Electricity

IGC© CHSS Ltd 2006 Sales ref: sc/639/v3
June 2002 Q8 & Dec 2003 Q10
(a) Describe the possible health effects of electricity on the body (4)
(b) Outline FOUR factors that may affect the severity of harm of injury from contact with electricity (4)
© CHSS Ltd 2006 Sales ref: sc/639/v3
Examiners’ Report
For part (a), most candidates were bale to specify the two main effects of electricity on the human body as interference with nerve/muscle action & tissue burns
Although some were content to rely on vague references to ‘shock’ or ‘heart attack’, which were insufficient as a description
More able candidates included reference to
Cardio-respiratory effects
In particular the risk of fatal injury due to disruption of heart rhythm
As far as tissue burns are concerned, candidates should have referred to the
Main sites of damage as being the entry & exit points
& to the possibility of damage to internal organs
For part (b), many answers concentrated almost entirely on the voltages involved
Relatively few candidates outlined additional factors such as
The route taken through the body
The length of contact time
The general health & age of the person involved
& those factors that might affect the size of current passing through the body
In particular, there was little understanding of resistance, based on such things as
Dryness of the skin
In relation to electrical safety
Explain the meaning of the following terms
(i) “Isolation” (2)
(ii) “Earthing” (2)
(iv) “Overcurrent’ protection” (2)
Examiners’ Report
The question aimed to test candidates’ knowledge of some key electrical terms
“Isolation” refers to shutting off the electrical supply to an item of equipment or part of an electrical system & preventing inadvertent reconnection in order, for instance, to carry out maintenance work
“Earthing”, on the other hand is a means whereby electrical equipment & conductive items are connected to earth by a cable or metal pipework such that the route to earth provides the path of least resistance to a current flowing under fault conditions
“Reduced low voltage”, commonly used on construction sites, involves the reduction of mains voltage by a transformer to a lower, safer voltage – typically 110 or 55 volts
while “overcurrent protection” is a method of preventing the flow of excess current by cutting the supply under fault conditions by means of a fuse or circuit breaker
Despite the question, or parts of it, having appeared on previous papers, it was poorly answered by most candidates, with only the more able producing answers to a reasonable standard
December 2005 Question 1
A joiner has received an electric shock from a hand-held, 230v drill while fitting floorboards to an upstairs room of a new property
The drill is 5 years old but has not been tested during this time
The injury to the joiner was fortunately not serious
(I) Identify the factors that may have limited the severity of injury on this occasion (4)
(ii) Outline the physical effects on the body that such contact with electricity could have caused under different circumstances (4)
(iii) Describe the types of inspection&/or test to which the drill should have been subjected , identifying the particular features that should be checked by EACH type & the factors that might affect the frequencies required (12)
Examiners’ Report
Many candidates had difficulty in answering part (i) of the question
However they could have identified factors that could lead to current limitation such as
High earth path resistance from the wooden floor or the dry conditions
The age & health status of the joiner
& the length of contact time which could also have been reduced by the speed action of the fuse or circuit breaker
For part (ii) candidates were expected to identify tissue burns as one possible effect of electricity on the body but should have qualified this by referring to
The main sites of damage as being entry & exit points
& to the possibility of damage to internal organs
Other effects which could have been outlined included interference with
Nerve/muscle action (leading to involuntary grip)
& cardio-respiratory effects
In particular the risk of fatal injury due to the disruption of heart-rhythm
Some candidates could produce only vague terms such as “burns” or “heart attack” which were not sufficiently adequate descriptions of the effects to gain good marks
In answering part (iii), candidates were expected to describe 3 types of inspection
The 1st of these should have been carried out by the joiner (the user)
He should have checked the general condition of the drill for signs of damage or overheating & the integrity of the connectors (plug & socket) & cable
This type of inspection should be carried out on every occasion that the equipment is to be used
The 2nd type should have been a more formal visual inspection carried out at periodic intervals (weekly or monthly) depending upon the extent & conditions of use
It should take the form of a more thorough inspection of the equipment & its connectors & cable & additionally should include a check to ensure that the fuses fitted were correctly rated
The 3rd type should have involved a combined inspection & test (PAT), carried out by a competent person on a
3 monthly
Half yearly
With the objectives of both checking
That the equipment was functioning correctly
& of detecting potential faults such as loss of earth integrity
Deterioration of the integrity of insulation
& possible contamination of internal & external surfaces
The factors that might affect the frequency of inspection (apart from the extent & conditions of use) would include
The age & robustness of the equipment
The type of cable fitted
The number & competency of the users
Manufacturers recommendation foreseeable misuse or abuse
& the results of previous inspections
This part of the question, as was the case with part (i), was poorly answered
Candidates generally referred to PAT but were unable to outline other types of inspections & therefore reported to explaining at great length what was required by PAT
June 2001 Q9 & Sep 2004 Q11
State the items that should be included on a checklist for the routine inspection of portable electrical appliances (8)
Examiners’ Report
Most candidates were able to provide reasonable checklists in answer to this question including items as
The need to check that the appliance is of a suitable type for the operations to be carried out
That the connecting plugs are in sound condition & sockets not overloaded; that the fuses fitted are of the correct rating
That the appliance is operated at reduced voltage (where appropriate) &/or protected by a RCD
That cables are undamaged & routed safely
& that the casing of the appliance is in good condition

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