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Service entry wiring (C) Carson Dunlop AssociatesElectrical Service Entry
Wire & Service Ampacity Inspection

Electrical service entry wiring, service entry cabling (SEC), & the electrical meter: how to inspect for & report service ampacity, service entry defects & hazards.

Carson Dunlop Associates' sketch at page top shows where the electrical inspection starts at a residential property.

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Inspecting the Electrical Service Entry Wiring bringing electrical power to the electric meter

Service entry wiring (C) Carson Dunlop Associates

This article series discusses procedures for safe and effective visual inspection of residential electrical systems including electrical panels and other components, when the inspection is conducted by trained building inspection professionals, home inspectors, electrical inspectors, and electricians.

[Click to enlarge any image]

Our photo illustrates an unstable and improper passage of electrical service wiring over the roof of a private home

. In this case the house was being used to support electrical wiring that was in turn bringing power to a separate home located nearby.

Examples of electrical service defects that can be spotted outdoors at the electrical service entry

Unsafe outdoor electrical service entry cables at a mobile home (C) D Friedman S Vermilye

A study by the author showed that very common sources of water leaks into and damaging electrical panels include frayed SEC, leaks at the top of the meter, and leaks at the building wall where the SEC passes from the bottom of a meter pan into the building electrical panel.

See details

at RUST in ELECTRICAL PANELS

How to Determine Residential Electrical Service Ampacity

Readers of this section should

see AMPS & VOLTS DETERMINATION

for a detailed article on how to determine the amps and volts of a building's electrical service.

Do not rely on the ampacity printed on the main fuse or breaker, though that information is important. Examine the following:

So what determines the actual service ampacity at a building?

 

Typical Electrical Service Ampacity vs. Service Entry Cable Sizes

AMPS Copper Aluminum
30 10* 8*
60 6* 6*
70 6* 4*
100 4 2
125 2 1/0
150 1/0 2/0
200 2/0 4/0

Notes to the table above

Electrical Service Ampacity Defects

Electric Meter Defects

Obsolete electric meters (C) Daniel Friedfman

...

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-06-24 - by (mod) -

Tom

You'll want to take a look at the SEC wire cable sizing tables above on this page, and you'll need to specify one more detail: the panel ampacity or service ampacity of the home. You need a bigger wire for 200A or 150A than for a 100A service.

On 2020-06-24 by Tom

Running 250' underground from meter to new house what size wire do I need?

On 2020-05-21 - by (mod) -

Forgive me but I don't understand the question, Harold. Perhaps you can post a photo.

On 2020-05-21 by Harold

Do you need to cap an electric. Coduit pipe inside an attic ceiling that goes down to a service box?/

On 2020-05-13 - by (mod) -

100 A
And all components should match

Service wire ampacity or size
Panel size
Main breaker size

On 2020-05-13 by thegreat11975

What size fuse panel does a mobile home need single wide, late 70's model

On 2018-10-14 - by (mod) - SEC Electric Service Entry Cable Specifications & Instructions

By private email:

SH asked:

I'm helping a friend out in a attic and noticed that he had thhn #2 awg feeder cables to a 100 amp subpanel that ran across his attic. The cables are not in conduit. I know generally, thhn should always be in conduit. Does the same rules apply to feeder cables of that size? My friend thinks it should be okay since the home was built in 2011 so it must have passed inspections.

Reply:

Used as an SEC properly sized, routed, supported, the wire is not required to be routed in conduit:
NEC 300.3(A) prohibits THHN (or any other type of single wire save for a few exceptions such as single conductor MI and SE/USE, overhead wires, or an EGC) from being run outside of conduit or approved protection.

"A) Single Conductors. Single conductors specified in Table 310.104(A) shall only be installed where part of a recognized wiring method of Chapter 3."

Here are Southwire's specifications and general instructions from that company's notes at
www.southwire.com/support/THHNGuideSpecifications.htm

Annex A Type THHN Conductor Specification 26 05 19 WIRE AND CABLE TYPE THHN

PART 1 – GENERAL

1.1 – SPECIFICATION INCLUDES

1.1.1 Cable Type: Type THHN/THWN for use as services, feeders and branch circuits

1.1.2 General Applications: Type THHN/THWN cable may be used in the following general applications per the National Electrical Code®

1.1.2.1 In Conduit

1.1.2.2 In Cable Tray

1.1.2.3 For Services

1.1.2.4 For Feeders

1.1.2.5 For Branch Circuits

1.1.2.6 Wet or Dry Locations

1.2 – SUBMITTALS

1.2.1 Product Data: Submit manufacturer’s product data confirming that materials comply with specified requirements and are suitable for the intended application.

1.2.2 Installation Instructions: Manufacturer’s installation instructions shall be included in submittal. Industry guides may supplement the manufacturer’s instructions.

1.3 REQUIREMENTS

1.3.1 Underwriters Laboratories: Type THHN cable shall meet the following Underwriters Laboratories (UL) standards and listings.

