Electrical conduits and boxes

Electrical conduits are tube to protect and route wires in buildings/structures.

Electrical conduits are either metal/plastic/fiber/fired clay. Most are rigid. Flexible conduits are for some purposes.

Electrical/Junction boxes hold a junction of wires from damage and reducing risk of electric hazards (e.g. shocks and fires).

junction:

Conductor types

Conductors installed in any suitable location for use shown in Table 19 for a particular location involved and with particular respect to:

moisture, if any;

corrosive action, if any;

temperature;

degree of enclosure; and

mechanical protection

Table 19 (CEC codebook)

Common raceways

EMT

Galvanized Steel Raceway

Galvanized steel raceways are often for industrial and commercial uses. It protect wires in corrosive environments. They're one of most used steel types with its long durability/strength, steel formability, and corrosion protection of zinc-iron coating.

Non-metallic conduit (PVC) raceway

Non-metallic/conduit raceway systems are often for homes/underground and are non-conductive and water-resistant.

Flexible metal conduit (FMC) raceway

Flexible metal conduit systems are ideal for curving/turn in other directions, for areas of high vibrations as it sflexibility of protects wires against sudden jolts and movements. A drawback of FMC raceways is they're unsuitable for very corrosive places.

CEC 2025 - 12-3000

Junction box types

Junction box requirements

Adequate mechanical and environmental protection.
Adequate size for splices, devices and conductors.
Affordable cost

Device box number codes

“2” – non-gangable
“104 – 2 ½ inches deep
“L” – clamps for NMSC
“LE” – less ears

“1” – gangable
“100” – 1 ½ inches deep
“L” NMSC clamp
The box has ears – for “rework”

Armoured Cable Clamp

device boxes are also used very with armoured cable

Utility box

Are for “surface” work

note the location of the device mounting holes

3 common sizes

Various of covers

Octagon boxes

“pan” box
½ inch deep
“54” – octagon box
“151” 1 ½ inch deep
“K” concentric knock outs – ½ and 3/4

“extension” ring increases the
volume of the box
“171” boxes are 2 1/8 inches deep

Octagon covers

“54-C-1” is the most common cover

4 Inch square boxes

1# E.g. “52” – 4 inch square box

“151” 1 ½ inches deep

“K” – concentric knock uts

2# 52-C-1 is the most common cover the “52-C-10” family of covers

allow a device to be mounted on

the box

Drywall covers the cover except for the device location

3# The “64” and “66” covers are for special receptacles.

Many more styles are available.

4 11/16 inch square boxes This is the box for a dryer or stove receptacle--must be 2 - 1/8 inches deep.

Used in residential construction

Built in NMSC clamps

Airtight – seal to vapour barrier

Concrete Ring

This is on the roof.

Concrete Slab Construction

Carpenters build a form decked with plywood

The bottom layer of reinforcing steel is laid concrete rings are fastened to the forms

Conduits are added to connect to outlets, switches and panel.
Conduits “stubbed” down through holes in the plywood connect to wall mounted devices.
The concrete ring gets a cover
The top steel is laid

Concrete slab construction

More info for boxes and covers: A-Boxes_Covers-E.pdf

Determining the size of needed device boxes

Couting conductors

Using Table 23 (top part)

A conductor going into a box without connection is 1 conductor;

All conductor entering/leaving a box and connected to a terminal or connector in in is 1 conductor.

a conductor of which no part leaves the box shall not be counted; and

Counting wire connectors

1 conductor per 1 pair of wire connectors with insulating caps (no deduction for 1 wire connector, deduct 1 conductor for 2- or 3-wire connectors, 2 conductors for 4- or 5-wire connectors, etc.); or

Flush Devices

2 conductors if the box 1+ flush devices mounted on a 1 strap

Example 1

How many conductors are in a 4-11/16 inch square box?

Answer: The conductor count for this setup is 6 conductors.

Example 2

How many conductors are there in the box using the 26th edition CEC rules? Include an allowance for wire connectors.

If the conductors are 10 AWG, is the box big enough?

Answer

Black - 4
White - 3
Blue - 1
Red - 1
Wire con - 1
Total: 10

The conductor count was 10. Checking

Table 23 shows the max number of conductors permitted is 9.

This box is too small.

Example 3

How many conductors are there in the box using the CEC rules? Include an allowance for wire connectors. 2. If the conductors are 12 AWG, is the box large enough?

Answer:

black - 4
white - 3
blue - 1
red - 1
wire con - 1
receptacle - 2
Total - 12

Yes this works.

ETM

Complex conduit system

Bigger conduits would feed panels or HVAC units.
Other conduits would contain control systems, motor feeds, fire alarm systems, lighting, receptacle circuits, etc.

Conduit sizes

Conduit size is the nominal internal conduit diameter.

Many conduit types have slight different internal diameters for the same nominal size.

Codebook give diameters in millimeters, but it's mostly in inches.

Places like stores write in imperials

Codebooks write in metric

Pulling wires through conduit

Conduit Installation issues

If the conduit is the bonding method,

lock nuts, set screws etc. must be tight and make good electrical contact.
the conduit cannot be subject to corrosion

The conduit must provide adequate mechanical and environmental protection for the conductors.

Is the conduit outside or subject to moisture?
Is the conduit in a location where vehicles might impact it?
Are there corrosive liquids or vapours present?

The conduit systems must let conductors installed without damage.

This limits the number of bends conductors pulled through.
This needs conduits big enough.

We cannot install these conductors in a smaller conduit.

Raceway

[1] Raceways/Raceway systems are enclosed conduit for a physical path for wires/cables/busbars, and qualified in codebook rules.

Some types of raceways:

Galvanized steel (flexible and rigid)
Non-metallic conduit or PVC (flexible and rigid)
Flexible metal conduits

Unless otherwise qualified in rules of the 2025 CEC codebook, "raceway" refers to conduit (rigid and flexible, metal and non-metallic), electrical metallic and non-metallic tubing, underfloor raceways, cellular floors, surface raceways, wireways, cable trays, busways, and auxiliary gutters.

12-910 Conductors and cables in conduit and tubing (see Appendix B)

1) Conduit and tubing shall be of sufficient size to permit the conductors to be drawn in and withdrawn without damage to conductors/conductor insulation.

3) The max number of conductors in 1 conduit/tubing shall not pass 200.

The maximum number of insulate conductors or

multi-conductor cables in one conduit or tubing

shall be such that the insulated conductors or

cables and their coverings will not result in a

greater fill than that specified in Table 8, and in this

determination,

Conduit fill

The max number of insulate conductors/multi-conductor cables in a conduit/tubing are the insulated conductors/cables and coverings won't cause a greater fill than that specified in Table 8, and in this determination,

References

[1] Types Of Raceways - Gracon
[2] Electrical conduit - Wikipedia
[3] Junction box - Wikipedia
[4] What Is a Junction Box? - the Spruce
[5]
[6]

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