180 VA per receptacle. In this light why would it not count for the branch?

 

[parttimer]

I would

I would

always try to get any customer to make it 6 duplex receptacles or 4 duplex plus 2 fourplex. We all know that today everyone plugs in everything they can and even adds power strips. We also find it easier to run all 20 amp rather than worry about the cost of 12 v 14 ga wire.

It is ussually not hard to get that kind of upgrade through the customer if it is commercial or an owner builder. We even try to assure that dirty appliances like a vacuum cleaner never run on the same circuit as tv and puters etc. We try and keep only two adjoining bedrooms on the same utility receptacle circuit and provide hall way receptacles for dirty appliances.

Isn't that more important than discussing the "theory" of what is allowed? Selling the customer the best you can provide? WE all know that we will build to the stamped drawing and code, the inspector will inspect to the same. But if the inspector wants a change (per his interpretation)and it is relatively cheap are you going to argue or just do it? We all know that on the next job we might pay highly for the argument.