Orion System VCM-X E-BUS Component - Manual (Page 10)

VCM-X Component & Systems Wiring 10
System Installation
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Wire & Transformer Sizing
JOB NAME
2 of 2 2 of 2
24VAC Power - Transformer & Cabling Considerations for Devices With Modular Connectors
Modular devices include the VAV/Zone Controller, Modular
System Manager & MiniLink Polling Device. When sizing
transformers for the devices it is important to design your
layout so that the fewest number of Power/Comm distribution
boards and the least number of transformers can be used.
The polarity problem discussed in regards to other devices
that do not have modular connections is not an issue with the
modular devices as they cannot be connected with reversed
polarity because of the modular board connectors and cable.
Also the prefabricated cable is always 16 gauge. Wire size
selection is therefore not an issue with the modular devices.
However, the same minimum voltage rules apply to modular
devices as with other non-modular devices. In order to
simplify wiring design and layout with modular devices the
following rules apply: Power/Comm Board maximum transformer size = 100VA.
This is due to the board circuitry and fusing. Each modular
device is to be calculated at 6VA. This allows for a maximum
of 16 devices per Power/Commboard. If more than 16
devices are required, multiple Power/Comm boards must be
used.
No more than 6 modular devices allowed per branch circuit.
(The Power/Comm board has a total of 4 branch circuits)
The longest total run per branch circuit is 240 Ft. This is due
to voltage drop on the prefabricated cable.
Below are some examples of transformer sizing and branch
circuit design.
120 / 24VAC
120 / 24VAC
120 / 24VAC
120 / 24VAC
80 VA
Transformer
Minimum
See Warning
Note Below
40 VA
Transformer
Minimum
See Warning
Note Below
100 VA
Transformer
Minimum
See Warning
Note Below
75 VA
Transformer
Minimum
See Warning
Note Below
Power/Comm
Board
Power/Comm
Board
Power/Comm
Board
Power/Comm
Board
Total length of all modular cables used on each branch ( A to B) cannot exceed 240 Ft.
Total length of all modular cables used on each branch ( A to B) cannot exceed 240 Ft.
A
A
A
A
12 Devices At 6 VA = 72 VA
Use 75 VA Transformer
WARNING!
DO NOT GROUND THE 24V TRANSFORMER THAT IS TO BE USED
WITH THE POWER/COMM BOARDS. GROUNDING OF THE
TRANSFORMER WILL DAMAGE THE POWER/COMM BOARD AND
ALL BOARDS CONNECTED TO IT. A SEPARATE TRANSFORMER
MUST BE USED FOR EACH POWER/COMMBOARD. NO
EXCEPTIONS. DO NOT CONNECT ANY OTHER DEVICES TO THE
TRANSFORMER USED FOR THE POWER/COMM BOARD!
6 Devices At 6 VA = 36 VA
Use 40 VA Transformer
16 Devices At 6 VA = 96 VA
Use 100 VA Transformer
13 Devices At 6 VA = 78 VA
Use 80 VA Transformer
6 Devices Maximum Per Branch Circuit
6 Devices Maximum Per Branch Circuit
O-VCMXWRSIZ1A.CDR
Orion VCM-X System
03/09/06
Transformer Sizing & Cabling For Devices With Modular Connectors
Figure 2: Transformer & Wire Sizing - Devices with Modular Connectors