In this video presentation we are going to look at working out the minimum internal bending radius of
cables we have been exclusively working PVC PVC twin and CPC cable over the first 14 weeks with
my learners I've been asking them to put a nice smooth bend in the cable we're now going to work
out what the minimum internal bending radii can be of the cable that we select we're going to need to
use BS7671 to do so we're going to use the on-site guide we're going to use Appendix D table D5 in
order to work out these bending radiuses so let's look at that in the next part of the presentation
so what we've got here is a blown-up version of the page in the on-site guide in Appendix D which
is for table D5 so I recommend you have that page in the on site guide open for yourself so
we're in appendix D table D5 as you follow this presentation through no point telling you the
page number as we move towards the 18th edition I expect this table to stay the same but may move
in its position on page number so that's the page we're using the on-site guide which is Appendix D
table D5 blown up version just here first of all I get my students to highlight some bits on this
page so first of all internal radii and bends in the title I also get them to highlight the bit for
overall diameter D in millimetres which is very important he's often misunderstood what that means
we'll look at that later on also we're going to start off by doing thermoplastic PVC cables
so we do PVC PVC twin CPC cables so we highlight that section we know they're
non armoured and then we're going to be looking at these here this is the diameter of the cable
and it's the diameter equal to ten millimetres in size so anything up to an equal to ten so the next
line down is greater than 10 and up to an equal to 25 and then we're beyond 25 in this section here
so up to 10 millimetres diameter above 10 but up to 25 and a beyond 25 in that section here
the final column is the factor for to be applied for the overall diameter so we highlight factor
and these we're going to apply the 3 4 or 6 when we multiply against the diameter of the cable
later on in the presentation so let's first all work out the diameter of a PVC PVC twin and CPC
cable then we're going to look at what factor to apply to it in order that we can create a radius
which we create a radius we can draw a circle which is or a circle we can work out bending
radii around it let's do that in the next part of the presentation so we're going to work out the
overall diameter of PVC PVC twin and CPC cables and it requires us to work out the axes here
the widest part of the flat PVC cable so we're going to measure that axis it says here there's
a little star here and the star down here says for flat cables the diameter first to the major axes
I'd get my learners at the bottom of their page of the on side guide to draw
the sides of a PVC cable put the conductors in and then bring lines down from the major axis
the widest part the cable we've got a "d" in there so we know that's the diameter of
the cable when we come back to it so we're looking at the diameter of the cable here
on our in this case 2.5 PVC PVC twin and CPC cable so we're going to measure that diameter next
so next I'm required to measure the diameter of the cable so the widest axis of my flat cable I
offer it down and I can see my diameter of my cable for 2.5 PVC PVC twin and CPC cables is
10 millimetres so the diameter of the cable is 10 millimetres let's make a note of that so diameter
equals 10 millimetres okay so we take that we look up here and we can see the overall diameter of the
cable we've got diameter up to an including 10 mil as a factor to be applied of either three or
two so if we look at this cross section here to work out whether we're gonna be using two
we can see that this is for single core cables or conductors and they're using stalled in conduct
trunkings ducting we have a flat twin and CPC cables so therefore we're going to be using
a factor of three so we've got a diameter of 10 millimetres and factor to be applied
in this case of three so in order to work out our bending radius we're going to take the diameter of
10 and multiply it by a factor of three to give us the radius of which we're going to draw a circle
at so let's look at that in the next part of the presentation so the radius equals the diameter
which we measured to be 10 mil multiplied by the factor which we found in BS 7671 to be 3
so radius equals diameter which was 10 multiplied by a factor of 3 the radius equals 30 millimetres
so we're going to need to do is take a compass set it with a radius of 30 millimetres pop it
down and we're gonna set it to 30 millimetres like so and then what we've got to do is we're going to
have to use that to draw a circle so I put that down and I draw myself a circle with a radius
it radius a little bit clearer to see like a radius and that radius there is 30 mil
and we've now created ourselves a circle again if I make it a little bit bolder for you
like so we've now got the internal bending radius that 2.5 cable can be at its tightest point
in order to conform with BS7671 so if I take a piece of 2.5 ml cable
and I was to perform a nice 90 degree bend around it see what we can set that to I
know I can't go any tighter than this
a little bit more always difficult I keep myself out the way at the same time I'm doing a activity
so if we position that like so approaching the point of which the internal bending radius of
this cable 2.5 millimetre squared PVC PVC twin and CPC cable can be no tight and then
that bending radii we worked out by first of all measuring the diameter of the cable to give us "d"
in this case 10 millimetres we looked in BS 7671 for the factor found a factor of three
multiplied 10 by 3 to get 30 we said a compass up with a radius of 30 mm we've drawn a circle
of which we've used half of that circle in order to work out the bending radius of the cable and
we now know that that bend conforms to BS7671 but it can't be any tighter than that it's as tight
