wiring electric cooktop 4 wires to 3 wires

1234mom · 06-29-2011, 11:02 PM

So if the cooktop has 4 wires does that mean it has both a 120v and 240volt component? Would the white wire from the cooktop be the neutral and would that wire be the one that operates the light that indicates the surface is hot and/or in use?

frenchelectrican · 06-29-2011, 11:07 PM

I will simplify with photos.,

10-2 NM

8-2 SE cable

Let us know the diffrence there.

Merci,
Marc

1234mom · 06-29-2011, 11:18 PM

Quote:

Originally Posted by mpoulton

Depending on the specific cooktop, the previous version may not have required a neutral. Some do, some don't. In the olden days, a three wire connection with an INSULATED neutral was used for stoves and dryers. That old-fashioned connection did not have a ground, and the metal case of the appliance was connected to the insulated neutral instead. This posed a major problem if the neutral connection ever became loose - the metal appliance itself would be electrified. That's why this is no longer allowed for new installations. It was never permissible to use an uninsulated grounding conductor as a neutral, which your prior cooktop may have.

So if wired the way I mentioned before, black to black, white from junction box to red from cooktop, and bare from junction box to white and bare from cooktop, how would if be unsafe? Would it be a fire hazard or an electrocusion? Is there a way with current wiring to connect it safely?

1234mom · 06-29-2011, 11:20 PM

Quote:

Originally Posted by mpoulton

It will function normally, and be unsafe. That's a code violation for good reason. The bare ground wire would be carrying current during normal operation.

And if the bare ground wire is carrying a current during normal operation what happens?

Techy · 06-29-2011, 11:22 PM

Shock hazard, using ground as a neutral conductor puts neutral current on grounded metal parts of the cooktop.

your 4 wire(hot hot neutral ground) cooktop cannot be safely connected to a 3 wire (hot hot ground) connection

1234mom · 06-29-2011, 11:26 PM

Quote:

Originally Posted by Techy

Shock hazard, using ground as a neutral conductor puts neutral current on grounded metal parts of the cooktop.

your 4 wire(hot hot neutral ground) cooktop cannot be safely connected to a 3 wire (hot hot ground) connection

Why do you think that the mfg. instructions actually give this as an option-connecting 4 wires to 3?

Techy · 06-29-2011, 11:29 PM

because prior to the 1996(?) NEC it was allowed

1234mom · 06-29-2011, 11:31 PM

Quote:

Originally Posted by Techy

because prior to the 1996(?) NEC it was allowed

so what is the likelyhood of getting shocked?

mpoulton · 06-29-2011, 11:51 PM

Quote:

Originally Posted by Techy

because prior to the 1996(?) NEC it was allowed

THIS installation was never allowed - a bare grounding conductor was never permitted to be used as a neutral. The formerly-common 3-wire connection used an insulated neutral, not bare.

mpoulton · 06-29-2011, 11:57 PM

Quote:

Originally Posted by 1234mom

And if the bare ground wire is carrying a current during normal operation what happens?

If everything is perfectly intact, nothing happens. However, if a loose connection develops in the grounding connection anywhere between the appliance and the panel, then all of the bare metal parts of the appliance will be electrified. Depending on how the circuit is run, other random metal things in your house may also become electrified. That's not good.

To answer one of your earlier questions: yes, the cooktop has both 120 and 240v components internally. Usually the clock, timers, lights, etc. operate on 120V (from one hot to neutral), while the heating uses 240V. There's a trend for newer cooktops to use only 240V to avoid this problem altogether.

rbj · 06-30-2011, 01:47 AM

Quote:

Originally Posted by mpoulton

If everything is perfectly intact, nothing happens. However, if a loose connection develops in the grounding connection anywhere between the appliance and the panel, then all of the bare metal parts of the appliance will be electrified. Depending on how the circuit is run, other random metal things in your house may also become electrified. That's not good.

I think what mpoulton and I are saying (my earlier post about a flawed toaster) did not get understood. So nothing happens at the cooktop with a tight neutral until a nearby appliance that is not polarized (neutral prong-phase prong reversed) can cause a lethal shock from the perfectly intact 4 to 3 wire cooktop connection. Sure the appliance mfr is going to give a quick solution to keep the sale...but it is a flagrant code violation due to the hazard and unsafe potential.

brric · 06-30-2011, 08:12 AM

Quote:

Originally Posted by mpoulton

THIS installation was never allowed - a bare grounding conductor was never permitted to be used as a neutral. The formerly-common 3-wire connection used an insulated neutral, not bare.

This statement is not true. SE cable was used for years on ranges and the like. The OP can install the new cooktop to the old wiring as per the exceptions if the existing cable is SE and it is large enough to carry the load of the cooktop.

HouseHelper · 06-30-2011, 09:20 AM

Quote:

Originally Posted by brric

This statement is not true. SE cable was used for years on ranges and the like. The OP can install the new cooktop to the old wiring as per the exceptions if the existing cable is SE and it is large enough to carry the load of the cooktop.

But the OP stated the existing wires were black/white/bare... if it were SE, they would be black/black or black/red/bare. So It is NM and if the old unit required 120/240V, it never was wired correctly.

And FWIW, SE could only be used if the circuit originated at the service panel.

brric · 06-30-2011, 10:25 AM

Quote:

Originally Posted by HouseHelper

But the OP stated the existing wires were black/white/bare... if it were SE, they would be black/black or black/red/bare. So It is NM and if the old unit required 120/240V, it never was wired correctly.

And FWIW, SE could only be used if the circuit originated at the service panel.

You are correct.

1234mom · 06-30-2011, 12:42 PM

Quote:

Originally Posted by brric

This statement is not true. SE cable was used for years on ranges and the like. The OP can install the new cooktop to the old wiring as per the exceptions if the existing cable is SE and it is large enough to carry the load of the cooktop.

How do I know if the existing cable is SE and large enough to carry the load? Like I said I have a Black, White, and bare in the junction box, what gets connected to what and what are the dangers?