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NMC electrical cable details (C) Carson Dunlop AssociatesElectrical Wire Stripping Tips for Homeowners

  • ELECTRICAL WIRE STRIPPING TIPS - CONTENTS: How to strip the ends of electrical wires. How much insulation should be stripped from the conductor wire for light switches or electrical receptacles? Types of electrical circuit wires used in homes: what are NM, NMC, UF, BX, Romex, armored cable wire types. Tools & tips for stripping electrical wires. Guide to Electrical Hazards in buildings: inspection, detection, & repair advice
  • POST a QUESTION or READ FAQs about how to strip electrical wires
  • REFERENCES
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This article provides basic tips on how to strip the ends of electrical wires used in homes.

This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions. Critique and content suggestions are invited. Credit is given to content editors and contributors.

Sketch at page top courtesy of Carson Dunlop Associates.



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Electrical Wire End Stripping Tips

Open electrical panels are dangerous (C) Daniel Friedman

Safety Warning: Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death. 

Even when a hot line switch is off, one terminal on the switch is still connected to the power source. Before doing any work on the switch, the power source must be turned off by set­ting a circuit breaker to OFF or removing a fuse

. See SAFETY for ELECTRICAL INSPECTORS and ELECTRICAL WIRING BOOKS & GUIDES

Different kinds of cables and electrical wire are commonly used by the homeowner or electrician when performing routine wiring tasks. 

These tasks are fairly easy to do but practice with the techniques involved always helps.  Before actually working with a type of wire or cable that is new to you, cut off a short piece and try stripping, joining, etc.  Experiment a bit to find out which of the tools you have available are easiest for you to use and which do the best job.  A little time spent in trial and error will make the job go faster.

How to Strip the Wire Ends for Plastic-Sheathed Electrical Cable

NMC electrical cable details (C) Carson Dunlop Associates

Permanent indoor installations are made by running lengths of wire between outlets and switches along or inside walls, floors, and ceilings. An electrical circuit always needs a hot and a neutral conductor plus a ground for safety.

When these individually insulated wires (black for hot, white or gray for neutral) are held together inside plastic or metal sheathing, the unit is called an electrical cable.

The most commonly used electrical cable for in­door wiring is the flat, white plastic type plastic-covered wire, or "Romex" (a trade name). Properly plastic-covered electrical wire is called "NMC" - non-metallic-sheathed cable. .

While there are many types and grades of non-metallic cable electrical wire, there are three basic kinds of interest to homeowners for most residential applications.

Sketch courtesy of Carson Dunlop Associates.


Aluminum NMC wire (C) Daniel Friedman

The type of electrical wire and its intended use is indicated by code letters printed on or embossed into the plastic wire jacket. (Our photo shows an obsolete aluminum conductor NM wire made by Primus).

How to Remove the Plastic Sheathing from Plastic-Sheathed Electrical Wire

Stripped aluminum wire (C) Daniel Friedman

Above: photo of stripped ends of aluminum electrical wiring. See ALUMINUM WIRING HAZARDS & REPAIRS - home

How to Remove the Metal Sheathing from Armored Cable ("BX") Electrical Wires or from Flexible Conduit

Armored cable or metallic-sheathed electrical cable has been in use since 1896 (in the U.K.) and in its most basic form contains two electrical conductors (black-hot and white-neutral) each individually insulated and both usually wrapped with a spiral of paper which is in turn enclosed in a flexible metallic sheathing such as shown in our abandoned-wire photograph below.

Abandoned BX armored electrical cable (C) Daniel Friedman

Hacksaw method for stripping armored cable (AC), BX cable, metallic cable (MC) or flexible metal conduit

Cutting-tool method for stripping BX armored cable

How to cut armored cable (AC) or BX flexible conduit or metal-clad (MC) Cables - NH Firebear (C) InspectApedia

[Click to enlarge any image] Our photo above of an AC cutting tool provided courtesy of NH Firebear and is discussed in more detail below.

Make certain that the electrical power has been turned off and that you've used a test tool such as a VOM or neon tester to confirm that the wires you're working on are not electrically live. Failure to take this step risks a fatal electrical shock.

Nicked electrical wire (C) Carson Dunlop Associates

After Stripping the BX jacket from electrical wire

Protect the conductor wires (hot & neutral) from future damage from the sharp edges of the cut armored cable jacket. To eliminate the possibility of sharp edges of the armor cutting into the conductor insulation, a fiber bushing should be inserted under the armor, at the point where the conductors emerge.

Reader Comments: on cutting armored cable (AC) or metal-clad (MC) Cables

How to cut armored cable (AC) or BX flexible conduit or metal-clad (MC) Cables - NH Firebear (C) InspectApedia

When cutting armored cable (AC) or metal-clad (MC) cables, you can either CAREFULLY use a hacksaw or tin snips or you can use a tool designed specifically for the job. The cable is laid inside the tool, which has a round cutting blade on a crank.

The BX cutting tool is squeezed with one hand to clamp the blade against the armor sheath and the crank is turned a few times with the other hand to cut a clean slot in the metal sheath without damaging the wires.

How to cut armored cable (AC) or BX flexible conduit or metal-clad (MC) Cables - NH Firebear (C) InspectApedia

The cable with the split armor is then taken out of the tool, the sheath is twisted and it pops apart cleanly.

Note that when type AC (trade name "BX") is used, there must also an insulated bushing (known as a "red-head") inserted to protect the internal conductors from damage and shorting on the cut end of the armor. Connectors for Type AC have a slot through which to inspect for the red-head.

