Three Phase Line to Chassis Filter Only X2 Capacitors - Page 1
Forum section: electronics / projects

author: b2theory
author_rank: Contributor
timestamp: April 21, 2017, 06:04:04 pm
content: I recently pulled apart a three phase line filter that has a capacitor configuration as shown in the picture. Surprisingly, all of the capacitors we X2 safety rated including the one that goes to chassis. I would have thought that the chassis connected capacitor had to be Y1. Does anyone have any idea why this is allowed?

author: Zero999
author_rank: Super Contributor
timestamp: April 21, 2017, 06:59:12 pm
content: That looks pretty dangerous to me but it depends on the application. Was it inside a domestic appliance or some equipment permanently installed in an industrial setting?Another thing to note is that there are two capacitors between the chassis and earth which isn't as bad as a single X capacitor. The leakage current (at mains frequency) should also be very close to zero as the phase all cancel one another out but this isn't enough for safety's sake, as one or more phases could go down, thereby increasing the leakage.

author: b2theory
author_rank: Contributor
timestamp: April 21, 2017, 07:03:23 pm
content: This circuit I described is in a Schaffner filter rated for 480V three phase.

author: mmagin
author_rank: Frequent Contributor
timestamp: April 21, 2017, 09:52:04 pm
content: 1. Age? I am not sure if the idea of X and Y capacitors were standardized at the same point.2. I have seen capacitors which are both X and Y rated. Maybe without the datasheet the full story isn't clear

author: Seekonk
author_rank: Super Contributor
timestamp: April 22, 2017, 12:15:33 pm
content: Industrial equipment allows much higher ground currents. You would never see that size capacitance in a Y capacitor.

author: wraper
author_rank: Unknown
timestamp: April 22, 2017, 12:19:15 pm
content: Quote from: b2theory on April 21, 2017, 06:04:04 pmWhat is the value of this capacitor? Are you sure it goes to Chassis (ground) and not Neutral?

author: wraper
author_rank: Unknown
timestamp: April 22, 2017, 12:22:39 pm
content: Quote from: Seekonk on April 22, 2017, 12:15:33 pmIt should not be of the same value as X capacitors. And 100nF+ Y capacitors are available almost everywhere.http://www.schaffner.com/products/download/product/datasheet/fn-258-book-style-emcemi-filter-for-three-phase-inverters-and-power-drive-systems/

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 22, 2017, 12:33:01 pm
content: Note that they specify low ground currentunless one line goes open. The three voltages are balanced, and therefore the currents as well... unless they aren't.As mentioned, industrial equipment can be made for much higher ground currents. These will usually be semi-permanent installations, withbondedgrounding.Tim

author: Zero999
author_rank: Super Contributor
timestamp: April 22, 2017, 03:58:54 pm
content: Quote from: b2theory on April 21, 2017, 07:03:23 pmPart number? Datasheet?Is it designed for use in portable equipment of fixed, industrial applications.As others have said, the requirements are less stringent for fixed, industrial installations. This is because, unlike a portable appliance, it doesn't move and it isn't repeatedly disconnected and reconnected to the mains, so there's a much lower chance of the earth conductor going open circuit.

author: b2theory
author_rank: Contributor
timestamp: May 01, 2017, 06:08:36 pm
content: They were all the same value 2.2uF 305VAC X2