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Electrical FAQs

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wyliesdiesels

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Welcome All

I have started this sticky as an FAQ thread for info on the basics that are encountered countless times every week on here.

Hopefully this will help some.

If u have a topic request, go ahead and post it.

And if you have an FAQ you would like covered let me know....

Or if you feel brave enough, go ahead and post it....

And an FYI- I'm in the US, so what I post is based on the NEC and mostly applies only to the US....
 
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wyliesdiesels

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3-wire feeder VS 4-wire feeder

First topic for this sticky is one that is beat to death :deadhorse every weak- the 3-wire vs 4-wire branch feeder.

The following pics are here to help those who are visual learners.

3-wire feeders to detached structures that had no other parallel metallic pathways(eg. conduit, water and gas piping, communication cabling, etc.) were allowed up until the 2008 NEC code cycle.

From then on, 4-wire feeders have been required.

4-wire feeders to panels in attached structures have always been required.

3-wire feeder to DETACHED building(no longer allowed as of 2008; existing feeders are grandfathered in as long as there are no parallel metallic pathways between the buildings):

1961d1199122156-detached-garage-sub-panel-grounding-q-3-wire-feeder-detached.jpg


4-wire feeder to DETACHED building:

1215778178-ground-rod-not-4-wire-subpanel-detached.jpg

4-wire feeder to panel in ATTACHED structure:

ng-subpanel-main-panel-4-wire-feeder-same-building.jpg
 
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wyliesdiesels

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Grounds, EGCs, Grounding Electrodes, Grounding Rods- whats the difference??

Another topic often misunderstood and confusing for many:

The Difference between grounds, officially known as grounding conductors or equipment grounding conductors(EGCs) and ground rods aka grounding electrodes.

This is a confusing topic for many, maybe because the two share the same name.

However, they have very different but distinct functions and both are required.

Instead of me trying to do a nice long write up, I will give a summary and then let a well written article @ Electrician Talk explain things in greater detail.

Grounds(EGCs) are there to provide an effective low impedance fault current pathway. This is so breakers will trip when metallic objects and pathways that shouldn't be energized, become energized.

Grounding electrodes, on the other hand, are primarily for grounding lightning as well as limiting the voltage to ground potential and providing a shunt for primary voltage should primary lines ever contact secondary lines.

Primary distribution lines(depending on the PoCos distribution system) often include neutrals that are bonded to earth via a grounding electrode at the base of telephone poles. At the substations, the breakers and re-closers are bonded to earth as well via ground rods. When and if a primary line contacts a bonded metallic object on the pole, the breaker for that circuit trips due to the fault.

If u have ever seen lineman working on lines that are de-energized, u will see a large wire connecting all primary lines to a temporary ground rod pounded into the ground next to the pole. This is for their safety should someone at the grid control turn on a circuit that shouldn't be on, the breaker will trip due to the bond to earth.

Now for the article. Enjoy:

http://www.electriciantalk.com/articles/the-confusion-of-the-term-grounding/
 
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Shiftless

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Re: Any admins available?

Great job so far wylie...keep 'em coming :thumbup:

Have you thought of a good thread title for the admins to change it to?
 
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pstemari

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Norcal

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wyliesdiesels

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Norcal said:
Here is a list of GFCI requirements & the years where each change occurred.

http://jerrypeck.com/IFCN/Other Items/_GFCI_requirement_page-2014.pdf

Somewhere he has a chart for snake oil (AFCI) requirements also, when it's found, it will be posted.

Edit: here is the list for the snake oil/AFCI requirement history.

http://www.constructionlitigationconsultants.com/_AFCI_requirement_page-2014.pdf
Click to expand...

Excellent Norcal! :thumbup:

I didnt see this til just now!

Should help with all the questions about GFCI requirements...
 
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ddawg16

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Norcal said:
Here is a list of GFCI requirements & the years where each change occurred.

http://jerrypeck.com/IFCN/Other Items/_GFCI_requirement_page-2014.pdf



Somewhere he has a chart for snake oil (AFCI) requirements also, when it's found, it will be posted.

