The Electricity News gains the support of the readers. For each issue, a lot of readers sent us letters to offer their comments and suggestions. Your valuable feedback is a great help to the continuous improvement of the content of this newsletter. To sum up the feedback about the last few issues, many readers hope that the newsletter could report more on electrical accidents and analyse the causes of these incidents, so that trade members could extract experience from them and avoid repeating the same mistakes. In view of this, in a feature article, we collect information on the electrical accidents for the past 3 years, analyse the causes and make suggestions for improvement for each type of accident. Moreover, as several electrical accidents involving shower type electric water heaters happened last winter, in another feature article, we highlight the safety tips for shower type electric water heaters for your reference.
The Electrical and Mechanical Services Department (EMSD) has done a lot of electricity regulatory work for the continuous enhancement of electrical safety in Hong Kong, including revising the Code of Practice for the Electricity (Wiring) Regulation , assisting building owners to complete the periodic inspection and test of electrical installations, adopting the latest international safety standards for electrical products, strengthening ties with the AQSIQ, and organising large-scale technical seminars in collaboration with the trade etc. The details are given in the “News” and “Preview”.
Safety Tips for Shower Type Electric Water Heaters
Some household storage type electric water heaters in Hong Kong are of shower type (also known as low-pressure storage type or open type electric water heaters). Apart from being equipped with cold and hot water pipes, a mixing faucet, a shower head and thermostat-controlled heating elements, a typical shower type electric water heater has a thermal cutout. Although these water heaters are provided with appropriate safety devices, electric water heater accidents due to incorrect installation did happen.
Normal shower type electric water heaters are designed for taking showers, but some people divert some hot water to wash basins. This modification requires the addition of normal on/off control valves, which is the cause of some accidents.
The mixing faucet of a shower type electric water heater is not a normal valve. Its hot water valve is installed at the cold water inlet of the water heater. There is no valve at the hot water outlet of the water heater. When only the cold water valve is opened, cold water will flow out directly through the mixing faucet (Figure 1). When only the hot water valve is opened, cold water will enter the storage tank from its bottom and displace the heated water through the outlet pipe at the top of the water heater. Hot water will flow out through the mixing faucet and shower head (Figure 2). If both the hot and cold water valves are opened, hot water will enter the mixing faucet and mix with the hot water flowing out from the storage tank. This allows the water at the outlet to be adjusted to a suitable temperature (Figure 3).
When the water heater is in standby condition (i.e. when both the hot and cold water valves are closed) and the water inside the storage tank is being heated, the water undergoes slight thermal expansion. As there is no normal valve between the mixing faucet and shower head, the pressure inside the storage tank can be released through the shower head. During the heating of water inside the storage tank, a small amount of water droplets may come out from the shower head, which is normal. Do not install a normal valve at the outlet just because of this.
However, if a normal on/off control valve is added at the outlet and there is a fault in the thermostat, the pressure built up inside the storage tank cannot be released. If the thermal cutout fails to disconnect the power supply, the storage tank will not be able to withstand the increasing pressure and this will result in a burst. Therefore, no on/off control valve should be added at the outlet of a shower type electric water heater, e.g. in the connection to a wash basin or bath tub.
The associated water pipes and the fixed electrical installation of the shower type electric water heater should be installed by a licensed plumber and a registered electrical worker (REW) respectively. When installing the fixed electrical installation, the REW should earth the water heater effectively . He should also check whether the electric water heater operates properly (including the function of the thermostat) and remind the user not to use any non-genuine open type mixing faucet and shower accessories or add any on/off control valve at the outlet of the water heater. When carrying out maintenance work on a shower type electric water heater, the REW should follow the manufacturer's instructions. He should in particular check whether the fixed electrical installation and pipes are properly installed and whether the thermostat operates normally. If necessary, he should consult the relevant agent or manufacturer. In case the REW finds that the outlet pipe is not properly installed, he should advise the user to appoint a licensed plumber to fix the problem immediately so as to prevent accidents.
In recent years, there was a slight increase in the number of electrical accidents involving fixed electrical installations. Records from 2005 to 2007 show that the main causes of electrical incidents were:
Most of the incidents arising from the failure of electrical equipment were caused by the lack of proper maintenance of the equipment. In accordance with the Electricity Ordinance, owners of fixed electrical installations shall have their installations inspected and tested periodically. Registered electrical workers shall conduct inspection and testing thoroughly according to the procedures stated in the Code of Practice for the Electricity (Wiring) Regulations . We also hope that registered electrical contractors will remind their customers of the need to have their fixed electrical installations regularly inspected, tested and repaired.
