Thermastat controled plugs

[Temper]

Hello everyone I would like to start off by saying Hello and glad to be here. My grandfather created a controler to use a thermastat to turn on and off 2 plugs for space heaters in my greenhouse. I will have to post the scematics later today once I get home. Basicly it has power in from 110V the hot line has a 20 Amp fuse. The main line is 12 or 10 guage stranded wire. after the fuse a transformer is connected to convert the 110v AC to 20V DC and that is run through a rectafier and one side of the 20V DC is connected to the coils of two 30 Amp relays. One relay for each plug. The plugs are running 1500Watt space heaters. The neutral and ground wires of the main line go straight through to the plugs. The hot wire goes to the open sides of the relays. When the thermastat trips and connects the terminals the relay coils activate and the hot line is connected to the spaceheaters.
Well with the description out the say here is my peoblem. My grandfather installed a panel mount fuse holder into the box that was rated at 10 Amps and put a 20 amp fuse in it, and the fuse holder itself burnt up. The fuse didnt look like it bluw at all, but it did melt the solder that held the fuse together and finaly did breal connection. When I went to replace the fuse holder I noticed the partnumber he sent me was rated for 10 Amps so I bought an inline fuse holder that was rated for 20 amps and installed it and the next day I found the same results the fuse holder burnt up and the fuse didnt look like it blew besides being burnt to hell from the holder melting. So I Tried a blade fuse holder for a car with 12 guage wire on either end and this time I ran the unit and noticed too that the fuse holder wires were getting hot, but everything else seamed to be ad normal temp. I will try to post the scematics my grandfather sent me when i get home just in case the general Idea can't be obtained from the description. I just want to know what I need to do to keep the fuse holder from getting to hot. The blade fuse holder was only rated for 32V, but my grandfather said that shouldn't matter. Is this accurate info? It seams to be a ratehr simple design, but don't know why its overheating the fuse holders. I;m trying to get this resolved so I don't have to send this back to my grandfather. Its a pain not having a relyable way to heat a GH in winter. The thermastats on the space heaters are so unrelyable. I have them set to keep it at 60 at night only to come out and its 90 degrees and the heaters are coming on. Its also a little dangerous aswell. I have an exauhst fan and other fans in the GH and if everything is running it trips the 20 Amp breaker the GH is supplied with, but its fine because the exauhst fan should not be running while the heaters are running it defeats the purpose. ;D Thanks everyone for your help.

Temper

[MP]

I did not catch whether this was a new circuit which deos not work or if it is a circuit which was working ok but quit working.
Would like to see the circuit....but in the meantime, here is a wild guess, provided it is a circuit which stopped working: With the power turned off and completely removed, go through the circuit with an ohm meter and see where your circuit is shorting to ground or finding a good path to ground.

MP