I am replacing an electric cooktop in a house that is ~40 years old. The service to the old cooktop has 2 black wires and 1 gray. I assume the blacks are L1 and L2 and the gray is neutral. I tested the neutral with a disabled 120v outlet and it ohms out with both neutral and ground on the 120v outlet.
The cooktop has 1 black, 1 red, and 1 green for L1, L2, and ground respectively. It doesn’t use neutral.
Do I need to have a ground run to the panel? Is it no longer appropriate to use neutral as ground?
Can you find the cable type markings on the house wiring? It should indicate a type such as NM, NM-B, SE, or SE-R, and a size (such as 8AWG or 6AWG).
Is it even a cable or do you have wires in conduit? Insulated black/black/gray would not normally be found in a cable.
Since your new cooktop does not need neutral, it may be possible to use the third wire as ground (after ensuring that it lands on a ground bar, if neutral and ground are on separate bus bars in the panel it goes to).
It is also nowadays permitted to retrofit just a ground wire when one is not present, without being required to pull a whole new cable.
The L1 and L2 are “6 AWG 600V MTW OR THHN OR THWN AND GASOLINE AND OIL RESISTANT 11” and also has a marking “E54488”. The neutral is “10 AWG 600V …”. They are stranded wires in conduit – not a combined cable.
I was also wondering if it would be possible to re-purpose the neutral as a ground and if 10 AWG is good enough. Or does code require the ground to be green?
Unfortunately I am not comfortable working on the service panel so I’ll have to get an electrician. I’ve been meaning to have someone out to look at the panel anyway.
Good point. Neutral and ground bus bars can be (must be?) bonded at the panel, so zero Ohms between neutral and ground does not necessarily mean you have a problem. They need to be distinct at the outlet, though.
Code requires it to be green, or bare copper. You would think that they would allow you to just wrap green tape around your re-purposed ground to properly identify it, but they don’t allow that. It has to be either green “continuous” insulation (i.e. no tape) or bare copper.
If everything is properly installed, the conduit should supply ground. If you’re not comfortable in the panel, it’s worth getting an electrician to confirm.
If it’s solid metal conduit, that should be providing ground. There should be a raised spot somewhere in the back of the junction box with a 10-32 threaded hole. You can get packs of a bunch of green 10-32 “ground screws” at HD/Lowes for a dollar or two. You can put the stranded wire from the cooktop directly on the screw but it may be tricky - other options include putting a short pigtail of solid wire on the screw and then using a wire nut to attach it to the cooktop ground, or crimping on a UL-listed ring/spade terminal.
Yes, it’s legal to do the same for a cooktop. Since the cooktop doesn’t need the neutral, just leave it unused - covered with a wire nut and secured with tape if necessary.
In the UK, where it’s all 240v a cooker would be connected to a double-pole switch with its own direct (not shared) connection to the main switchboard with a 2.5mm twin and earth (ground) cable.
When I bought a new cooker, I routed the cable, but employed an electrician to make the connections at both ends.
Gray wires cannot legally be used as ground under the NEC. Ground wires must be bare or green (or green/yellow).
Re-marking non-ground colors is not permitted.
The exception is for very large wires (4AWG and larger) - those are typically not manufactured in any color other than black, and re-marking them to neutral or ground is permitted.
Solid continuous metal conduit is perfectly “proper” ground - the NEC allows it, and it works (flexible products like type “AC” have some limits).
If the conduit was installed legally and permitted/inspected, it should definitely be pullable. There are limits to how many degrees of elbows you can have in a closed run of conduit. Exceed that and there must be an openable point (junction box or pull body) to facilitate pulling.
I wondered that too. I think it could be connected to either, but I can’t tell without opening the service panel. On the device side ground and neutral will look the same. My assumption is it is connected to neutral since everything else is.
I’m not sure what you’re trying to say. In many installations, the main panel does not have dedicated, separate “ground” and “neutral” bus bars. Because the main panel is where the neutral-ground bond is, it is legal to put all the neutral and ground wires on the same bus bar(s). The only difference between “ground” wires and “neutral” wires in that case will be the color (and usage). If a gray wire lands on a combined neutral/ground bus, there is no way you could say it is “actually a ground”.
As I said above, a three wire connection should be L1, L2 and ground (not neutral), regardless of the color. If you don’t need to worry about an inspection, confirm that the gray wire is connected to the ground bus. If it is, you’re good to go for now.
It may be a problem if you’re going to sell the house at some point, though. As has been said above, an electrical inspector will definitely go cross-eyed at a gray ground wire.
I am only speaking about a load center that has separate ground and neutral bus bars. If there is only one bus bar serving ground AND neutral, then the OP should confirm that the the gray wire goes to ground/neutral and will then be assured that the gray wire IS ground, regardless of the color or the wire.
Seems to me that this would only matter to an inspector.