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Do Squirrels Cause Power Outages? More Than Storms Do

Squirrels are among the most common causes of local outages on distribution networks. Why it happens, and why the squirrel usually dies.

By Zakaria 2 min read Save to Pinterest — opens Pinterest in a new tab
A utility pole crowded with transformers, insulators and conductors against blue sky
Photo: billcosmos, Pixabay Content License, via Pixabay
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Squirrels are one of the most common causes of local power cuts, and the mechanism is always the same: an animal that bridges two things at different voltages.

Why one wire is safe and two are not

situationcurrent flows?
Touching one conductor onlyno — same potential throughout
Conductor to a second conductoryes — fault
Conductor to grounded tank or guy wireyes — fault
Standing on a grounded pole, touching a live terminalyes — fault

What an outage looks like from the house

sequencewhat it is
Lights flicker once or twicerecloser attempting automatic restoration
Power drops and stays offfuse blown or recloser locked out
Restored within an hour or twocrew replaced a fuse
Longertransformer or hardware damaged

Never prune near an overhead line

A branch touching a service line is a utility job, not a ladder-and-loppers job. Report it. The same bridging physics that kills squirrels applies to a person holding a pole pruner.

What is actually done about it

  • Insulating boots over transformer bushings and cutouts
  • Animal guards on energised terminals
  • Disc baffles on poles to stop climbing
  • Tree clearance so squirrels cannot jump directly to hardware
  • Wider phase spacing on new build, so an animal cannot bridge two conductors

It is almost never the whole grid

A squirrel outage is small and local by nature — one transformer, a handful of streets. Regional blackouts have other causes. If your street is out and the next one is not, an animal fault is a reasonable first guess.

Common questions

Do squirrels really cause power outages?

Routinely. Utilities in North America consistently list squirrels among the leading causes of unplanned outages on local distribution networks — on many systems ahead of weather for sheer number of incidents, though well behind storms for the number of customers affected per event. The typical event takes out one transformer and a few streets rather than a region.

Why don't squirrels get shocked just walking on a wire?

Because current needs a path to somewhere of different voltage. A squirrel touching only one conductor is at that conductor's potential and nothing flows through it, the same reason birds perch safely. The fault happens when the animal bridges two things at different potentials — two conductors, or a conductor and a grounded transformer case, bushing or guy wire — which is easy to do on the cluttered hardware of a pole-top.

What actually happens to the squirrel?

It almost always dies, instantly. The fault current through it is enormous for the fraction of a second before protective equipment operates. From the network's side a fuse blows or a recloser trips, which is what restores power, often after one or two automatic attempts that households see as the lights flickering before going out.

Why transformers specifically?

Because that is where energised hardware and grounded metal sit close together, and because pole-mounted transformers are warm and sheltered, which attracts animals. Squirrels climb poles as readily as trees, and the bushings on top of a transformer are the classic bridging point between a live terminal and the earthed tank.

Can utilities prevent it?

Partly, and they spend heavily on it. Insulating boots over bushings, animal guards on cutouts, disc-shaped baffles on poles and tree-clearance programmes all reduce the rate. None of it eliminates the problem, because the network is enormous and squirrels are everywhere along it.

Does this mean squirrels in my trees are a risk?

Not directly to you. Trees touching or close to service lines are the realistic household concern, and that is a utility matter rather than a DIY one — never prune a branch near an overhead conductor yourself. Report contact between a tree and a line, and leave the climbing to the people with the right equipment.

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