Another electric question

Mike T., Swampeast MO

Regarding 220v appliances.

The used to have 3 wires--two hot, one ground. This supposedly created an unsafe condition in appliances like ranges, ovens, driers, etc. where timer motors, lights, convenience outlets, etc (110v) were not grounded.

Some questions regarding the old 3-wire system:

1) Weren't the chassis/frames of these appliances connected to the 3rd ground wire?

2) Did the 110v components actually use the ground as return? If so, how can this be with the appliance frame connected to ground--wouldn't that be EXTREMELY unsafe?

3) As the clincher--how on earth are the convenience outlets (110v) on such appliances grounded? They're often the ONLY grounded plug in older kitchens.

4) On driers/ovens/etc. WITHOUT convenience outlets why didn't they just use 220v timer motors and lamps to save the expense of that 4th wire and requiring people with older systems to re-wire for new appliances?

Household 110v is EXCEPTIONALLY difficult for me to comprehend. 220v and polyphase are MUCH easier. It has something to do with return/neutral/ground and how each seem to be the other at different times and from different perspectives--absolutely blows my fuses.

Joe_13

Frame should always be grouded also

I've never seen outlets on ovens/driers. I would have thought the timers and bulbs were 220V also. But to do things to code now, yes you probably will see a neutral and grounding terminal, expecting 3 wire plus a ground wire (sometimes a metalic BX tail comming out of an oven making the BX casing the ground.) The terminals are the same but it's just getting an extra ground wire in there for saftey.

tombig

3 or 4 wire 220v appliances

Mike, (you still got that ferrule ring?) the older appliances had 220v controls and grounding for safety. I don't think any actually used ground as a current carrying medium. If a 220v range happened to have a utility receptacle (110v) wired in they would have installed a stepdown t-former. Each leg would be 55v to ground but the ground itself would be intact with no current flow.

Don_4

Neutrals??

I cannot say I have ever seen a range wired in the way you describe (3 wires?)but I live in Canada and have heard many stories about state codes or lack thereof. Are you saying the third wire was a bare copper or a white wire? If it was a BX cable to the range and used a white wire as the third wire the cable casing was considered the ground. In Canada to the best of my knowledge the ground wire has never been allowed to carry current in mormal operation. The appliance outlet (in our codes) must be supplied with a neutral connection.

tombig

Early electricity

> I cannot say I have ever seen a range wired in

> the way you describe (3 wires?)but I live in

> Canada and have heard many stories about state

> codes or lack thereof. Are you saying the third

> wire was a bare copper or a white wire? If it was

> a BX cable to the range and used a white wire as

> the third wire the cable casing was considered

> the ground. In Canada to the best of my knowledge

> the ground wire has never been allowed to carry

> current in mormal operation. The appliance outlet

> (in our codes) must be supplied with a neutral

> connection.

tombig

Older 220v appliances

> I cannot say I have ever seen a range wired in

> the way you describe (3 wires?)but I live in

> Canada and have heard many stories about state

> codes or lack thereof. Are you saying the third

> wire was a bare copper or a white wire? If it was

> a BX cable to the range and used a white wire as

> the third wire the cable casing was considered

> the ground. In Canada to the best of my knowledge

> the ground wire has never been allowed to carry

> current in mormal operation. The appliance outlet

> (in our codes) must be supplied with a neutral

> connection.

tombig

Older 220v appliances

Don, most older 220v appliances had 3 wires. Two hot legs and a ground (not a neutral) All controls were either 220v or operated through a transformer. 4 wire units pretty much started showing up when digital and touch pad controls did. I still believe that a 1940's era range with a 110v outlet may have had a T-former to step down to 110v without a neutral. It still would be properly grounded but would have potential to ground from either pole of 110v. Back then it worked and was considered safe. This stuff was UL approved at the time. It's not really that unsafe if the utility outlet is internally fused. There were dead men electricians too, guys. Think about a 3way switch and an always hot receptacle to the 2nd floor using 4 wires. I've seen it more than once. Hint... The three way alternated the hot and neutral at the light bulb. Super unsafe but it worked back then.

tombig

Addendum

House wiring circa 1930's-40's didn't always consider proper grounding. Enough knob and tube, and two wire romex jobs attest to that. Electricians, homeowners, and especially governing bodies didn't realize the importance of the safety issues. Code upgrades over the years regarding proper grounding have undoubtedly saved countless lives. I do believe however that no manufacturer since the onset of electrical appliances would use the case/cabinet or wire shielding as a current carrier.

Joe_13

electronics today

Most electronic boards only use 5V max. So all the controls, timers, etc. have a trasformer on those boards somewhere. The new step-down transformers are variable and can run anything from 220V to 100V.

Mike T., Swampeast MO

Ring

Had to use it when finally installing the towel warmer--one of the other rings STILL failed. Surprise, surprise. Was lucky I kept the one on my finger!

Dale

From a utility perspective

The reason elect ranges and dryers had a 3 pin connector with 120 volt loads is the utilities got an exemption in the 1930"s as part of the REA effort. The idea was that the ground frame tied to the neutral wasn't dangerous because the feed went directly back to the service entrance where they are tied anyway. And, ground wire isn't bare but part of a covered cable.

