What kind of wire do you use to wire a shop?

There are a few key factors to consider when deciding what kind of wire to use for wiring a shop space. The main purpose of the wiring is to provide electricity safely and efficiently to power lights, outlets, machinery, and other electrical components. The type of wire selected needs to be compliant with electrical codes, rated for the expected electrical loads, and suitable for the specific installation location and environment. Some quick answers to key questions below provide an overview of the most important criteria for selecting shop wiring.

What are the different types of electrical wire?

The main types of electrical wire used for wiring buildings and shops are:

– Copper – The most common type of wire, made of copper metal. Can be bare or insulated. Good conductivity.

– Aluminum – Made of aluminum metal. Lower conductivity than copper but more lightweight. Primarily used for high-capacity feeders.

– Metal Clad (MC) Cable – Copper wires surrounded by a metal armor casing. Used for exposed runs.

– Nonmetallic Sheathed Cable (NM, Romex) – Copper wires with a plastic sheath. Used for concealed runs in walls and ceilings.

– Conduit – Plastic or metal tubing that wire is pulled through for protection. Common for exposed installation.

What wire gauge should be used?

The wire gauge (awg size) used depends on the required ampacity (current carrying capacity). Standard sizes used in shops are:

– 14 awg – For 15 amp general purpose lighting and receptacle branch circuits.

– 12 awg – For 20 amp outlet and machine circuits.

– 10 awg and thicker – For higher ampacity feeders and mains.

A qualified electrician can determine the correct wire size based on load details and electrical code requirements. Using wire that is too small for the loads can cause dangerous overheating.

Does the wiring need to be in conduit?

Shops often require exposed wiring runs along ceilings, walls, and machinery. Electrical codes require these exposed runs to be protected inside conduit – either rigid metal or EMT (electrical metallic tubing). The conduit protects the wires from damage and also provides an equipment grounding path. Flexible liquidtight conduit is commonly used to connect equipment.

What kind of insulation and sheathing is best?

For concealed branch circuit wiring like in walls, the preferred choice is NM cable (Romex) with PVC insulation and sheathing. The PVC holds up well to moisture, impacts, and chemicals. Individual THHN/THWN-2 copper wires having nylon insulation can also be run through conduit where allowed.

For feeders, XHHW aluminum wire is commonly used since it is rated for wet locations and can withstand the higher currents. The insulation is cross-linked polyethylene (XLP), one of the most durable insulations.

Does the wiring need to be weather and water resistant?

Shop environments often have exposure to moisture, chemicals, impacts, vibration, and other hazards. Using only outdoor-rated wires that can withstand these hazards is highly recommended. Look for wires with a ‘W’ (wet) rating such as THWN, XHHW, or RHW. Avoid standard building wire like NM cable in wet areas.

How do you determine the required number of circuits?

The National Electrical Code (NEC) provides guidelines on required branch circuits based on shop square footage and types of equipment. For example, a 2,000 sqft shop would need:

– 2 circuits minimum for lighting
– 2 circuits minimum for receptacles
– Dedicated circuits for larger equipment per code

A qualified electrician can perform load calculations to determine the exact number of circuits needed based on all connected loads. Never overload a circuit beyond its rating to prevent tripping or fires.

Types of Wire

There are several main options when selecting wire for a shop installation. The environment, installation method, and electrical loads will dictate the best wire type to use.

Nonmetallic-Sheathed Cable (NM)

NM cable, commonly known by the brand name Romex, is the standard wire used for indoor electrical wiring in walls, ceilings, and crawlspaces. It consists of 2-4 THHN copper wires bundled together and covered with a PVC outer sheath. NM cable is cheap, easy to install, and meets code requirements for concealed branch circuit wiring in dry locations. The main drawbacks are that it cannot be used in exposed conduit runs or wet areas.

Metal Clad (MC) Cable

MC cable features the same THHN wire cores as NM cable but with an outer wrapping of flexible steel armor. The metal casing gives added durability and protection for exposed runs along walls, ceilings, and equipment. MC cable can be installed exposed or concealed and is approved for damp locations. It costs more than NM but less than installing individual wires in conduit.

Armored Cable (AC)

Similar to MC cable, AC cable uses an outer metal wrapping around the inner wires. However, AC cable can only be used for concealed installations and not left exposed. It gives good physical protection against nails and impacts when run through wood framing and studs. AC cable is a cheaper alternative to NM for these concealed branch runs.

Conduit Wiring

Conduit wiring is required for all exposed shop wiring per NEC code due to the durability and protection offered. Individual THHN/THWN or XHHW wires are pulled through rigid metal, EMT, or PVC conduit runs. This gives very good protection against physical damage, moisture, and chemicals. Conduit installations cost more in labor and materials than cables but provide the highest level of durability and safety.

Liquidtight Flexible Metal Conduit

For connecting equipment and machinery in a shop, liquidtight flexible metal conduit can be used. This special type of flexible conduit has a water-resistant PVC outer jacket to protect the inner flexible metal conduit. It is used as a short whip to connect vibrating equipment to rigid conduit runs and junction boxes throughout the shop.

