Here's what you need to know before you call an electrician and let him give you an answer. It would be great if you have a friend that does electrical for a living so nobody tries to shuck n jive you into spending money you don't need to spend on "upgrading" your circuit box if it doesn't need upgraded.
1. How many "Amp service" is the breaker box in the barn set up for?
1.1 Hopefully the breaker box isn't so ancient that it's running on fuses - I wouldn't even attempt to hook up a tank heater to a fuse box but that's just me.
2. How much voltage is coming into the breaker box.
3. Do you have enought circuits to run wire from tank heater to the breaker box? If anybody's telling you to splice into another wire, don't do that either. What we have:
1. 100 amp service, 220 volt, and I think six circuits (maybe 8, I forget) in the box. Ours runs off our house electric which is 200 amp service.
2. We have two 100 gallon Rubbermaid tanks with Drain Plug style heaters. EACH tank is wired to its own circuit, so nothing was spliced.
3. The tanks and heaters both came from TSC. Our particular heaters are from Farm Innovators, Inc. They are 1500W/120VAC/Model DPH-15.
No, I'm not smart enough to remember that, it's taped to the monitor in case we have to order a replacement.
4. You HAVE to have a copper ground pole and copper grounding wire inside the tank that goes out of the tank and attaches to the ground pole -- unless you want to run the risk of the horses getting shocked.
These heaters seem to carry a constant current of .1 (point one); when one of ours went bad, the volt meter showed it was at .5 so no wonder the horses wouldn't get their whiskers wet.
As an FYI Mr. WTW stuck his hand in the water and couldn't feel a thing when the volt meter measured a .5 current - point being a horse's nose is much more sensitive to electric current than the human hand
If you're unsure of what to do, this is one of those things that somebody who understand Things Electrical needs to help you. You don't want to burn the barn down and you don't want to end up with horses not drinking water because they can feel the current.
Now that I've said all that ---- maybe you are planning on running extension cords from the house?? If so, buy the most heavy-duty & outdoor construction cords you can find.
Try to find one long enough that you don't have to use more than one extension cord. I have made my own; it's not hard to do.
Run the cord thru PVC pipe to further protect it from the weather and horses chewing on it.
Hope this helps