Ampacity Question

[One-eyed Jack]

I understand that part. But what I'm saying is we are limited to just one TV set (#4 THHN), not all that are available (16 to 2,000kcmil, and all types of insulation).

Right we have 76 amps allowable ampacity. See my other post and you will see that we have in essence applied a double derate in that we can only have 60.8 actual load amps on this wire. We still have a maximum allowable circuit ampacity of 76. We start with this value because of the 4 ccc. We must stay at or under this value "after" we have applied all the other factors such as 125% for continuous load. This is not an actual derate but a safety margin that most call a derate.

 

[480sparky]

Right we have 76 amps allowable ampacity. See my other post and you will see that we have in essence applied a double derate in that we can only have 60.8 actual load amps on this wire. We still have a maximum allowable circuit ampacity of 76. We start with this value because of the 4 ccc. We must stay at or under this value "after" we have applied all the other factors such as 125% for continuous load. This is not an actual derate but a safety margin that most call a derate.

Lemme back up a bit. I'm saying I don't understand the 'buying any TV with a $700 bill" analogy because we're not buying 'any' TV. I'm only able to buy one TV.... Make #4, model THHN. By the question itself, I can't reach into my bank account, withdraw another $300 and buy Make #2, modell THHN.

Forgive me.... I like a good analogy better than anyone, but this one has me experiencing a

 

[One-eyed Jack]

Lemme back up a bit. I'm saying I don't understand the 'buying any TV with a $700 bill" analogy because we're not buying 'any' TV. I'm only able to buy one TV.... Make #4, model THHN. By the question itself, I can't reach into my bank account, withdraw another $300 and buy Make #2, modell THHN.

Forgive me.... I like a good analogy better than anyone, but this one has me experiencing a

LOL The Model TV has not been determined yet. Max allowable current = 76 amps; Max allowable spending on TV = 700.00 Now we determine the load and apply all factors to increase the MIN circuit ampacity and keep it under 76. Now we look at the TV's and apply all the bells and whistles keeping the price under 700.00.

 

[480sparky]

LOL The Model TV has not been determined yet. .........

But it has. #4 THHN.

 

[charlie b]

OK 480. Since I am the one who brough up the TV analogy, I am the one who must apologize for the confusion it has created. Let me try to clarify one aspect of my intent: The "which TV" part of the analogy was not intended to represent "which wire do we use." Rather, the notion of "how much will I spend on a TV" was suppose to represent "how much current am I going to run through the wire." Then, the "how much budget do I have available for this purchase" was intended to represent "how much current can the wire handle." The two notions are independent of each other.

 

[LarryFine]

Question for you: if you go to a new store, and you see a different model, and it has different features than the others you have seen before, and if it is at a different price than the others you have see, does that fact cause your budget to become different?

Usually. :roll:

 

[One-eyed Jack]

Usually. :roll:

Yeah we usually bite off more than we can chew. But the NEC is going to hold us to the budget.

 

[charlie b]

Hitchhiker's Guide to the Galaxy?

Life, the universe, everything: All you need to know is "42"! :grin:

(Aside and well OT: Have you read the recently published book six of the trilogy?)

 

[Dennis Alwon]

I guess we'll never get a total agreement on this one. To be honest, IMO, there have been very few questions on this cd that were ambiguous or just wrong. Some answers that were given was just carelessness.

For instance, one question was taken from the section below. One choice was 3 lbs and there wasn't any 6 lbs to choose. It is obvious what happened here.

410.30 Supports.
(A) General. Luminaires and lampholders shall be securely supported. A luminaire that weighs more than 3 kg (6 lb) or exceeds 400 mm (16 in.) in any dimension shall not be supported by the screw shell of a lampholder.

 

[gulkhan123]

You guys are confusing the "required ampacity" with the "available ampacity." When you calculate the ampacity of a conductor, you don't ask what the conductor will supply. It does not matter if it is a continuous load, or a harmonic load, or an intermittent load. The ampacity of a set of 4 current carrying THHN #4 copper will be 95*80%, or 76 amps, even if the actual total connected load is one amp of lighting.

Right Charlie. Better we can explain in this way: Ampacity of a conductor tells us the capacity of a conductor in amps that it can handle.And the allowable amapacity is the current in amps that is allowed to pass thru it after derating.
The available ampacity is the load amps at a certain time that is passing through a conductor.
gk

 

[gulkhan123]

You guys are confusing the "required ampacity" with the "available ampacity." When you calculate the ampacity of a conductor, you don't ask what the conductor will supply. It does not matter if it is a continuous load, or a harmonic load, or an intermittent load. The ampacity of a set of 4 current carrying THHN #4 copper will be 95*80%, or 76 amps, even if the actual total connected load is one amp of lighting.

We can add: The 'required ampacity' is the ampacity or the capacity of a conductor that is required to provide to hanlde a load. for eaxample, say the load is 10 amps, then we need a conductor that can handle the 10 amps so the 'required ampacity' of the conductor is at least 10 amps.

Is that correct?

gk