Engineering Documentation

Appendix A – Discontinued Products
Modular Equipment Controller (MEC) and Point Expansion Module (PXM)
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Point Bus Wiring Restrictions
All point blocks wired to an MEC must be daisy-chained. The total wire length from the
MEC to the last point block in the chain must be no longer than 200 ft (61 m).
NOTE:
Unlike BLN connections, shield wires to the point blocks must be terminated at both
ends.
Multiple MECs on One Power Source
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 MEC to MEC.
Metal Oxide Varistors (MOVs)
For MECs, MOVs must be used across the DO terminals when connected to loads in
all cabinets. MOVs are factory-installed on all DOs in MECs. See the section
Controlling Transients [➙ 23] for MOV part numbers.
When installing MOVs across the DO relay contacts on termination boards, keep the
MOV leads as short as possible. This makes the MOV more effective in reducing
spikes from field wiring or controlled devices. Remove and reinstall any MOVs with
leads longer than 1 to 1-1/2 in. (25.4 mm to 38.1 mm).
Line Voltage Receptacle
V150LA20A MOVs are factory-installed on all MEC 115V service box receptacles.
MEC and PXM Wiring Diagrams
Point Type Specifics Diagram
Analog Input 4-20 mA, 2-wire Figure 71
4-20 mA, externally powered Figure 72
4-20 mA, 3-wire, internally powered Figure 73
0-10 Vdc, externally powered Figure 74
0-10 Vdc, internally powered Figure 75
1000 Ohm platinum RTD Figure 76