Basic Electricity

2

Basic Electrical Terms

• Voltage: the driving force, potential

– symbol is V, units are Volts

• Resistance: resistance to flow

– symbol is R, units are Ohms

• Current: a measure of flow

– symbol is I, units are Amps

• Power: rate energy is produced or used

– symbol is P, units are Watts

3

Voltage

•Water makes a great analogy for electrical systems.

•Higher voltage is just like running a pump at higher

pressure.

4

Current (amps)

•The fish are swimming in current (water).

•In a piece of copper wire the electron moves from orbital ring to orbital ring of adjacent atoms.

5

Resistance (ohms)

6

Resistance differences

7

The analogy

V RI

8

Ohm’s Law relates these terms

Ohm’s Law: E = I • RI = E ÷ R

9

Distribution system components

TransformerSubpanel with

circuit breakers

Heating cable

120, 208,277 Vac

480, 600,1K, 10K Vac

UtilityTransmits at high voltageto reduce line losses

Reduces voltageto useable levels

Distributes current andprotects circuits

Uses electricity togenerate heat

10

Standard Voltages

•Commercial and industrial facilities

–120, 208, 277, 480, 600 Volts, 3 phase

•Residential buildings

–120 and 240 Volts

•We differentiate our products by voltage

–120 Volt vs. 240 Volt

–120 Volt products are designed for 100 – 130 Volts240 Volt products are designed for 200 – 277 Volts

11

Standard circuit breakers

• Provide over-current protection for short circuits only– Trips if current flowing exceeds

breaker rating• Typical ratings for heat-tracing

applications:– 15, 20, 30, 40 and 50 amp

• Manufacturers:– Square D, GE, Cutler-Hammer

12

Ground fault circuit breakers

•In addition to over-current protection, these breakers trip if a small fault current flows to ground

- 5 mA level for personnel protection (GFCI)

- 30 mA level for equipment protection (GFEPD)

•Required for all heating cable circuits by NEC, CEC and by Tyco Thermal Controls

•Tyco Thermal Controls recommends 30 mA level equipment protection to avoid nuisance tripping

•Selection Guide on Web site shows breakers available for different voltages; available in Tyco Thermal Controls price list

13

Ground fault breaker operation

Line A

Line B

If currents in Line A and Line B are not equal, some current is going to ground through a fault. The ground fault circuit detects this

imbalance and trips the circuit breaker.

Heating Cable

Sensor

Circuit Breaker

Fau

lt

Ground

14

Electrical Issues in Heat-Tracing

•Maximum circuit lengths– Self-regulating cables draw more current at start-up temperature

than at steady-state temperature

– Thus, maximum circuit lengths are based on start-up current, not steady-state current

– Tyco Thermal Controls calculates maximum circuit lengths to ensure current draw does not exceed breaker rating

– Always use the design guide or TraceCalc for circuit lengths

•Transformer sizing– Safe transformer sizing is based current draw at start-up

temperatures rather than at steady-state

– A conservative solution is:

transformer load = breaker rating x 0.8 x voltage