On 1/1/2016 11:26 AM, Bertho Stultiens wrote: > On 01/01/2016 05:13 PM, Dave Cole wrote: >> Anytime you have a 120 volt source for computer, misc power etc, you >> need to declare one side of the 120 vac winding the neutral (white wire) >> and tie that terminal to the machine frame. >> It similar to what is required at the service entrance of your house. >> The neutral is always tied to the ground at the entrance box. >> Oftentimes they drive a screw through the neutral buss bar in the >> service entrance box into the box sheetmetal and then tie a green or >> bare copper ground wire to the same neutral buss bar and run that to a >> metal water pipe or ground rod. > You should never tie a secondary winding of a transformer to ground. The > transformer makes the secondary float wrt. the primary and that is just > fine. > > In this scenario, you would create a (capacitive) feed-through from the > transformer to ground because the primary is not referenced at ground. > The primary has two phases attached, which creates a virtual circuit at > the primary side. > > The difficulty here is that you must take account for the floating > references, which make most of the things you measure local phenomena. > Once you go through the transformer, your reference to the primary line > input is lost and you must not try to reestablish it. It would only make > things bad and worse. > Hi Bertho,
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. :-) ) 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. 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. One of way too many references on the web. http://ecmweb.com/bonding-amp-grounding/basics-bonding-and-grounding-transformers Dave ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
