Why four wire instaed of three for range and dryer?

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TerryBarnhill

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Tyler, Texas
I was asked this last week by a homeowner. I had never really had to explain the why's of it, it's just code and as a licensed electrician, I am to follow code. So, it made me wonder as to why it was actually changed back in 96 (I think ...).

Now, I understand why you don't bond ground and neutral together for a sub panel. I also understand the reasoning you don't want them bonded other places, as upstream you could break the neutral path and it goes through the ground instead. Although, on a dedicated, single run, I really couldn't explain for certain why it was changed. Other than not allowing any current to flow along the bare ground when either the dryer or range might use the 120 stuff. When else might it cause an issue? Especially since most every new unit comes from the factory with the ground strap bonded and many times it doesn't get removed.

Homeowner pointed out, as we all know, "his old one was three wire .."; I had to concede that there are probably several upon several thousands of circuits still in existence using three wire with no problems. However, code is code ...

Just curious as to others thoughts.
 
With the old three wire set up on ranges and dryers if the neutral failed the entire metal structure of the appliance would be 'hot' to anything grounded.
 
iwire points out the danger.

I don't know if it's an 'ole wives tale' or not, but I've often heard from old-timers (back before I became one of them) that the 3 wire install was instituted as a copper savings during a war effort.
I don't have any references to show if allowing 3 wire was ever a "change" or if it was acceptable until changed in the 90s (or whenever).
 
iwire said:
With the old three wire set up on ranges and dryers if the neutral failed the entire metal structure of the appliance would be 'hot' to anything grounded.
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1. How likely would that be?
2. In the event that it did happen, wouldn't the ground be a more conductive path anyway? Granted, we don't know the length of the run, but in general, wouldn't the existing path be more conductive than my elbow?

Not arguing your point, just really curious about this now that it was asked of me. :)

btw, Happy Holiday's to those celebrating!
 
What the op is asking can also be asked about all circuits. Why run an equipment grounding conductor when we have a neutral or why use a neutral if we have an equipment grounding conductor. It is no different for a range. You want a separate equipment grounding conductor from the neutral. Of course 99% of the time there probably will not be an issue but the code will try and protect that 1% chance
 
TerryBarnhill said:
2. In the event that it did happen, wouldn't the ground be a more conductive path anyway? Granted, we don't know the length of the run, but in general, wouldn't the existing path be more conductive than my elbow?
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What ground are you referring to? On a 3-wire circuit the neutral is used as the ground. If the neutral gets opened the frame of the dryer will become energized do to the neutral to ground bonding jumper.

Edited to add:
After reading the OP again i wanted to make sure they understand that a 3-wire range/dryer circuit consists of 2 hots and a neutral. There is no equipment ground. A 4-wire circuit adds the equipment ground.
 
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jumper said:
Is there any solid/documented evidence that a 3 wire range circuit posed/caused an electrical hazard.

Note that this install was legal until 1996 IIRC.
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Yes, there many cases over the years, both fire and electrocution. Fires from loss of neutral- the return path sometimes went thru, say, an alum flex dryer vent which burns open.
 
augie47 said:
iwire points out the danger.

I don't know if it's an 'ole wives tale' or not, but I've often heard from old-timers (back before I became one of them) that the 3 wire install was instituted as a copper savings during a war effort.
I don't have any references to show if allowing 3 wire was ever a "change" or if it was acceptable until changed in the 90s (or whenever).
Click to expand...

I've heard the same thing. Like you, not sure if it is fact or fiction.
 
Did some research... apparently the "war story" was indeed a war story. It appears availability of cable might have been the original reason.

quoted from: David A. Dini P.E.
Underwriters Laboratories Inc.

The permission for neutral grounding, the practice of using the neutral conductor as an equipment grounding conductor, was first permitted in the 1947 Code for electric ranges. At around that time many electric utilities were promoting the use of residential 240 V cooking for the post WWII housing boom, and many were even offering to install an upgraded service to older homes at no charge. However, there were no NM cables available at the time with conductors of sufficient ampacity to handle these higher amperage branch circuits. There were, though, service entrance cables of sufficient size, but they had a bare neutral conductor. This special Code permission allowed the frames of these large appliances to be grounded through the uninsulated grounded neutral conductor of the Type SE service entrance cable used to supply the branch circuit. The use of neutral grounding was also extended to electric clothes dryers in 1953. However, almost 50 years later, this special permission for neutral grounding was taken away in the 1996 Code for all but existing branch circuit installations.

Somone with 1966 ROC reports might be able to tell us more.
 
Nice Gus!

That makes more sense than copper shortages.

I have read that for the most part the metal collection drives they had during the war had more to do with getting everyone involved and not really for the metal. For instance most steel collected was not high enough quality to make war equipment with.
 
iwire said:
With the old three wire set up on ranges and dryers if the neutral failed the entire metal structure of the appliance would be 'hot' to anything grounded.
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Its like Bob said



I'm am quite a bit older than Bob and as a child growing up in the 50s and 60s I can remember people getting very bad shocks by touching the refrigerator and stove or maybe the sink. This was because of the old two and three wire systems using Neutral as both the grounding and grounded conductor. If anything that had a ground to its metal enclosure, it would become a shock hazard if it lost its Neutral.

The new Three and four wire systems solved this problem.

Please click here to see an example of the two different systems.

Ronald :)
 
And we have had more recently the change no longer allowing a feeder to a separate building to utilize a single conductor for both grounded and equipment grounding purposes, with exceptions for existing installations just like the ranges and dryers have exceptions for existing installations.

