• IMPORTANT: Please note that nobody on this forum should be seeking from or providing advice to those who are not competent and / or trained and qualified in their field (local laws permitting). There is a discussion thread on this global industry-wide matter HERE. This also has more information about the warning with regards to sharing electrical advice in some countries. By using this forum you do so in agreement to this.

Discuss Transformer tripping in the DIY Electrical Advice area at ElectriciansForums.net

Tommy Dee

Reaction score
Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

I installed a transformer for 5 smart thermostats, 1 of the thermostats trips the transformer fuse button right when I turn on the power. There is no call for heat, the c wire isn't connected at the thermostat, just the white and red and the c wire and red to the transformer. It is a 150VA transformer and I have no problem when its powering the other 4. I have a Taco SR506-2 controlling hydronic heating system.
Any help on what is causing the breaker on the transformer to trip would be greatly appreciated. I am using Functional Devices TR150VA001 Transformer.
Tommy Dee
Is it just the one thermostat? which would indicate that it was faulty,
or is it any combination of any 4 will work, and adding any random fifth trip it out?
It sounds like there is either something up with the wiring to (or from) that thermostat, or the thermostat itself.
If you disconnect all the thermostat 'output' wiring, just leaving transformer to thermostat, does it still trip?
Try using a multimeter to compare resistance measurements between the working circuits and the tripping one?

Added note: the transformer 'trip' is an overcurrent device, so immediate tripping indicates a severe overload, such as a short circuit or excessive load somewhere!
Last edited:

Reply to Transformer tripping in the DIY Electrical Advice area at ElectriciansForums.net

Electrical Advice

This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.