When attaching two or more wires to the
same terminal, other than 14 AWG (2.0 mm
be sure to twist them together. Deviation
from this rule can result in improper electrical
contact (see Fig. 15).
Each terminal can accommodate the following
gauges of wire:
Single wire: from 22 AWG to 18 AWG solid or
Multiple wires: up to two 18 AWG stranded,
with 1/4 watt wire-wound resistor
Prepare wiring for the terminal blocks, as
in. (13 mm) insulation from the
Cut a single wire to
the wire in the required terminal location
and tighten the screw.
If two or more wires are being inserted into
one terminal location, twist the wires
together a minimum of three turns before
inserting them (see Fig. 15).
Cut the twisted end of the wires to
(5 mm) before inserting them into the
terminal and tightening the screw.
Pull on each wire in all terminals to check
for good mechanical connection.
Do not overtighten the terminal screws to
avoid deformation and damage of the
terminal block. The maximum torque for the
terminal screws 4.4 lb.-in. (0.5 Nm).
Fig. 15. Attaching two or more wires at terminal
COMPACT VAV CONTROLLER WEB-VA423B24N – INSTALLATION INSTRUCTIONS
in. (5 mm). Insert
Automatic MAC Addressing
In contrast to other controllers the WEB-
VA423B24N controller features automatic MAC
The MAC addresses which the individual WEB-
VA423B24N controllers in the BACnet MS/TP
channel assign to themselves are not assigned in
Rather, they assign those numbers (MAC Address)
in the range of 1 to maxMaster currently not in use
by another device in the BACnet MS/TP channel
(the MAC Address of "0" is reserved by default for
the router / plant controller, itself).
All WEB-VA423B24N controllers are BACnet
MS/TP masters. Every master performs periodic
polling for the possible appearance of new masters.
Each master "knows" the identity of the "next"
master (i.e., that WEB-VA423B24N controller with
the next-highest MAC Address) on the BACnet
MS/TP bus and to which it must therefore pass the
token. The polling process includes a search for
new masters which might have MAC addresses
lying between its own MAC address and that of the
The property maxMaster specifies the highest-
allowable address for master nodes. The
maxMaster is set to 35 by default, thus
guaranteeing that, on a BACnet MS/TP bus with,
for example, 35 WEB-VA423B24N controllers, all of
the other WEB- VA423B24N controllers will be
found. Both the property maxMaster and the
property MAC address are writeable properties that
can be changed.
NOTE: You should not attempt to program a MAC
Address outside the range of 1 to
Fig. 16. Automatic MAC addressing
In the scenario depicted in Fig. 16, some of the
controllers in the BACnet MS/TP channel do not
feature automatic MAC addressing; rather, their
MAC addresses were assigned manually (for
example, using their two dip switches). Thus, when
a new WEB- VA423B24N is added to the channel,
when its automatic MAC addressing function is
triggered, it will assign itself an available (i.e.,
unoccupied) MAC address.