ElectricityElectrical Machines II (year 6)

Live working

The rule of the trade is to cut, lock out and verify before touching. But some jobs cannot be done with the supply cut, and for those there is a discipline of its own: methods, distances, insulating equipment, authorized personnel and a written procedure. This page explains how it is done and what the law requires, and closes with another core workshop task: the general overhaul of a machine.

Live working SRT Res. 592/2004 Stick · gloves · bare-hand General overhaul Vibration

01What it is and when it is justified

A live-working job (in Argentina, trabajo con tensión, TCT) is one done on an installation that is still energized, with the worker either in contact with live parts or inside the distance across which an arc could reach them. It is the exception to the five golden rules: the general rule is to work dead by cutting, locking out, verifying and earthing; live working is accepted only when cutting is not possible or would create a greater risk.

Situation	Why the supply is not cut	Example
Continuity of supply	The outage would leave many customers or an essential service without power, and the regulator penalizes interruptions (see power quality).	A tap on a medium-voltage line that feeds a neighborhood and a hospital.
A process that cannot stop	Stopping the process costs more, or is dangerous or irreversible.	A casting furnace, a cold room, a fire-pump system.
The task requires voltage	What is to be measured or adjusted exists only while the installation is energized.	Clamp-meter current readings, thermography, hunting an intermittent fault, setting a protection in service.
Cutting creates another risk	The switching operation itself is dangerous, or de-energizing a safety system is worse.	A board that feeds ventilation or gas extraction.

Convenience is not a reason

“It is faster” or “I do not want to bother production” does not justify live working. The decision is made in writing, with the reason, before starting, and by whoever is responsible for the installation. If the job can be done dead with a scheduled outage, it is done dead.

The physical principle. Current flows through the body when it is between two points at different potential, or when the air between a live part and the body ionizes and an arc strikes. A bird perched on a single conductor gets no shock: its whole body is at the same potential. Every live-working method is a way of achieving the same thing: that between the worker and every part at a different potential there is always enough insulation or distance. Dry air withstands in the order of 30 kV per centimeter under ideal conditions; in practice it withstands much less (humidity, dust, altitude, sharp metal points and switching overvoltages), which is why distances are not worked out by eye: the regulations set them according to voltage.

Dead working is the rule; live working, the justified exception

Working live is not “braver” or “more professional”. It is a specialized technique that rests on training, tested equipment and a written procedure. An electrician without that authorization does not do live work, not even “quickly, at low voltage”: the damage from an arc or a shock does not distinguish good intentions.

02The Argentine legal framework

There is no single live-working standard: there is a chain, from the general law to each company's procedure. For the hierarchy between law, decree, regulation and technical standard, see Regulations for electrical installations; here we look at what each link contributes to a live job.

Standard	What it contributes to live working
Law 19,587 on Occupational Health and Safety	The framework law: the employer must provide safe conditions, training, protective equipment and written procedures; the worker must follow them and report unsafe conditions.
Decree 351/79	Its regulation. It sets the safety conditions for electrical installations and work, and is the basis from which the specific live-working rules start.
SRT Resolution 592/2004	“Regulation for carrying out live work on electrical installations” (Reglamento para la ejecución de trabajos con tensión en instalaciones eléctricas), from the Superintendency of Occupational Risks. It is the specific rule: it requires trained and authorized personnel, written procedures, suitable equipment and working conditions. Its current text is consulted on the SRT website.
Law 24,557 on Occupational Risks	The ART system: prevention, accident coverage and the employer's duty to report and control risks.
AEA (Argentine Electrotechnical Association)	Technical regulations and guides for installations and networks. AEA 90364 governs installations in buildings; for networks and transformer stations, the 95000 series. Which ones apply to each live job is checked in the current AEA catalog.
ENRE / ERSeP	The bodies that oversee the distribution companies (in Córdoba, ERSeP). The utilities have their own live-working procedures, based on the rules above, and they are the reference on the public network.
IRAM and IEC standards	They set how gloves, sticks, tools and detectors are made and tested. See section 05.

Be careful with standard numbers

Resolutions are amended and standards are renewed. Before citing or applying one, check the current version. On this page the regulatory values that depend on voltage (safety distances, periodic tests, training requirements) are not given as loose numbers: the applicable regulation sets them, and they are read there.