Edit: here is the list for the snake oil/AFCI requirement history.

http://www.constructionlitigationconsultants.com/_AFCI_requirement_page-2014.pdf
Click to expand...

I dodged a bullet on this one.

At the time I started my 2-story addition, my area was still on the 2008 cycle....so I only had to do AFCI's in the new bedrooms.

With that said....I've had 0 issues with my AFCI's. And....when I did have a broken wire....they tripped on it. Except for that wire, I've never had a false trip.
 
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L5wolvesf

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akpingel said:
What year NEC code has my state adopted?

http://www.nfpa.org/nec/nec-adoption-and-use/nec-adoption-maps

nec-in-effect-0917.jpg


nec-in-process-0917.jpg
Click to expand...

It is interesting, but not surprising, that Arizona is doing things backward. So I got curious and searched to see if AZ has any kind of requirements. They have left it up to each county or city/town to handle it.

Here is the best thing I found that gives a general clue as the what is required where.

https://www.thebalance.com/arizona-building-codes-specific-county-requirements-844708

Thanks for putting this up great idea. But I'll probably still have dumb questions, :dunno:
 
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wyliesdiesels

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Yes i know.

Life has gotten too busy for me to be able to write anymore at the moment.

Rest assured i havent forgotten about my project here.

Will get back to it eventually...

Thx for the patience...
 
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Zeke

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Since T-12 conversion to LED info is buried somewhere deep in a sticky somewhere, I suggest that it become a FAQ.

I also suggest that a mod clean up this thread and delete any post that doesn't answer a question, including mine here, as soon as the info is posted.
 
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Dh3256

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karl1672 said:
If it is OK, then what's the point of isolating them on a sub-panel?
Click to expand...


Safety.


The EGC (Equipment Grounding Conductor - what many call "ground", the green or bare wire) should not have any current flowing in it, and the electrical system is designed for that. Given zero current flow, in the event of a fault the EGC is the best path to ground and electricity will flow through that conductor rather than a person, for example.


You are taking a DC measurement on an AC circuit, which will not give correct results. The DC meter will seen the single point ground connection at the main panel.


Regarding the AFCI, it thinks the ECG and neutral are reversed because it senses higher voltage on the ECG than neutral. The most common cause is that the neutral is disconnected, has an oxidized connection, etc. Check your neutral for issues.
 
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The Cobbler

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Hope this is useful
Common Power Cords (NEMA 120V 15A)

NEMA 1-15P: Two-prong plug.
NEMA 1-15P: Two-prong plug.
The Non-polarized version has two equal straight blades.
The Polarized version features 2 blades with one being wider.

NEMA 1-15R: Two-prong receptacle.
NEMA 1-15R: Two-prong receptacle.
'receptacle' connectors would have holes that would accept a plug with prongs to be inserted.

NEMA 5-15P: Three-prong plug.
NEMA 5-15P: Three-prong plug.
Features 2 straight blades with a third round or U-shaped ground pin. The ground pin is longer than the two blades which ensures the device is grounded before the power is connected.

NEMA 5-15R: Three-prong receptacle.
NEMA 5-15R: Three-prong receptacle.
This will be what you would typically see in your home (USA & Canada) as a power outlet or on the female end of a power extension cord. You would also see this as the receptacles on a surge strip.

Laptop

C7: Figure Eight.
C7: Figure Eight.
Non-Polarized connector featuring a 'figure eight' shape with two holes.
Although we list as a notebook power cord, the C7 connection is used in many devices.

C7PW: Polarized connector.
C7PW: Polarized connector.
Has basically the same shape as C7, but instead of rounded 'figure 8' style, one of the sides is flat, allowing the connector to only be inserted one way.

C5: Three-pin connector.
C5: Three-pin connector.
Typically connects a laptop power brick to a wall outlet.
Polarized connector. The shape of the connector prevents shocks. Sometimes called a 'Mickey Mouse' cable due to the resemblance to a certain cartoon character's silhouette. Also called "cloverleaf."

Computer/Monitor

C13: Three slot connectors.
C13: Three slot connectors.
Features a dog-ear shape and the three slots are in a staggered vertical orientation.

