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ELECTRICAL SAFETY

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Experience Sharing – Sharing  – Electrical Safety

Architectural Services Department 3 October 2012 3/10/2012

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• n ro uc on •   Electricity Principles •   Electrical Safety Devices •   DEVB Policy on Electrical Safety • •   Good Site Practice on Electrical Safety • •   Lessons learnt

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• n ro uc on •   Electricity Principles •   Electrical Safety Devices •   DEVB Policy on Electrical Safety • •   Good Site Practice on Electrical Safety • •   Lessons learnt

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On 3 October 2011, an experience sharing session has been held with ArchSD contractors and site supervisory staff to staff  to promote and . same powerpoint presentation materials used the ArchSD internet for reference.

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OHM’S LAW

 

V I 3/10/2012

Based on the above formula during an electric shock of the human body, the current (I) is inversely proportional to the resistance (R), i.e. a reduction body will lead to higher electrical currents assin through the body, the more serious will be the injury. 5

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Electric Shock The electric shock is caused the body. The lethality of an electric shock is dependent on:  Current   (the higher the current, the more likely it is lethal);  Duration   (the longer the duration, the more likely it is lethal);  Voltage   (the higher the volta e the more likel it is lethal);  Pathway   (if current flows , more likely to be lethal) 3/10/2012

Diagram showing how electric shock occurs: The severity of electric shock depends on the current flowing through the body (I) in Ampere, which is a function of the electromotive force (E) in volts, and the contact resistance (R) in ohms. ormu a: = ÷

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Electric Shock Dry

skin (resistance around 10,000Ω) Current = 220V ÷ 10,000Ω = 0.022A Current = 220V ÷ 500

Current (amperes)

Ω =

0.44A

Physiological effect

0.001A

Threshold of feelin an electric shock

0.005A

Maximum current which would be harmless. Sustained muscular contraction.

.



.

0.05A .



entr cu ar

ain

r at on.

Can be fatal.

. rhythm.

6A

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These are the operation levels for a defibrillator. Temporary resp ra ory para ys s an poss y urns. 8

Effect of Electric Shock Heartbeat Failure a n cause o eat : 

When current passes through the heart, it will disrupt the rhythmic pumping ac on o e ear an even ua y ceases heart beat.  The heart does not resume without . treated, death is rapid.

Breat ng Fa ure 

Current passing through the respiratory centre in the brain may disturb the nerve cen re an s op resp ra on

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EFFECT OF  ELECTRIC SHOCK

Suffocation: 

Current passing through the upper limbs and across the chest as long as the current flows, eventually causing death from



Continuous contraction of the forearm muscles when current is passing through, thus unable to get free from the electric source

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ELECTRICAL  HAZARD 

  Electric burns , passing through the body may lead to burns on the skin, muscles or internal . closely related, preventative measures should be considered together.



  Fires and explosions High temperatures caused by currents under abnormal conditions, may result in accidental fires and explosions. The common causes leading to high temperatures include: Insulator breakdowns

or short circuits Improper contact of electrical circuit Poor 3/10/2012

ventilation, etc. 11

CAUSES OF ELECTRIC  SHOCK Direct Contact A direct contact refers to a person coming into contact with

Indirect Contact An indirect contact refers to a erson comin into contact with a conductive part which is not normally alive, but has become insulation failure or some other causes)

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Electrical Safety Devices Electrical circuit are mainly protected by the following safety devices: use  It must be installed on “live” wires;  It is a copper wiring with a set current us on va ue;  If the current exceeds the set fusion value, the fuse will blow and cut‐off the .    Circuit

breakers (MCB)

on the thermal and electromagnetic principle.    Under short circuit condition, the MCB will trip instantaneously by electromagnetic force.    Under overload condition, the MCB will rpw me e ay y erma principle. 3/10/2012

Fuse for 13A plug

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Miniature circuit breaker

Electrical Safety Devices ar ea age rcu rea er or es ua curren device (RCD)  It monitors the operation of the “neutral” or “live” wires in .  During current leakage, the current flows to electrical appliance via the “live” wire are not equal to the current returns throu h the “neutral” wire  Such imbalance current flow detected by RCD or ELCB is then cut‐off the electrical source;  Ratin of the tri in current shall not exceed 30mA.

