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Service drop wire clearances (C) Carson Dunlop Associates Electrical Service Drop

How to Inspect Residential Electrical Service Connections to a Building

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Electrical service drop wire clearance distances and other defects.

How to inspect the electrical power service drop at a building.

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Inspecting the Electrical Service Drop or Service Lateral bringing electrical power to a building

Sketch of the electrical service drop (C) Carson Dunlop Associates

Sketches shown above are provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

Electrical Service Drop Wire Clearances and Other Defects: U.S. & Canada

Service drop wire clearances (C) Carson Dunlop Associates

Our photo below illustrates inadequate or unsafe clearance of electrical wires over a building roof.

Insufficient clearance distance of electrical wires over roof (C) Daniel Friedman

The required clearances for electrical service drop wiring

Other electrical service drop wiring defects include

Electric service drop clearances in Canada (C) Carson Dunlop Associates

 

Overhead Electrical Service Drip Loop Requirements

Improper SEC wiring leads to near-electrocution or fire (C) InspectApedia.com DCI Andrus Definition: An overhead electrical service drip loop is a downwards bend in service entry wiring at the connection between masthead and ovehead service wires in order to assure that water on the wires does not run into the masthead that carries the electrical service down to a building electrical meter or panel.

Our photo, courtesy of an inspectApedia reader, shows an overhead electrical service connection to the masthead (at left edge in our photo).

You can see that the installer included a drip loop in the wires, taking care that the bottom of the drip loop extends several inches below the openings in the masthead into which the descending electrical service entry wires enter to pass down the buidling wall into the electric meter.

Typical electrical service entry wiring specifications provided by your electrial supplier describe details of a proper and safe electrical service entry, including details of the overhead connection and drip loop using text such as the following:

Bottom of service head must be higher than loop wire at building.

Where it is necessary to place the house bracket or Wire holders at an elevation above the customer’s Service head, sufficient loop wire must be allowed to Connect the customer’s service wires to the loop Bottom of the drip loop.

Connectors on the covered Wire must be taped.

Wire holder (bracket) furnished and installed by Company. 

Note that a quantitative measurement of overhead SEC drip loop depth below the masthead is not given. Rather this is a performance specification that simply says "...Bottom of service head must be higher than loop wire at building. "

The intent is clear: rainwater contacting the overhead service entry wires should not run down the wire and into the masthead.

What about that highest drip loop of the three wires in our photo above? Is that highest wire loop sufficiently below the bottom of the masthead?

Fortunately, for an electrical service that has been installed long enough to have been exposed to rainfall, it's easy for an electrician to verify that the SEC drip loop depth below the masthead is sufficient by inspecting the interior of the electric meter box. There she looks for signs of water tracking down the entering SEC cable or signs of water, moisture or corrosion inside of the meter box itself.

Water tracking marks show leaks into electrical panel (C) Daniel Friedman

Above: yellow arrows mark signs of water stains on the service entry cable.

These marks suggest that water was running down the interior of an overhead service entry cable. Possible sources of such leaks include an inadequate drip loop at the mast head or frayed leaky SEC insulation or poor seals at the top of an electric meter box.

Electrical Service Entry / Service Drop Codes & Specifications

Electrical service components, City of Bloomington MN Inspections Dept, R HankeyIllustration adapted from City of Bloomington, MN Inspections Department. [Click to enlarge any image]

Electrical Vocabulary & Terms for Residential Electrical Inspectors

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DEFINITIONS of ELECTRICAL TERMS

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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

Flexible conduit OK for service entry wiring?

Hi All,
Are electrical drop boxes considered hard wired installations, or does NFPA/OSHA considered them flexible cables? Are there specific regulations for drops outside of clearance standards?, or do they fall under standard wiring standards ? - On 2020-07-10 by Anonymous

Reply by (mod) - OK but may need to be liquid-tight

Anon,

Thank you for the question. I think you're asking about whether or not it's ok to use metallic flexible-cable for service entry cable (US NEC Article 338)

that is, you're not asking about using flexible metal conduit,

You would not use flexible cable in a water-exposed location - not water tight. But it's not prohibited in general.

Here's a pertinent US NEC excerpt:

NEC 230.43 Wiring Methods for 600 Volts, Nominal, or Less.

Service-entrance conductors shall be installed in accordance with the applicable requirements of this Code covering the type of wiring method used and shall be limited to the following methods:

(15) Flexible metal conduit not over 1.8 m (6 ft) long or liquidtight flexible metal conduit not over 1.8 m (6 ft) long between raceways, or between raceway and service equipment, with equipment bonding jumper routed with the flexible metal conduit or the liquid-tight flexible metal conduit according to the provisions of 250.102(A), (B), (C), and (E)

Note: for an electrical service entry cable your cable will be marked SE or USE


Roofer won't work on roof because of electrical wires

The roofing company said it could not deliver and install shingles because our neighborhood service drop is connected to our two story house. How can we replace our roof? - On 2020-07-08 by Sally

Reply by (mod) -

Sally

Well we can't fault the roofer from being careful not to electrocute her workers,

But the problem is simple to resolve:

Arrange or have an electrician arrange that the electrical service drop to your house be disconnected at the utility pole by your electric company.

