3-prong range vs. hardwire (?bx)

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  #1  
Old 02-01-06, 03:44 PM
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3-prong range vs. hardwire (?bx)

Hello,
In a week I'll be installing a standalone in my '56 suburban MD home. I'll be replacing a cooktop that was fed by #8/3 in armored, hardwired to the
cooktop metal junction box and fed by 40A dp. I know I can grandfather
a 3-prong receptacle and use the 3-prong the store wants to supply, keeping
th neutral-gnd jumper strap in the stove. The old setup, though, had the
advantage (to my mind) of a separate frame ground path back thru armor...
I don't want to lose that; neutrals can break or go loose ;-) anyway-
what do you think of the std 3-prong PLUS I run a separate #10 green from
the metal recept box (clamped to armor) to a good screw on the range body?
any downside?
thanks
 
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  #2  
Old 02-01-06, 03:49 PM
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I don't like your idea. Get a four prong receptacle and a four prong cord and do it properly.
 
  #3  
Old 02-01-06, 04:20 PM
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re 3-prong

Can I avoid pulling #8/3 wg up to the kitchen?
Is new 4-prong plug with a 4-wire (3+g) run to box the only solution?
I've been told to just do the 3-prong and stop worrying, as that
was code for 'a long time' - I just hoped there was something
helpful to do without pulling a new set of conductors....thanks
 
  #4  
Old 02-01-06, 05:29 PM
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Thumbs down Can I cheat the Code and not get hurt?

Originally Posted by jaysan
>I'll be replacing a cooktop that was fed by #8/3 in armored, hardwired to the cooktop metal junction box and fed by 40A dp. I know I can grandfather a 3-prong receptacle
How do you know this?

I never heard that a new receptacle where there wasn't one before is grandfathered.

Tell us the NEC article so we all can look it up.


keeping the neutral-gnd jumper strap in the stove.
That is stupid. Tell them I said so. They just want your money.


> The old setup had the advantage (to my mind) of a separate frame
> ground path back thru armor...

I agree that it might have.
Did it have a frame to neutral bond also?

If not, then although less dangerous in normal operation, there is no guarantee that there was a safe fault current path.

Unfortunately, armor can rust, break, or come apart at the box connector.



> I don't want to lose that;
I'd have to see how yours was wired and test the ampacity of the armor.
Does yours have a bonding strip?


> neutrals can break or go loose
Can and do. You got this right!



> what do you think of the std 3-prong
No, three-prong anything double-pole is dead.
Forget it.


> PLUS I run a separate #10 green from the metal recept box
> (clamped to armor) to a good screw on the range body?

If you had said a four-prong, I would have been kinder that the idea wasn't all that bad.

If you said that the AC armor is your equipment ground per NEC 320.108, and you wanted to use a four-prong, I might have believed it.

Then I would have asked why you want to bet your life on the ampacity of 50-year-old steel armor.
Is the armor spiral wound or interlocked?



> any downside?

Solutions not consisting of a four-wire plug and no neutral-frame bond are out of the question.

What's the big deal with running a new cable?

If you like the armor protection, you can pull in new type AC, or run 3/4" or 1" FMC and pull the wires through it.



Your only real choice here is either to do it safely or to do it dangerously.

The only safe way is new four-wire cable, four-wire plug, and correct size breaker.
 
  #5  
Old 02-01-06, 09:23 PM
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Once you change a grandfathered circuit - grandfathering goes out the window. If you want to preserve the grandfathered state of code - just connect your new cook top in the same manner as the old one (provided it is listed by the range top manufacturer as suitable for direct wire and a 3 wire circuit). It will be as safe as the old one was if everything is the same. If you want to install a receptacle or otherwise alter the circuit (including your grounding idea - which while well intended, is a bad idea) it must be to current code. This direction will require a new circuit.

BTW - the only reasons for loose neutrals that I have experience with is back stabbed receptacles, poor workmanship and solid aluminum wiring - in that order. But my experience is very limited.

If you can bring your new range top connections to current code - do it. If you can't - then as long as you reconnect everything you disconnect (in the same manner) then I believe you are safer than if you add or invent things mistakingly. If you go this route, you will need to properly connect the armor...
 
