Replacing a cooktop in a house built about 1990. The old cooktop had four wires: Red, Black, White and bare. Feed from the panel to junction box had three wires: Red, Black, White. In the junction box, the bare was left unterminated. Was this acceptable? The new cooktop (same manufacturer) has Red, Black and bare. How should I connect this? Bare to white?
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Replies
......no,
B-B
R-R
W-W
bare-bare
make sure the bare IS connected at the panel......!
That's the way I would have done it, but there is no white coming out of the new cooktop, and there is no bare from the panel to junction box. That's what has me stumped and cautious.
hmm....well then, attach the bare to the W and wrap green tape around the white at both ends, if you have a ground bar in your panel ... move the green taped W to it....!
Is this a gas or electric cooktop? 240V? if elec.? If elec. connect the bare in the box and the bare to bare.
WSJ
WSJ.... OldProf says there is no bare back to the panel !!
El Professore,
Based on what you've said, it sounds like the old cooktop was 120/240V. The cooktop didn't have a bare or green-insulated ground because the Code didn't require an equipment ground for fixed apliances from the early 1940s until the early 1990s. The neutral served as the ground for the frame of the appliance.
This is not as safe as having a separate equipment ground, but because fixed appliance circuits are usually dedicated (run straight from the supply panel to the appliance), there would be no intervening splices in the neutral, and so less chance of an open neutral. This means that the neutral is a pretty reliable path and consequently a pretty good equipment ground. Code never allowed this for branch circuits, because there are so many neutral splices (at every switch and outlet). An open neutral combined with a hot wire touching the metal case of a tool or base of a fixture would energize the tool or fixture, but NOT blow a fuse or trip a breaker. Pretty dangerous.
Now (since '93 I think), any fixed appliance installed in a new home has to have a proper (separate) equipment ground. For a 120/240 appliance, that means a four-wire supply. It's O.K. to hook it up the old way if the manufacturer's instructions allow it. Sort of like installing an electric clothes dryer--use a four-wire cord in a new house, but it's O.K. to use a three-wire cord in an old one.
The info you've provided impies that the new unit is 240V only. So back and red supply 240V to power the cooktop. No neutral needed, since there's no 120V needed. You do need a ground, and the old white wire might be able to serve that purpose.
I suggest calling in an electrician to verify in the panel that the white wire is properly connected to the GROUNDING busbar, which means that it'll have to be determined whether the panel has separate neutral and grounding busbars (i.e., it's a subpanel). There are other issues, as well.
Good luck,
Cliff
Edited 12/4/2005 8:52 pm ET by CAP