Thermolec Application &Technical Notes - Manual (Page 10)

STEP 1 - (continued)
FUSING
The National Canadian and Electrical Code requires that each power supply to a heater be individually
protected by either fuses or circuit breakers external to the heater. Please see Pertinent Regulations.
Additional sub-circuit fusing within the heater (built-in load fuses) may be either mandatory or optional and
if optional, may or may not be recommendable. The following table supplies the information necessary for
decisions on built-in sub-circuit over-current protection.
As a general rule, built-in load fuses are rated 30 Amps for circuits up to 24 Amps and 60 Amps to protect
one or more internal circuits totaling up to 48 Amps.
TABLE FOR LOAD FUSING
LOAD FUSES: The minimum required sets of 60 Amp fuses for proper protection (Option U1).
Example of load fusing: A one stage, three phase heater rated 40 amps will use one set (3 fuses of 60
Amps).
STAGE FUSES: Mostly optional, one or more sets of fuses per stage (Option U2).
Thermolec standard fuses are 30 Amps for circuits up to 24 Amps and 60 Amps for circuits up to
48 Amps.
Example of stage fusing: A three phase heater rated
48 amps will use one set (3 fuses of 60 Amps)
if the heater is designed with one stage.
For two stages (24 Amps per stage), two sets
(6 fuses of 30 Amps) will be used.
For three stages (16 Amps per stage), three sets
(9 fuses of 30 Amps) will be used.
Because fuses require ventilation, the control box
must be louvered. If the control box is specified as
Nema 4 or 12, then the box must be oversized.
Typical sub-circuit fusing arrangements
For more detailed information, please refer to section 2 in brochure " Power supply and fusing considerations "
THREE EASY STEPS
SUPPLY VOLTAGE & PHASE
HEATER
RATED
AMPS.
THERMOLEC
COMMENTS
NEC
ELECTRICAL
CODE
INTERNAL
LOAD
FUSING
MANDATORY
THERMOLEC
RECOMMENDS
BUILT-IN
LOAD FUSES
HEATER TOTAL KW * UP TO
240 /
1 PH
208 /
3 PH
347 /
1 PH
480 /
3 PH
600 /
3 PH
12
38
39 & +
17
57
58 & +
277 /
1 PH
13
44
45 & +
17
55
56 & +
40
133
134 & +
50
166
167 & +
0 - 48
49 - 160
161 & +
NO
YES
YES
NO
YES
YES
NO
NO
YES
OPTIONAL LOAD FUSES NOT
RECOMMENDED - ONLY ONE POWER
SUPPLY ECONOMICALLY JUSTIFIED.
FUSES LIMIT EXTENT OF DAMAGE IN
TERMINAL BOX IN CASE OF SHORT
CIRCUIT.
MANDATORY IN CASE OF SHORT
CIRCUIT.
* For higher KW capacities consult factory regarding the most economical number of power supplies.