  #6  
Old 02-02-06, 02:18 PM
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more 4 prong questions

OK Guys thanks,
I'll be looking at the run to see if it's tough to fish fresh AC - I suppose I
can use the old to pull through the new; 70% of the run is bare bsmt joist...
plus a hole thru conc. block and a short run up thru floor (I hope the old stuff
isn't clamped somewhere I can't reach ;-)...
Do I need a separate ground wire in the new AC or can I trust the armor/
bonding wire combo as grounding (8/4 vs. 8/3)? In the latter case, I assume
the 4pr surf receptacle has a wire that screws to the box and thus contacts
the armor as my grounding means (thru bonding wire and clamp)...
If a fresh run is major hassle with big demo involved, GE offers instruction on
connecting the old AC directly to the stove j box... this gives me back the
armor-frame grounding path BUT doesn't meet new code, although it is
the "existing" setup...
small notes: 1. the old armor is in great shape, but lacks visible bond wire
(no antishorts either)
2. on further inspection, the old cooktop used only 2 hots-
white was not even connected. I had assumed a 120 leg but that
power on indicator light must be 220V
thanks
p.s. WEP I'll do safe and right, not just legal...
 
  #7  
Old 02-02-06, 03:16 PM
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Originally Posted by jaysan
I suppose I can use the old to pull through the new
It is not likely if any holes are just big enough.

Do I need a separate ground wire in the new AC or can I trust the armor/bonding wire combo as grounding?
If you get a new cable, you should get a cable with a separate EGC. You could use AC or MC if you like.



> I assume the 4-prong surf receptacle has a wire that screws to the box
> and thus contacts the armor as my grounding means
No, you would supply such a wire if you went that route.




> 1. the old armor is in great shape, but lacks visible bond wire
> (no antishorts either)
I don't know that the bushings are required. But you could get them (or improvise with PVC tape).

If the old AC is spiral wound and has the correct clamps, you are probably okay to use it.

You could test it with a 100W light bulb.
If the bulb burns brightly (0.8A), the armor probably will handle ample fault current.



> 2. on further inspection, the old cooktop used only 2 hots-
> white was not even connected. I had assumed a 120 leg but that
> power on indicator light must be 240V

I should have asked sooner... what 120V loads are in the new stove?
 
  #8  
Old 02-02-06, 03:30 PM
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more 3prong becoming 4

I checked (GE JB910) specs and they don't reveal what they
use the neutral to carry but the 120V is probably computer/display
and lights...they only spec 40A at 240...their installation manual
demands either 3-wire (neutral strapped to gnd in stove) or 4, with
separate neu and gnd, so they must want the 120 for something...
thanks
j
 
  #9  
Old 02-02-06, 04:10 PM
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Originally Posted by jaysan
they must want the 120 for something
Up to 100mA isn't likely to kill anyone if you do bond the frame to ground and then something goes wrong.

The unit might have some relays run by the thermostats or timers.
But relays use very little current once energized.

It's things like motors (clothes dryer) and 40W lightbulbs (inside dryer or oven) that have enough "neutral" current to really nail someone and that I consider to be a big deal.

So if you choose to save the cable and hardwire the new unit, you'll probably be okay.
 
  #10  
Old 02-03-06, 01:18 PM
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Another scenario 3 vs. 4 prong

OK , I'm still leaning toward running fresh 4 wire AC, but I'm curious
about the legality and safety of the following alternative:
(Assuming the old spiral AC is as good as it looks to me, etc.)
Use 4-wire plug and cord (neutral and gnd separate in stove),
put 4-prong (14-50R?) receptacle on old armor, with grnd in that receptacle
bonded to armor. then my armor is my grounding and no tie to neutral occurs.
I seem to remember something about armor being only good to 20A, though...

