Collecting Vintage Transformer Primary Bushing Covers (aka Squirrel Guards)

By Michael Gibbons; posted November 17, 2013

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I did a little bit of research and found out that one of the leading causes of power outages in the United States are animals, primarily squirrels, accidentally touching two spots simultaneously causing a short circuit. This squirrel effect is especially apparent in and around metropolitan areas during wet years where nut and fruit trees are not harvested allowing their numbers to clime unchecked causing still more problems. Unfortunately, the damage caused by animal contacts aren't confined to simple outages, because flaming carcasses falling from utility poles commonly start grass fires. Hence the great need for animal guards.

As I understand it, these animal guard insulators are used to cover a transformers primary bushing, to help prevent squirrels, snakes and birds (particularly starlings and crows) from electrocuting themselves and shorting out the lines. The major defining characteristics for a squirrel guard insulators is a plain dome, cone or chimney like shape with a circular hole or slot in the top used for the outgoing power line. This type of insulator apparently just rests on top of the transformers primary bushing and has no threads or bracket to attach it with, but a kind of wire clip may be present in the hole on top.

Side-Hole/Spout -- Although not common to all squirrel guard insulators, many come equipped with a side-hole or pour spout like shape. A thirty year lineman from Somersworth, New Hampshire described its purpose to me. Apparently, the side hole and/or spout found in some squirrel guards is the air gap for a lightning arrestor that mounts on the side of a transformer casing. This allowed a lightning strike to arc from the primary bushing, across through the gap and make contact with the lightning arrestor, so as not to burn out the transformer. This secondary purpose of passing lightning bolts through its side hole or spout opening is why many of these insulators suffer from glaze burns and cracks. The squirrel guard I purchased from the New Hampshire lineman came from a three phase 277/480 transformer bank (top shelf right side), but he stated they were also installed on capacitor banks and regulators.

A squirrel guard should not be confused with a ceramic Antenna & RF feed-thru Insulator, which is more like a wide rimed bowel or cone shape with a hole in it.


If you have any information or pictures confirming any of these insulators as squirrel guards please contact me.

I am ALSO INTERESTED IN BUYING squirrel guard insulators that I don't have in my collection, especially colored glass models.

Thanks for your time


See Also:

Clear Glass squirrel guard confirmed by 2 Pic's:

Richard Case


Dave Dahle


A modern cone shaped squirrel guards typically made of rubber, fiberglass or a composite like substance:


Modern dome shaped squirrel guards made of plastic or fiberglass:


Additional squirrel guard models held by other collectors:

Terry Drollinger



Zac Mirecki



Dave Fleishman....Do not confuse squirrel guards with guard squirrel's (smart ass)


COORS ASSOCIATION...The Coors porcelain factory made all kinds of products through the years, from bullets (US Pat 4939996 A) to insulators for nuclear bombs (Manhattan Project in WW II, etc... ), but I have never heard of them making utility line insulators. HOWEVER, Mike Johnson, a relative of the Coors family owned and operated Mesa, a fiberglass company that made the newer cone shaped squirrel guards. Therefore, I am now looking for a 1970 Mesa Squirrel Guard insulator.

Interesting web page called Scary Squirrel World, When Skwerls Attack

KeyWords:: AKA arrester caps and bushing covers... also Squirrel Shield, E/Getaway Guard, and free-spinning baffles to make squirrels lose their balance.... The Squirrely, raptor bird insulating covers, Perch Guard, Critter Guard - Line Guard, etc.

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