In all of the industrial controls that I ever designed we NEVER grounded either side of the 120 volt controls transformer output.

See the example circuit shown in NFPA79, Wiring for Industrial Machinery.
NFPA also publish NEC (NFPA70).
The two transformers shown display how the secondary neutral should be set up.
Max.

 

Thanks now I won't have to dig my code book out. I thought I threw it out when I retired but just found it in a box the other day...

But I don't understand why I wouldn't be shocked if grounded and grabbing a hot ungrounded secondary.

 

Because there is no other frame of reference to the other conductor to complete the circuit.
Max.

 

Well I thought I understood it... Now I don't, why won't they be shocked if grounded and grabbing a "hot" wire?

@SamR
If you picked up a battery by one of its terminals, would you expect to be shocked? Even if the battery happened to be a 90V battery, you'd feel nothing through only a single connection to the battery. If you stand barefooted on a metal floor and connect one terminal of a 90V battery to the floor, nothing happens. But if you then touch the OTHER battery terminal, you get a shock.

 

Note that in down under we have 240VAC as domestic supply. Our power points(GPO,general purpose outlet) are rated at 10 amps. Cable size is 2.5 sqmm. So usual plug appliances plug 10 amp max. Ovens, hot water systems are generally hardwired and can be up to 3600watt with bigger gauge wire. Some GPOs can be wired for 15 amp(for home welders, machines etc) and use an outlet with a larger earth pin.Some people have 3 phase wiring 415v phase to phase(fairly rare, farms and small industries). Large industries mostly have three phase from 415V to 11Kv as required.
SamR, You will not be shocked by grabbing an ungrounded supply of any kind since there is no way the current can flow from the supply of one lead through you to the opposite supply lead since there is NO COMPLETE CIRCUIT via your grounded self!.

 

Obviously, I need to reprogram some very old and deeply embedded synaptic pathways in my brain. The battery part I get, and I know DC was why Edison argued against AC being unsafe. I'm still having to come to terms with that it's safe to grab an ungrounded systems KV conductor (AC or DC) and be grounded and not die. Potential goes to ground and you don't want to be the pathway was drummed into me along the way to here and now over many years. Time for this old dog to learn new tricks. I guess I just don't understand AC and grounding like I thought I did...

 

Obviously, I need to reprogram some very old and deeply embedded synaptic pathways in my brain. The battery part I get, and I know DC was why Edison argued against AC being unsafe. I'm still having to come to terms with that it's safe to grab an ungrounded systems KV conductor (AC or DC) and be grounded and not die. Potential goes to ground and you don't want to be the pathway was drummed into me along the way to here and now over many years. Time for this old dog to learn new tricks. I guess I just don't understand AC and grounding like I thought I did...

@SamR
The critical point is that you won't feel anything unless there is a path for current to flow through you. To make yourself part of a path, you need to touch two things, not one. You can touch one terminal of almost (there are exceptions!!!) any voltage and not be shocked...or not be shocked very much. But if you put yourself between two voltages (one of which could be ground), then you get shocked. The exceptions: If you touch a 25,000V (AC or DC) point (wire, terminal, screw, whatever) while you are standing on the ground wearing well insulated rubber boots, you may still die--because that high voltage can penetrate the rubber. For a more complex reason, you can get a tingle--but not a deadly shock--by touching only one high voltage point--a good example is when you walk across carpet in the winter and your body acquires a static electricity charge equivalent to many thousands of volts...and you then touch something metallic, especially something metallic that is grounded...you will draw a nice spark between yourself and the metal. The electrons that your body acquired by rubbing against the carpet are anxious to not be so crowded together and some of them will pass from you to the metal, in the process creating a spark and a shock...but nothing lethal.

 

pass from you to the metal, in the process creating a spark and a shock...but nothing lethal.

Aha! Back to square one, I wasn't wrong. But it is a matter to the total potential difference. OK I can understand that fine.

 

Aha! Then I wasn't wrong. But it is a matter of the total potential difference.

 

Aha! Then I wasn't wrong. But it is a matter of the total potential difference.

There is one catch though, and that is with very high voltage which can find it's way to earth if it is high enough.

 

Well I thought I understood it... Now I don't, why won't they be shocked if grounded and grabbing a "hot" wire?

To receive a shock current must flow. Except for lightning and other "quite high" voltages, there must be a complete circuit for current to flow. The safety purpose of isolation is to avoid having that complete circuit via ground. The isolated circuit's voltage is not referenced to "ground", and so connection to a hot wire will not cause current to flow.
The same principle works when I am standing on a well insulated ladder working on an electrically "hot" wire that is at a voltage relative to ground. By not having a current path a shock does not happen because no current flows. If there is no complete current path there is no current.

 

There is one catch though, and that is with very high voltage which can find it's way to earth if it is high enough.

This is totally true. I have seen high voltage wires on the ground sparking to dry dirt. And consider that the voltage of lightning is high enough to find a path to ground through hundreds of feet, at 10,000 volts per inch needed to strike an arc. That is 120,000 volts per foot from the clouds.

 

This is totally true. I have seen high voltage wires on the ground sparking to dry dirt. And consider that the voltage of lightning is high enough to find a path to ground through hundreds of feet, at 10,000 volts per inch needed to strike an arc. That is 120,000 volts per foot from the clouds.

Oh that's an interesting thought. I guess the voltage must be extremely high. Some of the lower clouds are around 6000 feel so that would lead to over 700 million volts. Geeze.

From what i understand the arc starts at the bottom of the cloud and travels at 200,000 miles per hour until it gets somewhat near to the ground and then there is an upward surge that meets the downward surge.

 

Oh that's an interesting thought. I guess the voltage must be extremely high. Some of the lower clouds are around 6000 feel so that would lead to over 700 million volts. Geeze.

From what i understand the arc starts at the bottom of the cloud and travels at 200,000 miles per hour until it gets somewhat near to the ground and then there is an upward surge that meets the downward surge.

I think that your information is correct, but it all happens so fast that I have not been able to verify it by my observations.

 

It has been observed that as a storm cloud travels, there is an equal an opposite charge in the ground that follows the cloud.
Max.

 

I studied lightning protection years ago as some of the highest points on our plant were the very tall fractional distillation columns that required protection as they were filled with volatile liquid and gas. A lightning stroke is composed of 2 elements. A downstroke from the clouds and a backstroke from the ground up. There are some high-speed films clips and time-lapse photos out there that do show this as it happens faster than the human eye can see and interpret the image. When you enter Florida on I95 there are some truck weigh and agriculture inspection stations along the Interstate. When they upgraded them a number years ago they added some strange what look like light poles but instead of a light fixture on top, they have several mushroom-shaped radials coming out of the top of them. Looks about 10' radius with maybe 12 arced rods. It is their lighting suppression system.

 

My point in my post was that lightning is a very high voltage that does not follow the normal rules. The exact nature of a lightning discharge is not relevant to the point that I was making. Isolation that is effective at normal voltages may not help at all when lightning strikes.