Cables for Installations and Industry - Draka

44
The ta ble be low shows the types of in ter fer ence and
re spec tive screen ing:
In ter fer ence Cause Screen ing
Ca paci tive
In duc tive
Ra dia tion
Gal vanic
Cros stalk
Elec tric field
e.g. high- voltage ca ble
Mag netic field
e.g. power ca ble
Ra dia tion field
e.g. Radiotransmitter,
ra dar, re lay or tran sis tor
E.g. in cor rectly earthed
serv ice net work
Elec tro mag netic
cou pling be tween the
dif fer ent pairs of
the ca ble
Pair twist ing,con duct ing
metal shields
Pair twist ing, ar mour ing,
fer ro mag netic screen ing
Pair twist ing, con duct ing
metal shields, proper
earth ing
The cir cuits are in su lated
from each other and the
ground
Suit able twist length
pairshielding
Of course price is also an im por tant fac tor in
the se lec tion of a ca ble. When you com pare the costs of
e.g. screened and un screened ca bles, the fol low ing
de tails are im por tant to re mem ber:
— ca ble in vest ments are small com pared with
the equip ment in vest ments
— fail ures, for ex am ple be cause of in ade quate
screen ing, are usu ally de tected in the serv ice -
not be fore
— re place ment of a ca ble af ter wards is ex pen sive,
time- consuming and dif fi cult
Ease of in stal la tion
The slid ing prop er ties of the ca ble are im por tant for
in stal la tion.
The ca ble is eas ier to pull if the sheath is made of
low fric tion LINYL- PVC. This is the sheath ing ma te rial
used by NK Ca bles uses in our in door ca bles. The rat ings
should be ob served in the in stal la tion of each ca ble type.
Avail abil ity, qual ity and tech ni cal sup port are other
ma jor con sid era tions in the se lec tion of a ca ble.
The fol low ing sum ma rized ques tions cover most of
the es sen tial de tails:
CONTENTS
1. What is the type of the ca ble? (Even if the type is
not known, get in touch and check if there is
a simi lar type.)
2. What kind of con nec tion or cou pling is used in
the sys tem?
3. What is the trans mis sion fre quency or the data
trans mis sion speed?
4. How many con duc tors or fi bres are needed in
the ca ble?
5. What is the im ped ance of the equip ment?
6. What in ter fer ence is there in the en vi ron ment?
(See the sec tion on screen ing.)
7. What is the serv ice en vi ron ment for the ca bles and
what are they used for? Are they in door or out door
ca bles? Is the in stal la tion fixed, semi fixed or mo bile?
8. Is the ca ble sub jected to me chani cal or chemi cal
loads?
9. Con formity to stan dards?
IN DUS TRIAL NET WORKS
In dus trial auto ma tion has developed rap idly in the past few
years and will de velop at an ac cel er ated speed in
the fu ture. Ca ble de sign fol low the lat est trends very
closely. The ex ist ing ca ble de signs can be used in digi tal
field buses, but also new designs are to come. Lo cal area
net works have be come a part of in dus trial net works.
At the mo ment they are used to han dle the trans mis sion
at the high est level of in dus trial net works, i.e. Between
the plant com puter and the pro cess com puter.
More de tails must be taken into consideration in
the de sign of in dus trial auto ma tion than in of fice.
The buses of in dus trial auto ma tion sys tems are in tended
for con tinu ing serv ice. It is im por tant that the mes sages
are ab so lutely fault less and the re sponse times ac cu rate.
Pro tec tion against in ter fer ences must be firm. This is seen
e.g.in the ca ble con struc tions and their routings.
Ca bles have a long serv ice life and are there fore
an im por tant part of the in dus trial plant. Well- designed
ca bling works for sev eral ma chine gen era tion. That is why
spe cial at ten tion should be paid to the de sign and
im ple men ta tion of the ca bling.
SYM MET RI CAL HALOGEN- FREE
IN STRU MEN TA TION CA BLES
Halogen free, HF-ca bles, pro vide bet ter fire safety than
tra di tional PVC- sheathed ca bles. They are selfex
tin guish ing like PVC- sheathed ca bles and do not spread
the fire. In a fire they emit much less visi bil ity-re duc ing
smoke than PVC- sheathed ca bles giv ing peo ple more time
to es cape from the haz ard ous area and also more time for
fire fight ing. The smoke is also less ir ri tat ing and toxic. It
doesn’t con tain harmfull hydrochloric acid or other
cor ro sive gases for equipment of the structures. This
pre vents smoke dam ages which are of ten larger than
those caused by the fire.
The self- extinguishing prop erty of the halogen free
sheath ing ma te rial is based on eth yl ene co poly mers and
it’s sub stance which de com poses respond to heat with
cool ing the ca ble and re leas ing wa ter va pour. The re sult
of a pro tect ing layer of ash is formed on the ca ble and
around the ca ble an ex tin guish ing shield ing
at mos phere of wa ter va pour. A dis ad van tage of
the halogen- free ma te rial is that the sheath is less re sis tant
to me chani cal loads and stiffer than a PVC sheath.
Halogenfree ca bles are also sup plied by NK Ca bles.
Fir e performance prop er ties of ca bles
Prop erty Stan dard
Flame re tar dant
Fire re tar dant
Fire re sis tant
IEC 332-1
IEC 332-3
IEC 331
Low smoke IEC 1034-1 ja IEC 1034-2
Halo gen free,
zero halo gen
IEC 754-1 ja IEC 754-2
(hal.quan tity