Wiring requirements for new-fangled oven?

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Old 05-03-08, 09:29 AM
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Wiring requirements for new-fangled oven?

Greetings. I have read dozens of posts trying to glean the proper requirements for wiring the little womans (!) new electrolux built in oven and I think it's come to this:

In order to have a good ground connection, which my old oven did not require, is it necessary to run a new wire from the panel or can I ground to the metal box?

The panel in question is a sub panel that was originally the main panel. All neutrals and grounds are seperate in the panel and the grounds are bonded to the panel box. The only metal conduit leaving the box is the one which goes to the j box at the oven. Is it safe to assume that since the panel box is grounded that the metal conduit, and therefore the J box where the oven connctions are, is grounded as well? And if so, can I simply pigtail from the new oven ground wire to the j box?

The second question involves the skimpy wires coming from the back of the oven ( 14 awg awm style). I am used to wiring beefy 220 power cords for the power supply of ranges.
The new ovens wires are tiny and are cut too short to allow enough slack to install the new oven in it's cabinet. I understand they are smaller diameter with different insulation because the load requirements are different than in the older models. The question is : in order to lengthen these, do I have to use the same type and size of wire or is there a more readily available substitue?

Thanks in advance and I appreciate your help.
 
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Old 05-03-08, 10:37 AM
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It is never safe to assume anything with regard to electricity and electrical installations.

What kind of conduit is running from the panel to the box at the oven? If it is flexible are you sure that it isn't type AC cable?

IF it is conduit you can probably pull an equipment grounding conductor through it and solve the problem.

Concerning extending the leads from the oven itself, have you read the instruction manual to see what the manufacturer recommends?
 
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Old 05-03-08, 11:40 AM
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The conduit is solid metal to a j box and greenfield for about 1 foot to the oven connection j box. Original install was 1957 so no plastic is involved.As for a running new ground wire - thats what I was hoping to avoid. It' a long pull and only accessable at either end.

The oven manual is pretty short on technical questions. It talks a bit about three and four wire connections and combining the ground and neutral from stove to existing neutral from panel. But all it has to say about the wires from the oven it self is that..." the armored cable leads supplied are CSA recognized for connection to larger guage household wiring. The insulation of the leads is rated at temps much higher than household wiring.The current carrying capacity of the conductor is governed by the temp rating of the insulation around the wires rather than the wire guage alone".

I've opened up the back of the oven and the forementioned wires run a short distance to a terminal block with ground to the chassis.

So again the question is : is this special wire that won't melt in a hot environment or is it used for some other reason?

Another thought from a novice - could I check continuity from grounding bar in sub panel to the j box at oven and determine whether or not this would work?
 
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Old 05-03-08, 03:26 PM
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oven wire is pretty special

Special, as in typically fiberglass insulated, with a rating typically of 180 deg C. Can you describe the pigtail wire insulation as having a fiberglass, rough texture? If so, you could terminate the existing flex in a box, then extend it with 10AWG low temp wire/flex to the wall J-box. If it were my oven, I'd likely buy the correct 180 deg glass wire and the longer metal flex conduit to reach. You can get this wire for about $1.25/ft in 12 AWG.
 
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Old 05-03-08, 06:45 PM
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Properly installed non-flexible metallic conduit can be used as an an equipment ground. The key phrase is properly installed.

What this means is that if threaded conduit has been used that locknuts are used on both sides of any junction & pull boxes and all couplings are made up wrench tight. If non-threaded conduit and/or connectors are used then all the fittings must be made up tightly to ensure an unbroken path for any fault currents.

Is the Greenfield (flexible) conduit from the wall-mounted metal box to the connection box on the oven and just used for flexibility? If so, then you could just add a green equipment ground between a tapped grounding screw in the existing metal box and the oven through the Greenfield.

What does the nameplate (or manual) state as the maximum current draw or minimum circuit ampacity for this unit? What size wire is existing in the house wiring to the oven? What size fuse or circuit breaker do you have on this circuit?
 
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Old 05-04-08, 10:15 AM
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The name plate says 120/208 - 3.0kw or 120/240 - 4.0kw @ 60 hz

I tried to find a amps to kw converter and just became confused. I assumed( again) that I would have to downsize the breaker.
The existing breaker is a double pole 40 amp. The wire is 10 guage.
The greenfeild is mounted to a metal box that is buried in framing and without taking down a basement wall, inaccesable. I can see enough of it to see that it is solid coming into the box.

Would my continuity test mentioned earlier work or is it just a stupid idea?

The oven wire is definatley not glass. It is very smooth and flexible. More like rubber than the plastic like insulation on typical wire.
 
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Old 05-04-08, 11:00 AM
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Originally Posted by stevets View Post
I assumed( again) that I would have to downsize the breaker.
The existing breaker is a double pole 40 amp. The wire is 10 guage.
Yes, you need a 30 amp breaker.

Originally Posted by stevets View Post
Would my continuity test mentioned earlier work or is it just a stupid idea?
I would use an old fashioned incandescent test lamp to test for ground continuity. Either hot to ground. You can tell by lamp brightness if the ground is intact. Much better than neon lamp, etc.

Originally Posted by stevets View Post
The oven wire is definatley not glass. It is very smooth and flexible. More like rubber than the plastic like insulation on typical wire.
OK, its silicone rubber. Still a high temp appliance wire.
 
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Old 05-04-08, 12:39 PM
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To get amperage from kilowatts multiply the kw rating by 1000 and then divide by the applied voltage.

Four kilowatts equals 16.67 amperes at 240 volts.

As Telecom guy wrote, replace that 40 ampere double-pole breaker with a 30 ampere (or even 20 ampere) model. If you need to extend the wiring use #10 type THHN single strand wire between the oven and the junction box and then the appropriate wire nuts in the junction box.

Also, as Telecom guy wrote, use a lamp to test the quality of the ground at the junction box. The larger the lamp the better the test. Test from the neutral (white) wire to each hot wire and then do the same from the box (ground) to each hot wire. All four tests should be of equal brightness.

Use an appropriate length of green #10 type THHN wire from the junction box through the Greenfield and to the oven's equipment ground terminal. Be sure to remove any frame-to-neutral bonding straps or wires.
 
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Old 05-04-08, 01:32 PM
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Many thanks to both of you!

Regarding the amps to kw conversion - I had done the math correctly! It just seemed like such a small number when considering breaker size that it threw me off.
 
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