FAQs about buried or underground electrical service entry cable ampacity & underground electrical service ampacity ratings.

Questions & answers on how to determine the size, capacity, or ampacity of electrical service at a building.

This article series explains how to estimate the electrical service size, (or "electrical power" or "service amps") at a building by visual examination of the buried service entry cables and other details that are available by simple visual inspection.

Underground & Other SEC Electrical Service Wire Size Q&A

These questions & answers about the sizing of underground electrical service entry wires or service laterals were posted originally at UNDERGROUND SERVICE LATERALS - topic home - so you will want to be sure to see the wire sizing table givent here.

[Click to enlarge any image]

On 2021-03-31 by (mod) - What size of and type of conduit and service wire do I need for a small home, w

@Deneen, actually you are far-more "clued-in" than people who just run wires willy-nilly without trying to find out what is needed.

An underground electrical service can be run in conduit (special pipe used for electrial wiring) or it can be run directly if the proper UF or underground feeder wire type is purchased.

The wire size you need depends on the size of electrical service (main panel and switch) to be installed; for a small home you'd typically use at least
a 100-Amp rated electrical service and panel.

The wire size you need is going to be given in electrical codes, selected by your installing electrical contractor, based on BOTH the Ampacity (say 100A) and the total wire length - where your length of 150 ft. is pretty long, and is also described
at
SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS

The table of wire sizes I'll show below is excerpted from that web page.

You'll see that for 100A the service entry cable is typically a #1 or a #0 gauge wire depending on whether you're using copper (smaller diameter wire) or aluminum wire.

BUT
when running the service entry cable for a longer distance, like your 150 feet, it will be wire size 2/0 - copper or 4/0 aluminum. (More zeroes is a larger wire size).

Examples of wire sizes for longer runs are also at

SE CABLE & WIRE SIZES FOR LONG RUNS https://inspectapedia.com/electric/Long-Run-SEC-Cable-Sizes.php

The wire TYPE you will need is one rated for burial underground and will be marked at least
UF for "Underground Feeder"

There are additional letters and markings that reflect more wire properties like temperature range;

Watch out: if you are not familiar with proper, safe electrical wiring, making a mistake can cause a fire or kill someone. So be sure you have help from a qualified electrician. Also in most communities you're required to get an electrical permit to do or have done the work you describe. The electrical inspector's visits and inspections are there to help keep you and everyone else safe so be sure you get those done.

On 2021-03-31 by Deneen

What size of and type of conduit and service wire do I need for a small home, we are burring it underground from electric meter to home around 150 ft.i am a female that is totally clueless about these things. I need help

On 2021-03-31 by Anonymous

Ineed to know what size of service wire. And conduit I need for service from meter to home. I am burring it underground. From meter to home around 100 ft

On 2021-01-20 - by (mod) -

Todd

SE CABLE SIZES FOR LONG WIRE RUNS - SEE THIS ARTICLE for wire size for long runs

https://inspectapedia.com/electric/Long-Run-SEC-Cable-Sizes.php

On 2021-01-19 by Todd Benmark

I need to run underground wire 300 ft. to a cabin with a 150 amp panel from my barn. What type and size wire will I need?

On 2020-10-24 - by (mod) -

Normally yes;

On 2020-10-24 by Perry Balllinger

Does the underground power company wiring size need to be changed when going from 100 to 200 amp service?

On 2020-08-23 by Randy

I have a 250 foot run from the primary pole to the meter box. I have a 225 amp breaker box. What gauge wire do I need for the primary run and the meter to breaker box?

On 2020-07-03 - by (mod) -

Tim

Check out

SE CABLE SIZES FOR LONG WIRE RUNS - SEE THIS ARTICLE for wire size for long runs

at https://inspectapedia.com/electric/Long-Run-SEC-Cable-Sizes.php

and don't hesitate to ask if that leaves you with questions

Thanks

On 2020-07-03 by Tim

I'm putting underground electric service to my house. I have 200 amp service. I need 200 feet of underground. What size wire do I need.

On 2019-08-09 by (mod) - SEC wire size for a 650 foot run to a 200A panel

Greg

Using the online calculator itself cited at the article I'll cite just below to support a 200A load at the end of the run

you'd see an acceptable (under 3%) voltage drop of 2.80% with 350 kcmil wire

PROVIDED you're running 2 parallel sets of 240VAC cables, single phase power.

you'll find wire sized for long SEC runs documented at

SE CABLE & WIRE SIZES FOR LONG RUNS

Illustration: edited from output from Southwire's voltage drop calculator at southwire.com

[Click to enlarge any image]

On 2019-08-08 by greg

I have a 650' run from the service pole and I'm not sure with the voltage drop what size wire is needed for a 200 amp service.

On 2019-07-29 by (mod) - 200 amp box and running 300 foot

Daryll

Be sure you have the necessary permits, approvals, inspections as that will help your installation be safe.

See SE CABLE & WIRE SIZES FOR LONG RUNS for help with wire sizing.

On 2019-07-29 by Daryll

I'm replacing a old box with new 200 amp box and running 300 foot to new trailer can anyone give me any advice

On 2019-06-24 by Josh

Need to run a 200 amp service from pole to new house, 800' underground. What size wire?

On 2019-06-05 by (mod) - 200 amp box and running 300 foot

Sue please see the wire sizing help including run length and wire size increases are at

SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS

On 2019-06-05 by Sue

What sz of direct burial wire for 200 amp service, 200' away coming from on the ground transformer?

