LAARS MC4EXT User Manual

Installation and Operation Instructions Document 4206

Installation and Operation
Instructions for

MC Extension Box

Providing up to 12 Stages of Full Modulation Control

The MC Extension Box (MCX) increases the
number of stages a Laars Modulating Control (MC)
can control from 4 to 12. All logic, memory, and
control algorithms reside in the MC panel. The MC
panel directly controls four built-in stages. When an
MCX is connected to the MC, the MC will
automatically recognize eight additional stages. Any
of the twelve stages can be the lead stage and
automatic rotation provides even wear among all
active stages.

The MCX can be equipped with up to four
output cards, each of which controls a pair of stages.
There are two types of output cards: 135Ω cards
control up to two fully modulating 135Ω stages, and
Current/Voltage cards can be programmed to control
two 0-5V, 1-5V, 0-10V, 2-10V, or 4-20mA stages. To
select the type of output for Current/Voltage cards,
follow the directions in the MC I/O Manual (System
Startup, Selecting the Output Type).

EXTENSION MODULE

REAR VIEW

Each new stage must also be configured for its
Mode (Auto, Manual, Standby, On, and Off), Ignition
Start Point, and Modulation Start Point as described in
the MC I/O manual (Stage Settings). All other steps
and procedures to configure the MC presented in its I/
O manual must be completed to insure smooth
operation of a MC/MCX system.

SECTION 1.
Installation

1.1 Mounting the EXM

Select a location adjacent to the MC control and
within the reach of the provided Panel-to-Panel cable.

Remove the MCX panel from the metal
enclosure by removing the top center screw and
loosening the two bottom screws. Lift the panel out.

Screw the enclosure to the surface through the
mounting holes in the back of the enclosure.

Output Cards are ordered
separately as required

Connection to

MC

Card 4 Card 3 Card 2

Fuse

Figure 1. MCX Rear View.

Mount Output
Card 4 here to

control Stages

K and L

J12

Mount Output
Card 3 here to

control Stages

IandJ

Card 1

Mount Output

Mount Output
Card 2 here to

control Stages

GandH

Mounting Holes

EandF

Card here to

control Stages

Figure 2. Mounting Holes.

Page 2

LAARS HEATING SYSTEMS

1.2 Mounting the Output Cards

The Output Cards are mounted on the rear of the

MCX (see Figure 1).

Each Output Card controls two stages. The two
stages connected to one Output Card must have the
same type of output (135Ω, 0-5V, 1-5V, 0-10V, 2­10V, or 4-20mA). However, different types of Output
Cards can be combined on the MCX, and each Output
Card can be programmed differently.

Align the Output Card with the pins on the back
of the panel and gently press them on until the top of
the pins appear through the Output Card connector.

Mounting

holes

To header

MCX

J12

or

MCX

JP4

Header Cable

1.4 Attaching the Connecting Cable
to the MC

Remove the MC from its enclosure.
Secure the remaining Header cable to the

enclosure as described above.

On the rear of the MC, locate JP4 and attach the

three screw terminal connector.

Return the panel to its enclosure, replace the top

screw, and tighten the bottom two screws.

Reattach the Panel-to-Panel cable to the Header

cables.

1.5 Wiring the Power

Bring the 120VAC 60Hz power wires through a

bottom Knockout of the enclosure. The right front
Knockout is preferred.

Class 1 voltages must enter the enclosure

through a different opening from any Class 2 voltage
wiring.

Connect the hot line to terminal marked LINE.
Connect the neutral line to the terminal marked

NEUT.

The green ground screw MUST be connected to

earth ground (see Figure 5).

Panel-to-Panel Cable

Figure 3. Cable Connections.

1.3 Attaching the Connecting Cable
to the MCX

Disconnect the Panel-to-Panel cable from the

two Header cables (see Figure 3).

Remove a Knockout from the enclosure.
Insert the end of the Header cable with three

screw terminals through the Knockout into the interior
of the enclosure.

Use the mounting holes to secure the square end

of the Header cable to the enclosure.

Connect the three screw connector to the black

header on the rear of the MCX marked J12 (see
Figure 1).

Return the panel to its enclosure, replace the top

screw, and tighten the bottom two screws.

MC REAR VIEW

Output A&B

Output C&D

JP4

Fuse

Figure 4. MC Rear View.

Neutral

Line

SAFETY
GROUND
MUST BE

CONNECTED

Figure 5. Power Wiring.

120VAC

60 Hz

Earth

Ground

1.6 Installing the Output Relays

Each output stage (E through L) which is to be
used must have a relay installed in the socket. These
relays are ordered separately (p/n CA002300).

To install a relay, orient the pins and then press it
gently into the appropriate socket.

Any stage output which does not have a relay
must have its Mode set to Off (see MC I/O manual,
Stage Settings).

1.7 Wiring the Stage Outputs

Each Stage output (E through L) has one
Normally Open (N.O.) relay contact.

The N.O. contacts are dry contacts only. They do
not source any voltage.

Each N.O. contact is capable of switching 6A
resistive at 120VAC.

Total output of all stages must not exceed 15A.

Wire the N.O. relay contacts in series with the
unit’s limit circuit (see Figure 6).