Conduit Seal Effectiveness
By Scott T. McGlamery, P.E.; and Bret T. Heckman, E.I.
Department of Electrical Engineering, Hixson, Cincinnati, OH
Abs tr ac t - When there is a significant
temperature difference between two adjacent
spaces, maintaining an effective vapor barrier
between the spaces is essential to prevent
vapor infiltration and condensation in the cold
space. Conduit penetrations through walls and
ceilings can compromise the vapor barrier if not
done properly. This paper reports the results of
testing four different conduit vapor seals.
employed, or other issues, we tested four types
of conduit seals to determine which seal was
most effective.
The four seal types were:
neutral cure silicone, expanding polyurethane
foam sealant, duct seal compound, and
hazardous location sealing compound. The
tests evaluated ease of installation, vapor
infiltration, and pressure resistance.
II. Test Setup and Procedure
I. Introduction
GMP (Good Manufacturing Practice) facilities
often contain spaces that are conditioned to low
temperatures for product / ingredient storage
and to maintain product temperature during
processing and packaging. Typical temperature
requirements range from 60°F to 0°F or lower.
At these temperatures, the dew point in the
room is often below the temperature in the
adjacent spaces. This makes an effective vapor
barrier essential for preventing vapor infiltration
and condensation. Vapor and condensation
control is particularly critical in any penetration
that could provide a niche where microbial
growth could occur out of sight and in an area
that is difficult to clean. Conduit penetrations
are of particular concern, because they are a
closed system capable of transferring vapor
between spaces, and capable of holding water
in a niche that could go unnoticed for a long
time.
Condensation occurs when a conduit system
is open to a space with warm, humid air, and a
space with a dew point below the temperature of
the adjacent space. Vapor pressure pushes the
water vapor towards the cool, dry end of the
conduit, where the lower temperature causes
the vapor to condense inside the conduit. Over
time, the condensation can fill the conduit and
the enclosures they serve with water, creating a
dark wet niche that represents a food safety
concern. Conduit drains are sometimes used to
allow any condensation to drain out of the
conduit system, but the first line of defense
should be to prevent the condensation from
occurring in the first place.
Before testing could begin, an apparatus was
built to emulate facility conditions. This
arrangement consisted of 3/4" Schedule 80 PVC
conduits mounted vertically and horizontally.
Conductors were cut at 20” long to project out of
the top and bottom of the conduits. A conduit fill
of four Thermoplastic High Heat-resistant Nyloncoated (THHN) conductors and a conduit fill of
12 THHN conductors were used for the
experiment. A conduit body was affixed to one
end of the conduit to replicate a junction point in
the conduit system.
In the case of the
hazardous location sealing compound, a Class I
Div 2 conduit seal was used. See Figure 1 for
the apparatus set up.
Figure 1: From left to right – Silicone, Expanding
Foam, Duct Seal, and Hazardous Location
Compound Sealant
After observing the failure of several types of
conduit seals in the field, either due to
workmanship, effectiveness of the type of seal
6 5 9 V a n M e t e r S t r e e t C i n c i n n a t i O H 4 5 2 0 2 - 1 5 6 8 T: 5 1 3 2 4 1 1 2 3 0 F: 5 1 3 2 4 1 1 2 8 7
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Conduit Seal Effectiveness
A. Ease of Installation
Each one of the sealants was placed in the
vertical and horizontal conduits. Workmanship
of installation for each was conducted as good
as or better than observed in the field. The
sealants were then allowed to cure for at least
eight hours or per manufacturer’s requirements.
The ease of installation and level of workmanship required was recorded. After testing was
completed, the conductors were removed from
the seal to test the ability to remove conductors
for renovation or replacement.
the conduit body far enough to make an
effective seal. The installation was awkward
and cumbersome. See Figure 2. A light pull on
the conductors could easily break the seal and
remove the conductors.
B. Vapor Infiltration
The vapor infiltration test assessed the
sealant’s ability to prevent vapor from passing
through the conduit. The horizontal conduits
were mounted vertically for testing. Water was
used to simulate vapor infiltration due to the
logistical complexities of testing with water
vapor. The measured amount of 25mL of water
(approx.2 3/4” of water in a 3/4" conduit) was
poured into the top of each conduit. The bottom
of the conduit was then observed for any
leakage. The vapor infiltration test with 25mL of
water was the equivalent to approximately 0.1
psig of differential pressure on either side of the
conduit seal.
C. Pressure Testing
Pressure testing was conducted to find the
failure point of each sealant. The pressures
employed significantly exceed those that would
normally be found in a facility. To pressure test,
the remaining space at the top of the conduit
was filled with water. Then compressed air was
applied to the top of the conduit to force water
through the sealant. Increments of 1, 5, 10, and
15 psig were used to test the product’s
resilience. In some cases, the pressure was
increased beyond 15 psig to find its failure point.
III. Analysis
A. Ease of Installation
Neutral Cure Silicon:
The silicone was
applied using a standard caulking gun. A 1/4"
bead opening was cut on the end of the tube.
Next, the tube was inserted into the conduit
body as far as it could go. The caulking gun
trigger was pulled to full compression to apply
the silicone. The tube cannot be inserted into
Figure 2: The use of a caulking gun to apply silicon
Expanding Foam:
The expanding foam
straw attachment was inserted two inches into
the conduit. The expanding foam trigger was
then held for approximately one second to apply
foam. The installation was quick, simple and
error proof. A strong pull on the conductors was
required to break the seal and remove the
conductors.
