Basic Electricity
Cable College
Instructor: Aaron Cowdell
AT&T Proprietary (Internal Use Only)
Not for use or disclosure outside the AT&T companies
except under written agreement
What is Voltage?
A difference of potential.
Also explained as pressure.
What is it’s measurement?
Symbol?
VOLTS
V
What are normal voltages?
48VDC
POTS
120VDC
ONU
120VAC Ringing current
Page 2
190VDC
T1/HDSL
0VDC
ADSL/VDSL
AT&T Proprietary (Internal Use Only)
Not for use or disclosure outside the AT&T companies
except under written agreement
What is Current?
The flow of electrons.
What is it’s measurement? AMPS
Symbol? A
1 AMP = 6240000000000000000 electrons per second
Or 6.24 Quintillion electrons per second
Page 3
What is Resistance?
The opposition of electron flow.
What is it’s measurement?
OHMS
Symbol?
What is static Resistance?
A resistance that does not change
when voltage is applied
What is variable Resistance?
One that changes when
voltage is applied
Page 4
Resistance continued
Variable resistance explained
Applied voltage
Voltage
On the same pair
Change in
resistance
T1
meter
POTS
ONU
14VDC
48VDC
100VDC
190VDC
50
Mohms
30
Mohms
5
Mohms
25
kohms
HDSL
Resistance drops as we apply more voltage.
Our meter does not simulate circuit voltage
This is why we need higher resistance values when we test.
So that when we place our circuit back on the pair, it will still
Be in the millions of ohms.
Page 5
Resistance continued
What is a minimum good resistance reading?
POTS
3.5 Mohms
ADSL
3.5 Mohms
VDSL
100 Mohms
T1
100 Mohms
100 Mohms
HDSL
Page 6
Resistance continued
Terminology
ohms
1-999 ohms
Kohms
1000-999,999 ohms
Mohms
1,000,000-999,999,999 ohms
1 ohm = 1 Volt * 1 Amp
1 kohm = 1000 ohms
1 Mohms = 1,000,000 ohms
Page 7
What is Capacitance?
The ability of a conductor to store an electric charge.
What is it’s measurement? FARAD
Symbol? F
Where do we see capacitance in the phone company?
A twisted pair
Your meter uses this
to calculate the length
of a pair
Page 8
Capacitance continued
Your meter measures open using
Capacitance
1 foot = 15 pF
Or .000000000001 F
Page 9
What is Inductance?
What is it’s measurement?
The ability of one conductor to transfer
electrons from one conductor to
another using EMF (electromotive
force).
What is it’s measurement? Henries
Symbol?
Page 10
L
Inductance continued
What are two inductors in the phone company?
The cable
The cable induce
frequncies between
pairs
Page 11
Load Coils
Load coils add
inductance into the
cable to counter act
the affects of
capacitance
Understanding the relationship of
inductance and capacitance…
Our cable is both a capacitor and an inductor.
But they are imbalanced
Cables have large amounts
of capacitance and small
amounts of inductance
inductance
capacitance
Page 12
Understanding the relationship of
inductance and capacitance…
They are opposites
capacitors
Inductors (load coils)
Allow high frequencies to pass
(6001-30MHz)
Allow low frequencies to pass
(voice band 0-6000 hz)
Block low frequencies (voice
band 0-6000 hz)
Blocks high frequencies
(6001-30MHz)
Cables lengths over 18,000 feet must be loaded for Pots service (low
frequencies) to work.
Load coils must be removed to allow data sevice (high
frequencies) work a peak performance.
Page 13
Load Coil placement
>3000’ from
the last load
coil
>3000’ from
the last load
coil
6000’
CO
3000’
3000’
Why only 3000’?
6000’ total
Complete circuit is from phone to phone
Each load coil adds 88 mL (milli
Henries) at each loading point
88 mL = .088 L
Page 14
6000’
What is Impedance?
Impedance is the combined resistance of resistors,
inductors and capacitors.
It is measured in ohms.
What is attenuation?
It is the flattening of frequencies over a impedance.
