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Electrical service entry masthead (C) Daniel Friedman Electrical Service Entry Cable & Branch Circuit Wire Size FAQs

Electrical wire sizes & gauges vs Amps-ratings FAQs:

Questions & answers about electrical wire sizes, ampacity rating, run length, usage.

This article series gives Tables of Electrical Service Entry Cable Sizes, Electrical Circuit Wire Diameters, Circuit Ampacity, Allowable Voltage Drop, & Wire Size Increase based on Run Length assist in determining the electrical service size or other required electrical wire sizes at buildings.

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Electrical Wire & Service Entry Cable FAQs

Close-up measurement of the diameter of a #14 copper electrical wire (C) Daniel Friedman

These questions and answers about electrical wire sizes and servicve entry cable sizing were posted originally at SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS - be sure to review that article.

On 2019-07-05 by Anonymous

Depends as well on voltage

On 2019-07-04 by Oscarh

What size of cable is required for a load of 250w

On 2019-01-25 by (mod) -

Phil:

Agreed. You do not need to hire an engineer to get recommended cable sized for common lengths - that's the good news. The NEC and other sources include typical wire size tables matched to circuit amps or ampacity along with the maximum length before you should go to a larger wire size.

In MOST BASIC terms, voltage drop will be the product of

V drop = IxR

where

I = current measured in Amps
and

R = resistance measured in Ohms

A #14 copper wire rated typically for 15A in residential use (20A in some circumstances) has a resistance of 2.525 Ohms per 1000 ft of run or or 8.286 Ohms resistance per 1000 meters of length.

You can do the math from the formula above.

I think the nervousness about quoting a voltage drop to someone is that an engineer or other expert who actually understands wire and voltage drop is too aware that there are multiple factors that go into making a dependable statement that a particular wire choice is "safe" and NOBODY wants to kill you or burn down your house by giving an off-the-cuff, half-baked, generalized reply.

Examples include:

The specific wire product by the specific manufacurer and its temperature rating

The wire routing, above ground, underground, in particular spaces where temperature may be a factor

The wire insulation, exposure to elements, etc.

Number of phases used in the circuit - 1phase v 2 phase or 120V vs 240VAC for example.

And of course wire size, metallurgy or alloy, and insulation rating and age and condition.

Of COURSE the basic calculation of electrical wire voltage drop is widely known and given in texts and web articles

Metroidnet in Austrailia gives this simple explanation

To calculate the voltage drop for a circuit as a percentage,

multiply the current (amps) by the cable length (metres);

then divide this number by the value in the table.

For example, a 30m run of 6mm2 cable carrying 3 phase 32A will result in 1.5% drop: 32A x 30m = 960Am / 615 = 1.5%. - https://www.metroid.net.au/engineering/calculate-voltage-drop/

The maximum voltage drop considered acceptable in most applications is 5% from the point of supply.

On 2019-01-25 by Phil

It's sad that one needs to contact an engineer to calculate voltage drop for a length of cable... Is simple math no longer taught?

On 2018-11-05 by (mod) -

While Aluminum SEC and high-current circuit wiring is still permitted, I would prefer to use copper wire.

On 2018-11-05 by John

To run 350' for a 200 out breaker for house do you recommend 4/0 wire aluminum

On 2018-09-30 by (mod) - Definition of MCM as an electrical Wire Size & Conversion Chart: AWG, MCM, Inches and mm

Ricardo,

You may see MCM as part of the writing or stamping on some older electrical wires.

MCM is a term giving you the wire size or dimensions. You will usually find MCM wire sizes on large diameter wires such as service entry cabling.

Where "M" is an abbreviation for "Thousands"

and "CM" is an abbreviation for "Circular Mils"

1 M is 1 Mil or 1 1/1000 of an inch.

a 1/0 AWG electrical wire is about 106 mcm

a 4/0 AWG electgrical wire is then 212 mcm

To convert MCM to other dimensions I include a conversion chart provided by Anderson Power - cited below. [Click to enlarge any image]

Wire size conversion chart giving AWG, Metric mm2, Circular Mils, MCM and wire diameter in inches and mm Cited & discussed at InspectApedia.com original source Anderson Power Products andersonpower.com

Also see this helpful

On 2018-09-30 by ricardo - what does MCM mean when sizing wires

what is mcm mean

On 2018-09-23 by Dilip budhani

G floor and 1st floor 20 kw 2nd floor proposed 10 kw 100 meter length please suggest cable size from pole to meter aluminium or copper

On 2018-06-15 by (mod) -

Max

You are so right

thank you for your careful reading

I have corrected the text.

