Hole sizes for log home wiring runs

[handymann]

We are in the process of building a family log home in Ontario, and want to know the required hole diameter for holes drilled through the log walls for electrical outlets and switch boxes. Our log home supplier provided the logs predrilled with 1" access holes, but we have heard some opinions that they sould be larger now with recent Canadian codes changes. Can anyone clarify the requirement for us?

[electric-ed]

I am not aware of any CE Code changes affecting hole sizes for cables.

If you are referring to holes to run cables through, I would say 1 inch holes are large enough.
If two or more cables are installed in close proximity to each other for distances of more than 24 inches, they are required to be de-rated. (current carrying capacity reduced)

Or did you mean the recesses for the outlet boxes?

Ed

[handymann]

Ed, I am referring to the holes drilled up through the logs to bring the wiring into either lighting, plug or switch boxes. The mortised holes for the actual boxes are all sized appropriately to allow the boxes to be installed flush to the surface. They are entered by 1" holes drilled in from slots cut 2" deep into the keyway mortises for the door jamb logs. The slot in the keyway mortise is in turn entered from a 1" hole drilled up through the underlying subfloor benieth each log. Non-metallic cables of appropriate conductor sizes and number are then to be pulled up from the crawl space interjoist spaces through the keyway slots and on into the box mortises where they will then enter typical welded receptacle boxes. The most cable planned to run through any one 1" hole is one 14-2 NMC plus one 14-3 NMC. In all cases these are for residential lighting circuits located on the interior surface of the gable end walls or adjacent to the three exterior entrances. All of the outlet receptacles will be either wired up through and within interior partition stud walls on the first floor or the overlying loft floor as in a typical frame house, or will be contained in approved floor boxes fed from cables run through the interjoist spaces in the underlying basement crawl area.

[electric-ed]

Hi Bill,

That sounds OK to me as far as code compliance is concerned.

Ed

[Tony Moscioni]

Wiring for Log Type Construction

Questions have been asked about precautions to be taken where wiring log type construction.
There are many types of log construction.

For Ontario Electrical Safety Code purposes, we differentiate between two types.

One type uses a log finish with standard stud construction and our normal rules apply. The other type uses only logs and there are special requirements under the general provisions of Rule 12-100.


Meter Base Mounting for Both Types

To allow for shrinkage, some means must be provided to accommodate motion of the logs relative to vertical runs of conduit and cable forming part of the consumers service. The amount of shrinkage that may be expected over the life
of the installation has been estimated as up to 2% of the conduit run where the conduit crosses logs of profiled construction (kiln dried rectangular logs) and up to 8% of the conduit run for hand-crafted log construction.


Acceptable means include expansion couplings in PVC Conduit (with appropriate loops/bends in the cable), offsets
in the conduit, mounting the consumers service on a board with slots and mounting the consumers service independent of the logs.


Wiring Methods for Log Only Types (not standard stud construction)

For log only construction, NMWU cable should be used when on the outside of the thermal insulation. When on the inside of the thermal insulation NMWU is preferred, but armoured cable (AC), aluminum sheathed cable (RA) or nonmetallic
sheathed cable (NMD) is acceptable.


Restrictions as described on the attached sheets are required on how the logs are drilled to allow wiring to be pulled through because of the concern that the logs might shift.


Construction using Machined Kiln Dried Logs

This type of construction includes rectangular logs with dove tail joinery and *****ing between logs, machined rectangular logs with double tongue and groove and dovetail joinery and milled tongue and grooved logs.


Wiring Method Restriction

Branch circuit wiring using
non metallic sheathed
cables or armoured cables.

For vertical runs up to 18 inches length through one or more logs, a one inch minimum diameter hole for the cables is required. For longer
vertical runs, the cables must be in rigid PVC conduit or the hole size must increase to 2 inches minimum diameter.

Instead of drilling, the wiring may be installed in the spaces around doorways, windows and between logs with appropriate mechanical
protection.


For Other Log Types (e.g. round and logs with Swedish cope joinery)

Wiring Method Restriction

Branch circuit wiring using
non metallic sheathed
cables or armoured cables.

Electrical boxes may be wired by:
drilling a one inch diameter hole through one log with the box installed in the same log, or
drilling a one inch diameter hole through several logs, installing a PVC rigid conduit through the logs and terminating the conduit in a
box, or drilling a 2 inch diameter hole through several logs.

Instead of drilling, the wiring may be installed in the spaces around doorways, windows and between logs with appropriate mechanical
protection.

November 1996 Page 1 of 2 Bulletin 12-20-0

Tony Moscioni
Electrical Inspector
Electrical Safety Authority

? Electrical Safety Authority - 2002

[handymann]

Tony,

Thanks for your detailed authoritative reply. We
plan to contact our log home builder and make him aware of these requirements so that future customers will have an easier time installing their wiring in code compliance.

Most of our access holes are through one log and thus the one inch hole will be adequate, but several will need to be rebored to the larger 2" diameter. The wiring channels adjacent to our doors do go into a channel cut behind the keyway slot for the door post log after penetrating the single bottom log. In two cases they do not go further up than the keyway, but one door also has a 24" long hole leaving the keyway and extending up to the gable end wall stud spaces. This hole will need to be enlarged to 2" or a 1" rigid PVC conduit will need to be inserted.