Who is responsible. The employer must have the procedure, the authorized personnel, the tested equipment and the control that it is all followed. The work leader answers for execution on site. Each worker answers for following the procedure and can, and must, refuse to continue if any condition is missing. After an accident, the lack of a permit, an authorization or a tested piece of equipment worsens civil liability and may reach criminal liability, in addition to what the ART determines. For the general part of health and safety, see Occupational health and safety and Safety, hygiene and quality in installation work.

03The three methods and the safety zones

The methods differ in where the insulation is that protects the worker. In all three, the worker is never in contact with two parts at different potential at the same time.

Figure 1. The three live-working methods, animated. In the insulated-stick method the insulation is the stick; in the glove method, the gloves and the insulated support; in the bare-hand (line potential) method, the insulating boom that separates the worker from earth while a conductive suit brings him to the same potential as the line.

Method	How the worker is protected	Typical equipment	Typical use
At a distance (insulated stick)	Stays at a distance and works with long insulating-handle tools. He is at earth potential.	Insulating sticks with interchangeable heads, detectors and test sets.	Medium and high voltage. At low voltage, switching and cutting that cannot be done by hand.
In contact (gloves)	Touches the live part, but wearing insulating gloves and sleeves, and insulated from earth and the other phases with blankets and covers. He is at earth potential, with insulation interposed.	Gloves with leather protectors, sleeves, blankets, rigid covers, insulated tools, insulated platform or basket.	Low voltage, where it is done most. At medium voltage, according to the procedure and regulations.
At potential (bare-hand)	Is brought to the same potential as the conductor: he is lifted insulated from earth and bonded with a conductive suit. Between him and the conductor there is no voltage difference.	Long insulating boom or basket, conductive suit, equipotential bonding.	High and extra-high voltage, on transmission lines.

“In contact” does not mean “unprotected”

In the glove method the gloves protect the hand, but the rest of the body stays close to other live parts. That is why everything within reach is covered and no one ever works between two conductors. A punctured or wet glove lets current through: every glove is inspected before each use (section 05).

Zones and distances. Around an unprotected live part, zones are defined that depend on voltage. Their names vary from one standard to another; their functions are these:

Figure 2. Zones around a live part, animated. As the worker approaches the conductor he passes from the free zone to the proximity zone and to the danger zone: in each one, who may be there and what is required changes. The zone radii depend on voltage and are set by the regulations; the drawing is not to scale.

Zone	What it is	Who may enter and with what
Danger zone (live-working zone)	The closest: inside it an arc can strike the body or a tool, even if nothing is touched.	Only personnel authorized for live work, applying the method, the procedure and insulating equipment. Dead work only after cutting, locking out and earthing.
Proximity zone	The band around the previous one. A sudden movement, a long tool or a ladder can carry someone into the danger zone.	Trained and authorized personnel, supervised by the work leader, with barriers and signs. No long objects without control.
Free zone	Outside the other two.	Anyone; the proximity zone is still watched so that it is not entered.

The minimum safety distance applies to the body, tools, ladders, vehicles with booms and suspended loads, not just the hands. And it grows with voltage, altitude, humidity and the overvoltages the network can produce. The values of each zone, for each voltage, are set by the regulations: they are read in the standard or in the company procedure and are not “estimated by eye”. On site, the zone limit is marked with tape, cones, insulating fences or a lookout.

04Personnel, procedure and work permit

Authorization of personnel. A diploma or experience is not enough: to do live work a person needs specific training, theoretical and practical, in the method to be used; to have been assessed; to have proven medical fitness for the post; and to hold a written authorization from the employer, limited to certain methods and voltage levels. The authorization is renewed with retraining and is withdrawn if the person stops following the procedure. The number of hours, the contents and the periodicity are set by the regulations in force.

Role	What they do
Work leader	The only person responsible for execution. Checks the permit, the equipment and the weather, gives the briefing, orders each step and can stop the work. One leader per task.
Operators	Carry out the work according to the procedure. Nobody works alone: at least one other trained person who can act in an accident.
Safety observer	Watches the distances and the surroundings from the ground, without any task that could distract him.
Network or plant operator	The person in charge of the installation. Authorizes the work, disables automatic reclosing and restores nothing without the work leader's closing notice.

