Effect of sealant compounds on electrical wires

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Effect of sealant compounds on electrical wires

Blaga, A.; Lacroix, R.

Ser

m

,

._:

ISSN

EFFECT

OF

ON

by

A . Blaga and R. Lacroix

Installation of elecTsical wiring and electrical boxes involves making holes through vapor barriers. To maintain t h e integrity of the

vapor barrier the Residential S t a n d a r d s (Section 26 F 1 4 , 1977) require that these h o l e s be s e a l e d w i t h caulking [sealants), tape or other

approved material (1). Central Mortgage and Housing Corporation's field o f f i c e r s raised t h c qucstjon of w h e t h e r ingredients of the sealant

compounds would cause deterioration o f t h e electrical wire covering over

a short- or long-term period. The o h j e c t of t h i s n o t e , therefore, is _to

r e p o r t on a s t u d y of t h i s question i.e., t h e e f f e c t of common commercial

sealant compounds on t h e e l e c t r i c a l resistance of the i n s u l a t i o n . WIRE COVERING MATERIALS

The _{term "wire covering" r e f e r s to insulation and sheathing, o r} j a c k e t . Insulation normally refers to the p r i m a r y dielectric material

applied to individual electrical conductors

C

wires n o t insulated f r ~ m one another, suitable f a r carrying e l e c t r i c c u r r e n t ) . S h e a t h i n g is t h e outer covering [usually p l a s t i c ) t h a t may scrvc 3 numbcr o f f u n c t i o n s , i n c l u d i n g r e s i s t i n g abrasion, rnoisturc

and

in

A jacket i s a r u b b e r o r a p l a s t i c c o v e r i n g , sometimes f a b r i c reinforced,

o v e r t h e insulation or s h e a t h i n g of a cable.

EXPERIMENTAL

F i v e types o f commercial sealants (Table I ) currently used

in

junction w i t h installation of electrical cables in residential buildings

and approved by Central Mortgage and Housing Gorporatfon (OMC] were

employed i n the p r e s e n t investigation. The e f f e c t o f each sealant material on seven d i f f e r e n t cable s e t s (Table 11) purchased on t h e open market was t e s t e d . In the test, one end o f each c a b l e was covered w i t h s e a l a n t paste s o as to be

in

jacket material and bare ground wire (Figure 1 ) . The assembly was p l a c e d i n a rectangular polyethylene box covered loosely w i t h a l i d to simulate t h e enclosed space within a wall. After 6 5 days o f aging under s t a n d a r d

laboratory conditions [ 2 5 u ~ , 50 p e r c e n t R H ) , t h e sealant material was

removed and the i n d i v i d u a l conductors examined visually. The resistance

of t h e insulation sf t h e control cables and the _{treated cables was}

measured w i t h a 2500 V Megger i n s t r u m e n t (a direct-reading resistance

D 1 SCUSS IUN OF RESULTS

Visual examination indicated that t h r e e t y p e s o f sealants ( T a b l e I , Series Nos- 2 , 3 and 5 ) d i d n o t produce any visually detectable changes

in t h e insulations and jackets of the seven cables tested.

The

polysulfide r e s i n sealants (one and t w o components respectively, Serics 1 and 4 1 , caused slight softening and surface discoloration of the

insulation and jacket m a t e r i a l of c a b l e s Nos. 5 and 7 . The s o f t e n i n g

effect disappeared 15 t o 20 days a f t e r removal of t h e sealant material. The bare ground capper wires were not a f f e c t e d i n any of t h e s e experiments.

The e l e c t r i c a l resistance (R) o f the i n s u l a t i o n was generally n o t a f f e c t c d by contact with t h e sealants, Only t h e resistance of t h e insulation

in

cable No. 6 , t r e a t e d w i t h s'licone

_k

6

creased

from

8

considerably greater [by a factor o f 2700) than t h e minimum [l x 10 ohms)

r e q u i r e d by t h e O n t a r i o Hydro safety code ( 2 1 . The measured resistance o f

the r e m a i n i n g cables trea

_E

controls (R > 50,000 x 1 0 ohms].

CONCLUSIONS

Results i n d i c a t e that the c o n t a c t of

five

Board standards) with c a b l c s u s e d in b u i l d i n g s do not produce significant changes in the insulation. The measured resistance of the i n s u l a t i o n is

generally not affected.

Although the electrical cables used i n this study have PVC insulation, these results also apply to cables i n s u l a t e d with polyethylene, a p l a s t i c

inherently more resistant to chemicals.

KEFERENCES

1. Residential Standards Canada, Associate Committee en t h e National

Building Code, National Research Council Canada, Ottawa, (Metric

Edition, 1977).

1. t l l c c t r i c a l S a f c t y Codc IlunJbook, Ontario Ilydro, IXtll Iiclltion,

- M d C r r -4 4 x U V I W O W F r o 0 3 0 -0 -0 w - 4 0

g

5"'

F i g u r e

sealant

on