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.

Inspect the Electrical Service Entry (SEC) Wiring

The SEC or "Service Entry Cable" is the term used for the electrical cable that brings electrical power from the utility company's power drop at a utility pole or at an underground service system to the building and onwards to the building's electric meter.

Our photo illustrates an unstable and improper passage of electrical service wiring just a few feet above 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.

Article Contents

• SERVICE ENTRY / SEC DEFECTS
• SEC CABLE SIZES vs AMPS RATING
• ELECTRICAL SERVICE AMPS LIMITING FACTOR

If you are trying to find out the actual electrical service capacity (rated in Amps) for your building

please see  AMPS & VOLTS DETERMINATION

 

 

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Electrical Service Defects at the Service Entry or SEC

• Mast, conduit, cable weather tightness: watch for a mast or SEC cablle that is deteriorated or leaky
• Service cap not properly installed, sealed, properly positioned to keep water out of the SEC wiring.
  
  Watch out for service caps installed upside down, horizontally, or in positions that fail to keep water out of the service entry cable jacket or conduit.
• Missing or inadequate drip loop in overhead electrical wires where they enter the mast-head, causing water entry into the masthead, meter base, or electrical panel.
• Roof flashing errors at standards or masts
• Electrical conduit missing where required such as at roof penetrations made by the SEC
• Electrical conduit joint leaks - electrical conduit joints outdoors must be weather tight - note the damaged electrical conduit, open connections, incomplete conduit, wiring exposed to weather and water at our mobile home electrical inspection photo shown at left.
• Leaks at electric meter enclosure top or bottom: Top and base of meter must be weather tight, secured,

• Leaks at the SEC to building wall penetration.
  
  

  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

• Frayed SEC cables expose inner wiring to damage or deterioration and are a source of water entry in the electrical meter box as well as into electrical panels if the panel is located lower than the SEC
• Abandoned SEC cables may not have been properly disconnected - electrocution hazard
• Electrical Service Ampacity Defects such as:
  • Inadequate / marginal total capacity for the modern use of the building. Some lenders or local electrical codes require a minimum of 100A at a single family home.
  • Some utility companies will not replace an old 60A service (and meter) and will require that service be upgraded.
  • Load calculation of required service ampacity for buildings is not required during a home inspection but the inspector should be familiar with that procedure.
• Well connected to service entrance cable (SEC) using a metal well casing as the system's electrical ground

See

ELECTRIC METERS & METER BASES for details of additional unsafe electrical service conditions that can be spotted from outside the building.

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Electrical Service Ampacity vs. Service Entry Cable Sizes

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

Watch out: to avoid unsafe or excessive voltage drop, these wire sizes must be increased for longer wire runs (50 ft. and above) see

• SE CABLE & WIRE SIZE TABLES vs AMPS tables of service entry cable and other electrical wire sizes vs amps vs other factors
• SE CABLE & WIRE SIZES FOR LONG RUNS service entry cable sizes for longer wire runs and links to online wire size and voltage drop calculators.

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How to Determine Residential Electrical Service Ampacity

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

Examine all of the following:

• Service drop wire size
• Electrical mast diameter -
  
  1-inch 60A mast
  
  2-inch 200A lateral
• Electric meter base size
• Electric meter rating
• Main Electrical Switch or service box rating
• Main Electrical distribution panel rating
• Watch out: do not just add up the total of all fuses or breakers in panel (the sum is NOT the service ampacity as % utilization applies)

Find the Limiting Factor in Service Amps

So what determines the actual service ampacity at a building?

The smallest link in the chain of all of the components bringing electrical power to the building will be the limiting factor that determines the actual electrical service ampacity at a building.

An easily seen service amps limitation, but not the only one, is the size of SEC and its wire type: copper vs. aluminum or CU/AL. But watch out: we've found every imaginable combination of electrical components such as

A 100A electrical panel fed by a 60A SEC - the SEC is the limiting factor

A 60A electrical panel fed by a 100A rated SEC - the panel or its main fuse or breaker is the limiting factor determining the electrical system's amapcity available in the building.

A 100A SEC, 100A panel, but the panel's main breaker was 60A

Watch out: some of these combinations, such as a 100A main breaker on a 60A SEC would be both improper and unsafe, risking a fire.

What if the service entry cable (SEC) is completely hidden?

Watch out: unless you are trained and certified in proper and safe building electrical work, don't try to disassemble the electrical panel or meter enclosure; you coudl be shocked or killed.

But any building occupant should have access to the electrical panel (so that s/he can turn off power in an electrical emergency) and at the panel, if the SEC is not visible, look at service disconnect - the main circuit breaker or fuse size. That's at least a clue.

Home inspection standards require the inspector to open and inspect the electrical panel (unless she or he determines that doing so would be unsafe).

If the inspector is unable to determine the service ampacity the inspector should advise the client of that limitation, should explain why, explain the implications, and give advice on what to do further.

For complete details see our home page for this topic found

at AMPS & VOLTS DETERMINATION

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

What SEC wire size do I need for 250 foot underground service?

Running 250' underground from meter to new house what size wire do I need? - On 2020-06-24 by Tom

Reply by (mod) - Cable Size depends on BOTH Service Ampacity and Run Distance

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.

What size fuse panel do I need on a singlewide mobile home?

What size fuse panel does a mobile home need single wide, late 70's model - 2020-05-13 by thegreat11975 -

Reply by (mod) -

Currently you want 100 A in most jurisdictions, but you'll find older original installations that may be less, such as a 60A service.

And also all of the electrical serive components should match in ampacity and sizxe

Service wire ampacity or size
Panel size
Main breaker size

SEC using 20 Smaller Wires Twisted Together?

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 2018-03-21 by Josh -

Reply by (mod) - Sounds improper and unsafe

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 2018-02-24 by orlanzo

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

Reply by (mod) -

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

Is a 100A main switch fed by a 60A SEC safe?

Is a 60 amp service running into a 100 amp main disconnect a safety issue? - 2016-06-14 by Jim T-

Reply by (mod) - NO

Jim

If I understand correctly we have a 60 Amp service entry cable feeding an electrical panel that has a 100A main switch.

Watch out: Indeed that's improper and so unsafe. 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.

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

Or see these

Recommended Articles

• AMPS VOLTS DETERMINATION - home
• ELECTRIC METERS & METER BASES - home
• GROUND SYSTEM INSPECTION - home
• SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS
• SE CABLE & WIRE SIZES FOR LONG RUNS
• SERVICE ENTRY WIRING & AMPACITY - home
  • DETERMINE SERVICE AMPACITY
  • ELECTRICAL SERVICE DROP
  • ELECTRICAL SERVICE ENTRY DAMAGE
  • SE CABLE & BRANCH CIRCUIT WIRE SIZES vs AMPS
  • SE CABLE & WIRE SIZES FOR LONG RUNS
  • SERVICE AMPACITY
  • SERVICE AMPACITY DEFECTS
  • SERVICE GROUNDING DEFECTS
  • TABLE OF SERVICE AMPACITY
  • UNDERGROUND SERVICE LATERALS
• SIZE of WIRE REQUIRED for ELECTRICAL RECEPTACLES for receptacle circuits and similar wiring situations
• VOLTS / AMPS MEASUREMENT EQUIP

Suggested citation for this web page

ELECTRIC SERVICE ENTRY WIRING & AMPACITY at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

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

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