On 2018-06-14 by Max

The article says the photo looks like "2.5 mm" wire, but it clearly looks like 1.5 mm.

On 2018-06-14 by (mod) - actual wire size measurement

Max

You are so right

thank you for your careful reading I'll correct the text

On 2018-06-14 by Max

The SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS article says the photo looks like "2.5 mm" wire, but it clearly looks like 1.5 mm.

On 2018-05-15 by (mod) - match wire size to amps loading for the circuit

Magesh

Take a look at the data tag on your electric motor: find the voltage and the AMPERAGE that the motor requires. That will let you find the right wire size in the tables in this article series.

On 2018-05-15 by Magesh Kumar Srinivasan

For 7.5 HP Motor, 720 electrical wire is enough or what is to be used. please advice

On 2018-05-04 by (mod) -

Lee

No. 1 AWG copper

On 2018-04-28 by lee

what is the max size wire that will fit in a 100 amp breaker

On 2018-03-12 by Mike Burg

Can I use 2/0 aluminum service entrance cable for a small two family that has 100 amp panels for each unit?

On 2018-01-25 by (mod) -

Dave

The tables at AMPS & SEC SIZES note that using #10 copper you can run up to 200 ft. and be within acceptable voltage drop.

On 2018-01-25 by Dave

Need to run a direct burial line from a 200 amp box in my home out 200 ft to carport.at end I need one or 2 receptacles.this line is primarily for a 3 hp 26 amp motor to operate a car lift..my big concern is voltage drop..will use aluminum wire as I understand it is cheaper..in price thank you

On 2018-01-17 by Anonymous

What size wire and protection conduit can i use in 720.5 ampere?

On 2017-12-14 by saddiii

Total types of cables and wd current ratting

On 2017-10-02 by Brian

What size wire to use to hook up a 220 well pump at 150 ft

On 2017-06-25 by Anonymous

The table of voltage drops, is it in feet or metres?

On 2017-05-31 by (mod) - 2 conductors = 2 wires, probably 1 hot, 1 neutral

Thanks for asking, John as it helps me see where we need to clarify our text. But in this case I don't see the exact phrase you use

1 pair 16, 2 conductor 14

in our articles.

In general, in electrical talk,

2 conductors = 2 wires, probably 1 hot, 1 neutral

16 refers probably to the wire size or gauge - #16 or 16 gauge (which you wouldn't use for a residential 120VAC light or receptacle circuit)

15 probably refers to #14 or 14 gauge wire, typically used on a 15 amp circuit in buildings

On 2017-05-31 by John

Sorry, 1 pair 16, 2 conductor 14?

What does 1 pair 16, 2 conductor 4 mean?

On 2017-04-21 by Geoffrey

what size of the cable to use when connecting a 37kw machine?

On 2017-04-20 by Jon

I have a bell to install in a warehouse. It is 12v, .125A and needs to be 50' from the receiver.
What gauge wire should I be using?

On 2017-04-08 by (mod) - Dedicated Electrical Circuit

Terri

We call these, or the National Electric Code (for U.S. readers) calls these "Dedicated Electrical Circuits"

Heavy-usage appliances like an electric clothes dryer or water heater will have their own electrical circuit and breaker or fuse

Critical-use appliances, even though not using high wattage may also have their own circuit for reliability, such as refrigerators that we don't want going off because something else on the same circuit caused and overload.

Electrical expert Mike Holt and others point out that:

In the U.S. the National Electrical Code, since (I think) 1999, section 210.11(C)(2) requires one dedicated 20 amp branch circuit for receptacle outlets in the laundry area. This circuit is not dedicated for only the washing machine, all receptacle outlets installed in the laundry area can be on the laundry circuit.

