Electric Cooktop 3-Wire Connection

[RICK NAPIER]

If your talking about the OP's photos the neutral is insulated, if my memory serves me the service equipment limitation was when using a uninsulated neutral like in SE cable.

Your right I had forgotten. Thank you.

 

[david]

Lets untangle two differant things:


Also I mistakingly said you could only use the exception to 250.140 if the cable was fed from the main service panel, but this only applies to the use of SE type cable where the neutral would be the bare concentric conductor of that type of cable, in your case you have regular NM with no EGC so that part doesnt apply as the neutral is insulated.

The code use to not allow the use of the exception if it was in a mobile home, but I see that was removed in 2005.

This is because the only time you where allowed to supply a range or dryer (120/240) with a three conductor cable it was required to originate in the service equipment. You where never allowed to supply a range or a dryer from a sub-panel when the circuit utilized the third wire as a Neutral / equipment ground. It never mattered if the third wire was insulated or bare it had be supplied from the service eguipment or you needed the fourth wire.If the circuit originated from a sub-panel it would have been required to be four conductors if the appliance was 120/240 or 208/120.

3) The grounded conductor is insulated,( or) the grounded conductor is un-insulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.

not sure how you are saying this only applied to SE cable . i would agree it would be uncommom to see this in conduit but it is out there that way.

If your changing the circuit from 240/120 to just 240 you do not have a neutral you have an equipment ground.

 

[iwire]

not sure how you are saying this only applied to SE cable .

When SE was used for a 3 wire feed the neutral could be bare, if I used NM for the circuit the neutral would have to be insulated.

This meant when I would run a 3 wire dryer circuit I would actully have to use a 4 wire NM and leave the bare EGC unused.

 

[david]

When SE was used for a 3 wire feed the neutral could be bare, if I used NM for the circuit the neutral would have to be insulated.

This meant when I would run a 3 wire dryer circuit I would actully have to use a 4 wire NM and leave the bare EGC unused.

Yes but wouldn’t you agree the only time you could run the circuit as you described to a (three pronged) dryer or range rec. and use the (white) conductor as a neutral / equipment ground was from service equipment never a sub- panel.

You could not use a three pronged rec. for these appliances when the where feed from a panel that was not the service equipment.

I have seen the same circuit as you described in pvc conduit supplying a three pronged range rec. using three insulated conductors. This would have only been allowed from the service equipment.

My contention is this exception only applied to an appliance circuit that utilized the neutral to bond non-current carrying metal perhaps at a junction box and the bond strap at an appliance.

When you change the circuit from 120/240 to straight 240. This exception is no longer applicable and you treat it as you would any 240 branch circuit. You no longer have a neutral you have only an equipment ground. You cannot identify an equipment ground as a neutral and you cannot land an equipment ground on a neutral buss in a sub-panel.

This is no different than saying that I am going to utilize an existing 120/240 volt range circuit to feed a 240 V furnace.

 

[david luchini]

Yes but wouldn’t you agree the only time you could run the circuit as you described to a (three pronged) dryer or range rec. and use the (white) conductor as a neutral / equipment ground was from service equipment never a sub- panel.

No, when using an insulated grounded conductor, there was no requirement for the circuit to originate at the service equipment.

Using an uninsulated grounded conductor, it would have to be part of an SE service-entrance cable and the branch circuit would have to originate at the service equipment.

 

[david]

No, when using an insulated grounded conductor, there was no requirement for the circuit to originate at the service equipment.

Using an uninsulated grounded conductor, it would have to be part of an SE service-entrance cable and the branch circuit would have to originate at the service equipment.

when where you allowed to use a nutraul for equipment grounding beyound service equipment?

 

[david luchini]

when where you allowed to use a nutraul for equipment grounding beyound service equipment?

Prior to the 1996 Code. The 1996 Code changed to require new installations of Frames of Ranges and Clothes Dryers to be grounded with a separate egc, except that existing branch circuits meeting the older requirements for grounding the frames with the grounded conductor could still be used.