C14: Three prong inlet receptacle.
C14: Three prong inlet receptacle.
Features the same dog-ear shape as the c13 with 3 blades in a staggered vertical position.

Server/Appliance

C19: Three-slot connector.
C19: Three-slot connector.
Used in Enterprise-class servers and data center rack-mounted PDUs.
Rectangular with four rounded corners, and three staggered blades in the same orientation (horizontal).

C20: Three-prong Inlet receptacle.
C20: Three-prong Inlet receptacle.
Rectangular with four rounded corners, and three staggered slots in a recessed receptacle (horizontal).
 
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Terry D

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PNWguy said:
Great thread!
Can I request a chart or formula for sizing wire based on load and distance?
Click to expand...
Go to your app store and search southwire voltage drop calculator. I have been trying to figure out how to forward a link on my cell phone, but can't for the life of me. Anyway, this app will help you, or just google it.

Sent from my SM-G960U using The Garage Journal mobile app
 
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wyliesdiesels

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Terry D said:
Go to your app store and search southwire voltage drop calculator. I have been trying to figure out how to forward a link on my cell phone, but can't for the life of me. Anyway, this app will help you, or just google it.

Sent from my SM-G960U using The Garage Journal mobile app
Click to expand...


There was some errors on that app so you have to watch out. I dont know if they were fixed
 
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wyliesdiesels

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Wow its been awhile since I posted a comment on here (almost 2 years). Life has gotten very busy for me but I wanted to drop in and post a short one to keep the thread alive.

In the future, I'll do a welder circuit sizing post & motor circuit sizing post.

Today, I'm gonna touch on sizing circuits (mainly comes up with sizing branch feeders) for voltage drop. I see this topic come up numerous times every week.

There are numerous online calculators but myself & others have found bugs & errors in some of them so I don't trust them. Plus the math is very easy so it's not like anyone couldn't do it themselves.

so here is the equation (2 ways to do it; result is the same):

2 x I x R / 1000 x FT = VD / 240 = voltage drop % (at 240v)

2 x I x R x FT / 1000 = VD / 240 = voltage drop % (at 240v)

I= amps

R= resistance of wire- Found in NEC, chapter 9, table 9 (you can find it on a google search or get it from the NFPA.org site with a a free account). Look under the "effective Z" column for the correct type of wire & conduit. Then look for the correct size of wire in the rows. When you find the correct box of numbers, use the lower number in the boxes, which represents "ohms to neutral per 1000' "

FT= footage (one way length of wire)

When you input the values for I, R and FT, you will get the voltage drop at that amperage. Then, you take this number and divide by 240.

Let's do an example using 90a, 2/0 AL & 285'

2 x 90 x .16 = 28.8
28.8/1000 = .0288
.0288 x 285' = 8.208v
8.208v / 240v = 3.42% total drop for 90a on 285' of 2/0 AL

EDIT: Table 9 in chapter 9 can be found on either the NFPA website via the free access to the NEC (NFPA 70) or here on pg. 11

http://www.superb.org/power/nec tables.pdf
 
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MDchanic

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So, Wylie, before you disappear for a while, here's a question I've been unclear about:

Suppose I'm running 450' of AL in PVC in the ground, rated for 100A at about 3-4% drop (but not ever planning to draw more than about 50A).

I'm running 2 hots, a neutral, and a ground, at 240v between the hots, 120v hot-to-neutral.

Do I figure this as a 240v circuit, or do I figure it as, in essence, 2 120v circuits, which it would seem to be?

The reason, of course, is that the percentage drop will be much greater, and require a larger gauge cable, if the voltage is lower, so I'd like to believe it's a 240v calculation, where I could comfortably run 4/0 AL.


Okay, actually two questions:

When buying the cable for this undertaking, do all 4 conductors need to be 4/0, or can it be 4/0, 4/0, 4/0, 2/0, or similar?


Thanks,

- Eric
 
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Toomanytools?

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Just to touch on this (but not ever planning to draw more than about 50A).
Maybe you don't but what about the next guy? Just saying.
 