Duct Seal: The duct seal was immediately
ready for use out of the package requiring no
additional tools. Being of a clay-like substance,
the duct seal could be broken into pieces and
placed around and between the conductors
relatively easy. In the 12-conductor conduit, the
number of conductors in the conduit made it
more difficult to install the duct seal. A light pull
was required to break the seal and remove the
conductors.
Hazardous Location Sealing Compound:
This compound sealant required damming
fibers, water, a mixing container, and measuring
and stirring devices. The damming fibers were
placed into the conduit seal to create a dam
between the conductors and the conduit seal
walls. The sealing compound was measured
and mixed per manufacturer’s directions. The
sealant was then poured into the conduit seal
6 5 9 V a n M e t e r S t r e e t C i n c i n n a t i O H 4 5 2 0 2 - 1 5 6 8 T: 5 1 3 2 4 1 1 2 3 0 F: 5 1 3 2 4 1 1 2 8 7
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Conduit Seal Effectiveness
and allowed to cure before further testing. The
sealing compound was found to be messy, time
consuming to install, and difficult to get around
and between conductors in the 12-conductor
conduit. The use of a hammer and chisel was
needed to free the conductors from the sealing
compound. Damage to the conductors was
inevitable upon removal.
B. Vapor Infiltration
Neutral Cure Silicon: The silicone sealant
immediately failed all vapor infiltration tests. It
showed little or no ability to contain water.
Expanding Foam:
The expanding foam
sealant was able to prevent all water from
passing through to the other end of the conduit
body. To analyze the seal, the foam plug was
removed and cut into sections to examine the
form’s ability to surround the conductors. The
foam extended 8”-10” into the conduit and was
able to force its way in between and around all
the conductors present in the conduit. See
Figure 3.
See Table 1 for Vapor Infiltration Prevention
Results.
4-Conductors
FAIL
PASS
PASS
PASS
Silicone
Foam
Duct Seal
Hazardous
12-Conductors
FAIL
PASS
FAIL
FAIL
Table 1: Vapor Infiltration Prevention Results
C. Pressure Testing
Neutral Cure Silicon: Pressure tests were
not conducted on the silicone sealant due to its
failure at ambient conditions.
Expanding Foam:
The expanding foam
sealant was able to prevent leaks up to
approximately 20 psig before failure.
Duct Seal: One pressure test was conducted
on the duct seal. This conduit contained four
conductors and passed the vapor infiltration test.
When 1 psig was applied to one end of the
conduit, the seal broke and the water passed
through the conduit.
Hazardous Location Sealing Compound:
This sealant was able to prevent water
infiltration from going through the conduit seal
filled with hazardous location sealing compound
at pressures above 30 psig. Water infiltration
was observed at the conduit seal plug, but not
going through the entire conduit seal.
See Tables 2 and 3 for Pressure Testing results.
Figure 3: Expanding Foam Section
Duct Seal: The duct seal installed in the
four-conductor conduit was able to prevent
water infiltration. When the vapor infiltration test
was conducted on the 12- conductor conduit, it
was unable to make an adequate seal.
Hazardous Location Sealing Compound:
This compound sealant was able to prevent
water infiltration. Similar to the duct seal, the
number of conductors impacted the results of
the seal. The four-conductor conduit was able
to prevent vapor infiltration. When 12 conductors
were tested, water was observed leaving the
other end of the conduit seal indicating an
inadequate seal.
Silicone
Foam
Duct
Seal
Hazard
1PSI
N/A
PASS
FAIL
Four Conductors
5PSI
10PSI
N/A
N/A
PASS
PASS
N/A
N/A
15PSI
N/A
PASS
N/A
+15 PSI
N/A
PASS
N/A
PASS
PASS
PASS
PASS
PASS
Table 2: Pressure Test (Four Conductors) Results
Silicone
Foam
Duct
Seal
Hazard
1PSI
N/A
PASS
FAIL
FAIL
Twelve Conductors
5PSI
10PSI
15PSI
N/A
N/A
N/A
PASS
PASS
PASS
N/A
N/A
N/A
N/A
N/A
N/A
+15 PSI
N/A
PASS
N/A
N/A
Table 3: Pressure Test (Twelve Conductors) Results
6 5 9 V a n M e t e r S t r e e t C i n c i n n a t i O H 4 5 2 0 2 - 1 5 6 8 T: 5 1 3 2 4 1 1 2 3 0 F: 5 1 3 2 4 1 1 2 8 7
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Conduit Seal Effectiveness
IV. Conclusions
In conclusion, expanding foam was a more
effective conduit sealant than neutral cure
silicone, duct seal, and hazardous location
sealing compound. The foam was easy to install
and guaranteed an adequate seal with an
almost foolproof installation method. Silicone
and the hazardous location sealing compound
were cumbersome to install and required
additional tools and / or materials to complete
the task. The foam was able to force its way in
between and around all the conductors present
in the conduit, whereas the silicone, duct seal,
and hazardous location sealing compound were
only able to fill the conduit partially, making an
inadequate seal. The pressure test established
that the expanding foam would perform
sufficiently even at pressures well above typical
plant conditions. In addition to being the most
effective sealant, expanding foam is also the
lowest cost solution.
References
National Electric Code, 2008. National Fire
Protection Agency, Inc. Quincy, MA, 2007.
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6 5 9 V a n M e t e r S t r e e t C i n c i n n a t i O H 4 5 2 0 2 - 1 5 6 8 T: 5 1 3 2 4 1 1 2 3 0 F: 5 1 3 2 4 1 1 2 8 7
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