During the leakage of  electricity the return current (I   out) is less than the entering current (I   in). The res ua curren s ows away after passing through the human body or the earth. So the difference of magnetic field produced and resulted in an automatic power cutoff in tripping device.

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ELECTRICAL  SAFETY DEVICES    Earthing

Connection

  Earthing provides

e groun

a low resistance way of discharging electricity to n case o curren ea age;

 The current

passes through the “earth” wire and is prevented from entering the human body and causing injury.

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ELECTRICAL  SAFETY DEVICES    Double

Insulation

The basic requirement is that no single failure exposed so that it might cause an electric shock and that this is achieved without relying on an ear e me a cas ng. s s usua y achieved at least in part by having two layers of insulating material surrounding live parts or by using reinforced insulation. Electrical appliances with double insulation bear the “ ” mark.   Extra‐low

Voltage (ELV)

Electrical tools using extra‐low voltage not exceeding 50 V a.c. may minimise injury in case of electric shock. 

Voltage (V) ≤ 50V A.C.

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Electric drill engraved with a “double insulated” “ ” .

CABLE  COLOUR CODE Since 99% of colour blind peop e are su er ng rom red‐green colour blindness and combination of them (e.g. yellow), new cable colour enforced for the electrical installation since 1 July o ac a e ca e s identification for the people who are colour blindness or colour deficient.

Diagram 1: For single phase: Brown denotes phase (line) conductor, Blue denotes neutral conductor, Green-and-Yellow denotes earth conductor. For 3 phase: Brown denotes line 1 phase conductor, Black denotes line 2 phase conductor, Grey denotes line 3 phase conductor; Blue denotes neutral conductor; Green-and-Yellow denotes earth conductor.

Diagram 2:  An example of 13 Amp power plug connected to new colour code cables

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FACTORIES AND INDUSTRIAL UNDERTAKINGS ORDINANCE (CAP. 59), Enforced by Labour Department

 –  ac or es an Regulations,

n us r a

n er a ngs

 – 

ec r c y ,

.

.

,

Enforced by Electrical and Mechanical Services Department

 – 

,

 –   Electricity Supply Lines (Protection) Regulation, etc. 3/10/2012

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Legislative requirements:

(ELECTRICITY) REGULATIONS

Cover page of the “Reference Manual for Inspection Reports on Construction Sites” published by Labour Department

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Legislative requirements:

. Electricity (Wiring) Regulations 2009 Clause26K ‐ Temporary Supply Installation for Construction and Demolition Sites or Repair and Testing Purposes

Extract phrase of EMSD’s Code of Practice on Electricity (Wiring) Regulations 2009: Clause 26K – Temporary Supply Installation for Construction and Demolition Sites or Repair and Testing Purpose – The parts “operating voltage” and “lighting accessible to public”

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Legislative requirements:

. Electricity (Wiring) Regulations 2009 Clause26K ‐ Temporary Supply Installation for Construction and Demolition Sites or Repair and Testing Purposes (cont’)

Extract phrase of EMSD’s Code of Practice on Electricity (Wiring) Regulations 2009: Clause 26K – Temporary Supply Installation for Construction and Demolition Sites or Repair and Testing Purpose – The parts “selection and erection of installation” and “protection of circuits”

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Legislative requirements:

. Electricity (Wiring) Regulations 2009 Clause26K ‐ Temporary Supply Installation for Construction and Demolition Sites or Repair and Testing Purposes (cont’)

