Mail*Link(r) SMTP FWD>RE>DES: Re[2]: Conductor Widths
Doug, Terry, et. al.
Don't forget that house wiring is insulated with 0.5-1.0 mm of primary
thermoplastic insulation and at least two insulated conductors an the
uninsulated ground wire are encased in a secondary thermoplastic insulation of
about another 0.5 mm. None of these "electrical" insulators are good thermal
conductors, therefore the temp of the conductors goes up.
Ralph Hersey, e-mail: [log in to unmask]
--------------------------------------
Date: 4/11/96 3:12 PM
From: George Franck X2648 N408
Doug,
I am doing some wiring in my basement. My observations is that the current
limiting, high resistance areas are all in the connection hardware. Have
you every wondered about wire nuts? They are used all over your house, and
these look to be the weakest link in the whole wiring system.
So I propose that the NEC code is set to reflect the current carring
capacity of the connection hardware for a certian size wire, not the wire
itself. If you compare the connection technology between house wiring and
PWB's, you will conclude the PWB's really are an order of magnitude better,
or more.
>
> Terry,
>
> I can certainly appreciate that and we have considered that as a
> possibility. Under analysis, the higher current rated solid wire has
> MORE surface area than the IPC recommended trace width!
>
> For instance,
>
> Say, I have 10 amps on a 2 oz. trace and I can handle no more than a
> 30 degree rise. IPC crosses over to (as best my eyesight can handle)
> a cross-sectional area of about 175 square mils. Dropping down to
> trace width, that correlates to about 70 mils. Assume the trace width
> is much much more radiative than the trace sides. The total radiative
> area is 70 mils.
>
> 10 amps for NEC correlates to 16 gauge solid wire. 16 gauge solid
> wire has a nominal diameter of 50 mils. The available surface area
> for heat radiation is 2*pi*(50/2) = 157 mils!!!
>
> Now, under analysis, the IPC recommends 175 square mils to handle 10
> amps whereas the NEC is recommending a cross-sectional area of 2027
> square mils to handle 10 amps!!! These numbers differ by a factor of
> 11. Basic electricity tells me that two conductors that differ in
> cross-sectional area by a factor of 11 also differ in current carrying
> capability by a factor of 11.
>
> This does not make me feel good. What am I missing here?
>
> Doug McKean
> ADC Video Systems
> [log in to unmask]
>
>
>
>______________________________ Reply Separator
>_________________________________
>Subject: Re: Conductor Widths
>Author: [log in to unmask] at internet-mail
>Date: 4/11/96 8:57 AM
>
>
>Doug has queried the difference in recommended cross-section between the NEC
>specs. for solid wire and IPC specs for PCB tracks for the same current
rating.
>
>I would suggest that since temperature rise is the limiting factor, the
>difference may be explained by the different surface area between a wire and
>a track. The larger surface area of the track will give a lower thermal
>resistance to ambient, and thus allow a larger current flow for the same
>permitted temperature rise (viz. same Amps and X-section area).
>
>Terry Davey
>[log in to unmask]
>
>___________________________________________________________________________
>
>
>--- Forwarded mail from [log in to unmask]
>
>To: [log in to unmask], [log in to unmask]
>Resent-From: [log in to unmask]
>
>
> Is your board being directly connected to AC power distribution of a
> building? If so, you'll have to make sure that it conforms to the NEC
> (National Electrical Code). This is where I have a problem with IPC
> specification of trace construction.
>
> The NEC rates 14 gauge wire for 20 amps and 10 gauge wire for 35
> amps. Since this is for solid wire, 14 gauge wire has a
> cross-sectional area of 3227 square mils, 10 gauge wire has 8156
> square mils. If your 2oz. copper is 2.8 mils thick, then your
> corresponding widths are 1.2 inches and 2.9 inches!!!
>
> Cross-sectional areas that are specified by the IPC as opposed to the
> above procedure can lead to a difference in areas of up to of 5 TIMES.
>
> Someone have an answer for this?
>
> Doug McKean
> ADC Video Systems
> [log in to unmask]
>
>
>______________________________ Reply Separator
>_________________________________
>Subject: Conductor widths
>Author: [log in to unmask] at internet-mail
>Date: 4/10/96 9:54 AM
>
>
>Help,
>
> We are laying out a power distribution board. We have current
>requirement of 35 amps and 15 amps. Our design is using 2oz copper,
>2 layers, and 20 degrees temperature rise.
>
> I am not sure of the conductor width required for both 35 & 15 amps.
>Can anyone help answer this question?
>
>
>
>Any help would be appreciated....
>
>
>Ray.....
>
>--
>
>
>
> _/ _/ _/ _/ _/_/_/
> _/ _/ _/_/ _/ _/ _/ Hughes Network Systems
> _/ _/ _/ _/ _/ _/ 11717 Exploration Lane
> _/_/_/_/ _/ _/ _/ _/_/_/ Germantown, Md. 202876
> _/ _/ _/ _/ _/ _/
> _/ _/ _/ _/_/ _/ _/
>_/ _/ _/ _/ _/_/_/
>
> Ray McKinnon Email: [log in to unmask]
>
>
>
> ph (301) 212-7958 fx (301) 212-2099
>
>
>
>
>--- End of forwarded mail from [log in to unmask]
>
>--- End of forwarded mail from [log in to unmask]
>
>--
>Terry Davey, Reliability Engineer,
>European Development Engineering (108),
>Motorola Ltd, GSM Products Division, Tel: +44 1793 545390
>
>
>16 Euro Way, (switchboard: 541541)
>Blagrove, Swindon, Fax: +44 1793 541228
>England, SN5 8YQ. E-mail:
>[log in to unmask]
>
>***************************************************************************
>*****
>"Forget the calm at the end of the storm. If you sense calm,
> it's only because you're in the eye of the hurricane" - Tom
Peters
>***************************************************************************
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>
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Date: Thu, 11 Apr 1996 16:55:55 -0500
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From: [log in to unmask] (George Franck X2648 N408)
Subject: Re: DES: Re[2]: Conductor Widths
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