Specifications

Crestron Quick Guide to Touchpanel Connections

Doc. 4903B 41

Cresnet Touchpanel Power Q&A

We prefer to place Cresnet power supplies in our “Head End” equipment rack for large residential

systems. It has come to our attention that many of the newer touchpanels draw considerably more

Cresnet power then their predecessors. (For instance, the TPS-15G-QM draws 75 watts of Cresnet power.)

Considering power loss (due to resistance) in cable, and the 75 Watt maximum output of Crestron power

supplies, it appears that the maximum distance between a power supply and a newer touchpanels will be

much less than previous.

1. Why does the TPMC-15/17 (CH/QM) come with its own 12.5 Volt power supply, instead of using

Cresnet power?

2. Is there any possibility of producing a larger power supply to deal with the incresed Cresnet

power consumption?

3. Does Crestron have any recommendations or guidelines regarding power delivery over Cresnet

(and other) cable?

1. The higher resolution, brightness, and added capabilities of the new Crestron touchpanels have

come at a price. More power is needed to drive these devices. This is especially true for the

wired “TPMC” panels. Their embedded computer capabilities draw a great deal of power. Their

power draw makes it impractical to drive them with 24 Volt Cresnet power. A dedicated 12.5

Volt power supply was chosen as the best way to supply power.

TPMC-15CH/QM-(L) and TPMC-17CH/QM-(L) panels are shipped with an interface module called a TPMC-

L-IMC. This interface is used to convert the power from the panels power supply to two wires, allowing for

extensions in distance between the power supply and the panel. The following chart illustrates cable-

length limitations:

Recommended wire lengths between TPMC-L-IMC and TPMC touchpanel.

WIRE GAUGE SINGLE WIRE DOUBLE WIRE

14awg (2.5mm) 30ft 60ft

16awg (1.5mm) 20ft 40ft

2. The answer is “no”. The National Electrical Code prohibits running more than 75 Watts of

Cresnet power through low-voltage wiring. Larger power supplies could present a fire hazard.

3. When “sizing up” an installation, pay attention to the touchpanel sizes and their distance from

the main equipment rack. In many cases, it may be best to locate a power supply local to the

touchpanel. In multi-story projects, utility closet locations should be noted as a possible site for

Cresnet power supplies on that floor.

In some cases, it may make sense to use larger gauge wiring for Cresnet power on long runs.

Use the following formula to determine the maximum length of wire that you can use to send power from a

dedicated 75 Watt power supply to a specific touchpanel.

L < 40,000/(PF x R)

Where: “L”= length in feet, “PF”= Crestron ‘Power Factor’, “R”= Cable “Resistance”

Refer to the following table for maximum cable lengths.