80% continuos load

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iggy2

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from the Mike Holt site, for reference (citations may be out of date):

Q. What is the maximum number of duplex receptacles on a two-wire 20 ampere circuit?

Section 220-3(c)(6). The NEC does not have a specific rule that says 10 receptacles on a 15 ampere circuit or 13 receptacles on a 20 ampere circuit. For 15 ampere circuits, the calculation is as follows: 120 volts x 15 amperes = 1800 VA/180 VA = 10 receptacles, and for 20 ampere circuits, 120 volts x 20 amperes = 2400 VA/180 VA = 13 receptacles.

Many people think that when calculating the number of receptacles the load should be reduced by 80%, but this is not the case! Yes, the NEC limits the load on receptacle circuits to 80% for portable appliances [210-23(a)] and, yes, the maximum continuous load on a branch circuit shall not exceed 80% of the circuit rating (protection device) [220-3(a) and 384-16(c)], but these rules don't apply to the number of receptacles per circuit. I wish the NEC were more specific, but it's not.
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MY QUESTION IS - what is the circuit required for (3) plasma displays, at 703 VA each, assuming they are continuous (3+ hours) loads? (commercial application)

3 x 703 = 2,109 VA. I would say this exceeds 80% of a 20 ampere CB, so cannot go on a 20 ampere CB. But, table 210.24 shows "maximum load" for a 20 ampere receptacle circuit to be "20 A" with no reference to 80%. Can I show (3) receptacles on a 20A branch circuit to feed these three displays??? 220.14(A) says I need to use the load of the appliance served - so I cannot use 180 VA.

As always, Thanks.
 
What makes you think they draw 703VA continuously?

TTBOMK, for a display (with no audio capability) to have continuous maximum current draw, it would have to display a continuous white screen. That would sort of defeat the purpose of a display... unless you simply use it as a light source (there are much cheaper methods :p).
 
20A would be the permissable load using the following.

210.19 Conductors ? Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity
not less than the maximum load to be served. Where
a branch circuit supplies continuous loads or any combination
of continuous and noncontinuous loads, the minimum
branch-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.

210.20 Overcurrent Protection. Branch-circuit conductors
and equipment shall be protected by overcurrent protective
devices that have a rating or setting that complies
with 210.20(A) through (D).
(A) Continuous and Noncontinuous Loads. Where a
branch circuit supplies continuous loads or any combination
of continuous and noncontinuous loads, the rating
of the overcurrent device shall not be less than the noncontinuous
load plus 125 percent of the continuous load.
 
What makes you think they draw 703VA continuously?
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I like your thinking, but the nameplate says 703 VA (or so I am told) and I have to use that value per 220.14(A) regardless of any fluctuation in actual load current there may be.

jumper said:
20A would be the permissable load using the following.

210.20 Overcurrent Protection. Branch-circuit conductors
and equipment shall be protected by overcurrent protective
devices that have a rating or setting that complies
with 210.20(A) through (D).
(A) Continuous and Noncontinuous Loads. Where a
branch circuit supplies continuous loads or any combination
of continuous and noncontinuous loads, the rating
of the overcurrent device shall not be less than the noncontinuous
load plus 125 percent of the continuous load.
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Exactly - so a 20 amp circuit does not work based on 210.20(A), since 703 VA x 3 = 2109 x 1.25 = 2637 = 22 amp circuit required. I could use a 25 ampere circuit breaker - but 1) then I would have to use #10 AWG, and 2) I cannot put a 20 amp receptacle on a branch circuit larger than 20 amp. (The code seems silent on the idea of a receptacle on a 25 ampere circuit - see table 210.21(B)(3). Or maybe I can put whatever receptacles I want on a 25 ampere circuit, since the table does not restrict me to 25 ampere receptacles!!! 240.6 says 25 amperes is a 'standard rating'....)
 
A television is not a continuous load. It would have to run at maximum output, meaning both video and audio at maximum output for three or more hours.
 
jumper said:
The code is not silent on the issue. Neither the table or the associated article will allow 20A receptacles on a 25A breaker.
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Disagree.

Neither table in 210 addresses 25 ampere circuits. Both tables give explicit ampere ratings - not ranges or min-max. I see nothing in the text of the article that addresses 25 ampere circuits. If a single receptacle, it would have to be rated not less than the circuit rating - but in this instance, there would be three receptacles. So, as there can be multiple 15 ampere rated receptacles on a 20 ampere circuit, I see nothing that would prevent multiple 20 ampere receptacles on a 25 ampere circuit.
 
infinity said:
A television is not a continuous load. It would have to run at maximum output, meaning both video and audio at maximum output for three or more hours.
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These are not TVs. They are plasma displays, in a commercial application, which will be on for 8 hours or so per day. I do not believe there is any audio component.

Not that I know that the load will fluctuate, but what code provision allows less than 125% branch circuit rating if the load fluctuates?

For example, when I design for a 5 HP motor, I have to design based on the nameplate HP. I can't look at the brake horsepower and design for say 3.75 HP.... Or design a lighting circuit for the load dimmed to 50%, etc.
 
iggy2 said:
These are not TVs. They are plasma displays, in a commercial application, which will be on for 8 hours or so per day. I do not believe there is any audio component.

Not that I know that the load will fluctuate, but what code provision allows less than 125% branch circuit rating if the load fluctuates?

For example, when I design for a 5 HP motor, I have to design based on the nameplate HP. I can't look at the brake horsepower and design for say 3.75 HP.... Or design a lighting circuit for the load dimmed to 50%, etc.
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The definition of continuous load from article 100 dictates that the maximum load must be sustained for 3 hours or more.

Continuous Load. A load where the maximum current is
expected to continue for 3 hours or more
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iggy2 said:
Disagree.

Neither table in 210 addresses 25 ampere circuits. Both tables give explicit ampere ratings - not ranges or min-max. I see nothing in the text of the article that addresses 25 ampere circuits. If a single receptacle, it would have to be rated not less than the circuit rating - but in this instance, there would be three receptacles. So, as there can be multiple 15 ampere rated receptacles on a 20 ampere circuit, I see nothing that would prevent multiple 20 ampere receptacles on a 25 ampere circuit.
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Seems pretty clear to me that 20A receptacles on a 25A circuit are not allowed as that circuit/ampere value is not listed in the table. 15A receptacles on a 20A circuit are listed.

210.23(B)(3) Receptacle Ratings. Where connected to a branch circuit
supplying two or more receptacles or outlets, receptacle
ratings shall conform to the values listed in Table
210.21(B)(3), or, where rated higher than 50 amperes, the
receptacle rating shall not be less than the branch-circuit
rating.
 
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