Hi Michael. It wasn't in the first release but IPC/WHMA-A-620A (July 2006) has the following in Clause 3.4:
These criteria apply to all cable or harness bundles, whether they are twisted pairs of the same wire type and size, or cables incorporating various wire types and sizes. The length of lay (or ''twist'') as measured from the midpoint of wire's crossover through a complete spiral to the next crossover midpoint of the same wire shall be 8 to 16 times the outer diameter of the bundle (Figure 3-9). <Fig 3-9 is a drawing showing midpoint to midpoint measurement>
Acceptable - Class 1,2,3
* The length of lay for each twist is 8 to 16 times the outer diameter of the bundle.
Defect - Class 1,2,3
* The length of lay for each twist is less than 8 or more than 16 times the outer diameter of the bundle.
Jack
Jack Crawford, IOM
IPC Director Certification and Assembly Technology
IPC - Association Connecting Electronics Industries(r)
3000 Lakeside Drive, Suite 309 S
Bannockburn, IL, 60015
847-597-2893
FAX 847-615-5693
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www.ipc.org
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Forrester, Michael (H USA)
Sent: Wednesday, July 27, 2011 10:32 AM
To: Technet
Subject: [TN] Wire Twists per inch
Does IPC/WHMA-A-620 specify how many twists per inch you should have when you twist the wires in a cable assembly(like a twisted pair) instead of using tie wraps or lacing?
I was unable to find anything. Thank you.
Best Regards,
Michael Forrester
Sr. Product Engineer
CSMTPE
Siemens Healthcare Diagnostics
101 Silvermine Rd.
Brookfield, CT 06804
PH: (203) 740-6452
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