Voltage drop calculations for test

[Joe perkins]

When figuring voltage drop calculations for the test do you use the voltage that is actually stated or do you use nominal voltages

 

[roger]

Unless there were or are specific instructions to the contrary, you should use the voltage in the question.

Roger

 

[weressl]

When figuring voltage drop calculations for the test do you use the voltage that is actually stated or do you use nominal voltages

It is up to the fairness of the instructor.:grin:

At point of delivery - main panel, switchgear - you would use the nominal system voltage and allow -2% maximum. At the distribution level delivery point you would use the allowed voltage drop allowed at that point - that would be 2% - and use the maximum -3% for the voltage to be delivered to the user terminals.

 

[roger]

At point of delivery - main panel, switchgear - you would use the nominal system voltage and allow -2% maximum. At the distribution level delivery point you would use the allowed voltage drop allowed at that point - that would be 2% - and use the maximum -3% for the voltage to be delivered to the user terminals.

These numbers, (2% & 3 %) are not requirements only suggestions.

I would think in an exam the question would be more on the line of "what is the VD of a circuit..." or "What is miniumum size conductor for a VD of _____ in a feeder 1500 feet in length...


Roger

 

[weressl]

These numbers, (2% & 3 %) are not requirements only suggestions.

Roger

These numbers are ANSI/IEEE requirements that are designed to allow the manufacturers uniformly design equipment that will operate within the expected voltage variations and allow the desing engineers to appropriately design the sytem with the load flow studies.

 

[bth0mas20]

voltages

voltages

220.5 (A) may help you.

 

[roger]

These numbers are ANSI/IEEE requirements that are designed to allow the manufacturers uniformly design equipment that will operate within the expected voltage variations and allow the desing engineers to appropriately design the sytem with the load flow studies.

That's fine and dandy but, most (I would say all) electrical exams don't give a hoot about a manufactures design criteria.

Another point is that most electrical exams are dealing with theory and NEC requirements, not ANSI/IEEE requirements.

Roger

 

[weressl]

That's fine and dandy but, most (I would say all) electrical exams don't give a hoot about a manufactures design criteria.

Another point is that most electrical exams are dealing with theory and NEC requirements, not ANSI/IEEE requirements.

Roger

Oh really? I did not know that NEC was elevated to the rank of an engineering Standard. Nor do I expect any electrical examiner to divorce themselves form reality.

The design criteria is imposed upon the manufacturer by the existence of the ANSI Standard, they may add even narrower design criteria with additional NEMA standards so the USER can expect uniform performance. NEC did and does not establish voltage drop allowance levels.
It would behoove any electrical educator to explain to the electricians how the whole system works, how utilities generate power, what regulations guide them, what happens when it is distributed - yet another entity -, the local independent distributors, the users, the engineering firms role to assure the quality of power delivered, how OSHA, NFPA fits in and so on. When one clearly understands his or her role in the system as a whole, could perform their work with more responsibility, and understand where their role starts and stops and who is responsible for what. The questions and comments on this site testify that there is a mass confusion in this area and that results in a lot of misunderstanding and misconception.


(as he gingerly steps off the soapbox as the audience errupts in..

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no, a hearthy laughter......

 

[roger]

Oh really? I did not know that NEC was elevated to the rank of an engineering Standard.

How do interpret my post as saying it was, reread it off of your soapbox, the elevation may be making you light headed.

The design criteria is imposed upon the manufacturer by the existence of the ANSI Standard, they may add even narrower design criteria with additional NEMA standards so the USER can expect uniform performance.

Once again, that's fine and dandy but, I doubt any Journeyman exam takes this into a very deep consideration or even cares.

NEC did and does not establish voltage drop allowance levels.

I think I was the one who pointed that out earlier.

It would behoove any electrical educator to explain to the electricians how the whole system works, how utilities generate power, what regulations guide them, what happens when it is distributed - yet another entity -, the local independent distributors, the users, the engineering firms role to assure the quality of power delivered, how OSHA, NFPA fits in and so on.

And I think most do.

When one clearly understands his or her role in the system as a whole, could perform their work with more responsibility, and understand where their role starts and stops and who is responsible for what.

I pretty much agree with this.

The questions and comments on this site testify that there is a mass confusion in this area and that results in a lot of misunderstanding and misconception.

Uh, what, I don't understand. :grin: (sorry, cuoldn't help myself)

(as he gingerly steps off the soapbox as the audience errupts in..

a hearthy laughter......

I know I did.

Roger

 

[bhsrnd]

The design criteria is imposed upon the manufacturer by the existence of the ANSI Standard, they may add even narrower design criteria with additional NEMA standards so the USER can expect uniform performance.

Unless I'm misunderstanding you the NEC is not intended to be a design standard. See 90.1(C). An installation code yes, but not a design standard. ANSI/IEEE may be what manufacturers have to follow when designing their products as well as the NEC, when applicable.

Oh really? I did not know that NEC was elevated to the rank of an engineering Standard.

I don't know about the omnipotence as you had stated, but yes the NEC is used by ECs/engineers when designing electrical layouts, etc..

Call it right...call it wrong...but it's just my $0.50 Now I'm gettin outta this before I get something thrown at me!

 

[weressl]

These numbers, (2% & 3 %) are not requirements only suggestions.

I would think in an exam the question would be more on the line of "what is the VD of a circuit..." or "What is miniumum size conductor for a VD of _____ in a feeder 1500 feet in length...


Roger

The numbers ARE requirements, not suggestions. Otherwise you have no business in calculating volatge drop to begin with.

If you don't know what the answer should be how do you judge what a reasonable result would be?

If you get a 60V voltage drop on a 480V circuit, not knowing that 5% max. is alloved, would force you to recheck your calcs as to where you made the error or conclude that this was one of those stupid trick questions and you supposed to say; increase the conductor size, voltage drop too great.