Conductor Size and Ampacity

Selecting the proper wire size, known as conductor ampacity, is critical for safe and effective shop wiring. Ampacity refers to the maximum current a wire can safely carry without overheating. Several factors determine the required ampacity, including:

Circuit Breaker Rating

Standard building wiring uses 15 amp and 20 amp circuit breakers. Their ampacity should match that of the wire used in the circuits they protect. For a 20 amp circuit, 12 awg THHN wire rated for 20 amps would be used. #14 awg for 15 amp circuits. Higher capacity 30, 40, and 60 amp circuits will use thicker 10 awg, 8 awg, or 6 awg wire.

Load Calculations

While code sets minimum requirements, the actual connected load in amps dictates the true wire ampacity needed. The total wattage of lighting, receptacles, and equipment determines the amp draw. An electrician performs thorough load calculations to design the electrical system.

3% Voltage Drop Rule

As wire length increases, voltage drop along the conductors increases due to resistance. Excessive drop can affect equipment operation. Wires must be sized so that voltage drop does not exceed 3% of supply voltage. Longer runs require thicker wire.

Motor Loads

Motors used in shops have high starting current surges that can be 6-8 times their full load amps rating. Wires for motor circuits need to be significantly oversized to avoid voltage drops during starting. The NEC provides required wire sizing for motor circuits.

Distance to Panel

The farther electrical runs are from the main panel, the thicker the wire must be to avoid excessive voltage drop. Longer circuit runs will need wire one size larger than code minimums.

Ambient Temperature

Wires derate ampacity in higher temperature environments. Wires in hot locations like attics require the next size up to compensate for heat effects.

Properly sizing wires using these factors ensures safe operation and reliability of shop electrical systems and equipment.

Installation Location and Environment

The conditions where the shop wiring will be installed are important considerations for selecting suitable wire.

Indoors vs. Outdoors

Outdoor runs require wire specifically rated for wet locations, like THWN and XHHW. Indoor wires like NM can only be used where sheltered from weather and moisture. Underground burial requires special UF cable.

Wet or Damp Locations

Shops often have exposure to moisture from refrigeration systems, process piping, washdowns, and more. Using only wires listed for wet locations is critical. THWN wire in conduit is a common choice.

Corrosive Areas

Some shops handle corrosive chemicals or materials that can damage insulation and sheathing over time. Wires with chemically resistant insulation like XLP must be used in these locations.

Extreme Temperatures

Heat and cold can make wires become brittle or degrade faster. Check wire ratings to ensure it can withstand the ambient temperature range expected.

Physical Hazards

Mechanical rooms and industrial areas pose risks of impacts, abrasion, and vibration. Wires need robust cut, crush, and impact resistance. Conduit or armored cable provides an extra layer of mechanical protection.

Proper wire selection helps withstand hazards posed by various environmental conditions in and around shops.

Cost and Budget Considerations

The costs of shop wiring includes both material and labor expenses. Several factors affect the overall budget.

Conduit vs. Cable

Conduit wiring takes more time to install but offers durability. Cables cost less but cannot be used for all applications. Balance cost vs. physical protection needs.

Copper vs. Aluminum

Aluminum costs less than copper but has reduced capacity and more difficult terminations. It can yield savings on large feeders and services.

Wire Size

Smaller wire gauges have lower material cost, but labor is the same regardless of size. Properly sizing wire prevents the need for future upgrades.

Sheathing Material

Basic PVC insulation is inexpensive. For durability against chemicals, impacts or moisture, upgraded sheathing like XLP, XHHW, or SOOW cost more.

Metal Conduit Type

EMT conduit offers the lowest cost threaded rigid steel. Long term value may justify the added cost for rigidity and strength of RMC.

Prioritize safety and code compliance when selecting wiring. But also look for areas to optimize costs, such as strategic use of cables or aluminum conductors. Discuss options with electrical contractors to find the ideal balance.

Electrical Code Requirements

All shop wiring installations must comply with the National Electrical Code (NEC) and local jurisdiction codes. Key requirements include:

Approved Wiring Methods

NEC Chapter 3 specifies permitted wiring types based on application and environment. Cables, conduit, and other wiring methods described in this article meet these requirements.

Protection from Damage

Exposed cables less than 8 feet high must be protected from physical damage. Running wires in conduit meets this requirement.

Damp and Wet Locations

Only wire rated for wet locations may be used. Conduit seals, waterproof fittings, and GFCI protection required where moisture is present.

Minimum Wire Size

NEC Table 310.5(B) sets minimum sizes, such as #12 awg for 20A branch circuits. Larger may be needed for voltage drop.

Conduit Fill

The maximum fill capacity for conduit is specified in NEC Chapter 9, Table 1. Allowable wires depends on conduit size and wire gauge.

Box Fill

Every junction box must meet NEC 314.16 volume requirements for the number and size of wires inside.

Always defer to the NEC and local codes for all details on proper, legal, and safe wiring methods in your area.

Conclusion

Specifying the optimal wire for a shop environment depends on many important considerations – installation location, electrical loads, environmental hazards, and cost. While NM cable is fine for indoor concealed runs, shops typically require conduit and THHN or XHHW wire for exposed runs and wet areas. Copper conductors are preferred over aluminum. A qualified electrician can assess the specific needs and recommend compliant wiring solutions that balance durability, safety, and cost based on NEC requirements. Robust and code-compliant electrical wiring ensures reliable power and safe operation for any shop space.