Flickering cooktop controls

[lechner]

Hello, an 8.4kW induction cooktop ran fine on a 40A circuit in an old house. After reconfiguration using a 30A circuit, the controls flicker under load.

Based on Table 220.55 Note 4 (2008) derating the sole cooktop is not permitted (and I'll upgrade the circuit), but the factory leads are 10awg like the branch circuit.

Is the unstable voltage more likely caused by the insufficient wire gauge, or is there something wrong with the wire inside the wall? Thank you.

 

[Little Bill]

Hello, an 8.4kW induction cooktop ran fine on a 40A circuit in an old house. After reconfiguration using a 30A circuit, the controls flicker under load.

Based on Table 220.55 Note 4 (2008) derating the sole cooktop is not permitted (and I'll upgrade the circuit), but the factory leads are 10awg like the branch circuit.

Is the unstable voltage more likely caused by the insufficient wire gauge, or is there something wrong with the wire inside the wall? Thank you.

What do you mean by "reconfiguration using a 30A circuit"?
An 8.4kw would require a minimum 35A circuit.

With that said, I don't think the 30A or 40A circuit is causing that. You would either be tripping a 30A breaker or overheating the wire. You're not reducing the voltage. It sounds like you either have a faulty control board or a loose connection. A loose connection would more than likely be in the grounded (neutral) conductor because the control circuit is probably where the 120V part of the circuit is used.

 

[lechner]

Thank you for your response. I hope it's not the control board. You answered my question as I had hoped.

I checked all connections. The cooktop has only a ground (but no neutral) so I think the controls run on 240V. Perhaps a bad ground is causing a shielding issue between the controls and the induction elements.

The new location has no 8awg wire. Based on the thinner factory leads and my first reading of Table 220.55, I thought the 30A circuit was permitted. I thought a cooktop was a type of range.

 

[Ponchik]

It could be a loose connection anywhere on that circuit.
Turn all 4 burners ON then measure voltage at the appliance see if you get any voltage fluctuations.

 

[pjholguin]

From what I gather is you relocated the cook top, most likely a loose connection internal to the unit. Card edge connector or such.

PJHolguin

Hello, an 8.4kW induction cooktop ran fine on a 40A circuit in an old house. After reconfiguration using a 30A circuit, the controls flicker under load.

Based on Table 220.55 Note 4 (2008) derating the sole cooktop is not permitted (and I'll upgrade the circuit), but the factory leads are 10awg like the branch circuit.

Is the unstable voltage more likely caused by the insufficient wire gauge, or is there something wrong with the wire inside the wall? Thank you.