 

[roger]

The numbers ARE requirements, not suggestions.

Sorry Laszlo, you are wrong.

Remember, this is a code forum and the NEC is the code most talked about here (not saying discussions outside of code do not have a place here, they certainly do) and as far as the NEC is concerned 2% and 3% VD numbers are not part of the NEC, they are only suggestions/recommendations that show up in a FPN, for example. 215.2(A)(3)

FPN No. 2: Conductors for feeders as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, will provide reasonable efficiency of operation.

Now for clarification of what part a FPN plays in the NEC

(C) Explanatory Material Explanatory material, such as references to other standards, references to related sections of this Code, or information related to a Code rule, is included in this Code in the form of fine print notes (FPNs). Fine print notes are informational only and are not enforceable as requirements of this Code.

Roger

 

[weressl]

Sorry Laszlo, you are wrong.

Remember, this is a code forum and the NEC is the code most talked about here (not saying discussions outside of code do not have a place here, they certainly do) and as far as the NEC is concerned 2% and 3% VD numbers are not part of the NEC, they are only suggestions/recommendations that show up in a FPN, for example. 215.2(A)(3)


Now for clarification of what part a FPN plays in the NEC

Roger

I beg to differ.

This is a Mike Holt's Forum that has NEC as ONE of the subgroups. The title of this subgroup is Electrical Calculations/Engineering, therefore when one refers to engineering and national standards it is not only appropriate but prevalent to the subject.

 

[roger]

Laszlo, most people find these forums from this starting point (notice the header) which is recognized as the

and would most likely be accessed by clicking on the "code forum" icon in the left hand column.

With that said, I don't know what the OP was referring to as far as the test he was talking about any more than you do but, I would think it had to do with a electrician level exam and the NEC.

I provided the information from the NEC to back up my statements and all you have provided is that you say it "is an ANSI/IEEE requirement", this may very well be true, but I must ask that you tell us exactly where we can find this requirement so that we may all be privy to where we can read it for ourselves.

Once again, it is not an NEC requirement.

Roger

 

[bhsrnd]

Enforcable??

Enforcable??

Playing devil's advocate, I see both sides of the discussion here and have to ask...Can, at any point in the design process, ANSI and/or IEEE standards be enforced on the final "product" for residential, commercial or industrial installations before drawings (and the final installation) will be approved or is it only NEC codes that can/will be enforced? My question is solely referring to the installation and wiring of (and not the manufacturing aspect of) equipment. I know there are additional building codes, etc.. which would be enforcable but I'm just asking about the discussion at hand.

I feel the answer to that question may clear things up in this thread. Either that or I'm in for the forum tounge lashing of my life.

 

[roger]

Vaughn, it would have to do with what is code (as in local rules) in the area and if a voltage drop limit were included in the design. The problem here is, what would be the starting voltage measured at what point in the distribution. One buildings voltage may be measure at 127V L-N at the Main and down the street another building may be 117v

As far as the NEC, voltage drop limits are not enforcible.

IMO, a designer would better off to use 220.5 and include a minimum voltage allowed from these numbers in the plans but, the designer may end up in a war with the POCO in the end or have step up transformers sitting everywhere for voltage correction purposes.

Now, actually none of this has anything to do with the OP's question, but I guess this is no different than any other thread.

Roger

 

[don_resqcapt19]

Laszlo,
Where do you start the calculations when the Illinois Commerce Commission permits a range of 113 to 127 for a circuit that we would call 120?

410.300(a) Standard voltage. Each entity supplying electrical energy for general use shall adopt a standard service voltage of 120 volts (when measured phase to neutral) and shall maintain the service voltage within the allowable variations from that value at all times.
(b) Allowable voltage variations. For service rendered at the standard service voltage, voltage variations as measured at any customer's point of delivery shall not exceed a maximum of 127 volts nor fall below a minimum of 113 volts for periods longer than two minutes in each instance. For service rendered at voltages other than the standard voltage value, voltage variations as measured at any customer's point of delivery shall not exceed 10% above or below the service voltage for a longer period than two minutes in each instance.

Don

 

[George Stolz]

Laszlo, I can virtually guarantee you that the authors of the electrical tests for electricians do not expect their applicants to be familiar with or even contemplate the existence of IEEE standards. They are not mentioned on any of the state's material for reference in regards to the tests.

Advice to study those references, or try to encorporate them into the test-taking process, is just flat out bad advice. The person looking for help from this site applying that information will likely get the test question wrong (since the author of the test did not consider it), which is 100% the opposite of the desired result we'd like to see.

 

[WDeanN]

Laszlo,
As much as I'd like to agree with you, I must go down with Roger here as well.
The IEEE documents are recognized world-wide as the best electrical engineering documents to be found. They form the basis for many of the other codes and standards that are used. They are referenced in nearly every other electrical document recognized by the industry. They are used by nearly every electrical engineering firm and school in the states.

I don’t think they are enforceable in and of themselves, however. Even the titles of the color book series suggests this. “The IEEE Recommended Practice for …”

Since I primarily do arc flash these days, I’ll go back to one of the controversies currently in the works in that field. IEEE wrote the standard in arc flash calculations, IEEE 1584. The NFPA 70E is an OSHA enforceable document that references 1584. It is NOT the only calculation method referenced, however. NFPA 70E only says a study should be performed. They then go on to demonstrate about three or four different methods to calculate the arc flash energy. The 1584 method is not one of those that is illustrated in the appendix, even though it is the industry standard.

This is all a long way to say that the IEEE documents are not enforceable by themselves, so, unfortunately, you’ve missed the boat on this one.

To return to the original question, though, I would use the voltage stated.