Hi Ray, there was an article in the Route that discussed the tables for
conductor spacing in depth.. here is the link
http://www.ipcdesignerscouncil.org/oldroutes/dec00route.pdf
The copy of a conductor spacing chart I have based on a combination of UL,
CSA, VDE specs, ( before CE came out) indicates that on the Primary side of
any transformer:
Hot (AC Line 120VAC up to 250VAC) to Neutral creep (over surface) spacing
minimum is 2mm or .079 in.
AC Hot to Gnd creep spacing minimum is 3mm or .120 in.
AC line Primary to Secondary is 8mm or .320 in.
If the circuit is not protected from dirt or contamination the spacing
increases by 1mm.
As voltage increases you can apply a rule to calculate the appropriate
spacing. That is .023 inch plus .0002 inch per volt peak over surface or
through air. 250 peak volts AC would be .073 inches using that calculation.
Understand these are safety requirements and you will need to contact the
agency you are trying to get approval from for less spacing... I know these
numbers work for VDE or TUV and UL. UL actually has less stringent
requirements than the EU groups do. If your product violates the minimum
spacing, you will have to demonstrate that the system does not present a
fire or shock hazard and pay for the testing to verify it. That's the only
way to get approval if you do not meet the minimums.
The values they use are de-rated and have large safety margins built in, I
have demonstrated that much smaller values will pass under controlled
conditions, however you must take into account all the variables. A batch of
boards that passes at the physical minimums may not pass on the next batch
due to contaminants or residue left on the surface by poor rinsing or bath
quality, or handling at the manufacturer, or changing vendors, humidity
etc...
So they safety margins have real value in that they will work under all
conditions...
Hope that helps a bit...
Bill Brooks
PCB Design Engineer , C.I.D., C.I.I.
-----Original Message-----
From: Ray Johnston [mailto:[log in to unmask]]
Sent: Thursday, December 18, 2003 10:58 AM
To: [log in to unmask]
Subject: Re: [DC] UL Specification for 120VAC
David,
In UL 60065 table 8, with a voltage peak or d.c. V of 420 / Voltage r.m.s. V
of 300 the minimum clearance is 3.0mm and in table 9 (Additional Clearances)
has an added 0.1mm which gives you about 3.1mm (.125") Clearance.
This is a standard for Audio, Video and similar Electronic Apparatus.
This is about as much as I can dig up not knowing all factors and what
standard you are using.
Ray Johnston
Lead CAD Designer
Rane Corporation
Mukilteo, WA 98275
425-355-6000
rayj@rane,com
----- Original Message -----
From: "David Baldwin" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, December 17, 2003 10:39 AM
Subject: [DC] UL Specification for 120VAC
> Does anyone have the UL Specification for clearance of the L, N, & G
traces
> for 120 VAC?
>
> Thanks in advance for any assistance.
>
> David Baldwin CID+
>
> ___________________________________________________
> Baldwin Technologies - 1736 S. Nevada Way - Suite B
> Mesa, AZ 85204 (480) 539-4400
> http://www.baldwin-tech.com
>
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