' —
‘
,
'
EleCtrcallstallatiori
,
..
93
us
can be ignored here.
if we have aheater which
‘
maker tells us is suitable for operation on a 240V supply and has a -
_
power of 100 W,we can calculate the current it will draw as follows:
'
,
watts
=
ampsX volts
'
Thus
amps
=
watts + volts
'
=
100—5—240 = 0.417A
_
'
,
If we approximate to a convenient'round number we can say
that a 100 W heater takes a current of just under half an amp. lt
may not seem important at first glance to know this fact, but the ,
point is that electrical wiring, switches and other items through
which the current flows on its way to any appliance are
'
to carry only a certain maximum current, and if this is exceeded,
_
either -a fuse will blow to protect the circuit, or thewire or switch
will overheat and be damaged, or a fire may
Start. lt follows
when electrical apparatus is installed it is important to know theÏ
maximum value of current needed and then to use materials
can carry all of this current safely.
'
it can also be seen from the above that an appliance only
forms at its specied power when it is connected .toa supply
_
system which prOvides the proper voltage. Thus a 240 V light bùlb_
applied to a 12 V supply would only glow feebly, if at all, and a 12
lamp applied to a 240 V supply would burn out
might even explode“. Some items such as heaters and“ light bulbs
can work equally well on a.c. or d.c. supplies, provided the voltage.
is correct, but others such as air pumps
and uorescent
Wlll
only/work with an a.c. supply.This_lastpoint ismehtionedonlyasa
of interest as there is no point *in the
the ruse of any other supply thanthe domestic one.—.
,
be bought, for instance some
gQldfîsÿh‘ponds,' WhlCh
_
operate at a lower voltage, but these are then suppliedvwithf atransfÔrm€r which conVei1ts the normal mains voltage tothatusedbythe
appliance,
the Whole apparatus isΑ still plugged intoÊthe domest1c
-
Supply system“'
'
"
:
’î
'
'ä 'îi
Installations. of«one or two average sized .aquaria»1nthehomewl
in electricity supply ‘becausertheif‘ totalcurrent
,
‘Wil'l£'b€ low. «For instance,, two 3 ft aquaria,eachW1th
=
-_
'
of 46W ÜiA—dding a little
currentConsumptionnôf 2
Aîs«modcrnç domest1c1nstaaünsare
‘
,
'
EleCtrcallstallatiori
,
..
93
us
can be ignored here.
if we have aheater which
‘
maker tells us is suitable for operation on a 240V supply and has a -
_
power of 100 W,we can calculate the current it will draw as follows:
'
,
watts
=
ampsX volts
'
Thus
amps
=
watts + volts
'
=
100—5—240 = 0.417A
_
'
,
If we approximate to a convenient'round number we can say
that a 100 W heater takes a current of just under half an amp. lt
may not seem important at first glance to know this fact, but the ,
point is that electrical wiring, switches and other items through
which the current flows on its way to any appliance are
'
to carry only a certain maximum current, and if this is exceeded,
_
either -a fuse will blow to protect the circuit, or thewire or switch
will overheat and be damaged, or a fire may
Start. lt follows
when electrical apparatus is installed it is important to know theÏ
maximum value of current needed and then to use materials
can carry all of this current safely.
'
it can also be seen from the above that an appliance only
forms at its specied power when it is connected .toa supply
_
system which prOvides the proper voltage. Thus a 240 V light bùlb_
applied to a 12 V supply would only glow feebly, if at all, and a 12
lamp applied to a 240 V supply would burn out
might even explode“. Some items such as heaters and“ light bulbs
can work equally well on a.c. or d.c. supplies, provided the voltage.
is correct, but others such as air pumps
and uorescent
Wlll
only/work with an a.c. supply.This_lastpoint ismehtionedonlyasa
of interest as there is no point *in the
the ruse of any other supply thanthe domestic one.—.
,
be bought, for instance some
gQldfîsÿh‘ponds,' WhlCh
_
operate at a lower voltage, but these are then suppliedvwithf atransfÔrm€r which conVei1ts the normal mains voltage tothatusedbythe
appliance,
the Whole apparatus isΑ still plugged intoÊthe domest1c
-
Supply system“'
'
"
:
’î
'
'ä 'îi
Installations. of«one or two average sized .aquaria»1nthehomewl
in electricity supply ‘becausertheif‘ totalcurrent
,
‘Wil'l£'b€ low. «For instance,, two 3 ft aquaria,eachW1th
=
-_
'
of 46W ÜiA—dding a little
currentConsumptionnôf 2
Aîs«modcrnç domest1c1nstaaünsare