Control Transformer: Primary or secondary fuse sizing

[shooon]

I need a zone controller for my in floor heat to control the 120v pump. It's $130+tax for an off the shelf controller from my local HVAC supplier VS free since I have a transformer and a bunch of relays.

Since it's a single zone I think it's fairly straightforward, just wanting to double check some numbers.
I'll be using:
120:24VAC control transformer to control relay / power thermostat
24VAC Relay to switch 120v pump



So I have a transformer rated at 600V:120v 50VA I'm thinking I can use this to step down 120:24 since the windings are 5:1. Given that its 50VA, that would mean I'd need like 0.4A fuse on the primary or 2 amps on the secondary.

These numbers look correct? Should I fuse the primary, secondary, or both?

 

[wyliesdiesels]

The fuse numbers are correct if u dont factor in continuous load and Im tired so i cant remember code for sizing fuses off the top of my head.

however what is the current rating on the relay coil? This is important so u dont overload tranaformer and or pop fuses. Probably not much but better to check.

 

[mm08822]

The turns ratio matches but the windings may not be able to handle those currents. For the original nameplate application, primary at 600v would be maxed out at 0.08a and secondary at 120v would be maxed out at 0.4a.
You now want to protect those windings at 5x the orignal design value. Could very likely burn out either/both the windings at that level of "protection".

What is your load current?

 

[Steve from Socal]

You can buy the correct control transformer at a big box or ebay for under 20.00 Why even bother?

Steve

 

[brewchief]

You can buy the correct control transformer at a big box or ebay for under 20.00 Why even bother?

Steve

A fan center is only a little more and will have a relay already mounted, mounts on a 4x4 box to make wiring easy.

 

[zmaxmotorsports]

A fan center is only a little more and will have a relay already mounted, mounts on a 4x4 box to make wiring easy.