Page 15
Laws of a series circuit
+
R1
R2
E = VOLTS = ADD
R = OHMS =
ADD
I = AMPS = CONSTANT
P = WATTS = ADD
Page 16
_
Laws of a series circuit
+
R2
R1
FORMULAS
E
P
2
I R R I
Page 17
2
P
E
I E
R P
_
E = ADD
Laws of a series circuit
R = ADD
I = CONSTANT
+
52VDC
R1
R2
20
135
P = ADD
TOTAL
TOTAL
E
52 V
R2
R1
R
155
I
P
E
6.8 V
E
45.9 V
.34 A
R
20
R
135
17.68 W
I
.34 A
I
.34 A
P
2.31 W
P
15.61 W
Page 18
_
E = ADD
Laws of a series circuit
R = ADD
I = CONSTANT
+
120VDC
TOTAL
R1
R2
13
45
P = ADD
E
120 V
R
58
I
2.07 A
E
26.91 V
E
93.15 V
P
513.9
3
R
13
R
45
I
2.07 A
I
2.07 A
P
55.7 W
P
192.82
W
Page 19
R1
R2
_
E = ADD
Laws of a series circuit
R = ADD
I = CONSTANT
+
190VDC
TOTAL
E
R1
R2
60
100
P = ADD
190 V
R1
R2
R
160
E
71.4 V
E
119 V
I
1.19 A
R
60
R
100
P
225.63
W
I
1.19 A
I
1.19 A
P
84.97 W
Page 20
P 141.61 W
_
E = ADD
Laws of a series circuit
R = ADD
I = CONSTANT
+
30VDC
E 30 V
R1
25
R2
82
R3
P = ADD
_
125
R 232
I .13 A
P
3.9 W
Page 21
E 3.25 V
E 10.66 V E 16.25 V
R 25
R 82
R 125
I .13 A
I .13 A
I .13 A
P .42 W
P 1.39 W
P 2.11 W
Laws of a Parallel circuit
+
_
R1
R2
E = VOLTS = CONSTANT
R = OHMS = INVERSIVE
I = AMPS =
ADD
P = WATTS = ADD
Page 22
Laws of a Parallel circuit
+
_
R1
R2
E
P
2
I R R I
Page 23
2
P
E
I E
R P
R1 X R2
R1 + R2
= R TOTAL
E = CONSTANT
Laws of a Parallel circuit
R = INVERSIVE
I = ADD
+
R1
52 VDC
P = ADD
_
30
TOTAL
E
52 V
R
24.55
I
2.12 A
R2
R1
P
Page 24
110.24 W
R2
135
E
52 V
R
135
E
52 V
I
.39 A
R
30
P
20.28 W
I
1.73 A
P
89.96 W
E = CONSTANT
Laws of a Parallel circuit
R = INVERSIVE
I = ADD
+
P = ADD
R1
120 VDC
_
22
TOTAL
E
120 V
R
4.71
I
25.45 A
R2
R1
P
Page 25
3054 W
R2
6
E
120 V
R
6
E
120 V
I
20 A
R
22
P
2400 W
I
5.45 A
P
654 W
E = CONSTANT
Laws of a Parallel circuit
R = INVERSIVE
I = ADD
+
R1
190 VDC
P = ADD
_
1.2 K
TOTAL
E
190 V
R
513.51
I
.37 A
R2
R1
P
Page 26
70.3 W
R2
900
E
190 V
R
900
E
190 V
I
.21 A
R
1200
P
39.9 W
I
.16 A
P
30.4 W
E = CONSTANT
Laws of a Parallel circuit
R = INVERSIVE
I = ADD
+
R1
48 VDC
R1
TOTAL
R3
233
527
P = ADD
R3
E
36.89 V
E
15.85 V
R
527
R
233
I
.07 A
R
753.41
I
.07 A
P
2.58 W
I
.07 A
P
1.11 W
P
3.36 W
E
48 V
R2
R12
Page 27
8K
R2
E
15.85 V
226.41
R
8000
I
.07 A
I
.002 A
P
1.11 W
P
.03 W
E
15.85 V
R
_