New oven hook up

[Greg Gillis]

My father in law is replacing an old wall mounted oven. The branch circut has two black and one red conductor. The new oven has a black, red, white and a bare copper conductor. My question is, I know the NEC says that after 1996 you need to run a 4 wire branch to the circut. Before 1996 they would crimp the neutral and grounding conductor together. (I think that is a bad idea).
But if they are bonded at the SE anyway is this still a bad idea? The old stove had a grounding conductor screwed into the box. (We live in Illinois and use conduit).
Also, Why would the existing circut have two black and a red conductor? Maybe the red is miss marked and is a neutral? Any thoughts?

[Paul W. Abernathy]

Greg,

The problem with the bonding of the Grounded and Grounding together was an issue of the fact it created parallel paths as well as you would have an issue where stray voltage could be carried over onto the equipment in the event of a fault.....the metal could become energized and cause..well DEATH...

Now as stated today you are not required to change it...but you also cant put a 4 wire plug on a 3 wire setup....but if it is a 3 wire setup you can buy a plug for the range to work with a 3 wire layout....it is allowed however I feel it is wrong........

Now....in your example.....I can't imagine why they used (2) Blacks and (1) Red and not have a grounded conductor as chances are the range has a clock and so on that needs the 120V potential...

The BEST thing you can do ( and this assumes you are not a HI ) is as the homeowner you have the right to do this......look at the conduit as it enters into the panel...see where the RED conductor terminates and see where the (2) black conductors terminate....before you start testing anything...you may notice one of the BLACK wires onto the grounded/grounding terminal bar.......and THAT black should be marked with WHITE tape at both ends.......it appears it is not....hard to diagnose without seeing it.

This is something usually I see in the DIY forum I am a MOD for.....ensure the breaker is OFF in the panel that leads to this circuit.....Now if it is all in conduit it sounds like you can work around this......re-identify the wires and get it working using the conduit as the EGC....

If you are not able to determine this from the panel ( which you should be able to.....very hard NOT to identify this.......) you can always use a volt meter and test between the BLACK and the conduit for a voltage reading...

But looking in the PANEL is the best place to start the identification process.

[Greg Gillis]

Thanks Paul. I'm not an HI, but I'm about half way there in my studies.
I've learned so much from this message board. So all things being equal, you feel the same way as I that bonding the Grounded and Grounding conductor together at the appliance is not a good idea. My suggustion to him (and he won't like it) is that a licensed sparky come and run a proper 4 wire branch circut. I know his response will be, "It has worked for 40 years this way, wny should I change it now?"

Thanks again for the quick response.

Greg Gillis

[Paul W. Abernathy]

Greg,

Yes I agree on the 4-wire being better......However this sounds like it will be an easy fix for them......re-identify one of the conductors as the Grounded conductor ( can't tell you which as it may already be one hooked to the grounded/grounding terminal bar, just not identified correctly )

The Conduit can serve as the 4th wire so to speak....the grounding conductor so he can get away with the 3-wires in the pipe and the conduit as the 4th so to speak.....just need a jumper from the metal BOX attached to the conduit to the grounding terminal on the 4 wire plug.....

Anyway...yes, a electrician can fix that for them quite easy....atleast based on what has been listed.

[Greg Fretwell]

I would never assume a conduit system was a good ground without some hard testing or actually knowing how it was installed. I agree 100% you need to figure out what you have but a common neutral/ground is safer than a marginal ground using a conduit that may not be continuous.

[Paul W. Abernathy]

Oh Greg......now you KNOW that conduit is fine fella........and we know they are going to check it 100%...come on now..have faith...