as it can be that's the minimum internal bending radius that you can be let's repeat the process
now but this time let's use six millimetre squared PVC PVC twin and CPC cables and let's workout the
minimum internal bending radius of this cable so we're going to repeat the process again
first of all I need to work out the diameter of six millimetre squared PVC PVC twin and CPC cable
and I'll offer it down and we're looking like that is coming between 14 and 15 mil
if I'm unsure of which one to go for let's go for 15 let's take it up a fraction rather than down
a fraction so we're going to go for 15 mil so the diameter of my cable "d" diameter now is 15
millimetres now need to work out from the overall diameter which factor I'm going to apply
I can't use the top one because top one's up to an including 10 so I need to go to the next one down
which is above 10 up to including 25 giving me a factor to use this time of 4 so my factor now is 4
let's go on and work out the radius of a circle and draw the circle in order that
we can put a bend in 6 millimetre squared PVC PVC twin and CPC cables to work out the radius
radius equals diameter which we measured to be15 we've multiplied by a factor which we
found in BS7671 to be 4 the radius now is 15 times 4 which is 60 millimetres so once again
I take my rule and I've now got to set it to 60 millimetres my compass needs setting out to 60
and again I then draw a circle with a radius of 60 ml I now come all the way around
let's make that a little easier to see so this line here gives us the radius of 60 ml
and we're going to bend our cable around like so take my 6 millimetre squared cable
start to perform my smooth bend to see if we can conform with the radius
as its minimum according to BS 7671 can i smooth bend
so I'm looking to make a nice smooth 90-degree bend I can be a fraction tighter than that sighs
pull it in a little bit more we're looking to set up end like so probably needs a little bit
more work I can't quite get myself in the right angle to stay out a shot so we're trying to work
out a smooth 90-degree bend so that radius will conform to the minimum allowed by BS 7671 and we
can see that we can form into that by producing a bend like so it can't be any tighter than that
as as tight as the bend can be but it can be considerably bigger than that and still obviously
conform to BS7671 some look at a different type of case because steel wire armoured cable next
so steel wire armour is still in this top section here thermoplastic and thermosetting PVC but this
time we're in a section which says armoured and it's any and has a factor of six to be applied
to a steel wire armoured cable we still need to measure the outside diameter of the cable
and I get more learners to annotate their own side guide by drawing the end of a steel wire
armoured and noting it's the major axes to be the diameter of the cable okay so let's now measure a
steel wire armoured cable so let's take a steel wired armoured cable and measure the maximum
diameter of the cable so we've got a diameter it is widest this point of I've got 14 millimetres
so we're going to take that measurement of 14 millimetres for the diameter of the cable
multiplied by 6 to create a radius radius we draw a circle and then we can work out the minimum
internal radii of the bend of steel wire armoured cable let's do that next so we need to work out
the internal radius for the steel wire armoured by "r" radius equals the diameter of the cable
multiplied by the factor that becomes radius equals and we measured the diameter to be 14
millimetres multiplied by the factor which is 6 mean the radius that we'll need to draw be 84
millimetres we take our ruler again and our compass and we set it to 84 and draw a circle
highlight the centre and the radius there which was 84 give ourselves a point for starting
and then we make our bend accordingly so I take our steel wire armoured
and our bending radius must fit that just like so giving us an internal bending radii that doesn't
exceed the requirements of BS7671 in this case it was an 84 millimetre radius that we drew with our
circle and created a bending radius around the outside of it for our steel wire armoured cable
let's move on to MICC cable next next we're going to work out the bending radiuses of mineral
insulated cable my MICC mineral insulated copper covered exactly the same as we did with the steel
wire armoured we're going to measure the diameter of the cable and measure the diameter to be its
major axes once again to be seven millimetres I go back to D5 table D5 in order to work out the
factor to be applied as I scroll down now I can see the mineral insulated cable is our bottom one
as I move across I can see the factor of six is to be applied however there is a double asterisk
there the double asterisk says if the mineral insulated cable is to be bent only once and not
reworked you can use a factor of just three I still get my learner's just to be aware of that
but actually we're going to put a bend in radii with the factor of three as the process and we do
seven times six in order to work out to radius in the next part of the presentation but to be aware
if it was only to be work once you can apply a factor of three I see the bending radius in the
next part so once again to work out the radius of the circle we're going to draw we do "r"
equals "d" which was seven times the factor which was six the radius is seven times six which is 42
millimetres once again we set our compass up at 42 millimetres draw a circle
highlighting a little bit better in the 42
and now we can perform the internal bending radiuses that's the minimum it can be so know as
a tightest bend it can be if we've got a factor applied 6 I start to make my bend like so
we can see how that one sits there so we're looking to produce
the minimum internal bending radius again radius is diameter x factor the radius of the
circle we drew had a radius of 42 millimetres and therefore we've got the minimum internal
bending radius this time of mineral insulated cable I hope this video has been some help
you