Oh yeah, if I get the new AC should I think about getting #6 instead of #8?
I'd still use the 40Adp breaker, but the receptacle can handle more so,
aside from cost and stiffness, why not add ampacity for the 'future'?
thanks guys
j
 
  #11  
Old 02-03-06, 05:01 PM
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Originally Posted by jaysan
(Assuming the old spiral AC is as good as it looks to me, etc.)
Use 4-wire plug and cord (neutral and gnd separate in stove),
put 4-prong (14-50R?) receptacle on old armor, with grnd in that receptacle
bonded to armor. then my armor is my grounding and no tie to neutral occurs.
It sounds goods to me other than the missing bonding strip.
Perhaps if you work the jacket back a little bit you'll find it.

If so, you need to cut back a ring to get the bonding strip out.


I seem to remember something about armor being only good to 20A
I never heard this. It has to be untrue or the NEC would not permit it.
Just looking at the armor, my estimation is that if correctly bonded at both ends it would handle current long enough to trip the main breaker.



if I get the new AC should I think about getting #6 instead of #8?
With no derating, #8 THHN is 55A. Your old TW was 40A.
The temperature rating of the insulation has improved.
 
  #12  
Old 02-04-06, 02:42 PM
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progress

I shut off breakers, pulled the armor out of cooktop jb clamp,
and found the bonding (flat) wire WAS there- it was hidden
by the clamp, broke off when it came out.
I now plan to use the armor as my EG; I'll cut back enough to get
some bonding lead to fold back and wrap around armor under the clamp.
Meanwhile I found the guys who did my heavyup mixed up 'wall oven' and
'range' labeling on the door list...went to HD, bought surface 14-50R,
will make the install preparations midweek.
I happen to have plenty of #10 stranded green around - maybe I'll run that
from the 14-50R alongside the old bx back to the grnd bus just to be sure
...(now that I save $120 in AC, I can put $10 worth of redundancy in ;-))
-unless that violates a rule.
 
  #13  
Old 02-04-06, 05:15 PM
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Originally Posted by jaysan
I found the guys who did my heavyup mixed up 'wall oven' and
'range' labeling
That's why you always test before you touch.



unless that violates a rule.
I believe you are allowed any number of fault paths so long as they don't create an objectionable current path.
 
  #14  
Old 02-15-06, 09:20 AM
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Outcome

Hi, I just wanted to let you all know the result.
I had plenty of slack so cut back about 8", bought a
bag of antishorts at Rexell, put one in, folded the bonding wire back over and around the armor, taped around it to secure. Installed 14-50R ...PLUS I screwed a lug to its grounding screw, ran #10STR green back out, alongside the BX, back to my box where I clamped it to my #4bare Cu grounding electrode conductor. Now the fun begins. The tech from the
appliance store shows up with 4prong attached. I ask to see where the grounding strap WAS, he opens it up and says he sees nothing, doesn't know what I'm talking about (Uh-OH).
I take a closer look, Cu strap is in place between neutral block and gnd plate. I show him, ask him to cut and/or remove. He says it doesn't come out, "look, it's under the N block and I can't remove it"
I say OK, fold it over or cut it - "Nope, he says, I've been doing this for 3 years and we NEVER do that.
It might void your warranty. I won't do it." I show him installation manual, he says sorry, he won't do it. OK, I say, he tests oven and leaves... I call GE,
they say of course, go ahead, so I reopen the back,
bend the strap back so it is attached only to Neu,
well clamped away from Grnd...as I put back the
cover plate I notice a sticker that clearly explains
strap removal for 4prong... I'm beginning to see
why Qtip boxes say don't put in ear.
I realize Grnd and Neu are tied at box, and I don't
mean to imply my original impulse to install a 3p
as told by store + add EG was much better...
still, I wonder how many stoves out there are getting safer 4-prong plugs defeated by the strap.
 
  #15  
Old 02-15-06, 09:27 AM
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If I were you I would write a clear and concise letter to the store that sold you the appliance. Photocopy the installation instructions where it states the proper four wire installation and include a copy. Take a picture of what is states inside the unit and include a copy. Also detail what GE told you over the phone.

Sends a copy to GE. Send a copy to your local town or city codes enforcement officer. Send a copy to your state attorney general.

If they charged you a delivery or setup fee, politely ask for a refund based on their not following proper manufacturer instructions.
 
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