I'm doing a job for a church and need to run a few 20a cicuits for lighting and cameras, probably 150 ft or more. Wondering if I should size up to # 10 wire?

From http://www.dot.state.ak.us/anc/Engi...Construc tionStds/16120WireandCable.pdf

• On 20A circuits, with one-way conductor lengths measured from panel to farthest receptacle, or center of lighting string (as applicable):
  1. #10 AWG for 120V circuits of 75 feet to 120 feet.
  2. #8 AWG for 120V circuits of 120 feet to 200 feet.
  3. #10 AWG for 277V circuits of 130 feet to 215 feet.
  4. #8 AWG for 277V circuits of 215 feet to 330 feet.

[This message has been edited by Bjarney (edited 02-06-2004).]

Voltage drop is dependant on the load. You should figure the voltage drop per the N.E.C., not some arbitrary standard. JUST BECAUSE IT IS PUBLISHED ON THE INTERNET, THAT DOESN'T MAKE IT RIGHT!
Certainly, if a client has a standard in place, you should comply with it. The document that is hyperlinked isn't even approved, it's a draft. I doubt your church conforms to a state D.O.T. DRAFT standard. This will assure a safe, proper installation.

Seeks,

did you find anything technically wrong with the information Bjarney provided?

seeks, you are welcome to propose something different. I don’t see where the posted material is a draft—apologies for my oversight. My purpose was to point out that one organization has significant experience in this area, and has found that their problems with voltage drop in receptacle circuits are reasonably minimized by using some basic considerations.

Obviously, cord-connected loads vary widely, and this may be one reasonable compromise. The material was not claimed to be a cure-all. Clearly the suggested is by no means mandatory anyplace else. But—a church could have their own ¾-horsepower floor waxer in a hallway or 1440-watt portable heater in a nursery, powered from a multi-outlet circuit. {Er, take your Ritalin, Garth.}

I'm with Seeks on this one. There is no blanket rule that can address voltage drop, as it is dependant upon the load served.

What seeks says is correct, but IMO he was a little aggressive with his condemnation of Bjarney's info.

I agree with Bjarney's figures, for GP circuits I like to assume 80% loading of the branch circuit and staying around 3% drop.

Hey guess what, thats what those figures from Bjarney result in.

Most of the jobs I work have something in the spec. about moving up a size for every 75' to 100' of additional one way length.

Sure if you know all you are powering is a security camera transformer you could run 1000' with 12 AWG @ 120, but for general use in these branch circuit sizes, you will not break the budget figuring the load at 80% of the branch circuit size.

Start talking feeders and I would want to know the load not guess at it.




[This message has been edited by iwire (edited 02-06-2004).]

aldav53

In case you are not familiar with voltage drop there are many variables.

I will give you some examples to show how much the load effects the length for a given amount of voltage drop.

Say we allow 3% voltage drop on a 120 volt circuit wired with 12 AWG.

A 1 amp load on this circuit and we could run 900 feet one way.

A 5 amp load on this circuit and we could run 180 feet one way.

10 amp load on this circuit and we could run 90 feet one way.

20 amp load on this circuit and we could run 45 feet one way.

Bjarney;

That'll teach you for trying to help!

Just joking!

What Bjarney has posted will be of assistance in figuring general consideration points for voltage drop issues.
It's not the "Be-All, End-All" 100% rule document, it's only a helpful approach item.

Would like to know how one would "Figure Voltage Drop Per The NEC". Isn't this only an FPN in the NEC (NFPA 70), or did I miss the Article(s) with the Mandatory Rules of Voltage Drop (Shall / Shall Not rules).

Keeping voltage drop low is a Design issue, and done in the best interest for the Client.

Use of the percentages shown in the NEC's suggested examples (FPNs in Articles 210-19(a) and 215-2 of 3% from "Sub Panel" to load, and 5% total from Service / Power source to load), are general use guidelines which work well for common installations.

For "aldav53"'s situation, the text presented by Bjarney can be used to design these branch circuits with compensation for voltage drop, without having to perform the actual Math of a volts lossed calculation.

The lighting loads will likely be the higher loads, and the most noticably effected from voltage drop.

Are the Cameras just CCTV types, or are they something which draws upwards of 50 Watts each?
The latter example type Cameras might have maximum voltage drop specifications per the Manufacturer (available Line voltage minimums / maximums specs).

Not trying to be an a$$, just get ticked off when members try to help out, then later get toasted.

With that being said, does my Dicketry here in this message, qualify as poor excuse / approach?

Oh no, a Logical Paradox!!!

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Scott35

I would also consider the voltage coming in from the poco. Alot of the newer transformers supply you with a solid 125/245 system single and 125/215 3 phase, at least around here. Also we wire alot of boat lifts that are anywhere from 100 ft. to 1000 ft. or more from the main power. We generally go by the specs on the motor which includes a v/d allowance for 120/230. And everyone I have seen allow more than the 3-5%.

Bjarney's chart is close. While I agree the
voltage drop is load dependent you have to
consider the fact that if you install a 20 amp circuit someone is going to try and plug in a 20 amp load. VD=2k*L*I/CM
where: VD= voltage drop
L= length of conductor
I= current in circuit
CM= area of conductor in circular mill
K= resistivity of the conductor- 11
for copper
Thus in this case:
VD=2(11)*150*20/16510=
a voltage drop of 3.99 volts for no.8 wire
A little over 3% for 120 volts or 3.19 volts
for an 80% load.

Thanks for the input everyone. The loads on the screens and cameras will not be much, but the loads on the stage lighting will be high. I will run everything in # 10 wire to be on the safe side.

10 awg. is a lot better than 12 awg. but you
will still have a 5 volt drop with an 80% load. If that is acceptable then you are good
to go.

Bjarney - I apologize for sounding harsh. I did not intend it that way, but after reading it again, I realize I was. (Crusty, grumpy electrical guy, sound familiar?) I guess my point was this: Doing something because you read it somewhere can be really dangerous. If it goes wrong, it is your butt that is exposed, not some anonymous author. No one knows the exact particulars of your installation except you. Always check information, and perform your own calc's, and read the N.E.C.

again - my apologies for being rude.

Article 210.19(A)(1) requires branch circuit conductors to "have an ampacity not less than the maximum load to be served." A little later in the same article it requires branch circuits to "have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load."

(As an aside: What load is there if not continuous, noncontinuous or none? Or any combination of these?)

I deduce from this that the intent is to require the electrician to consider voltage drop. This is supported by the FPN that comes out with the familiar 3%, 5% overall rule of thumb.
Same thing in 215.2 for feeders.

That said, the NEC has not left us in a vaccum about the formulas either. They have provided us with Tables 8 and 9 in Chapter 8.

Use ohms law: E=IxR, or with Table 9: E=IxZ.
The tables provide resistance of the wires per 1,000 feet. To compute the resistance of your wire run, simply divide the total length by 1,000.

For a single phase circuit, there and back, the allowable length from the load to the supply to limit the VD to 3% would be equal to: 15xE/IxR. Obtain the R from the value given by Table 8 across from your chosen wire size.

Have you considered running 240V circuits, either by using multiwire branch circuits, or by installing a subpanel? To supply a given number of watts at 240V rather than 120V means that your current is halved at the same time that the headroom for voltage drop is doubled.

seeks, no offense taken, and none intended from this end. Many organizations publish their CSI-format specs on the web, and while not statutory, give an idea of what works in their area. That was my point.