Another main cause of electrical incidents was non-compliance of electrical installations with relevant requirements, which means having design faults or failure to comply with the requirements of the Electricity (Wiring) Regulations in the course of installation. The following were the most common problems:
Normally, the above problems will not cause immediate danger. But since the fixed electrical installations are not protected sufficiently, these factors will become “lethal traps” and jeopardise the safety of workers and others when workers work on those installations or when other incidents happen. All registered electrical workers should ensure that electrical installations are installed in accordance with the requirements of the Electricity (Wiring) Regulations .
Besides the failure of electrical equipment, electrical incidents might be caused by electrical workers not following the correct working procedures. This type of incident often caused casualties directly. Investigations into previous incidents showed that the most common incorrect working procedures were as follows:
The following electrical incident happened because the registered electrical worker did not isolate the power source properly before performing the work:
A registered electrical contractor was undertaking busbar replacement work for the switches for sub-circuits to individual floors of a building when the incident occurred. The registered electrical worker concerned had not made arrangement with the management company of the building to disconnect the riser of the building from the power source. So only the switch was turned off before the work started and the incoming busbar before the switch was neither disconnected nor isolated. Eventually, the worker touched the busbar before the switch accidentally when working, causing short circuit and “flashover”. His face and hands suffered severe burns.
To sum up, registered electrical contractors and workers should note the following points:
According to Code 4 “General Safety Requirements” of the Code of Practice for the Electricity (Wiring) Regulations (Code of Practice) , where practicable, work on low voltage electrical equipment should be carried out after the electrical equipment has been isolated. Registered electrical workers should learn a lesson from the above accident and avoid carrying out work on energised installations. They should also strictly observe Code 4 “General Safety Practices” of the Code of Practice - check before act, isolate and lockout, de-energize and take other safety measures.
With the approach of festivals, many shopping centres, housing estates and even families buy delicate and dazzling festival luminaires for decoration and enhancement of the festive atmosphere. To ensure safety of the public and buildings, if festival luminaires are to be installed in public places, they should be installed by registered electrical contractors and registered electrical workers. The electrical installations should be energized only after the completion of appropriate tests and inspections, and Work Completion Certificates (i.e. Form WR1) should be submitted to owners of the installations. Please note the following points when installing festival luminaires:
With effect from 1 January 2008, electric fans and exhaust fans sold in Hong Kong should meet the new International Electrotechnical Commission standard IEC 60335-2-80: 2002. According to an agreement reached by the EMSD and the trade, suppliers should import the other 66 types of electrical products meeting the new IEC 60335 standard series from 1 December 2008 onwards.
The EMSD and the trade have also agreed on the handling of stocks of imported electrical products meeting the old standards. Suppliers may still supply the market with stocks meeting the old standards upon registering them with the EMSD between 1 September and 30 November this year. They must also submit the information as shown in the sample form below in order to continue supplying them. If they have not registered their stocks with the EMSD, they must do so by 30 November. From 1 December onwards, only electrical products meeting the new IEC standard series IEC 60335 will be allowed to be supplied locally.
Please click here for standards which specific products have to meet.
The Government is implementing the Mandatory Energy Efficiency Labelling Scheme (EELS) through the Energy Efficiency (Labelling of Products) Ordinance, Cap. 598 (“the Ordinance”). In the initial phase of the mandatory EELS, three types of prescribed products, namely room air conditioners, refrigerating appliances and compact fluorescent lamps, shall bear energy labels before being supplied in Hong Kong.
The energy label classifies energy performance into five grades. A product with Grade 1 energy label is the most energy efficient while a product with Grade 5 energy label is the least energy efficient.
A product supplied by a manufacturer or an importer shall be of a listed model having a reference number assigned in his name by the EMSD and bears an energy label. A person other than a manufacturer or an importer shall supply a product of a listed model with a reference number assigned by the EMSD and bears an energy label.
The Ordinance was gazetted on 9 May 2008. There is an 18-month grace period after the gazetting of the Ordinance for the trade to make necessary preparations for complying with the requirements. The grace period will end on 8 November 2009.
For details of the mandatory EELS, please click here .
The Code of Practice for the Electricity (Wiring) Regulations (CoP) was first published in 1992 and has been widely adopted as the local electrical standard. To keep pace with the development of international electrical safety standards and technological advancement in the electrical industry, the EMSD and the trade associations are reviewing and revising the 2003 Edition of the CoP. It is expected that the revision exercise will be completed at the end of this year and that the new CoP will be published early next year. We will organise seminars to explain the revisions after the finalisation of the new CoP.