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MDchanic

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The next guy will still be within the required 3-4% voltage drop, so he'll be okay.

Also, the next guy will probably put solar panels on the roof (if I don't first) - 74x27' facing due south will make enough power to ship back up to the house through the same wires...

- Eric
 
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mendozer

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Thanks for the information on this thread, it's a pleasure to learn these things!
 
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MDchanic

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Thank you, Alfred E. It's always good to have some idea of what the latest rules will be.

And let me take this moment to re-ask the two questions I posted above four months ago:

1. Suppose I'm running 450' of AL in PVC in the ground, rated for 100A at about 3-4% drop (I'm not ever planning to draw more than about 50A, but may want to use the drop one day to feed solar up to the house, when solar gets cheap enough, so I don't want to under-size it).

There will be 2 hots, a neutral, and a ground, at 240v between the hots and 120v hot-to-neutral.

For purposes of calculating voltage drop over a distance, do I figure this as a 240v circuit, or do I figure it as, in essence, 2 120v circuits, which it would seem to be most of the time?

- and -

2. When buying the cable for this undertaking, do all 4 conductors need to be 4/0 (or 250), or can it be 4/0, 4/0, 4/0, 2/0, or similar?

Thanks,

- Eric
 
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wyliesdiesels

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MDchanic said:
Thank you, Alfred E. It's always good to have some idea of what the latest rules will be.

And let me take this moment to re-ask the two questions I posted above four months ago:

1. Suppose I'm running 450' of AL in PVC in the ground, rated for 100A at about 3-4% drop (I'm not ever planning to draw more than about 50A, but may want to use the drop one day to feed solar up to the house, when solar gets cheap enough, so I don't want to under-size it).

There will be 2 hots, a neutral, and a ground, at 240v between the hots and 120v hot-to-neutral.

For purposes of calculating voltage drop over a distance, do I figure this as a 240v circuit, or do I figure it as, in essence, 2 120v circuits, which it would seem to be most of the time?

- and -

2. When buying the cable for this undertaking, do all 4 conductors need to be 4/0 (or 250), or can it be 4/0, 4/0, 4/0, 2/0, or similar?

Thanks,

- Eric
Click to expand...

Why couldnt you start a new thread 4 months ago?

This sticky was created for general FAQs not individual situations.
 
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MDchanic

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My questions are general FAQs:

1. When calculating the voltage drop over a distance, four factors are used:
Conductor material, Conductor diameter, Conductor length, and Circuit voltage.
(You may also add in a fifth factor, heat generation within a conduit, but for a feed to an outbuilding, this is not generally needed.)
Of those four factors, wire gauge, wire length, and wire material are all obvious, but since the average power feed is 3- or 4-wire 220/110, and since most electrical equipment used (other than, say an air compressor, welder, or lift) will draw 110v,
Does one make the calculation using 110v or 220v as the nominal voltage?

- and-

2. When feeding power to an outbuilding from the main entry panel of a house, using four-conductor cable with separate neutral and ground, as required by the electrical code, can the cable have one conductor smaller (such as 4/4/4/2, which seems to be commonly available), or must they all be the same size (such as 4/4/4/4, which seems to be less common)?

These both seem to me to be common general questions that anyone who is running power to a outbuilding (such as... a garage) might ask and would need to know, but perhaps I am mistaken and they are extremely specific.

Regardless, I will not repeat them.

- Eric
 
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alfredeneuman

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MDchanic said:
Does one make the calculation using 110v or 220v as the nominal voltage
Click to expand...
Neither. In the case that you mentioned, a 4 wire 120/240v circuit should be figured at 240v for VD. With individual branch circuits, the VD should be figured at whatever voltage the circuit is operating (120 or 240).
(EDIT) There's no such thing as 110 or 220 in the US
 
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MDchanic

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Good.

I had used either 240 or 220, but I just wanted to be sure, because, obviously, the voltage drop over a distance is twice as large at 110/120v as at 220/240v.

Sometimes these doubts creep in after you think you've got the whole thing figured out.

Thank you.
 
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