Electrical Service Connections and Hazards

Questions and Answers

What is the primary consideration when isolating an electrical problem in high-rise buildings?

Minimizing interruptions to building services (correct)

Ensuring all floors are treated equally

Preventing electrical fires

Reducing the risk of acid release

Which hazard is presented by the UPS rooms in commercial occupancies?

Risk of electrical overload

Increased fire hazard due to flammable materials

Potential for high-voltage shock

Potential for acid release from batteries (correct)

When should the electricity be shut off at a residential fire?

When firefighters arrive on scene

Only after the fire has been extinguished

When the fire reaches overheard wires

As soon as possible (correct)

What should thermal imaging cameras (TICs) be used for in residential occupancies?

Identifying potential fires inside walls Signup and view all the answers

What indicates an open neutral or faulty ground in a residential occupancy?

Lights that flicker and appliances that give shocks Signup and view all the answers

What is the potential danger of a wire with 'reel memory'?

The wire could whip back towards the point of connection. Signup and view all the answers

What happens after a recloser detects a fault and energizes the circuit?

It tests the circuit and may repeat this up to four times. Signup and view all the answers

What should firefighters be cautious of when responding to manholes that are smoking or on fire?

The cover may become airborne due to an explosion. Signup and view all the answers

When will the TFD enter or attempt to fight fires in manholes?

After PSO is on scene. Signup and view all the answers

What is a critical piece of information about the Wilbur TAC stick?

It is for checking live electrical wires. Signup and view all the answers

What is the primary risk when a downed, energized wire is in contact with the ground?

Ground gradient creating step potential Signup and view all the answers

What is the safest immediate action a responder should take if experiencing a tingling sensation near a downed wire?

Bring both feet together and hop away from the wire Signup and view all the answers

What configuration will typically be seen in the service wires entering a residential structure?

Triplex wiring Signup and view all the answers

What voltage will each of the two main service wires carry in a typical residential setup?

120 volts each Signup and view all the answers

Which scenario accurately describes step potential?

Shock occurring when a responder’s feet are at different voltages near a downed wire Signup and view all the answers

What should firefighters do when investigating lines down?

Establish a guard around the scene and protect the public. Signup and view all the answers

What is the purpose of establishing a 'Danger Zone'?

To keep all persons and vehicles out of a hazardous area. Signup and view all the answers

How far should the 'Danger Zone' extend around damaged poles or wires?

One full wire span beyond damaged poles or wires. Signup and view all the answers

What action should be taken if an energized vehicle poses an imminent fire or explosion risk?

Instruct occupants to jump clear of the vehicle. Signup and view all the answers

What should be included in the report to PSO when responding to downed lines?

A specific address nearest the damaged pole or line down, and if safe to do so, the pole number. Signup and view all the answers

Study Notes

Service Connections

Service connections deliver power to customers through wires that enter the structure via weatherhead or conduit.
Triplex wiring is common in residential structures, consisting of two 120-volt wires and one neutral wire.

Electrical Hazards

Ground Gradient

A downed, energized wire in contact with the earth creates a current running to ground at the point of contact.
A gradient of decreasing current emanates from the point of contact, potentially extending several feet.
This creates a step potential hazard.

Step Potential

Step potential occurs when responders create a circuit with their feet near a downed wire.
This can cause a shock or even death if the voltage is great enough.
To escape, bring both feet together and hop away from the downed wire location.

Reel Memory

Electrical wire/cable can recoil in the direction of its original winding when unrolled from a spool.
This can cause the wire to whip back towards the point of connection, especially if under extreme tension.

Recloser or Line Restorer (LR)

A recloser recognizes a problem, waits a few seconds, and then energizes and tests the circuit.
If the fault persists, the recloser repeats the process up to four times before requiring manual reset.
Be aware of this when checking a downed wire using a TAC Stick.

Manholes

Manholes are confined spaces where PSO splices wires.
Beware of the cover becoming airborne due to an explosion.
TFD will not enter or attempt to fight fires in manholes until PSO is on scene.

Wilbur TAC Stick

The TAC stick manual is available on the Intranet.
The manual covers the use and limitations of the TAC stick.
Use the TAC stick when responding to downed lines.

Commercial Occupancies

High-rise buildings may have electrical rooms on every floor.
Isolating an electrical problem to a particular floor is crucial to avoid interrupting service to the entire building.
Commercial occupancies may have UPS rooms with batteries that can deliver over 500 volts of direct current.
These batteries pose an additional hazard of acid release.

Residential Occupancies

When dealing with electricity at residential occupancies, consider the following:
- Shut off electricity to the house as soon as possible.
- TFD members will not engage in fire suppression or property conservation if energized electrical circuits or objects create an imminent life safety risk.
- Exercise extreme caution when using ground ladders.
- Be aware of signs of electrical issues, such as flickering lights, dimming lights, and shocks from appliances or plumbing.
- Thermal Imaging Cameras (TICs) can be useful in locating potential fires inside walls and identifying overheating wires and equipment.

Response to Downed Lines

Attempting to locate a downed line/wire is extremely dangerous and has resulted in firefighter fatalities.
Use extreme caution when carrying out these activities.
Identify where the electricity will enter the structure and proceed to locate both ends of the downed wire.
Always consider that there may be multiple downed wires or wires in contact with fences.
Use the TAC stick to check gates before entering.
Do not attempt to move downed electrical lines.
Establish a guard around the scene and protect the public.
Beware of covered overhead wires, as the covering is designed to protect the wire from weather or tree contact, not to protect responders.
Establish a "Danger Zone" around damaged or downed electrical lines.
The danger zone should extend at least one full wire span beyond damaged poles or wires.
Instruct persons in energized vehicles to remain in the vehicle until the electrical energy is eliminated by PSO.
In situations with an imminent life safety risk, instruct occupants to jump clear of the vehicle.
Do not attempt to rescue persons in contact with energized lines or objects.

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Description

Learn about electrical service connections, triplex wiring, and ground gradient hazards, including downed energized wires and current flows.