The way a Control company sizes Transformers for their equipment differs, but here is the BEST Power Supply I can recommend and we use this in Control Panels and for VAV Power feeds.
Typically the VA required for each device at a VAV Box is, 6VA for the Controller, 6VA for the Actuator Motor
, & 6 VA for the Valve, totalling 18VA. Multiply that by 5 = 90 VA & that is how we determine how many Tansformers we need. So for this basic setup, we would use 1 96VA~100VA Transformer for 5 VAV's & add them as needed. There is really no need to buy something at 80%, which ultimately knocks off 1 VAV per Transformer & the reason for this is that there is a Built in Circuit Breaker, which will trip if you cross the power wires on a VAV Controller or have a Controller go Bad.
So, for the sake of Controls & the Engineering of a Control System, bidding work and making sure that your VAV's have sufficient power, these values are all you need to know for VAV's. The Spec Data Sheets for each part will tell you its max operating VA & if there are other power using devices, such as a 2nd Valve Actuator for a Baseboard control valve, then you would obviously do your math Differently and settle with 4 VAV's per 96~100VA Transformer.
These can be purchased from KELE.
The parts # for a 100VA transformer in a box, with a circuit Breaker, receptacle On/Off Switch & LED to let you know that power is present.
The T-PB Series power source provides 24 VAC from a 115 VAC input. Each T-PB Series unit contains an LED that illuminates when the 24 VAC output is operational. An on/off switch is provided in the 115 VAC input. This switch disconnects or connects both the hot and neutral of the input power. A convenience outlet is located on the front panel. This convenience outlet is not controlled by the on/off switch and is always hot. A circuit breaker is incorporated in the 24 VAC circuit, which must be manually reset if the rated 3.0A (Class 2) or 4.0A (Class 1) is exceeded and the breaker operates.The T-PB Series is available in a metal enclosure (UL Listed) for field applications or without the enclosure (UL Recognized) for panel mounting.
T-PB202: 4.0A, 96 VA (Class 1) ,T-PB303: 3.0A, 72 VA (Class 2)
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