Extract phrase of EMSD’s Code of Practice on Electricity (Wiring) Regulations 2009: Clause 26K – Temporary Supply Installation for Construction and Demolition Sites or  Repair and Testing Purpose – The parts “protection against earth leakage” and “precaution against danger”

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Legislative requirements:

. Electricity Supply Lines (Protection) Regulation

Di ag ram 1, 2, 3 & 4: Same as the descriptions on the top of the respective diagrams

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Legislative requirements:

. Electricity Supply Lines (Protection) Regulation (cont’)

Di ag ram 5, 6, 7 & 8: Same as the descriptions on the top of the respec ve agrams

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DEVB POLICY REQUIREMENTS

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DEVB policy requirements: Chapter 3 – Contractual Provision of Construction Safety ( Construction Site Safety Manual) Rev. in Feb 2011 A. Weekly Safety Walk •   Checkin that the tem orar li htin and electricall owered hand‐held tools and equipment are all rated at 110V CTE (centre tapped to earth) in compliance with Particular Specification . •   Checking scaffolding •   Checking site tidiness and cleanliness 

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The Contractor shall prepare and agree with the Architect's Representative a comprehensive check‐list for use during safety walk and site inspections. It shall contain a table listing out the deficiencies identified during the walk /inspection with the proposed rectification measures, the names of the persons responsible for taking any necessary rectification measures and the corresponding completion dates.

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DEVB policy requirements on Electrical Safety: Chapter 3 – Contractual Provision of Construction Safety ( Construction Site Safety Manual) Rev. in Feb 2011 A. Weekly Safety Walk (cont’) 

.

The Contractor shall take prompt action to rectify those deficiencies identified during the walk and shall report the status of actions taken at the forthcoming SSMC meeting.

. .



(1) Employ Registered Electrical Worker (REW) to handle the entire temporary electrical systems (TES) (2) Upon completion of TES, REW REC to complete an individual Work Completion Certificate (WR1). Each of such Certificates shall include a circuit diagram. (3) TES, such as lighting fittings, distribution boards, socket outlets, plugs and cable couplers in outdoor or damp environment shall be of IP 54 or above. (4) The sheath of all electric portable cables shall be of heavy‐duty type. They shall be hung overhead as far as possible. PVC cables shall be enclosed in metallic conduits or trunkings and properly maintained. 3/10/2012

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DEVB policy requirements: Chapter 3 – Contractual Provision of Construction Safety ( Construction Site Safety Manual) Rev. in Feb 2011 2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’) ’ for routine inspections. Monthly comprehensive checking include checking the followings with the REW’s signature:



 –   TES,  –   temporary generators,  – 

,

 –   integrity of cables and connections,  –   measurement of earthing resistance and those items listed in Checklists Nos. 3 an 4 o t e COP w ere appropr ate

(6) Establish regular maintenance programme for permit‐to‐ ‐ 3/10/2012

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DEVB policy requirements: Chapter 3 – Contractual Provision of Construction Safety ( Construction Site Safety Manual) Rev. in Feb 2011 2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’) of the temporary distribution boards), WR1 (complete with supporting documents) and records of inspection and checking of the TES by REW/REC in a dedicated file for inspection by site supervisory staff upon request. (8) Keep lock all temporary electrical distribution boards and accessible only by authorized persons. Legible warning , ‐ names and telephone numbers of such authorized persons shall be osted on the tem orar distribution boards. 3/10/2012

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DEVB policy requirements: Chapter 3 – Contractual Provision of Construction Safety ( Construction Site Safety Manual) Rev. in Feb 2011 2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’) , , connection of fixed electric equipment directly to any existing permanent distribution boards, only through temporary distribution boards. (11) For arc welding machines and electrode holders:



‐ comply

with BS 638 : Part 7, IEC 60974 – 1 (or BSEN60974 – 1) and BS EN 60974 – 11 or equivalent standards, ‐ fitted

with no‐load voltage reducing device

‐ enclosed

type with metal casing connected to earth, cable termina s e ective y insu ate 3/10/2012

