Safety earthing of equipment - Page 1
Forum section: electronics / beginners

author: dalpets
author_rank: Contributor
timestamp: February 11, 2024, 01:09:19 pm
content: I am seeing a number of electronic test equipment reviews that might be posing safety hazard warnings for newcomers, such as myself, because equipment is not earthed. Is the simple solution to replace a two pin power plug with a 3 pin plug? (I'm assuming there would be an earth wire available)Are there other approaches where no earth wire is available?

author: Andy Chee
author_rank: Super Contributor
timestamp: February 11, 2024, 01:28:55 pm
content: Many two pin appliances are designed to be completely safe without an earth. In fact, adding an earth to these appliances can in some instances make the situation more dangerous!It's the appliances which are designed to be earthed, that become potentially dangerous when unearthed.Wikipedia has a pretty decent summary of the basics:https://en.wikipedia.org/wiki/Appliance_classesAnd then there's earthing test equipment when testing and probing a device under test. That discussion is a whole different topic to daily use appliances.

author: jonpaul
author_rank: Super Contributor
timestamp: February 11, 2024, 02:24:26 pm
content: neither a forum like this nor wiki are relaivle sources where safety, fire, mains are incolved.Tey an ekectrical/electrician foum like Mike HOLT.Key wordsDOUBLE INSULATED, UL, VDE, MAINS EARTHINGj

author: CaptDon
author_rank: Super Contributor
timestamp: February 11, 2024, 02:59:40 pm
content: As crazy as it seems, many years back here in the states non-professional test equipment such as B&K Dynascan, Heathkit, Eico and others started using two prong 'polarized' cords where the wide prong was neutral (but not exactly 'earth') and the wide prong lead was connected to the chassis of a non-double insulated piece of test gear. Since some of these units were built from kits often the 'hot' mains lead ended up connected to the chassis!!! I had a Heathkit signal generator fall onto a B&K vacuum tube tester and actually welded the two units to each other which then tripped the 30 amp mains screw-in fuse. These units had been in service for years in an electronics course lab at a local Vo-Tech school. It is amazing no one ever got zapped!! Personally, I prefer my test gear to be earthed and my Unit Under Test to be powered through an isolation transformer. There were a few times when I had to put my oscilloscope on an isolation transformer so that I could connect the probe tip and probe ground lead to hot circuits. There was no doubt that configuration posed a dangerous situation so nothing was allowed to be touched when the circuit under test was energized!!! A differential probe of proper bandwidth and voltage ratings would have been a better answer but sometimes you do what you have to do when testing in the middle of B.F.E.!!!

author: calzap
author_rank: Frequent Contributor
timestamp: February 11, 2024, 06:01:56 pm
content: I recommend reading a starter book on building wiring. If you were in the US, it would be Wiring a House by Cauldwell. Perhaps someone can recommend a book more oriented to Australian codes and practices.Mike

author: audiotubes
author_rank: Regular Contributor
timestamp: February 11, 2024, 07:21:48 pm
content: Quote from: jonpaul on February 11, 2024, 02:24:26 pmI get a 403 when trying to view that site. You can get to it from where you are?

author: calzap
author_rank: Frequent Contributor
timestamp: February 11, 2024, 08:45:26 pm
content: Mike Holt is an excellent instructor. He is in the business of selling education to U.S. licensed electricians and folks who want to be licensed electricians. He has a lot of free material on his website and youtube channel. However, I don’t recommend him for complete beginners; he assumes some basic knowledge. In addition, he is focused on the U.S. NEC, which may differ significantly from codes and practices elsewhere.One can learn a lot on forums; I’ve learned a lot here. But forums tend to be hit or miss and not always accurate (putting it mildly). Last time I checked (a few years ago), only U.S. licensed electricians could post on Holt’s forum although anyone could read the entries.Mike

author: S. Petrukhin
author_rank: Super Contributor
timestamp: February 11, 2024, 09:17:13 pm
content: Often on older equipment there is a plug with two contacts, but there is a separate grounding terminal on the housing. The fact is that the grounding wire in the power line did not appear immediately. Grounding was performed on a separately mounted circuit if necessary. If the device has a grounding terminal, it can be connected to a three-pin plug.

author: Jwillis
author_rank: Super Contributor
timestamp: February 12, 2024, 09:49:46 pm
content: Quote from: dalpets on February 11, 2024, 01:09:19 pmHere North America the common is connected to earth, keeping all the house wiring reference to earth ground. Being split phase the 0V tap is referenced to earth at the transformer. So even older homes that don't apparently appear to have common tied to earth at the panel, it will be at the transformer. So even two prone polarized plugs have technically a ground.In Australia it appears the the common and live are floating (correct me if I'm wrong here), so you need a separate ground.Simply pounding an earthing rod into the ground outside and running a wire to a buss bar mounted on the wall in your lab, you can just attach wires from the chassis of the equipment to the buss bar. Some equipment have an external earth connector you can connect to the buss bar. That assumes you don't live in a multi story apartment.