The written procedure. Each type of task has its own procedure, written beforehand and reviewed by someone technically competent. At a minimum it contains:

The scope: installation, voltage level, method and task it covers.
The personnel required and the authorization each one must hold.
The list of tools and equipment, with a valid test date.
The steps of the task, in order, and the hazards of each one.
The distances and zones that apply.
The weather conditions in which work is suspended.
What to do in an accident or anomaly: who calls, whom, and how someone is rescued from height.

The work permit. It is the document that authorizes one specific task, in one place and on one date, and is not valid for another. It goes through these steps:

Step	What happens	Who
1	The permit is requested, stating task, place, method and the reason the supply is not cut.	Work leader
2	The task is analyzed and approved or rejected. If approved, automatic reclosing of the affected protections is disabled.	Network operator
3	Briefing on site: the procedure, the roles and the way to cut off in an emergency are reviewed.	Whole team
4	Equipment (inspection and test date), signs, weather and the state of the work point are checked.	Work leader
5	The task is carried out. Any member can stop it.	Operators
6	Closing: people and tools are withdrawn, completion is reported and only then are the protections restored.	Work leader and operator

Weather conditions. Rain, drizzle, thick fog, humidity condensing on insulators, strong wind and above all thunderstorms with lightning in sight or earshot require work to be suspended. Moisture and dirt lower the insulation of sticks, gloves and supports; wind moves conductors and ladders into the distances; and in poor light the zones cannot be seen. The precise limits (wind, humidity, visibility) are set by the applicable procedure. Doubt is resolved by stopping: any member of the team can ask for it, and the work leader cannot force anyone to continue.

Stopping a live job out of doubt is never a fault

The decision to stop is always the right one when a condition is unresolved: an expired piece of equipment, a change in the weather, an unclear instruction. Resuming requires the work leader to check everything again, not just what caused the interruption.

05Insulating tools and equipment, and their tests

What protects the worker in live work is the equipment, and equipment protects only if it is intact, clean, dry and tested on time. Each item carries an individual identification, and its purchase date, tests and incidents are recorded.

Equipment	What it is for	What is checked
Rubber insulating gloves, with leather protectors	Insulation for the hand in the glove method. The protector shields the glove from cuts and punctures.	Visual inspection and air test before each use; periodic dielectric test; store without folding, away from heat, light and oils.
Insulating sleeves, blankets and rigid covers	Cover the conductors and live parts that are within reach and are not touched.	No cuts, deformations or dirt; periodic test.
Sticks and insulating-handle tools	Work at a distance. They replace the worker's arm.	Clean and dry; dielectric test of the insulating section; not used with cracks or damaged coating.
Insulating platforms, baskets and booms	Lift the worker and insulate him from earth.	Dielectric test of the insulating boom and the aerial lift; cleaning and condition of the coating.
Voltage detectors	Confirm the presence or absence of voltage.	Tested before and after each use on a known source. Type and category suited to the voltage.
Helmet, face shield and arc-rated clothing	Protect against the arc even when the method is correctly applied.	Helmet for electrical use, face shield and garments with the arc rating given by the manufacturer (IEC 61482). Never synthetic clothing.
Earthing and short-circuiting equipment	In dead work on medium and high-voltage networks.	Condition of cables and clamps; cross-section suited to the short-circuit current.

Glove classes. The class indicates the glove's maximum use voltage; it is not the voltage at which it is tested, which is considerably higher. The values in the table are those of IEC 60903 (and of ASTM D120, which match): they should be confirmed in the current edition of the standard cited by the procedure.

Class	Maximum use voltage (a.c.)	Test voltage (a.c.)
00	500 V	2.5 kV
0	1000 V	5 kV
1	7500 V	10 kV
2	17,000 V	20 kV
3	26,500 V	30 kV
4	36,000 V	40 kV

Example · What glove class is enough for a 13.2 kV line?

A procedure provides for live work on a three-phase line of 13.2 kV phase to phase. We want to know whether a class 1 glove would be enough.

