Engineering Documentation

Table Of Contents
Appendix A Discontinued Products
MEC Service Boxes
164
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125-3002
Multiple Service Boxes on One Power Source
The table Number of MECs Allowed on a Single Three-Wire Circuit shows the number
of MECs allowed on a single three-wire (ACH, an ACN, and Earth Ground) circuit, if
local code permits.
Number of MECs Allowed on a Single Three-Wire Circuit.
Circuit Breaker Size
1
Maximum Values for
Concentrated Loads
Maximum Values for Evenly
Spaced Loads
Length
2
MEC Length
2
MEC
15 amp (No.14 AWG THHN) 75 ft (22.87 m) 7/10
100 ft (30.48
m)
7/10
20 amp (No.12 AWG THHN) 115 ft (35.06 m) 7/10 130 ft (40.63
m)
7/10
1)
Assumes minimum voltage of 102 Vac at circuit breaker and 5 Vac maximum voltage drop (97 Vac at loads). See
Class 1 power trunk information in the Wire Specification Tables section of Chapter 1.
2)
Conduit length from Service Box to Service Box.
115V Version
Standard source power is 115 Vac. The high-voltage supply enters the enclosure from
the top through the right-hand side conduit knockout. The source voltage of the MEC
must be current limited to 20 amps or less (15 amps or less for Smoke Control),
depending on the requirements of any particular installation.
Two pigtails and grounding studs are provided under the wire cover for easy
connection by the electrician. The pigtails come from the factory pre-wired to the
transformer through a single pole On/Off switch and circuit breaker. The duplex
receptacle is not switched. MOVs (3 x 150V) are installed on input power.
Low voltage is routed from the transformer and supplies 24 Vac power at 175VA
maximum. (The power source to the Service Box must be current limited to 15 amps
or less.) The CTLR, POINT BLOCKS connector is rated at 100 VA. The 24V
ACTUATOR connector is rated Class 2 and limited to 60 VA. A MOV (30V) is installed
on 24 Vac side of transformer.