# Safe load on a 40 VA Transformer

I apologize ahead of time for this elementary, and quite possibly poorly posed, question, but I am a coward and want to make sure that I am understanding everything correctly, and not blow four motors...

We have a hydronics heating system, and we are adding a fourth heating zone. Each zone is controlled by a motorized zone valve (https://forwardthinking.honeywell.com/related_links/water/5000_series/install/95c_10932.pdf).

The (above) manual says that the motors have, as

Actuator Electrical Rating:
24Vac 60 Hz, 0.30 A Current Draw,
5 W, 7.2 VA maximum


[The label on the actual device says 0.32 A; in any case, I note that 0.3 X 24 = 7.2 above]

Now, these are on the 'secondary' side of a transformer; the relevant portion of the transformer label says

40 VA
PRI 120 V
SEC 24 V


My practical question is:

• Since $$40 > 4 \times 7.2,$$ am I reading things correctly, and it is safe to add the fourth motor?

I also have an 'enquiring minds want to know' question:

• Are the numbers above enough to know what is the power draw on the 120 Vac side, when no motors are running, and when the 4 motors are running?

Thank you very much...

Peter

• Provided there aren't any other loads, your 40VA transformer will safely drive 4 valves, each pulling about 7VA. – Dwayne Reid Oct 30 '17 at 17:11

Note its VA not watts because power also depends on phase and shape of the current taken by the load. Transformers like this are typically better than 95% efficient so the input VA will be slightly higher than this but not much. We can estimate this $VA_{input} \approx \dfrac{28.8}{0.95} = 30.3 VA$ About 0.28 amp from your 110V mains.