180 VA per outlet

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franktek150

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Article 220.14 (I) 2008 NEC uses the value of 180 VA per yoke or strap; my question is: where does this value come from? Is it just an arbitrary number picked by the NEC or is there a mathematical/logical/engineering reason this value is 180 VA per outlet?
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
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franktek150 said:
Is it just an arbitrary number picked by the NEC or is there a mathematical/logical/engineering reason this value is 180 VA per outlet?
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Frank, welcome to the forum! :)

As far as I know, someone just decided that, for unknown loads, it would be a good idea to assign a load of 1.5a for GP receptacles.

In other words, it's arbitrary. ;)
 
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hurk27

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Portage, Indiana NEC: 2008
What confuses me is in commercial there is no required General purpose receptacles (6'-12' rule) as they are placed for a load, and in dwellings there is no 180va requirement, so if you are placing a receptacle for a known load, why wouldn't we be required to use the load value and maybe some derating for diversity?
 
glene77is

glene77is

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Memphis, TN
hurk27 said:
What confuses me is in commercial there is no required General purpose receptacles (6'-12' rule) as they are placed for a load, and in dwellings there is no 180va requirement, so if you are placing a receptacle for a known load, why wouldn't we be required to use the load value and maybe some derating for diversity?
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Hurk,

I have always viewed this (my opinion) this way.

Commercial circuits must cover all planned loads.
Commercial circuits are designed with Planned Loads in mind.
Designers know where the equipment, desks, etc., are to be placed.

Residential circuits don't get used ALL the time, just part-time.
Residential circuits are designed with the rule of "Diversity" in mind.
Designers cannot know for certain where loads will occur, just probably.

HTH,
 
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franktek150

Member
I did some research and I think there used to be a rule or trade practice that required 1 circuit every 500 or 600 sq. ft. My thinking was that you could have a maximum of 10 outlets on that circuit which would have been 15 amps, 120V. If you multiply 120V x 15 A gives 1800 VA; divide by 10 outlets gives 180 VA per outlet.
 
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Dennis Alwon

Dennis Alwon

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hurk27 said:
What confuses me is in commercial there is no required General purpose receptacles (6'-12' rule) as they are placed for a load, and in dwellings there is no 180va requirement, so if you are placing a receptacle for a known load, why wouldn't we be required to use the load value and maybe some derating for diversity?
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We do in some cases. If you have a 110 window a/c I would calculate that window a/c load not 3 watts/ft.sq. Other situations such as sump pumps, freezer etc would be figured with the actual load also.
 
Dennis Alwon

Dennis Alwon

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franktek150 said:
I did some research and I think there used to be a rule or trade practice that required 1 circuit every 500 or 600 sq. ft. My thinking was that you could have a maximum of 10 outlets on that circuit which would have been 15 amps, 120V. If you multiply 120V x 15 A gives 1800 VA; divide by 10 outlets gives 180 VA per outlet.
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Frank I think the 600 sq. ft comes from 3 watts/ft.sq. Thus 600 * 3 = 1800 va. 1800/120= 15 amps.

Thus the question is where did the 3 watts/ ft.sq come from? :grin:
 
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franktek150

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Dennis: Hmmm, I think we are nearing the truth. It may be the 180 VA does come from some old square foot/outlet consideration. However, finding the exact origin may be difficult.
 
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