Watch the Width
Reduce Potential Defects - A Helpful Tip from BD Loops

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Recent testing by BD Loops shows the width of the saw-cut critical to preventing defects in the installation of inductance loops. The following chart data shows the importance of using the proper saw-cut width to provide space for epoxy/sealant to completely flow around the loop wires to minimize air spaces between the wires. Air spaces between wires can fill with water, which can freeze and cause the wires to become exposed by pushing them out of the saw-cut groove. Air spaces allow movement of the wires within the groove, this movement can be caused by any form of ground vibrations resulting in a false detection.

Test data shows that even when using the thinnest two-component polyester epoxy sealant on a 1/8” groove, there was not enough space between the wires and the saw-cut wall to allow the epoxy to fill the void. A Polyurethane sealant was also used and its data is listed below. Bondo P-606V epoxy had a viscosity of 4,000 – 7,000 cps (much like the consistency of hot honey). The other, Chemque Q-seal 290S had a viscosity of 9,000 – 30,000 cps (the consistency of thick ketchup).

Clearance Chart:

Saw Blade Width

Width Of Cut

Wire Gage

Wire Size

Clearance

Wire Vendor

New 1/8”

.125

20

.118

.007**

Brand X

Used 1/8”

.111

18

.109

.002**

Brand Y

New 3/16”

.187

16

*

Built in backer rod*

BD Loops

Used 3/16”

.183

16

*

Built in backer rod*

BD Loops

*BD Loops are designed to fit within a 3/16” groove and has an outer jacket with built in backer-rod that completely seals the bottom portion of the groove, so sealant does not need to flow around the wire.
**  Two sheets of 20# copy paper measures .006 in thickness

Epoxy/Sealant

Width Of Cut

Wire Gage

Wire Vendor

Air Pockets Present

Bondo P-606V

.125

20

Brand X

YES

Bondo P-606V

.122

18

Brand Y

YES

Bondo P-606V

.111

18

Brand Y

YES

Bondo P-606V

.185

16

BD Loops

NO

Bondo P-606V

.180

16

BD Loops

NO

Chemque Q-seal 290S

.125

20

Brand X

YES

Chemque Q-seal 290S

.122

18

Brand Y

YES

Chemque Q-seal 290S

.111

18

Brand Y

YES

Chemque Q-seal 290S

.185

16

BD Loops

NO

Chemque Q-seal 290S

.178

16

BD Loops

NO

These tests are supported by the following pictures,
which show clear evidence of the air gaps between the wires.

Watch the Width Images

Conclusion:

The 1/8" Groove test (which can be viewed here) proves that a 1/8” saw-cut (as claimed by some vendors) will not provide durability and reliability due to the high possibility of air pockets forming in and around the loops. The tests clearly indicate the wider 3/16” saw-cut and the preformed loops from BD Loops provide the best possible installation to minimize air pockets and potential failures.