220V 3-wire to 4-wire query

superscouser

To add a ground/earth to an existing 3-wire cable, is it acceptable to run a single 6 gauge wire? Or do I have to replace the whole 3-wire cable with a 4-wire cable?

Thanks in advance.

Speedy Petey

How about some more details???

Why #6?
What size circuit is it?
What is the circuit for?
WHERE did you plan to run it? The "earth" does NOT ground anything.

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Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

KE2KB

Try telling that to POCO!

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AllanJ

If all of the conductors in the cable are insulated individually and one is white for the neutral, then I would go ahead and run a separate ground wire alongside the cable. The separate wire would have to suit the situation, for example be suitable for direct burial in the earth (no pun intended).

A properly installed ground system including grounding electrodes such as ground rods will not serve as an emergency return for large numbers of amperes should the neutral be breached, but should protect people from electrocution should a hot wire come in contact with a metal appliance cabinet or tool housing when these items are also grounded.

superscouser

It is an existing installation for a range that is only 3-wire - yeah an old house, two hot & one neutral and I wish to connect a UK 220V appliance which needs 220V and ground. As I understand it new range connections are four wire, so I would like to install a 4-wire socket leaving it correctly configured for future.

My plan is to connect the UK appliance to the 220V (two hots) and ground - three wires only on the UK appliance. I would not connect the UK apliance to the neutral.

I am basing this on the understanding that the US 220V is 2 x 110V to the neutral and 220V across the two hots.

The UK appliance doesn't need the 60 AMP 6 gauge (rated at 13amp on 220V) but the exisitng cable looks like 6 gauge so I was matching that - though I would expect for a ground I wouldn't need that gauge.

J. V.

For a range circuit you need 4 wires in ONE cable. No exceptions.
You can use a smaller breaker on the #6 wire. Do not use a 60 amp breaker unless the range requires a 60 amp breaker.

Speedy Petey

Elaborate please.

The earth does not have ANY bearing on short circuits and circuit grounds, which is what we are talking about. The POCO has nothing to do with it.
Even in the POCO's case, the earth ground is for a totally different purpose.

__________________
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

Gigs

What do you mean?

Speedy Petey

He means that the earth is NOT a path for fault current back to the transformer.

__________________
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

Gigs

Oh, he meant the service neutral. Makes more sense now.

KE2KB

OK. I see where you're coming from.
The Earth does not ground anything if there is no return circuit through the Earth.
I realize that POCO uses Earth for a return on the HV side of the distribution transformer, and that it is not an acceptable conductor for branch circuits.
Sure, it would not even serve as a safety ground if we didn't have the ground bus in the panel bonded to a water pipe and Ground Rod.

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InPhase277

The poco doesn't use the earth as a return any longer. As far as I know, this is a long dead practice. They ground their neutrals at every pole to dissipate a lightning strike as quickly as possible, or operate a fuse in case of a higher voltage line cross over.

It still doesn't serve as a safety ground except for the same reasons I stated above. The earth serves no purpose in the operation of a building's electrical system, including the ground wire in every circuit. The confusion that the actual dirt of the earth has something to do with fault clearance is apparently widespread, and stems from the fact that we still call an equipment grounding conductor a "ground". In reality, it is, and should be renamed, an "equipment bonding conductor", because it bonds the metal of appliances to the neutral at the main bonding jumper of the service, and creates a low impedance path for fault current to complete it's circuit.

That round hole on every receptacle isn't a "ground". It is a "bond".

Gigs

There is single-wire with earth electrical service in some extremely rural areas, like australian outback and Canada.

http://en.wikipedia.org/wiki/Single_wire_earth_return

InPhase277

Well, I be. I know what SWER is, but I didn't think anyone with any sense would still be using it. That's just stupid. And the Canadians like to think they have a better electrical system...