Voltage to earth. In a three-phase system, the voltage between one phase and earth is the line voltage divided by $\sqrt{3}$ :

V_{f} = \frac{V_{L}}{\sqrt{3}} = \frac{13.2 kV}{1.7321} = 7.62 kV

Comparison with class 1. Its maximum use voltage is 7.5 kV, lower than 7.62 kV: it is not enough even to touch a single phase. To work with the phase-to-phase voltage we must look at class 2 (17 kV), and that is the one that fits the case:

\frac{13.2 kV}{17 kV} = 0.776

The class 2 glove works at 77.6 % of its maximum use voltage. A comfortable margin, but not a license to touch two phases at once.

Cross-check another way. At low voltage: $\frac{380 V}{500 V} = 0.76$ , so a class 00 glove is enough for 380 V between phases; in practice class 0 is preferred for its greater mechanical strength. That a glove “can take it” does not define the method: the procedure and the regulations say which one applies and with what equipment.

Before each use, always

The glove is inspected inside and out, looking for cuts, cracks, blisters and deformations. The air test is done: the cuff is rolled toward the fingers to trap air and squeezed, listening and feeling for leaks. The test date on the label is checked. An expired glove, even if it looks perfect, is out of service. The periodic test is done in a laboratory with calibrated equipment, and the interval is set by the standard of use and the company procedure.

06The general overhaul of a machine

The general overhaul (recorrida general) is the intervention in which a machine is taken out of service, completely dismantled, checked part by part, repaired as needed, and then reassembled and tested. It is done with the machine dead and locked out, with the five golden rules applied on the supply side: here the work is the opposite of live working. It is scheduled when service hours, the trend of predictive maintenance or a serious failure indicate it (see Maintenance of electrical components and Maintenance management).

Stage	What is done	What is recorded
1 · Inspection	The nameplate is read, the history is reviewed and the symptoms are measured with the machine still assembled: current per phase, temperature, vibration, noise and grease leaks.	Nameplate data, reason for the intervention, entry values.
2 · Dismantling	Disconnect and mark terminals and cables. Remove end shields, rotor and bearings with a puller, marking position and orientation. Shaft and air-gap clearances are measured before the rotor is removed.	Photos, marks, measured clearances, order of the parts.
3 · Diagnosis	Cleaning and inspection of each part: winding, core, rotor, shaft, bearing seats, frame. Insulation and winding resistance are measured (see Motor and transformer tests). With that it is decided what to repair and whether repair makes sense.	Measured values, damage found, list of parts and jobs.
4 · Repair	Replace bearings and seals, correct seats and shaft, rewind if needed (see Motor winding), balance the rotor, apply protective paint.	Work done, parts used and their make.
5 · Reassembly	Reassemble in reverse order, with the specified tightening torque and the right lubrication. Check that the shaft turns freely by hand and that clearances match those measured at dismantling.	Final clearances, grease and quantity.
6 · Testing	Insulation, resistance, no-load run and, if possible, a load run; bearing temperature, noise and vibration. Only if everything is within expectations is it delivered.	Final report with entry and exit values, to compare with the next overhaul.

Repair or replace? A repair is uneconomic when buying and commissioning a new machine costs less than repairing the old one, taking into account everything that weighs in the calculation. Many workshops use as a rule of thumb not to repair if the cost exceeds half the price of a new unit, but that rule ignores other factors. The full calculation, with the equivalent annual cost and the example of rewinding versus buying a motor, is in Maintenance management. Always look at:

The repair cost compared with the replacement cost, including parts and transport.
Efficiency: an old or rewound motor consumes more than a new high-efficiency one, and the difference is paid every running hour.
Core damage: if the iron is burnt or deformed, the repaired motor never recovers its efficiency.
The number of previous repairs and the remaining service life.
Lead time and criticality: how much downtime costs, and whether there is a spare in stock.
Availability of spare parts for an old model.

Vibration as a symptom. Almost every rotating machine that is about to fail vibrates differently before it does. Vibration is measured with an accelerometer on the shaft supports, in the horizontal, vertical and axial directions, and expressed as RMS velocity (mm/s), the severity indicator used by ISO 20816-3 for industrial machines. Severity tells how much it vibrates; the spectrum, which breaks the signal down into frequencies (see Signal generation and processing), tells why.