The key proposed revisions will further enhance the safety of electrical workers and the public. We will draw up new guidelines on the installation of residual current devices, supplementary equipotential bonding and suitable means of isolation for temporary electrical installations for exhibitions, shows, booths, festival lighting etc. We will also require renewable energy power systems to be designed and installed according to the Technical Guidelines on Grid Connection of Renewable Energy Power Systems published by our Energy Efficiency Office. In addition, as mentioned in the last issue of the Electricity News, we plan to increase the minimum insulation resistance (raise the minimum insulation resistance of low-voltage circuit from 0.5 megaohm to 1 megaohm), update the installation requirements for electrical equipment in bathrooms (require the installation of residual current devices), and include the latest lightning protection standard (international standard IEC 62305) in the CoP. Details of the revisions will be released later.
According to the Electricity Ordinance and its subsidiary legislation Electricity (Wiring) Regulations , communal fixed electrical installations of general buildings shall be inspected, tested and certified at least once every five years to protect property owners and users and to prevent electrical accidents.
Experience shows that for buildings without owners’ corporations, there were difficulties in coordinating the inspection and test of the electrical installations. Therefore, besides taking enforcement action against property owners failing to arrange periodic inspection and test, the EMSD will, through education and persuasion, assist property owners to complete periodic inspection and test as soon as possible and to comply with the statutory requirements. When we inspect the electrical installations of buildings, we will visit the owners of the buildings, explaining the statutory requirements and how to arrange period inspection and test of electrical installations and providing technical advice. Moreover, we join hands with the District Offices, the Buildings Department, the Hong Kong Housing Society and the Urban Renewal Authority in offering assistance to the property owners. We attend the meetings of the property owners and provide them with technical advice. The District Offices help property owners form owners' corporations, while the building maintenance loan schemes administered by the Buildings Department, the Hong Kong Housing Society and the Urban Renewal Authority provide financial assistance to the property owners.
The EMSD will organise a large-scale technical seminar for the electrical trade at 7 p.m. on 8 December 2008 at the Jockey Club Auditorium of the Hong Kong Polytechnic University. The purpose of the seminar is to provide the trade with the latest safety and technical information and maintain communication with them.
As usual, the EMSD will organise the seminar in collaboration with the Hong Kong and Kowloon Electrical Engineering and Appliances Trade Workers Union (the Union) and the Hong Kong Electrical Contractors’ Association (the Association). After discussion between the representatives of the Union and the Association and our organising committee, it was decided that this year’s seminar will cover the following topics:
In order to encourage the attendees to have greater involvement in the seminar, there will be a question-and- answer session during the seminar. Questions on the above topics will be put to the attendees. Those who are selected to answer will receive a small gift if they give correct answers. In addition, those who return the questionnaires to us after the seminar will be given a souvenir. We look forward to your strong support and active participation in the seminar.
Those who are interested in attending this seminar may contact the Union
(Tel. No. 26261927 or 23939955) and the Association (Tel. No. 25720843).
The E & M Safety Campaign 2008, a large scale publicity campaign, is a collaborative effort of the EMSD and 18 leading organisations from the electricity, gas, public transport, public housing and recreation sectors and E & M trade associations. It comprises a series of activities including school drama, colouring competition and on-line quiz etc., which will be held between September and December 2008. The E & M Safety Carnival, which is the highlight of the Campaign, is to be held on 15 and 16 November 2008 at the Victoria Park in Causeway Bay, Hong Kong. The carnival will include game booths, pop singers’ performance, drama shows and a children’s corner. Members of the public are welcome to attend the carnival.
For details of the E & M Safety Campaign 2008, please click here or call the Integrated Call Centre at 1823.
1. |
Which of the following conductive parts does not require connection to the main earthing terminal by equipotential bonding conductors? |
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2. |
When testing a lightning protection installation, the measured earth termination network resistance to earth shall not exceed_____ohms (Ω) after the connection to main earthing terminal is disconnected. |
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3. |
A schematic wiring diagram showing the main distribution system should be displayed near the main switch with rating_____amperes (A) or above. |
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4. |
The Electricity (Wiring) Regulations stipulate that fixed electrical installations at “places of public entertainment” are required to be inspected, tested and certified at least once every_____. |
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5. |
Which of the following is incorrect when designing a temporary supply installation? |
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(Answers: 1d, 2b, 3b, 4b and 5c)
We look forward to receiving your valuable feedback about this newsletter so that we may continue to improve it. Please complete the feedback form below and return it to our Electricity Legislation Division by post, fax or e-mail on or before 30 November 2008 (please refer to the contact information at the bottom of this page). To show our appreciation, the first 500 
respondents will receive a small gift by post.
Electricity Legislation Division, EMSD, 3 Kai Shing Street, Kowloon, Hong Kong
1823
2895 4929