8 Gauge Wire connected to 14/2 extension

Sounds like something you should have a licensed professional electrician do, or at the least, consult on.

Your description is a bit confusing, Greg. Is the "aluminum covered wire (twisted aluminum on the outside)" describing your service wire?

"On the inside" of what?

If you are in the UK you need an electrician to do it, if you are letting the property and do not undertake this work in accordance with the Regulatory Reform (Fire Safety) Order 2005 you can be held liable under common law (i.e. jail time). Its part of the building regs, get professional advice from the RICS. UK only.

You don't say where you are.
In the US the wires in MC cable would normally be black white and green.
White would be neutral if wired properly.

Black and Red are usually hot lines and would be used in a 220v system

By connecting a 14/2 wire to the system you would lose the ground. That is not recommended. If you are sure the wire is 8 g then I wouldn't suggest running a smaller size wire.

@simcoetech,

Hi Greg Here Again,

Some clarification - the wire is covered on the outside with aluminum/metal coil. The "inside" of the cable has 3 wires that I believe are 8 gauge Black/Red/ and a solid copper ground wire (all three wires are copper). I guess this was set for 220 initially but was never used.

I am in Canada - sorry the wire that I am connecting this to is not 14 / 2 but 14 / 3 (Black/White and a Ground Wire). So I would connect the Black to the Read, the White to the Black for Neutral and ground to ground.

Greg

That's not 14/3 wire, Greg. It's 14/2 wire. The bare grounding wire is not counted in the description.

14/3 has a black, a red and a white neutral plus a bare grounding wire.

Where does this wire - the one believed to be 8 gauge, run from and to?

If this mysterious wire, you've described, is an unused stub proceeding from the 15 amp breaker, why not start fresh with 14/2 from the breaker.
It does appear, though, that you lack proper knowledge of the task you intend to undertake, in which case it would be best to seek professional assistance.