On 01/01/2016 05:47 PM, Dave Cole wrote: > That's done all of the time. In fact it is part of the NEC (National > Electric Code) that is followed (for the most part) in the US. > Pretty much every house in the US is wired like that. (I'm not making > this stuff up. :-) )
I agree with the connection at power entry in the house. That is quite a different story. That is actually the same here in EU (most countries). I think that we should separate two things: - house installation - machine wiring House installation is pretty much standardized with a lot of rules and reasons. Specifically to ensure referencing and protection. Machine wiring is different in that you can have scenarios where references are moved, especially in a 2-phase system where you are not using the neutral, which is the scenario we have here. > Now, if you don't want to do that inside the panel for some reason > (which I might have missed), that may be a different story. > I'm just saying that is standard practice in the US and on the European > machines I have worked on as well. The reason for /not/ connecting the ground on a secondary winding is to prevent a capacitively coupled ground path. Especially if you cannot guarantee a 100% balanced primary-to-secondary side wrt. ground (*). What happens is that there will be a current in the ground connection which causes an imbalanced current on the primary side (remember: primary is 2-phase circuit without neutral reference). This is a differential current discrepancy on the primary side. If you have an RCD (which you should), then it can or will trip due to the current imbalance. (*) and from the example measurements presented by JT, we can be assured that there is an imbalance, as seen from the phase shift causing a difference in voltage measured wrt. ground on the secondary. > There are a lot of good reasons to tie one leg the transformer to ground > besides to establish the safety ground and neutral as is common on the US. > Intermittent faults to ground, with an ungrounded system, can cause the > secondary of the transformer to fly way above absolute ground causing > connected devices, or the transformer to suffer from insulation > breakdowns. That's the extreme, but it can happen. Actually, the secondary should normally be floating. Most transformer setups are to ensure galvanic separation and that means you may never connect neutral to the secondary side. Connecting ground on a secondary is a different scenario, where you most often see the 0V (DC) potential connected to protective ground. This is often done in the PC's power supply. The 0V (DC) to protective ground connection prevents the scenario to which you refer to. The 0V (DC) to protective ground connection is repeated in many devices, which have both power and signal connections. This gives rise to ground-loops, which are to be prevented at all times and it is the cause of the whole thread. > One of way too many references on the web. > http://ecmweb.com/bonding-amp-grounding/basics-bonding-and-grounding-transformers It looks like the link is about a 3-phase system, where you would connect the center point in a star-configured secondary to ground. That is a different scenario. -- Greetings Bertho (disclaimers are disclaimed) ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
