What is going on in this safety example from textbook? - Page 1
Forum section: electronics / beginners

author: Copernicus
author_rank: Newbie
timestamp: September 11, 2017, 10:23:27 pm
content: I think they screwed up the diagrams.Diagram A - Implies Voltage source isnotearth referencedDiagram B - Voltage source is earth referencedI thought ground fault meant contact between hot and ground, can it also mean an open ground circuit?I think Diagram A the boys would not be electrocuted where in Diagram B they would be?Why do they single out the boy outside the pool for heart failure, not both?

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: September 11, 2017, 11:20:04 pm
content: QuoteI agreeQuoteI would normally assume that it would be a live conductor is low impedance to protective earth. But if the 'protective earth' became disconnected I guess it could also be called a ground fault.QuoteI agreeQuoteBecause they are wrong, any current flowing could pass through both boys hearts.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 11, 2017, 11:34:51 pm
content: I think the single out the boy on land because they are assuming that the water is a "very good" conductor, and that most of the current will not flow through the core of the boy immersed in water -- just his arm. The boy on land is instead set up to receive an arm-to-arm shock, which is the most dangerous. But that is really making a pointless distinction -- both are at substantial risk.I also agree that their diagram is wrong, the voltage source in figure a should be earth referenced.I would call a ground fault anything that lets the return current flow in a path that bypasses the designated neutral. That could be either to a provided safety ground wire, or via the pool and its occupants to any piece of grounded metal. But from the diagram I would say there are two faults: the hot contacting the water (which can be a ground fault), and the broken safety ground connection (which I wouldn't call a ground fault, but maybe they do.

author: Electro Detective
author_rank: Super Contributor
timestamp: September 12, 2017, 02:55:54 am
content: If I'm following all this correctlyin most places the neutral and earth ground are directly LINKED aka connected at the switchboard,regardless of layout diagram abovei.e. a guaranteed zapping is imminent on a direct connect fault, without an in line isolation transformer to tone things down,and a double funeral to organize after the pool party comes to an abrupt halt

author: vk6zgo
author_rank: Super Contributor
timestamp: September 12, 2017, 06:10:44 am
content: When I had a pool, the light was connected to the same very low voltage floating dc supply which was used for the saltwater chlorinator.I didn't think mains operated pool lights were legal anywhere.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 12, 2017, 06:58:56 am
content: Quote from: Electro Detective on September 12, 2017, 02:55:54 amNot around here at least. But ussualy always somewhere in the distribution. Doesn't matter if its miles away.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: September 12, 2017, 07:15:44 am
content: Anyway, despite its inaccuracies, this example does illustrate an important point about electronic service work. The boy in the pool is in much the same situation as anyone working onopenedhigh voltage gear.When the equipment case is closed an earth is protective, but when the case is open an earth is a hazard.The boy in the pool had inadvertently touched a live connection, but would have been OK had he not then been touched by the second, earthed, boy.

author: helius
author_rank: Super Contributor
timestamp: September 12, 2017, 07:32:52 am
content: Whether he would be safe without the connection to earth depends on the electric field strength in the water. If the entire pool is not electrically bonded, there is a possibility of an electric field between one side of his body and the other side, which can lead to electrocution or (more likely) spasm and drowning.