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DEVB policy requirements: Chapter 3 – Contractual Provision of Construction Safety ( Construction Site Safety Manual) Rev. in Feb 2011 2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’) . .



submersible pumps) ‐ examined

b the REW visual ins ection for eneral condition functional checking for continuity, polarity and insulation aspects, ‐ registered

and recorded for each after examination,

identification labels (i.e. registration no., type, name of the owner and date of examination stamped with the Contractor's company chop) ‐

‐ re‐examine

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every 3‐month or after repairs 33

DEVB policy requirements: Chapter 3 – Contractual Provision of Construction Safety ( Construction Site Safety Manual) Rev. in Feb 2011 2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’) ‐

be operated at a voltage of 110V or less supplied from a step‐ down transformer with its output winding centre‐tapped to earth and comply with BS 3535 : Part 2 : 1990 or equivalent. All cables shall be terminated within the transformer enclosure of  ass an an e ou go ng c rcu s a e prov e w short circuit protection. In confined and damp environment, the ‐

exceed 25V. 14 For heav e ui ment such as hoists tower cranes etc. use voltage in excess of 110V equipped with an earth leakage circuit 3/10/2012 34 breaker.

DEVB policy requirements: Chapter 3 – Contractual Provision of Construction Safety ( Construction Site Safety Manual) Rev. in Feb 2011 C. Safety Plan (14 elements)



, . .



,

,

.

•   Safety Training, e.g. tool‐box talk on electrical safety talks on trainin kits ublished b HKCA etc. •   Safety Inspection ‐ TES •

Process Control Pro ramme – one of the hi h‐risk activities : Electrical Equipment and Installations  –    include safety rules, regulations, safe working procedures, and in particular method statements and permit‐to‐work systems incorporating the findings of risk assessments conducted; co‐worker system adopted if working near or over water, or electrical work at or near exposed live conductors

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Construction Site Safety Handbook (CSSH) D. Chapter 3 of CSSH



.

ec r c rc

e

ng

•   3.16 Electric Hand Tools E. Chapter 7 of CSSH



7.2 E e Protection



7.8 Safety Footwear .

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REQUIREMENTS ON ELECTRICAL SAFETY

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A. Follow DEVB olic B. Guid Guidan ance ce Notes on Supervising High Risk Activities  –   Item 16. Electrical works  –   – 

. utility services

.

.

 –   Item 28. others risk (relating to electrical safety) ‐

and prepare risk assessment assessment;;

• updating of   of risk risk assessment, wherever necessary. •   routine updating

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C. Ele Electr ctrical ical Safety Audit Checklist 2012 1. Electr Electrica icall insta installa llatio tion n . Electrical Worker (REW)? b. Are there there checklist checklistss developed developed by REW for for carrying carrying out periodic periodic comprehe comprehensive nsive checking on the temporary electrical system (TES)? c.

Are electric electrical al circuit circuit diagrams diagrams and and WR1/WR1a WR1/WR1a of of the TES TES updated updated and and kept kept by the the Contractor?

d. Are circuit circuit breakers breakers or suitabl suitable e fuses fuses insta installed? lled? e.

Are earth leakage leakage circuit circuit breaker breakerss inst installed alled? ?

f.

Is the the post poster er of “Fir “First st‐Aid for Electric Shocks” displayed?

g.

ave

e e een any egu a

epa s an ma n enance

h. Is the the tower tower crane crane connected connected to a lightning lightning protection protection system? system? i.

Are the the metal metal hoard hoardings ings connected connected to earth earth by by equipot equipotenti ential al bondin bonding g conduct conductors? ors?

 j.

Is the contact information information of REW displayed at power distribution boards?

S = Satisfactory; IR = Improvement is required; IIR = Immediate improvement is required; N/A = Not applicable

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