Can you connect a copper fitting into a cast iron pipe without a dielectric union?

Answer 1

Certainly, if the pipes are kept dry, and don't carry an electrolyte, such as water.

Otherwise, it's a bad idea to directly connect different metallic pipes. In fact, most Plumbing codes prohibit such a connection.

That's because anytime any two dissimilar metals contact each other -- while in the presence of an electrolyte -- whichever metal has the higher electropotential will corrode, through electrolytic action.

So, in the case of copper vs iron, the copper side of the joint will eventually fail due to corrosion -- unless you electrically isolate the two metals.

You can do this via a dielectric union, or dielectric nipple. Or, you can use a hardened brass fitting, which resists corrosion and also smooths the dielectric potential between the copper and steel.

Of course, another author may have a different opinion (like the one below.) So my advice is to understand the 'why' of electrolytic corrosion, so you can determine whether or not, in your case, a dielectric union is advisable.

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Of course , NO Problem and there are many ,many options of doing so.

The electrolytic conditions happens when connecting ferrous metals to non ferrous metals that contain zinc (galvanized) if you think about it EVERY SINGLE CAST IRON RADIATOR has a brass shut off valve, Most black steel gas line have a BRASS gas valve. Brass bolts are the best way to go when installing CAST IRON ROOF DRAINS

Also why use a dielectric union when there are dielectric nipples less chance of leakage