1.3.1.1 UL 83 Thermoplastic-Insulated Wires and Cables

1.3.1.2 UL 1063 UL Standard for Safety Machine-Tool Wires and Cables

1.3.1.3 UL listed sunlight resistant in black sizes 2 AWG and larger.

1.3.1.4 Sizes 1/0 AWG and larger listed for CT USE

1.3.1.5 Sizes 14 through 1 AWG shall be rated VW-1

1.3.1.6 Sizes 8 AWG and larger shall be rated THWN-2

1.3.2 ASTM Standards: Type THHN cable shall meet all applicable ASTM standards.

1.3.3 Federal Specifications: Type THHN cable shall meet Federal Specification A-A-59544

PART 2 - PRODUCTS

2.1 MANUFACTURER

2.1.1 Southwire Company, One Southwire Drive, Carrollton, Georgia, 30119. Website: http://www.southwire.com/

2.1.2 Senator Wire and Cable, 102 City Hall Ave., Carrollton, Georgia, 30117 Website: http://www.southwire.com/

2.2 CABLE CONSTRUCTION

2.2.1 Conductor: The conductor shall be soft annealed copper

2.2.2 Insulation: The insulation shall be high-heat and moisture resistant PVC.

2.2.3 Jacket: The jacket shall be abrasion, moisture, gasoline and oil resistant nylon or listed equivalent with

2.2.4 Self-Lubricating Jacket: Jackets on conductor sizes 2 and larger shall be SIMpull™ or equivalent having integrated self-lubrication such that the cable coefficient of friction is less than or equal to 0.17.

PART 3 - INSTALLATION

3.1 INSTALLATION

3.1.1 Manufacturer’s Instructions: Type THHN cable shall be installed per the manufacturer’s published installation instructions. Industry guides may supplement the manufacturer’s instructions.

3.1.2 Field Support: Manufacturer shall provide, when requested, field engineering support for Type THHN cable installation.

3.1.3 Manufacturer: Type THHN cable for circuits, feeders and services shall be supplied from a single manufacturer.

3.1.4 Minimum Bend Radius: Bends in Type THHN shall be made so that the cable will not be damaged.

3.2 SPECIFIC USES

3.2.1 Type THHN cable may be used in conduit, raceways and cable trays for services, feeders and branch circuits as specified in the applicable section of the NEC®.

3.3 USES NOT PERMITTED

3.3.1 Type THHN cable shall not be used in direct burial applications.

3.4 AMPACITY

3.4.1 The ampacity of Type THHN cable shall be determined in accordance with Article 310.15 of the National Electrical Code®. The installation should not exceed the temperature ratings of the terminations and equipment.

On 2018-03-21 - by (mod) -

Josh

There may indeed be safety problems with your electrical panel but I cannot reliably assess them from your brief e-text. Perhaps a licensed electrician or even a home inspector (see page top EXPERTS DIRECTORY) can take a look for you, on-site, and give more useful advice.

Also see ALUMINUM WIRING IDENTIFICATION https://inspectapedia.com/aluminum/Aluminum_Wire_Identification.php

On 2018-03-21 by Josh

Main feed 200amp wire from meter to main panel. Grounds or neutral wires aluminum looking.. looks likes there are many smaller wires maybe 20 twisted together. A few of the smaller wires are frayed n broken. What issues come with that.

On 2018-02-24 - by (mod) -

Compare tha be size of the service entry main cable with the amps rating of the main dis connect breakers or fuses.

On 2018-02-24 by orlanzo

how can in determining that i am get full capacity from my service wire that is coming into the building or house

On 2016-06-14 - by (mod) -

Jim

If I understand correctly we have a 60 Amp service entry cable feeding an electrical panel that has a 100A main switch. Indeed that's improper. If all of the circuits in the panel below the main draw more than 60A the service entry cable is overloaded, could overheat, and could be a fire risk;

We often see this problem when someone adds a higher capacity electrical panel (called "heavying-up" by some of my friends) without making sure that the incoming service entry cable wiring has been updated as well.

Under-fusing is "safe" but inconvenient.

Over-fusing is dangerous. You are describing over-fusing.

On 2016-06-14 by Jim T

Is a 60 amp service running into a 100 amp main disconnect a safety issue?

Question: short circuit & current leaks at electrical service entry wiring

2016/09/06 I am hoping to get some suggestions.

I power cleaned a drain and felt mild electrocution in my hands. I further discovered the ground from the outlet in the home had current.

I flipped the main breaker and ground still has current as does the panel box itself. The city has an old wiring system where neutral is ran back through the power line.

Ground to neutral connection outside the main panel is not allowed.

Home has 200 amp service ran through 2/0 stranded copper SEC. However city line is aluminum half as thick.

Main transformer blew power to the block when I started pulling close to full 200 amps.

What do I do? - Anonymous by private email

Reply:

This SEC wiring damage case report has been moved to ELECTRICAL SERVICE ENTRY DAMAGE


...

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