On 2019-03-28 by (mod) -

Paul

MOre-detailed wire sizing help including run length and wire size increases are at

SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS

On 2019-03-20 by Paul

Need to carry 100 amps 500 feet. What size under ground wire do I need

On 2019-03-05 by Anonymous

See the voltage drop info at

SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS

On 2019-03-04 by Paul

Sorry 400 feet under ground

On 2019-03-04 by Paul

What size wire do I Need to go 400 feet for a 200 amp service?

On 2018-10-22 by (mod) - 200amp service at 300ft underground what size wire do I need?

see SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS for more detailed wire size guidelines that include adjustment for length

https://inspectapedia.com/electric/Electrical_SEC_Sizes_Amps.php

On 2018-10-22 by Anonymous

200amp service at 300ft underground what size wire do I need

On 2018-10-18 by Perry - what size wire do I need for a 150A service and 200 ft run?

I have a 150 amp service I need to run 200 feet of wire what size wire do I need

On 2018-03-26 by Salvatore

I have a 200 foot run to a 200 amp household service. I am doing underground. What size wire do i need?

On 2018-03-16 by (mod) -

Fred

Service entry wiring sizes are given at SE CABLE SIZES vs AMP

On 2018-03-14 by Fred

A new self-protected transformer, 15 kVA, 34.5/19.9Kv 120/240 V was recently installed 520 feet from my home in Costa Rica. The elec. utility insists that the meter be installed at the street. I want to run underground cable straight up to my house (with a 100 amp service). What size AL cable will I need?

On 2017-10-20 by (mod) -

Anon

At the ARTICLE INDEX see the live links for

SE CABLE SIZES vs AMPfor more wire size guidelines

SIZE of WIRE REQUIRED for receptacle circuits and similar wiring situations

And beware: you'll need an individual disconnect and fuse protection (breakers) for both of those services.

On 2017-10-20 by Anonymous

We have 400amp service split with 200amp to house with quick disconnect. The other 200amp will go to our barn and workshop of the other quick disconnect. My question is what size al wire should we use for 230' run to barn? It will be underground 3" pic. What size quad 250 or 350?? Thanks

On 2017-09-27 by (mod) - calculating voltage drop: what size of underground wire do I need to run a 100 amp service, 250 feet away?

Mike

Using Southwire's voltage drop calculator, for 100A service and a 250 ft. run single phase, 240VAC, aluminum SEC buried,

1 conductors per phase utilizing a #3/0 Aluminum conductor will limit the voltage drop to 2.82% or less when supplying 100.0 amps for 250 feet on a 240 volt system.

If we change the voltage to 120VAC the result is: 1 conductors per phase utilizing a #400 Aluminum conductor will limit the voltage drop to 2.94% or less when supplying 100.0 amps for 250 feet on a 120 volt system.

Typically, the maximum allowed voltage drop for residential installations is 3% that's why I chose that number. You can see you'd be ok with direct buried 3/0 Al.

You may want to run your wire in 3" conduit - double check with what your local electrical utility will accept.

Check out the definition of VDI - voltage drop index, and also "Maximum Wire Length vs Wire Size & Circuit Amps" at SE CABLE SIZES vs AMPS inspectapedia.com/electric/Electrical_SEC_Sizes_Amps.php and of course go to UF (underground feeder) rated wire.

On 2017-09-26 by mike

what size of underground wire do I need to run a 100 amp service, 250 feet away?

On 2017-06-07 by Anonymous - 300 feet from out to panel to run 110volt motor off a 15 amp breaker... What gauge wire do I need?

You are always safe for going to the next larger size or diameter wire for a longer run. So since a 15 amp circuit would use 14 gauge wire you could go up to number 12 wire. Be sure you're using the proper wire type for underground feeder.

On 2017-06-07 by Dee

I need to run 300 feet from out to panel to run 110volt motor off a 15 amp breaker... What gauge wire do I need?

On 2016-04-27 by Anonymous

Going to upgrade to a 200 amp service. Going to run from pole transformer to house breaker panel 150 feet underground. 120 volts. What cable size and conduit is required.

On 2015-11-09 by (mod) - wiring size information for 200 amp underground service with a 450 foot run.

Sure Mike

You didn't specify voltage but I assume you meant 240V. At 208V you'd need bigger wires and at 120V much much bigger wires.

There are many wire sizing tables online and in the NEC, and some reasonable online wire size calculators

Generally I found that for 200A at 450 ft and 240V you need to use 300 MCM copper wire or 500 MCM aluminum wire.

You'll want to check again the NEC tables and UF notes.

see http://www.jhlarson.com/

On 2015-11-09 by Mike

Can you provide wiring size information for 200 amp underground service with a 450 foot run.

Thanks

...

Continue reading  at UNDERGROUND SERVICE LATERALS - topic home or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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• AMPS VOLTS DETERMINATION - home
• ELECTRICAL INSPECTOR SAFETY PROCEDURES
• ELECTRICAL WIRE TYPES CODES USES
• SERVICE ENTRY WIRING & AMPACITY - home
  • ELECTRICAL SERVICE ENTRY DAMAGE
  • SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS
  • SE CABLE & WIRE SIZES FOR LONG RUNS - SEE THIS ARTICLE for wire size for long runs
  • SERVICE AMPACITY
  • SERVICE DROP
  • SERVICE GROUNDING DEFECTS
  • UNDERGROUND SERVICE LATERALS
• SIZE of WIRE REQUIRED for ELECTRICAL RECEPTACLES

Suggested citation for this web page

UNDERGROUND SERVICE LATERAL FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to ELECTRICAL INSPECTION & TESTING

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