GFCI (ground fault circuit interrupter) protection may also be required, e.g. for electrical receptacles near a laundry sink.

On 2017-04-08 by Terri

Do you have to have separate circuits for all house appliances like washer n dryer

On 2017-03-22 by (mod) - determine size or diameter of a wire

Thanks for the question Amyan.

In one of the tables above I give actual "normal" diameter of various wire gauges.

One can sometimes see the wire gauge or size printed on the insluating jacket

One can guesstimate the wire gauge by the overall conductor dimension, but that's just approximate as insulation thicknesses vary depending on the wire type and rating.

See SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS and

See ELECTRICAL WIRE TYPES CODES USES

One can also use a simple micrometer or measuring gauge to measure the thickness of the metal wire itself.

On 2017-03-22 by Amyan

How do you find the diameter of wire

On 2017-03-17 by (mod) -

Yep. We're a Two Harbors MN bunch ourselves.
Daniel

On 2017-03-17 by Mike white

Thank you. I figured I was good. Minnesota is throughout.

On 2017-03-16 by (mod) -

That sounds right, Michael. The breaker in the panel is only protecting wiring that is "downstream" from that point. So the wire between the overhead or underground service point and the panel is, in effect, not protected by that breaker in any event. Using a larger diameter wire in that location than would be required by the panel ampacity is always safe.

On 2017-03-16 by Michael White

I have a outdoor amusement concession trailer and I am changing the main breaker from 200 to 100amps can i get away with keeping the 3/0 125 ft .lead line and pass the electrical requirements for Minnesota's inspection.

On 2017-03-10 by Martin

If I have a 600A incoming service...what would be the size of the conduit and the size of the wire and how many wires

On 2017-01-28 by Joshua

What size of 4core amould cable is appropriate to install a 350kva 3phase generator at a 45meter distance.

On 2016-06-27 by (mod) -

Mahboob,

Please see our instructions on how to print any InspectApedia page nicely formatted, found at

HOW to PRINT InspectAPedia.com WEB PAGES - - https://inspectapedia.com/Admin/How_to_Print_Web_Pages.php

On 2016-06-27 by Mahboob

This is the good page & very helpfulness its need Down loaded page

On 2016-03-22 by Alan Firby

I am trying to find out how much load that aerial aluminium 7/4.75 conductor is good for

On 2016-02-09 by (mod) -

JD I've added tables and content to the article above to address increasing the wire size for long runs.

For an SEC, rather than simply applying the rule of thumb to increase the wire size for each 100 ft of run, I suggest that you need to consult an electrical engineer who will consider the voltage drop and specify the wire size. Otherwise your cost may be unnecesssarily high.

On 2016-02-09 by JD

What size wire do i need to run from a 200 amp pole service to a house 450 feet away?

On 2015-08-14 by paul

You produce a great information.

Comment:

(Nov 23, 2015) Anonymous said:
In the wire size table below give the typical diameter of #14 copper wire as 2.05 to 2.32 mm or about 0.081 - 0.092 inches

Table reads .
#14 0.073- .064 / 1.84-1.
#12 0.092-0.081 / 2.32-

Question:

(Jan 27, 2016) Carl said:

I’m studying on my own to become a home inspector. With that said after trying to interpret what this article is trying to convey to me and I’m left a bit confused and hoping you could clear somethings up.
I get MAX AMP Allowed according a specific wire size for branched circuit wiring; however, what I’m confused about is the Service Conductor Wire sizes.

Is it a separate set of wire/amp ratings then mentioned for the Max Amp Allowed for branched circuit wiring?

When comparing Service Conductor Wire Size with the fuses (or) breaker I’m getting confused.

Here’s an example of what I’m referring to:
(Service Conductor Wire Size)
100 AMP Breaker… (#4 copper wire) …. #2 Aluminum wire

(MAX AMP Allowed – Branched circuit wire sizes)
#4 Wire gauge… 70 amps (CU) … 45-50 amps (AL)

So, am I to read that as there has to be an additional 30 amps pushed through that wire before the breaker pops?

Wouldn’t the #4 wire burn out before the 100 amp rating of the breaker? This is where I’m getting confused.


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