 

[david]

Prior to the 1996 Code. The 1996 Code changed to require new installations of Frames of Ranges and Clothes Dryers to be grounded with a separate egc, except that existing branch circuits meeting the older requirements for grounding the frames with the grounded conductor could still be used.

that dosn't change the fact that this was only allowed when the circuit was supplied from service equipment.

even if the nuetral was insulated you could not use it to bond the frame of a range to it unless it was supplied from the service.

you would never have a circuit from a sub-panel using a nuetral as an egupment ground, because the nutral other then 3 wire range rec and dryer rec. where not allowed for equipment grounding. and these where only allowed from service equipment.

 

[david]

No, when using an insulated grounded conductor, there was no requirement for the circuit to originate at the service equipment.

Using an uninsulated grounded conductor, it would have to be part of an SE service-entrance cable and the branch circuit would have to originate at the service equipment.

i din't say nuetral i said nuetral / equipment ground

 

[david luchini]

that dosn't change the fact that this was only allowed when the circuit was supplied from service equipment.

even if the nuetral was insulated you could not use it to bond the frame of a range to it unless it was supplied from the service.

you would never have a circuit from a sub-panel using a nuetral as an egupment ground, because the nutral other then 3 wire range rec and dryer rec. where not allowed for equipment grounding. and these wher only allowed from service equipment.

That is not correct. The Code simply didn't say what you think it did. Here is the text of the 1993 Code.

250.60. Frames of Ranges and Clothes Dryers. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be grounded in the manner specified by Section 250-57 or 250-59; or, except for mobile homes and recreational vehicles, shall be permitted to be grounded to the grounded circuit conductor if all of the conditions indicated in (a) through (d) below are met.
(a) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire wye-connected system.
(b) The grounded conductor is not smaller than No. 10 copper or No. 8 aluminum.
(c) The grounded conductor is insulated; or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.
(d) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

As you can see, the only requirement for the branch circuit originating at the service equipment is where there is an uninsulated grounded conductor. That requirement does not exist when the grounded conductor is insulated.

 

[david luchini]

No, when using an insulated grounded conductor, there was no requirement for the circuit to originate at the service equipment.

Using an uninsulated grounded conductor, it would have to be part of an SE service-entrance cable and the branch circuit would have to originate at the service equipment.

i din't say nuetral i said nuetral / equipment ground

Huh :?

I didn't say 'neutral' either. I said 'grounded conductor.'

The issue is using the 'grounded conductor' to ground the frame of an electric cooking appliance.

 

[david]

That is not correct. The Code simply didn't say what you think it did. Here is the text of the 1993 Code.



As you can see, the only requirement for the branch circuit originating at the service equipment is where there is an uninsulated grounded conductor. That requirement does not exist when the grounded conductor is insulated.

ok,
but once you changethe cercuit to 240 verses 240/120 the exception does not apply

 

[GoldDigger]

That is not correct. The Code simply didn't say what you think it did. Here is the text of the 1993 Code.

(c) The grounded conductor is insulated; or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.

As you can see, the only requirement for the branch circuit originating at the service equipment is where there is an uninsulated grounded conductor. That requirement does not exist when the grounded conductor is insulated.

The 2011 code actually seems to have made it less clear by changing the semicolon to a comma:

The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service- entrance cable and the branch circuit originates at the service equipment.

But the lack of a comma after "uninsulated" still makes the meaning relatively unambiguous.

The possibility exists for creating an improper ground to neutral bond situation in a sub panel if the frame of the range is also grounded via a pipe connection or some other means. But the exception does not address that.
And since there are no loads downstream of the connection point of the range (should be a dedicated circuit), there is nothing else which might elevate the voltage of the grounded conductor causing elevation of the frame above ground.

