Hi:

I just bought a new 30" Induction cooktop. The relevant installation instructions for the electrical portion is as follows:

BEGIN
Electrical Requirements
This appliance must be supplied with the proper voltage and frequency, and connected to an individual, properly grounded branch circuit, protected by a circuit breaker or a time delay fuse as noted on name plate.

...

The cooktop conduit wiring is approved for copper wire connection only, and if you have aluminum house wiring, you must use special UL approved connectors for joining copper to aluminum. n Canada, you must use special CSA approved connectors for joining copper to aluminum.

You must use a two-wire, three conductor 208/240 VAC, 60HZ electrical system. A white (neutral) wire is not needed for this unit.

Refer to the name plate on your cooktop for the KW rating for your cooktop.

These cooktops require 40 amp service.

END

Now my house does have a 40 amp circuit breaker for the existing cooktop and a 30 amp circuit breaker for the oven. But both have greenfield feeds coming out of a common junction box. It looks like I just need to take out the old stove and put in the wiring for the new one. Please let me know if there is anything else I need to watch out for.

Do I need to double check that I have 8# wiring in a conduit? Do I have to separate out the oven wiring from the new cooktop wiring and put it in a separate junction box? Etc.?

BTW, I live in Silicon Valley, if that helps in any way.

Thanks!

 

As long as this circuit was wired with #8 copper, it will be appropriate for your new induction cooker. Use large wirenuts to join the conductors in the junction box The package will indicate which size wirenuts are approved for (2) #8 conductors.

If the old oven circuit is now unused, simply cap off the existing 30A oven wiring with wirenuts and switch the breaker off. If the oven is still in-use, leave that circuit as-is.

It needs to be #8 copper, but not necessarily in conduit. There should be a "8 AWG" marking on the cable or conductor.

It is okay to be in the same junction box.

The BEGIN/END block gave that away.

 

Thanks for your reply.

The oven is still being used. So I will leave it as is.

I will check on it. Hopefully the junction box has enough insulated cover visible to show me that. Else, I will probably have to go into the crawlspace to look at it.

Any comments on this? The wires coming out of the greenfield on the new cooktop are red, black and green stranded wires. They also seem to be aluminum wires. Can I just splice them with the (presumably) #8 copper wires using #8 wire nuts?

 

Another thing you can do is to to eyeball it against other wires nearby. The #8 should be one step bigger than the #10 in your 30A oven circuit, which should be one step bigger than the #12 used in the rest of the kitchen receptacles. If you want to be sure, go to the hardware and buy one foot of #8 and compare them side-by-side. Only compare the metal thickness as modern insulation is thinner than the older stuff.

Your existing circuit should have two blacks or black and red hots plus a bare or green ground. Match them up.

Yep -- they're actually tinned copper. It can be joined directly to copper.

 

I opened up the junction box and you are right. The wires feeding the stove are thicker than wires going to the oven. The wires are Red, Black and White. I assume that I match up the colors and connect the green to the white, right?

BTW, the old connections were only taped up with electrical tape and crimped with a small ring like thing.

Couple more things: While the rest of the house has only two prong outlets and they show "Open Ground" in the Outlet Tester, the kitchen has three prong outlets and they test out correct. I also tested continuity between the white 220V wire in the junction box and the metal of the box itself using the ohmmeter function of my multimeter and I got a continuity reading. This seems to indicate that the white wire is grounded, right?

 

The white can not be used for a ground. It would be capped with a wire nut and not used. If the box is metal and wired with conduit or metallic cable (AKA BX, AC, MC, FMC) you may be able to pigtail a ground from the box. If it is non-metallic cable (AKA Romex) you may need to run new cable. The usual way to test for ground is to measure the voltage between the red wire or black wire to the box. It should be 120v. Do this with an analog meter. A digital meter could give a false reading.

 

Do you know if there is a conduit between the stove junction box and the main panel? If so is it solid metal pipe or corrugated, flexible pipe? There also might be a bare ground in the back of the box -- sometimes it's hard to tell unless you look in directly with a flashlight. If you can't tell whether the stove circuit is in a conduit or cable from the kitchen side, sometimes it's easier to see where it leaves the panel from the other end.

If it's a solid metal pipe, then you're good to go, but if it's a corrugated metal pipe it would help to see a picture of it to identify the type. This site doesn't allow uploading of images, but you can post to any public photo site and link to the images here.

If you could please, set your meter to resistance (ohms) scale, and measure the actual resistance from white to the box. Don't just use the continuity scale checker as that varies between meters.

 

I went into the crawlspace and found a solid metal pipe going diagonally across the house from this junction box straight to the main panel.

I set the ohms scale to the lowest value (200ohm) and measured between white and the box and got values of around 1.1 to 1.8 ohms.

I took some pics. I will post them ASAP.

ray2047:
As for testing voltage drop between the lines and the junction box, red and box measured 120V to 130V and black and box measured the same 120V to 130V. I only have a digital multimeter now.

 

This shows the junction box as soon as I opened it up.
Junction box as it existed on Flickr - Photo Sharing!

This shows the junction box with the old cooktop greenfield removed. There is a screw at the top right of the box. Is that the grounding screw?
Removed old greenfield on Flickr - Photo Sharing!

 

Excellent.

You can cap off the white wire with a wirenut and leave it unused. Drill a 3/16" hole in the back of the metal junction box and install a 10-32 self-tapping green ground screw (electrical aisle item). The bare/green wire from the new cooker goes to the newly installed ground screw in the box.

 

Great! Can I use the top right screw in the pic that seems to be unused? Or do I have to drill a hole and use a new green screw?

 

No it has to be tapped into the solid metal of the box. Some boxes already have a 3/16" hole that you can use, but the mounting holes showed in your picture look bigger than that.

 

Just to update you. I jury rigged a cutout, connected the wires up and then turned the circuit breaker on. Voila, the cooktop works!

Thank you very, very much for helping me through the install. Getting the self tapping grounding screw was the toughest challenge of all once you showed me the way.

 

I just have a question for the old boys.....why when in conduit can you not remark a white conductor completely green with green tape or green marker.. if it was 3 wire NM with no ground that would be another story..

IMO its not any less safe then when a person uses a white as a hot in a switch loop and doesn't remark it ...or uses it for a hot in a 240v feed and doesn't mark it red...anyways not trying to argue I just want you to explain the logic that seems to be lacking in it...

 

In conduit, no remarking is allowed on wires smaller than #4 according to code. Most inspectors in my experience, do allow remarking smaller conductors when other solutions are not practical. In this case however, there was a solid ground so remarking was not necessary.

In cables, the only remarking allowed is to identify the white conductor as a hot. There is no provision for marking the white conductor as a ground.

I suppose it's hard to measure safe vs. more safe. The code making panel must have believed it's more important to have permanently identifiable grounds. If you're following safe work practices you should treat hots and neutrals the same anyway as either can be dangerous.

 

ibpooks
Ok makes sense thanks for explaining that.... I did know that cables can only be remarked for hots.... and its always good to assume a white lead might be hot..

Ben HVAC-R Tech

 

I understand the code coloring but personally since we assume this goes back to the MAIN entrance panel I wouldn't have an issue with using the white vs that greenfield. This looks as old as the hills, before 4 wire appliances were the norm????

 

The greenfield goes to the old appliances that are being replaced. There is rigid or EMT coming in the bottom of the box which should be a decent ground.