How to cut armored cable (AC) or BX flexible conduit or metal-clad (MC) Cables - NH Firebear (C) InspectApedia

Most types of red-heads now have a "tail" that can be left sticking out of the hole for easier inspection. Ref NEC® Article 320.40. The bonding conductor may be bent back, over the sheath, either before or after the red-head is inserted.

How to cut armored cable (AC) or BX flexible conduit or metal-clad (MC) Cables - NH Firebear (C) InspectApedia

Type MC installations do not generally require a red-head and have no inspection hole, although some local codes may still require them. Type MC connectors are designed to prevent the conductors from contacting the armor. Not all electrical inspectors can recognize the difference without taking things apart.

How to cut armored cable (AC) or BX flexible conduit or metal-clad (MC) Cables - NH Firebear (C) InspectApedia

These photos used a Type MC cable having 12-2 with ground. A type AC would have a bonded ground. The red-head and AC connector were used for demonstration only. Do not use the wrong type of connectors for your particular type of conduit as they may damage the metal sheath. For instance, a set-screw connector could crush an aluminum AC sheath and damage the conductors inside.

It is worth noting that Type AC and Type MC, while similar in appearance and construction, have different code restrictions on where they may be used. - NH Firebear by private email 2016/07/27

Reply:

Excellent and helpful details, published above. Thank you NH Firebear.

Indeed, as I've reported elsewhere, my brother-in-law, a theater electrician in New York City, re-wired his apartment into an electrical disaster when he used BX armored cable throughout (as required in NYC), with no protective "red-head" plastic protective inserts in the cable ends. That mistake combined with zealously over-tightening the set screw in every BX cable clamp at every electrical box.

Where the BX cable cut into the hot wire the circuit breaker shorted immediately and sparks flew when power was restored. Those mistakes were quick to find. But additional shorts between the neutral conductor and the (grounded) BX cable exterior shell meant that Matt's GFCI breaker kept tripping until all of those snafus were also found and fixed.

"Fixing" the short circuits in this case was a pain as the nick into the wire insulation was right at the cut end of the BX metal jacket. A proper repair would have involved stripping back past that nick into the insulation and preparing new stripped wire-ends - a proposition that proved difficult where not enough slack or extra length remained in the original wires.

How to cut armored cable (AC) or BX flexible conduit or metal-clad (MC) Cables - NH Firebear (C) InspectApedia

NH Firebear's moisture-resistant or more generically "waterproof" flexible conduit shown in the photo above is most-often seen at outdoor compressor/condenser units of air conditioners or heat pumps but may also be proper indoors in damp locations such as shown above. Defects often found in the flexible conduit installed in these spots are shown separately at CONDUIT, ELECTRICAL.

How Much Insulation Should Be Removed From the Actual Wires Themselves?

NMB_3-wire_with_Ground_Stripped (C) Daniel Friedman

How much insulation should be stripped off of the individual wire conductors once the wire jacket has been removed? As my friend and mentor Mark Cramer, Tampa home inspector and educator, says, "Well ... it depends." It depends on the device to which the wire is to be connected. We want to remove enough insulation to assure good contact area between the wire and the connecting device, but not too much.

Black wire Red wire White wire

Watch out: not all devices use the same conductor insulation strip-back amount. In general you will need to remove more insulation to wrap a wire around a binding head screw connector than to push the wire into a push-in type connector. Above I've removed the jacket from 14-3 NMB electrical wire. The ground wire is already bare but I'll need to remove insulation from the black, red, and white conductors before they can be connected to a device or to a splice.

Excerpting from HOW to CONNECT WIRES to a RECEPTACLE or SWITCH

Strip gauge on an electrical receptacle shows how much insulation to remove when back-wiring the device. (C) Daniel Friedman

Above I'm showing the wire strip-back gauge area marked on the back of a 15A electrical receptacle. This gauge shows the amount of insulation that should be removed presumably for either of the types of connectors provided on this particular device. For the device shown above we are to remove from 1/2" to 5/8" of insulation, or about 16mm.

Below is a rather shorter wire stripping gauge telling us that for the device where this gauge appears - in this case a screw-clamp type wire connector, somewhat less insulation is to be removed. For the device shown below we are to remove 9mm of insulation - about 0.35" - quite a bit less insulation than for the device above.

Strip gauge dimensions on a pressure plate screw clamp connector of an electrical receptacle (C) Daniel Friedman

Watch out: don't strip off too little insulation or the wire will not make a safe, reliable electrical connection: either the wire won't push far enough into the screw-clamp connector or the insulation may prevent the binding head screw from pinching the wire - it'll pinch onto the insulation instead, making a loose, poor electrical contact.

And don't strip off too much wire insulation or the extra length of bare wire may cause a short circuit when you push the device back into its electrical box. That's more than embarrassing, it's dangerous. Trust me.

Most light switches and receptacles include this indicator that tells you how much insulation the manufacturer recommends stripping off when wiring this device.

Typically we're removing from 1/2" to about 5/8" of insulation, taking care not to damage or notch the wire. It makes sense, then, to actually look at these instructions given by the manufacturer, as not all strip gauges show the same strip-back quantity.

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Continue reading at ELECTRICAL WIRING COLOR CODES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see ELECTRICAL BASICS

Or see ELECTRICAL OUTLET, HOW TO ADD & WIRE

Or see ELECTRICAL RECEPTACLE CONNECTION DETAILS

Or see ELECTRICAL SPLICES, HOW TO MAKE

Or see HOW to CONNECT WIRES to a RECEPTACLE or SWITCH

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