RCD toroids with windings on them

Bear in mind that the ones actually used in RCDs will have been designed specifically for that application and for that manufacturer. "All Products are manufactured to order, with a full custom design service available." They won't be normal stock items but, if you ask nicely, antrimtransformers may give you a couple of them as samples.

However, what I tend to do is to go to a *core* supplier and pick a suitable core from their range, buy those and wind my own. Again, if you ask nicely, a few samples to allow you to prototype your design are often forthcoming.

For a one-off pretty standard non-critical application, a raid of the junk box will find a few candidates. A few measurements will usually find one, at least, with suitable core material.

Thanks. Great site for this stuff.