Figure 3. Vibration spectrum of a 4-pole, 1450 rpm motor, animated. Each fault leaves a signature in the spectrum: imbalance at the rotation frequency; misalignment at twice that; a bearing defect at frequencies that are not exact multiples. Amplitudes are illustrative; the frequencies are those of the example.

Cause	What is seen in the spectrum	How it is confirmed
Imbalance	Dominant peak at $1 \times$ the rotation frequency, especially in the radial direction.	Improves after balancing the rotor; on a fan, dirt stuck to the blades.
Misalignment	Peak at $2 \times$ the rotation frequency (and also at $1 \times$ ), with high axial vibration.	Laser or dial-indicator alignment. Corrected by moving the machine.
Mechanical looseness	Several harmonics of the rotation frequency ( $1 \times$ , $2 \times$ , $3 \times$ …).	Soft foot, loose base bolts, play in the support.
Defective bearing	Peaks at the race, ball or cage fault frequencies, which are not whole multiples of the rotation frequency.	Sandy noise, rising temperature, grease with particles.
Electrical origin	Peak at twice the supply frequency ( $100 Hz$ on a 50 Hz network).	Disappears at once when the motor is disconnected, even while it coasts: it is not mechanical.

Example · Which bearing defect gives the 86.6 Hz peak?

A three-phase 4-pole, 50 Hz motor runs at 1450 rpm. The spectrum shows a strong peak at 86.6 Hz that is not a multiple of the rotation frequency. The fan-end bearing has 9 balls, and the ratio between ball diameter $d$ and pitch diameter $D$ is $d / D = 0.2034$ (typical values for a 6205; exact ones are in the manufacturer's catalog). Radial contact, contact angle $0 °$ .

Rotation frequency. $f_{r}$ $= \frac{n}{60}$ $= \frac{1450}{60}$ $= 24.17 Hz$ . The slip, with $n_{s} = 1500$ rpm, is $\frac{1500 - 1450}{1500} = 3.3 %$ .

Outer-race fault frequency, with $Z$ balls:

f_{BPFO} = \frac{Z}{2} f_{r} (1 - \frac{d}{D}) = 4.5 \cdot 24.17 \cdot (1 - 0.2034) = 86.6 Hz

Inner-race fault frequency.

f_{BPFI} = \frac{Z}{2} f_{r} (1 + \frac{d}{D}) = 4.5 \cdot 24.17 \cdot (1 + 0.2034) = 130.9 Hz

Check. The two add up to $Z f_{r} = 9 \cdot 24.17 = 217.5 Hz$ , and $86.6 + 130.9 = 217.5$ . The peak matches $f_{BPFO}$ : there is a defect on the outer race of the bearing on that side. It is confirmed by dismantling; had the peak been at 130.9 Hz, the defect would be on the inner race.

07In the workshop

Practice 1 · Inspect and test an insulating glove

Materials: a pair of insulating gloves with leather protectors (the school's own, with their label), paper towels, water and neutral soap, record sheet.

Steps: 1) read the class and test date on the label and record both; 2) inspect the glove by eye, outside and inside; 3) do the air test on each glove; 4) wash them with water and neutral soap and dry them; 5) store them without folding.

Acceptance criterion: valid test date, no cuts, cracks, blisters or deformations, and the inflated glove does not lose air. Any fault puts it out of service, even the first time.

Practice 2 · Write a procedure and a permit

Task: in groups of three, write the procedure and work permit for a simulated task on the training board: “measure the current of one phase with a clamp meter on an energized board”.

Minimum content: scope, people and roles (work leader and observer), equipment with dates, steps with their hazards, conditions to suspend, and actions in an accident. Another group reviews the procedure and tries to find gaps.

Acceptance criterion: no step without its hazard, no role without a name, and the reviewing group cannot find a situation the procedure does not resolve.

Practice 3 · General overhaul of a 1.5 kW motor

Materials: an out-of-service three-phase motor, bearing puller, wrenches, megohmmeter, ohmmeter or bridge, caliper, grease, new bearings, record sheet. Everything dead, with the motor disconnected.

