Google: appliance hardwired to house aluminum wiring

The link is given in the second item listed.

There is also a Garden Web item further down. "220 etc "

Here is a link that might be useful: AMP Splicing system

"I read somewhere that a household cooking appliance of up to 12KW can work with a 40A circuit. Can I just connect the cooktop to existing circuit?"

Yes, you are correct.

Just as importat as the NEC circuit limits are the instalation instructions for the equipment.

If the instructions for the unit say a 50 A circuit is required you must then instal a 50 amp circuit.

The NEC determines what wire gauge are allowed for the circuit.

I talked to two electricians and got different opinions (just like brickeyee and petey_racer).
First one said (talked to him on phone) it's okay to use the existing wiring since the cooktop will draw more than 10KW only if all 5 burners are turned on at max power which is extremely unlikely. He suggested to not change the breaker so if we ever turned all burners, breaker will trip.

Second one came by and said I can keep existing wiring if it's #4 otherwise it needs to be replaced. Cost would be approx 1400 including 12 hours of labor, 80ft of #6 cu wire and 50A breaker.

If replacing the wiring cost few hundred dollars, I would do it in a heartbeat but need to research more before spending 1500 dollars on it.

To further compound the matter, my panel is Federal Pacific stab-lock.

decisions... decisions...

"The new unit is rated at 10.8 KW and requires a 50A circuit."

If the installation instructions say "requires a 50A circuit" you do not have a choice.

You need to run conductors large enough for a 50 amp circuit protected by a 50 amp breaker.

The NEC requires manufacturer's installation instructions to be followed.
They supersede any NEC rules in this case.

The NEC still controls the wire size required, but you need a 50 amp circuit.

The NEC does allow for diversity for multiple stoves, but you only have one device.

here's something to think about..
voltage drop..while this will not cause the cooktop to draw more current like a motor. but it will reduce the heat output.this could lead to turning up the burners..hum..
maybe there is another reason besides CODE to use the proper wire size..or LARGER! but use a 50amp breaker(say 4ga copper instead of 6ga).. at 80ft at 50amp is #6 large enough? just asking I don't know the numbers off the top of my head..the NEC and other wire gauge tables exist. look them up.

other dumb question..what's the voltage? 240V or 380v?

-dkenny

"I'm planning to replace a electric radiant heat cooktop with an induction unit. " OP

"voltage drop..while this will not cause the cooktop to draw more current like a motor. but it will reduce the heat output.this could lead to turning up the burners..hum.. "

Not necessarily true for an induction cook-top.

One of the first things most do with the the incoming power is turn into DC, to then be chopped to high frequency AC (many thousands of cycles per second) to produce the fast varying magnetic field for induction heating.

Depending on the power supply design chosen the current may increase when voltage declines.

To further compound the matter, my panel is Federal Pacific stab-lock.

decisions... decisions...

The FIRST decision to make is to REPLACE the Federal Pacific panel!

Then start from there!

Grouped of induction hobs are typically are not capable of putting out equal to the additive total power of the hobs. If you turn then all on to their highest setting, the power will be chopped to some or all of them.

Just an example to make it clear. If you want to boil a large volume of water in two pots on a 4-hob cooktop, you need to know which pairs of hobs are on the same power supply and choose the hobs accordingly. Typically the hobs are paired on two power supplies. If you choose two on the same supply, you might only get 70-80% of the rated power. Probably, it will be in the manual for the appliance.

If your power supply to the cooktop is not optimal, you may get less than you can from the appliance. Few people will notice any difference, but if you are a heavy-duty cook, you might.

Get rid of the F-P panel.

While old ones did not have problems, as the brand name was bought and sold defective breakers ended up being made and installed.

The worst offenders are 240 V double pole breakers that fail to open, or only open one side in an overload.

The overall connection of the individual breakers to the bus in the panel also left much to be desired, especially for heavy loads.

If the manufacturer's installation instructions require a circuit size, you do not get to adjust that downward based on the nameplate load of the equipment.

The electric code requires you to follow the manufacturer's instructions.

"voltage drop..while this will not cause the cooktop to draw more current like a motor. but it will reduce the heat output.this could lead to turning up the burners..hum.. "

Not necessarily true for an induction cook-top.

um..yes..its true..
the cooktop controls the strength of the magnetic field..it doesn't output more if 2 pans are placed on the same burner. the equivalent of loading a motor for no-load to full load..at least that's my thinking..

-dkenny