Another thing not yet mentioned is that even if this conductor is not compromised, you still have some voltage rise in relation to "ground" if you have neutral current flowing on it, because anytime you have current flow in a conductor you will have some voltage drop.
 
Dennis Alwon said:
What the op is asking can also be asked about all circuits. ...
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While yes, this could be asked about all circuits, it's not what I'm asking. I understand about outlets downstream having affects on outlets upstream if damaged or disconnected. I was simply wondering about a single, dedicated circuit going to one outlet. Generally, nothing is going to happen between the panel connections and the connection at the unit.

What ground are you referring to? On a 3-wire circuit the neutral is used as the ground. If the neutral gets opened the frame of the dryer will become energized do to the neutral to ground bonding jumper.

Edited to add:
After reading the OP again i wanted to make sure they understand that a 3-wire range/dryer circuit consists of 2 hots and a neutral. There is no equipment ground. A 4-wire circuit adds the equipment ground.
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Yes, I know there is no true ground in a 3 wire. I was meaning, for example, if the neutral opened in the unit, being bonded still, that the current would go through the unit's ground, and down the ground/neutral wire. I should have said bare instead. :)

I'm am quite a bit older than Bob and as a child growing up in the 50s and 60s I can remember people getting very bad shocks by touching the refrigerator and stove or maybe the sink. This was because of the old two and three wire systems using Neutral as both the grounding and grounded conductor. If anything that had a ground to its metal enclosure, it would become a shock hazard if it lost its Neutral.
Click to expand...

I mainly know of, (hearing and personal experience), shocks coming from the fridge or freezer, not a stove. Not saying it can't happen, just what I experienced. I always equated that to having motors and possible voltage leakage through such. Was always just a guess, though.

At any rate, good points made by all. Thanks!
 
TerryBarnhill said:
While yes, this could be asked about all circuits, it's not what I'm asking. I understand about outlets downstream having affects on outlets upstream if damaged or disconnected. I was simply wondering about a single, dedicated circuit going to one outlet. Generally, nothing is going to happen between the panel connections and the connection at the unit.



Yes, I know there is no true ground in a 3 wire. I was meaning, for example, if the neutral opened in the unit, being bonded still, that the current would go through the unit's ground, and down the ground/neutral wire. I should have said bare instead. :)



I mainly know of, (hearing and personal experience), shocks coming from the fridge or freezer, not a stove. Not saying it can't happen, just what I experienced. I always equated that to having motors and possible voltage leakage through such. Was always just a guess, though.

At any rate, good points made by all. Thanks!
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If the neutral opens in the unit there is nothing else for current to return through, if the "grounded" conductor to frame bond is on upstream side of the "open" then any voltage from what would otherwise be returning via that conductor happens to be energizing eveything connected to it including the frame. Touch that frame and another grounded object (maybe a refrigerator) at same time and you will be subject to what ever voltage is present.

You will not get a shock from a fridge with a proper and intact equipment grounding conductor, if you do it is because it is grounded and the source is actually something else, or the fridge does have a fault as well as a compromised equipment ground, in which case you need to touch something of different potential and the fridge at the same time.
 
augie47 said:
iwire points out the danger.

I don't know if it's an 'ole wives tale' or not, but I've often heard from old-timers (back before I became one of them) that the 3 wire install was instituted as a copper savings during a war effort.
I don't have any references to show if allowing 3 wire was ever a "change" or if it was acceptable until changed in the 90s (or whenever).
Click to expand...

It was explained to us at a recent IAEI meeting that the most persuasive comment for the change from 3 to 4 wire was "The war is over."
 
TerryBarnhill said:
While yes, this could be asked about all circuits, it's not what I'm asking. I understand about outlets downstream having affects on outlets upstream if damaged or disconnected. I was simply wondering about a single, dedicated circuit going to one outlet. Generally, nothing is going to happen between the panel connections and the connection at the unit.
Click to expand...

This is harder to explain than to draw but I will give it a shot.

Picture a running electric dryer supplied by a four wire circuit.

Now cut the neutral with it running. The dryer stops, but if you grab the cut neutral from the dryer and anything grounded what happens to you?

You get blasted because your body is trying to complete the circuit.

Now imagine a dryer with a 3 wire feed, inside the dryer the neutral is bonded to the dryer frame. Again cut the neutral, and again if you grab the neutral from the dryer and any grounded object you will get blasted trying to complete the circuit.

BUT ... That same neutral that will blast you is also bonded to the dryer frame, so if you touch the dryer frame and a grounded object you get blasted.

The current path would be from the breaker, through the motor, out the neutral, to the bonding point in the dryer, through the dryers frame to you and out of you where you are grounded.
 
There has been a lot of IF scenarios posted here and of course we all know that IF is one of the biggest words in the English language. Anyway, it was my understanding that older model ranges and dryers operating on 240 volts did not need a neutral as they had no digital displays or internal electronics requiring the need for one. Newer models require a neutral to run the internal electronics and displays which leads me to my age old gripe that I've posted here many times "why can't manufacturers make the units with a transformer and re-manufacture the voltage they need for the internal electronics"? That way you only need the ground.

Now, let me post some of my own IF's
  • IF you check the units when they're shipped to the residence, the neutral and ground are bonded together at the connection terminal.
  • IF you don't separate them at the unit you haven't accomplished anything by running a 3-wire cable
How many homeowners know enough to do this ?
 
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