Issue installing electric downdraft cooktop

[putergod]

Need advice from a professional electrician.

I just had my counters replaced and I had to install the new downdraft cooktop myself.

Details:
House predates 4-wire code requirement for ranges/cooktops. So, my house wiring to the island consists of 1 solid black wire (hot 1), one black with red stripe wire (hot two) and one multi-strand bundle of bare wire (neutral/ground). All connections verified in panel.

Cooktop consists of one black wire (hot 1), one red wire (hot 2), one white wire (neutral), and one green wire (ground). Parenthesis based on installation manual.

Connection wire consist of 1 black wire, 1 red wire, 1 white wire, and 1 bare wire.

Manual states to connect the ground and neutral wires together in a 3-wire setup (like I have)

I installed a junction box in the island and ran the house wire and connection wire into the junction box. I connected the black wire of the connection wire to the black wire of the house wire, the red wire to the black w/ red stripe, and both the bare wire and the white wire to the mass of bare wires using large wirenuts and double wrapped them with electrical tape to be safe.
At the cooktop I connected black to black, red to red, white to wire, and green to bare. When I flipped on the breaker I heard a loud pop, saw a flash of light (breaker panel is within feet of the kitchen island) and it tripped the breaker - all immediately upon my flipping the breaker on. So, I disconnected the cooktop and double-checked the wires for the correct voltage - 243 between black and red, 121.5 between black to white and black to bare, 121.5 between red and white and red and bare. I also verified there was no continuity between the hot legs or between either hot leg to the neutral or ground. So there doesn't seem to be a short. Also, when turning on the breaker with the cooktop disconnected (and ensure none of the bare ends of the wires are touching anything of course) the breaker does not trip, and all the voltage readings are as above.

So, now I am at a loss as to what the heck happened. Any help will be greatly appreciated.

 

[Avo Mk8]

Presumably not a GFCI breaker fitted in this circuit?!

 

[putergod]

Presumably not a GFCI breaker fitted in this circuit?!

No GFCI that I am aware of. Breaker looks pretty standard.

Also, I want to say that I didn't realize this was a UK based site till recently (didn't pay attention to the ads and was wondering why it seemed every responder was overseas - just thought maybe it was a really well-known global site among electricians, lol). I know the electrical systems between our countries are different, and I apologize for bringing a problem that you wouldn't normally face, since y'all don't use split phase in the home.

As soon as I have the time, I'm going to troubleshoot the cooktop itself. Then I'll likely call a certified electrician.

Thanks everyone!!

 

[telectrix]

No GFCI that I am aware of. Breaker looks pretty standard.

Also, I want to say that I didn't realize this was a UK based site till recently (didn't pay attention to the ads and was wondering why it seemed every responder was overseas - just thought maybe it was a really well-known global site among electricians, lol). I know the electrical systems between our countries are different, and I apologize for bringing a problem that you wouldn't normally face, since y'all don't use split phase in the home.

As soon as I have the time, I'm going to troubleshoot the cooktop itself. Then I'll likely call a certified electrician.

Thanks everyone!!

being in the USA is not a problem with this forum. we have several US members, some of whom (megawatt for example) make great contributions esp. regarding USA electrics. whist there are a lot of differences betwen out systems and yours, it's still the same electrions getting shoved around. even donald trump could turn a light switch on.

 

[Megawatt]

Screenshot from the installation manual attached

I don’t care what the instructions say, do not put the ground and neutral together. You need 4 wires on your application. The equipment ground hooks up to the metal of the hood and not with the neutral. I’m not sure what exactly your problem is but if it tripped immediately then you have a phase to phase short circuit.