# Why does the (expletive Deleted) transformer fuse keep popping?!

**I’ll bet you’ve changed more than a few 24vac transformer fuses in your career.**

** Sometimes, the cause was obvious…other times, not so much. **

**The first question when the fuse blows is “how many amps is this transformer good for?” **

**The second question is “How many amps should the circuit draw?”**

**Maybe you have a zoning system and the transformer is powering a bunch of zone dampers. How many dampers can the transformer handle?**

__Answer to the first question: How to calculate rated transformer amps__

**Divide the transformer’s VA rating by the secondary voltage. **

**Example; the transformer secondary is 24 volts rated at 75va. **

**Question; How many amps can it handle?**

**75va÷24vac = 3.12 amps**

__Answer to the second question: How to calculate how many amps the circuit can draw?__

** First, add up the loads. If they have a va or watt rating ( va and watts are kinda the same thing) it’s easy; add up the individual load’s watt ratings and divide by 24 (sound familiar?).**

**Example; 10 damper actuators. Each one is rated at 0.5 watts.**

**10 actuators X .5 watts each = 5 watts. Obviously 5 watts is way below the transformer’s rated 75va.**

**So, for troubleshooting purposes, what amp draw should we see? **

**5va ÷ 24volts = .20 amps if all actuators are running at the same time. **

**In this case, if you're drawing more than .20 amps,there's a problem. **