ELECTRICAL STUFF FOR MECHANICAL ENGINEERS. ELECTRICAL DATA FOR SYSTEM DESIGN. FLA vs. MCA VOLTAGE DESIGNATIONS VOLTAGE UTILIZATION VOLTAGE AND PHASE SELECTION FIRE ALARM & ELECTRICAL SYSTEM INTERLOCKS MOTOR STARTERS. FLA vs. MCA.
120/240 volts, 1 phase
208Y/120 volts, 3 phase
Vented fixtures release a large amount of heat into the ceiling cavity and less into the room. This may be more efficient if the ceiling cavity is used as a return air plenum.
If a ducted return is used non-vented fixtures would not be a good choice.
In toilets, it is a good idea to interlock the light switch with the exhaust fan. Relays are available with a time delay that will allow the fan to run for a designated period after the lights are extinguished.
To install a lay-in troffer takes a clearance of approx. 1 foot in the ceiling cavity. For large ducts in tight ceiling cavities, coordination is a must.
Minimum Width: 30” or the width of the equipment which ever is greater.
Minimum Depth: 240 or 208 v = 3 ft.
480 v = 3 1/2 to 4 ft.
No ducts, pipes, etc.to structure above or a maximum of 6 ft.
Exhibit 110.12 The 30 in. wide front working space, which is not required to be directly centered on the electrical equipment if space is sufficient for safe operation and maintenance of such equipment
Exhibit 110.19 The two distinct indoor installation spaces required by 110.26(A) and 110.26(F): the working space and the dedicated electrical space.
Exhibit 110.20 The working space in front of a panelboard required by 110.26(A). This illustration supplements the dedicated electrical space shown in Exhibit 110.19.
Exhibit 110.21 The dedicated electricalspace above and below a panelboard required by 110.26(F)(1).
With the exception of transformers and motor controls, the heat rejection from electrical equipment is minor. For transformers, the KVA rating X %Z will give an approx. KW value. % Z approx = 5. MCC’s and VFD’s are a bit more complex due to the varying size of motor starters and other factors. Ask your EE.
Most electrical equipment and wiring is rated to operate in an environment of of 40°C (104°F). Ventilation with office air is usually adequate.
To Calculate the speed of a induction motor, apply this formula:
Srpm = 120 x F P
Srpm = synchronous revolutions per minute.120 = constantF = supply frequency (in cycles/sec)P = number of motor winding poles
Specify a motor rated for a VFD.