You'll either have to do without electricity while the area of roof in danger of touching the service entry wires is re-done or, if multiple days of no-power are needed you might arrange for temporary restoration or a backup generator with a transfer switch to be sure no power is fed back out of the house to the roof service entry wiring.

Followup by Sally

Thanks for the reply. It wouldn’t be that much of a problem if we were the only ones who would be without power, but supposedly it’s 4 other neighbors who may have a problem doing without power for too long. I think the power company needs to upgrade.

Reply by (mod) -

Unkess there's something odd and not yet mentioned, its entirely possible and usual to drop power to just on one building.


At what height do underground electrical service wires penetrate the building wall to get to the panel?

I am putting a new electrical service to my detached garage through a buried conduit.

At what height do I penetrate the exterior wall to continue the conduit to the sub panel?

The conduit will exit the ground and will be surface mounted to the penetration as the garage is on a concrete slab with no way to continue the trench under the foundation without a jackhammer. - On 2018-12-31 by Rick

On 2019-01-01 - by (mod) -

Rick

I have not found a specification requiring a particular height for the wall penetration for your conduit bringing electrical wiring from underground up through conduit through the foundation wall and into the structure interior.

Remember that the conduit needs to be weatherproof including the fitting used to give access to the 90 degree angle to make the turn to penetrate the wall.

Even though that fitting is required to be weatherproof , in my opinion I would prefer to make the height of such a penetration high enough to be well above any likely standing water, puddles, Etc.


Electrical mast just 1 foot above roof gutter

I have added on to a house with overhead service. The addition makes the mast less than 1 foot near the new gutter of the roof. Is there not a required distance the mast should be from the roof gutter/valley? - On 2018-04-12 by Willie E

Reply by (mod) -

As the guidelines include 8-10 ft above any flat roof and no less than 24" above a gable roof at the mast head, your cables are too close to the gutters.


Service drop wires touch both pole and guy-wire.

Hi. The electric service drop to my house was so tight it pulled the weather head toward the pole and warped the roof shingles. I complained and they loosened the drop. The service is a terminal pole.

The drop also touches the guy wire at the top of the pole. The fix was to place a yellow protection cover over the guy wire. I asked the utility company about it and they said unless it starts to arc, I shouldn't worry about it. I have had 4 lightning strikes this year. Any thoughts or help? Thanks much! - On 2017-08-09 by mullen

Reply:

Your electrical company is responsible for both meeting code and safety; if you're still nervous about this "fix" - as am I - you might try first a friendly conversation with the company's service manager and after that a notice in writing of your concerns. Often, putting something in writing is more-effective.

In my opinion, service entry wires too close to or touching a utility pole guy wire could indeed be a lethal shock hazard.


Equation to figure the sag in an overhead service spanning 200' with #2 quadplex

Is there an equation to figure for sag in an overhead service spanning 200' with #2 quadplex - On 2017-05-04 by DC -

Reply by (mod) -

Sure DC in several engineering texts and also in college and university material.

The standard equation is

T2 (T - K + aEa (q2-q1)) = W2 L2 aE / 24 x q2

T = Tension at temperature q2 (kg)
K= Constant
a = Area of conductor/Earth wire (mm2)
E = Modulus of Elasticity kg/mm2
a = Linear Coeft. of expansion (per degree celcius)
W = weight of conductor (kg/m)
L = Equivalent span (m)
q = Wind load factor = P2 + W2 / W2 = 1 (At no wind condition)
q1 = Initial condition temperature

- Source: Sag and tension calculations for conductor earth wire are done for the river crossing by following steps - Uttar Pradesh Power Transmission, Corporation, Limited, Web: https://upptcl.org/, retrieved 2024/08/30 Local copy on file as Sag and Tension Calculations For Conductor_Earth Wire For River Crossing _ Welcome to Uttar Pradesh Power Transmission Corporation Limited, Government of Uttar Pradesh, India_.pdf



Why is my electric meter not working? Electrician says service drop needs replacement

Would you please tell me what are the reasons why the electric meter is not working, as per my electrician the service drop is rusted and need to replace. Is this correct? - On 2017-04-10 by Bong

Reply by (mod) -

Watch out: I suggest calling your electric utility company immediately to ask them to look at your electric meter since what you describe sounds unsafe and possibly a fatal shock or fire hazard


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