Steps: 1) inspection: nameplate, external condition, turning the shaft by hand; 2) measure the insulation of each winding to frame and between windings before dismantling; 3) photograph and mark terminals, end shields and rotor; 4) dismantle, remove the bearings and measure shaft clearances; 5) inspect winding, core, seats and shaft; 6) replace bearings and seals; 7) reassemble with the specified torque; 8) repeat the measurements and do a no-load run measuring current.

Acceptance criterion: insulation equal to or better than at the start and above the procedure's minimum; the three phase resistances equal to each other; shaft turning freely; balanced no-load current and no abnormal noise; report with entry and exit values.

Practice 4 · Cause and recognize an imbalance

Materials: a small motor with a disc or fan, an accelerometer or a phone with a vibration app, a washer or small mass with tape.

Steps: 1) measure vibration at the supports with the rotor clean; 2) tape the mass at one point on the disc and measure again; 3) move it to another point and repeat; 4) calculate the rotation frequency and locate the peak in the spectrum.

Acceptance criterion: the peak appears at $1 \times$ the rotation frequency and grows when the mass is added; the group explains why it does not appear at $2 \times$ .

08Common mistakes

Mistake	Consequence
Doing live work “because it is faster”	People are exposed to a risk that could have been avoided with a scheduled outage.
Doing live work without authorization or a written permit	If there is an accident, the employer's liability and the worker's own are worsened.
Estimating the safety distance by eye	The arc strikes before the body touches anything. The regulations set the values.
Using gloves without inspecting them or with an expired test	A punctured glove lets current through. The test label is not decoration.
Continuing in rain or a thunderstorm “because there is little left”	Moisture lowers the insulation of equipment and supports; lightning gives no warning.
Working alone or without an observer	No one can cut the supply or rescue the person who stayed exposed.
Not disabling automatic reclosing	The protection can close again onto a fault while people are working.
Reassembling a motor without first measuring insulation and clearances	There is nothing to compare with at the end, and a machine that fails again is handed over.
Repairing a motor without comparing with replacement	Money is spent on a machine that consumes more and will fail again; see Maintenance management.
Ignoring a growing vibration because “the motor still runs”	A faulty bearing ends up seizing the shaft or burning the winding.

09Self-assessment

When is live working justified and when is it not?

It is justified when cutting is not possible or creates a greater risk: continuity of an essential service, a process that cannot be stopped, a task that can only be done with voltage (a measurement), or a cut that is dangerous in itself. It is not justified by speed or convenience. The rule is to work dead.

Which Argentine standards regulate live working?

Law 19,587 and its Decree 351/79 (health and safety), SRT Resolution 592/2004 (the specific regulation for live work), Law 24,557 on Occupational Risks, the AEA regulations and the utility's procedures, under the oversight of ENRE or ERSeP.

What are the three live-working methods and where is the insulation in each?

At a distance: the insulation is the stick and the distance. In contact: the gloves and sleeves, plus the blankets and the support insulated from earth. At potential: the insulating boom that separates the worker from earth, while the conductive suit keeps him at the same potential as the conductor.

Why can safety distances not be given “from memory”, and who sets them?

Because they depend on voltage, altitude, humidity and the overvoltages the network can produce, and the regulations set them for each case. They are read in the standard or the procedure; estimating by eye is dangerous because the arc strikes without anyone touching anything.

Can a class 1 glove be used on a 13.2 kV line phase to phase?

No. The voltage to earth is $13.2 / \sqrt{3} = 7.62$ kV, higher than the 7.5 kV of class 1. At least class 2 (17 kV) is needed, with 13.2 kV working at 77.6 % of its maximum use voltage.

When is a repair uneconomic?

When buying the new machine and commissioning it costs less than repairing, counting efficiency (energy), core damage, previous repairs, lead time and criticality. A rule of thumb is not to repair if it costs more than half the new unit, but the full calculation is the one in maintenance management.

A 4-pole, 50 Hz motor runs at 1450 rpm and the spectrum shows a peak at 48.3 Hz. What is it?

The rotation frequency is $1450 / 60 = 24.17$ Hz, and $2 \cdot 24.17 = 48.3$ Hz: it is twice the rotation frequency, the typical signature of misalignment between motor and load. It is confirmed by measuring axial vibration and aligning with a dial indicator or laser.

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