1. Yes 2. Yes, and not unsafe as the neutral is a separate wire going to the cable junction at the rear of the appliance. 3. I see mostly ungrounded convience outlets on ranges, the more interesting question is fusing since the range uses 40 amp fuses. The answer is a separate 15 amp screw in fuse found hidden under the range top, on a drop in range it's reached past the RF burner. There are no more convience outlets on ranges since the cords kept getting set on fire from the burners. 4. Many ranges use 120 to the elements on top to give the lowest heat settings and the lower the voltage the less the insulation needed so the only thing 240 on an electric clothes dryer is the heating element, the motor and everything else on a simple dryer ( not new dc controls) is 120. We regularly get the " my 60 amp main fuses must both be good cuz the dryer is still working ( tumbling but not heating) and it's 240 volt." Many moblile homes had electrical connections with long cords from a master meter board, I can't tell you how many of these get "fixed" outlets to use the standard 3 pin cord. The issue now is the dryer being moved into the new house and needing a new cord to plug it in.

220/240 doesn't have any current flow on the ground if the loads are balanced, so with 120 loads there will be some current returned on the ground/neutral. Interesting question, always more to learn.

Dell Hardison

240 volt appliance

To answer your questions

1. Yes, the grounded conductor (neutral) was allowed to be used for grounding the metal noncurrent-carrying parts of the appliance. New installations must have 4 conductors, 2 power, 1 neutral, and 1 equiptment ground.

2. Yes, the conductor you are reffering to is not an equiptment grounding conductor, it is a grounded conductor (neutral), which is also used as an equiptment grounding conductor. This can become unsafe if this conductor is disconnected at any point on the line side of the ground. The metal noncurrent-carrying parts of the appliance will then carry the neutral current and could pose a shock hazzard.

3.They used the neutral for both neutral current and grounding.

4. Don't know. Have seen some new cooktops that were completely 240 volt and don't require a neutral conductor only an equiptment grounding conductor.

These only apply to existing branch circuits, all new installations require a 4 wire system.

Hope this helps,
Dell

Mike T., Swampeast MO

Yes, it helped a bit Dell & Dale

Pretty well as I thought, but neutral, return and ground still confuse me TERRIBLY despite much study.

Most interesting is what I suspected, "They used the neutral for both neutral current and grounding." Maybe people were sometimes electrocuted by such appliances, but it must not have been too common...

Please forgive the ignorance of the following--110 just mystifies me.

The "third" (bare) wire of a typical household 220/240 service is connected to the earth at the utility company step-down transformer, correct?

Even if the service at the house doesn't have it's own earth ground it still works (albiet unsafely)?

In a service box under load I can touch the neutral bar (DON'T DO IT!!!) in that box or any ground without harm whether or not my body is grounded. Yet, electrons must be flowing through this line as the load will not work unless provided a return.

Is it correct that the true return path when using 110/120 alternating current is in fact the earth itself?

Since this return path seems utterly safe what truly prevents the supply from coming (just as safely and in large quantity) through the earth as well? I know that is what Tesla intended but was prevented by industrial forces who found no way to charge money for such power.

Don_4

Grounding

I cannot definitely say I have worked on ranges from pre 1950 but I have yet to see one wired with two hots and a ground. The house I am living in was built in 1922. The house was wired with knob and tube. When I moved into the house in 1963 it had a three wire cable (no ground except for bx casing) wired into the original service panel for the range. As you stated the casing is not supposed to carry current and wouldn't unless there was a short. I have worked on fridges that only had a two wire cord (and plug) with one side grounded to the chassis. Not a good situation without a polarized plug.

Dale

Terminology

Mike, one of the problems is the terminology. The code refers to the ungrounded conductor or the black wire we see on common 120 V systems. Then they refer to the grounded conductor which is the usual white. Then there is the "equipment grounding conductor" the bare or green wire. This is the safety part of the circuit and should usually carry no current. The key with the white is "grounded" and "conductor" . If you take any 120 volt energized circuit and use a clip on ammeter on the black and then white wires you will see the same ammount of current flowing under normal conditions. You can touch the whites in the panel because the path to ground is much easier to the earth through the gound stakes or water pipe than it is through you. I have been shocked a few times taking a wire nut off whites in a junction box where I missed a load still being on.The earth is the return path, the old farmers would make a 120 volt light work by using one side of the 220 and the other wire to a stake in the ground, try it it works. Of course the stray voltage issue wasn't well understood then. The white or neutrals as commonly called can ONLY be grounded at the entrance panel. If you ground the white or mix ground bare copper wires at a sub panel you get current on the grounding wires and a shock it you touch the shower head if any of the mixed circuits are being powered. Even guys who understand this mess up sometimes by not checking that the white bus bar in the sub panel is indeed insulated from the sheet metal. Very easy to tighten that grounding screw or lose the little cardboard insulator from under the bar. Try stuff out Mike, after 20 years or so it starts making sense.