sparks
ELECTRICAL NEWS
april
2013
This publication is distributed to electrical
contractors, wholesalers, distributors, OEMs, panel
builders, Eskom, mining electricians and
consulting engineers (electrical) as well as
libraries, members of IESSA, the Institute of
Electricians and public utilities.
July to September 2012
Sold 74, free 6 720. Total 6 794
Editor:
Erika van Zyl
Consultant:
Ian Jandrell PrEng, BSc(Eng), GDE, PhD, FSAIEE, MIEEE
Production & layout:
Colin Mazibuko
Advertising:
Carin Hannay
Publisher:
Jenny Warwick
Published monthly by:
Crown Publications cc
P O Box 140
Bedfordview, 2008
Tel: (011) 622-4770
Fax: (011) 615-6108
e-mail:
sparks@crown.co.za
Website:
www.crown.coza
Printed by:
Tandym Print
The views expressed in this publication are not
necessarily those of the editor or the publisher.
MAY FEATURES
Regular topics such as cables, cable
Energy management, load management,
load shedding, load control devices, meters,
transducers, lamps, lighting control, timers,
water heating, time-of-use tariffs, power
factor correction, relays, heating, ventilation,
air conditioning, control gear, alternative
energy.
ENERGY EFFICIENCY
DISTRIBUTION BOARDS,
SWITCHES, SOCKETS AND
PROTECTION
Enclosures, earth leakage devices, circuit
breakers, fuses, surge and lightning protec-
tion, metering switches, dimmers, sockets,
disconnectors, Certificate of Compliance,
testing andmeasuring instruments, tools and
accessories, cabling glands, flameproof.
28
people on the move
Bright Sparks
March solution
Covering the chessboard
No, it is not possible! However you place the 31
dominoes, there will always be two squares left
as this diagram shows. Trial and error will also
show that the two squares which remain are
always both black squares. This is a clue to the
explanation. When a domino is placed on the
board to cover two adjacent squares, it covers
one white square and one black square.
However many dominoes you place they
will always cover equal numbers of black and
white squares.
Safety numbers
Here are seven queens placed on an ordinary
chessboard so that none of these queens
attacks any of the others.
It is not possible to add another queen to
this arrangement with these same conditions
because each unoccupied square is already
attacked by at least one queen.
Can you arrange eight queens on the board so
that none of them attacks any of the other?
Philips Lighting SA
Charles Gaobotse Mdwaba,
RAMTrade.
Jenny Heyes,
marketingmanager
South Africae
Robert Hertz,
KAM trade and
Voltex.
Jack Carne,
SAM: outdoor
southern Africa.
Mohammed Kharva,
business development-
manager – Africa.
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