Hi John, To me it still looks like you have the 120VAC side of the transformer totally isolated from frame ground.
As John Kasunich has also stated it's incredibly dangerous to have that 120VAC voltage floating. One side of the transformer should be immediately connected to Earth (Frame) right out of the transformer before any filters. With a ring terminal to a double nutted stud. That same connection inside your cabinet becomes the white wire and the green wire. The other the Black wire. Connecting to your AC outlets is done with the black wire going to the darker bronze screw which is the narrower blade and the white wire goes to the nickle or light coloured screw and the wider blade. The green which is the protective ground goes to the ground terminal of the outlet. It is not good practice to connect the outlet ground pin to some other location. Certainly not to Earth unless one side of your AC is also connected to Earth. As you have it in your drawing the ground provides absolutely no protection in your circuit. If you wish to filter noise out of the 120VAC side it's always best to do it at the source of the noise, so the devices creating the electrical interference don't have the cabling to use as an antenna. A noise filter on the output of the transformer doesn't really make any sense to me. Perhaps think of it this way. Current always flows from source to destination and back. There has to be a complete circuit. This is true for power wiring and it's true for electrical noise. John Dammeyer > -----Original Message----- > From: John Thornton [mailto:[email protected]] > Sent: January-02-16 4:26 AM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Rewiring the BP > > I do have a "control transformer" which can be identified by the three > fuses on top. One for X1 (secondary) and one each for L1 and L2. I went > back and found out which was X1 and X2 and will correct my wiring today. > My question is I have a filter on X1 and X2 should I ground before or > after the filter? > > JT > > On 1/1/2016 6:41 PM, John Kasunich wrote: > > 120V transformer secondaries (in the USA) need to be grounded on > > one side, even if they are part of a machine control panel. > > > > Such transformers are referred to as "control power transformers" > > and traditionally powered electro-mechanical control devices such > > as relays and contactors. Today they still power those things, and > > they also power AC-to-DC supplies that run the electronic parts of > > the control. The low voltage DC power distribution (typically 24V) > > is sometimes un-grounded, sometimes single-point grounded, for > > exactly the noise reasons Berthos mentions. But the 120V "control > > power" isn't used a the "reference" for anything - it is still "dirty" > > power, although not as dirty as the main power that might be going > > to a VFD or whatever. ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