 

[david luchini]

ok,
but once you changethe cercuit to 240 verses 240/120 the exception does not apply

If he changed the existing 'grounded conductor' to an 'equipment grounding conductor', then yes, the exception would no longer apply. But it wouldn't need to as the appliance frame would then be grounded by an equipment grounding conductor rather than a grounded conductor.

But as has been pointed out earlier by others, there is no need to change anything. The existing circuit meets the requirement in 250.140 for using the grounded conductor to ground the frame of a range.

 

[david]

So you are saying this is still a 120 / 240 volt branch circuit. How is the third wire carring circuit current in the new aplication. It has to be a 120 / 240 volt branch circuit to still apply.

 

[david luchini]

So you are saying this is still a 120 / 240 volt branch circuit. How is the third wire carring circuit current in the new aplication. It has to be a 120 / 240 volt branch circuit to still apply.

The existing circuit is 2 ungrounded conductors and 1 grounded conductor connected to a 120/240V system panelboard. This is a 120/240v, single phase, 3 wire circuit any way you look at it (2 ungrounded conductors would be a 240v, single phase, 2 wire circuit...1 ungrounded conductor and 1 grounded conductor would be a 120v, single phase, 2 wire circuit.)

Whether or not there is current being carried on the third wire is not one of the conditions set forth in 250.140.

 

[david]

The existing circuit is 2 ungrounded conductors and 1 grounded conductor connected to a 120/240V system panelboard. This is a 120/240v, single phase, 3 wire circuit any way you look at it (2 ungrounded conductors would be a 240v, single phase, 2 wire circuit...1 ungrounded conductor and 1 grounded conductor would be a 120v, single phase, 2 wire circuit.)

Whether or not there is current being carried on the third wire is not one of the conditions set forth in 250.140.

Well we just going to have to disagree on two points
1. I think it is a leap to say you have an allowance that a grounded circuit conductor can bond non- current carrying metal in 250.140 that section did not have to be coordinated with other code sections that prohibited the grounded conductor to be bonded past the service equipment, i.e. sub-panel. In commercial buildings that I have seen and I am told in Chicago these circuits from a sub-panel would be in metal conduit. By doing this you would bond the equipment ground in a sub-panel to the neutral through the range and dryer circuits.
2. I feel what is being discussed in 250.140 is a multi wire branch circuit. I do not think you define 120 / 240 circuit conductors that way if they are not designed to be connected to a load.

 

[GoldDigger]

Well we just going to have to disagree
1. I think it is a leap to say you have an allowance that a grounded circuit conductor can bond non- current carrying metal in 250.140 that section did not have to be coordinated with other code sections that prohibited the grounded conductor to be bonded past the service equipment, i.e. sub-panel.

But you are NOT bonding the grounding conductor in your wiring or anything that is grounded to the grounded conductor at the outlet. There is no ground at the range. You are just connecting the ungrounded frame (via the grounding conductor of the range pigtail) to the grounded circuit conductor.
If there were both a grounding conductor and a neutral (make that grounded conductor!) in the range pigtail, that would still apply. You have not changed the status of the grounded conductor of the branch circuit at all.
It takes awhile to get used to it.

Now if you were extending the branch circuit to a new outlet, it would be a whole new can of worms, since the connection would have to go to the grounded conductor at the old outlet and yet you would not be connecting the frame ground of the range directly to it. May not make any difference after analysis, but will spawn a lot more discussion.

 

[david]

But you are NOT bonding the grounding conductor in your wiring or anything that is grounded to the grounded conductor at the outlet. There is no ground at the range. You are just connecting the ungrounded frame (via the grounding conductor of the range pigtail) to the grounded circuit conductor.
If there were both a grounding conductor and a neutral (make that grounded conductor!) in the range pigtail, that would still apply. You have not changed the status of the grounded conductor of the branch circuit at all.
It takes awhile to get used to it.

assuming the pig tale is not using flex metal conduit

 

[GoldDigger]

assuming the pig tale is not using flex metal conduit

Not a problem, since it is still not grounded anywhere and it is part of the appliance wiring rather than your house wiring. Or is it?