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Group the grounds, or not?

Currently having the following discussion with another engineer at work:

We have a product that has (3) DC power sources, and (1) load connection. All the grounds are electrically the same. Each power source is nominally

48 VDC negative ground, individually fused at 10 amps.

On the PCB, I want to lay the board out so that each Positive and Negative get grouped together, functionally. In other words, each power source will have it's + and - presented at the PCB-mounted barrier strip right next to each other. Positive on the left, negative on the right. Each source has a dedicated 2-position barrier block terminal strip, as does the load.

This one:

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All of this will be wired at the factory. I anticipate that any need for a n end-user to adjust this factory wiring during the lifetime of the product will be somewhat rare, but not zero.

My colleague is (almost) insisting that we group all the grounds together o n one side of the board and present them as a "community" ground bus arrang ement.

His concern is that an end-user might reverse the polarity, or inadvertentl y short the terminals during a repair (or re-installation) operation (while energized, of course) once it leaves our factory.

I want to keep the + and - grouped together functionally (for ease of under standing the overall device operation if nothing else, and to prevent mista kes) and just crowbar the inputs and outputs to blow the associated fuse. (We really don't have the option to bridge-rectify it and just allow the mi s-wiring, etc..., as the voltage drop and heat become issues. - which other wise might have been my next choice.)

And on top of that, I don't recall ever seeing products similar to this tha t segregate the common grounds to one bus. (?) Not that I can think of tha t many right now... (Well, maybe really large capacity battery plants / in verters / chargers with built-in bus distribution.) ?

Anyway, what do you think? Segregate all the grounds to one location, or go side-by-side (with a safet y provision to blow the fuse(s) if someone does something stupid)?

Reply to
mpm
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Color-code the wires, and silkscreen the color (as text, like BLACK) next to each barrier strip position.

Clustering the grounds together seems simpler to me. Or put the grounds at the same end of each barrier strip.

Why not use connectors?

Or fastons.

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--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
John Larkin

Den tirsdag den 6. februar 2018 kl. 13.53.18 UTC+1 skrev mpm:

All the grounds are electrically the same. Each power source is nominall y 48 VDC negative ground, individually fused at 10 amps.

e get grouped together, functionally. In other words, each power source wi ll have it's + and - presented at the PCB-mounted barrier strip right next to each other. Positive on the left, negative on the right. Each source h as a dedicated 2-position barrier block terminal strip, as does the load.

an end-user to adjust this factory wiring during the lifetime of the produ ct will be somewhat rare, but not zero.

on one side of the board and present them as a "community" ground bus arra ngement.

tly short the terminals during a repair (or re-installation) operation (whi le energized, of course) once it leaves our factory.

erstanding the overall device operation if nothing else, and to prevent mis takes) and just crowbar the inputs and outputs to blow the associated fuse. (We really don't have the option to bridge-rectify it and just allow the mis-wiring, etc..., as the voltage drop and heat become issues. - which oth erwise might have been my next choice.)

hat segregate the common grounds to one bus. (?) Not that I can think of t hat many right now... (Well, maybe really large capacity battery plants / inverters / chargers with built-in bus distribution.) ?

ety provision to blow the fuse(s) if someone does something stupid)?

this is how a psu looks, ...

formatting link

Reply to
Lasse Langwadt Christensen

Proper designs, especially those that consume a bit of power, tend to utilize a single, central grounding point, and there is good reason.

One can generate unwanted ground loops. Another good reason is that the product chassis, if metallic, becomes an integral part of the safetey element should some circuit element experience a failure mode.

Reply to
Long Hair

Oh please... :) I can write a book about how screwed up MeanWell chargers are (although I realize they are very popular low-cost Chinese designs.) I have zero desire to imitate MeanWell on anything.

Anyway, an important difference is all those bussed connections (3-positives, and 3-neatives shown in the link) are the SAME node. In our product, they are different, and could be (likely are!) different voltages, just all referenced to the same ground.

IF they were all truly the same, then I wouldn't have as much issue grouping them as shown on the MeanWell example.

Reply to
mpm

I guess we could use connectors rather than screw-terminal barrier strips. Just adds a little to the BOM. (And I'm not sold on the underlying reason to do so. At least not yet.)

If it were something people were going to get their hands in to more often, then I'd be more inclined. Not saying I'd adopt it, even then - but certainly a push in that direction.

Reply to
mpm

There are cable shops that will make (and test) connectorized cable assemblies for you. They have all the automatic strippers and crimpers.

I like to use multiple connector pins for high currents. The wires in the cables are smaller and flexible, and the wire resistance forces current sharing in the connector pins.

formatting link 

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

Their open-frame offline switchers are great. We've used hundreds of them.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

All the grounds are electrically the same. Each power source is nominall y 48 VDC negative ground, individually fused at 10 amps.

e get grouped together, functionally. In other words, each power source wi ll have it's + and - presented at the PCB-mounted barrier strip right next to each other. Positive on the left, negative on the right. Each source h as a dedicated 2-position barrier block terminal strip, as does the load.

an end-user to adjust this factory wiring during the lifetime of the produ ct will be somewhat rare, but not zero.

on one side of the board and present them as a "community" ground bus arra ngement.

tly short the terminals during a repair (or re-installation) operation (whi le energized, of course) once it leaves our factory.

erstanding the overall device operation if nothing else, and to prevent mis takes) and just crowbar the inputs and outputs to blow the associated fuse. (We really don't have the option to bridge-rectify it and just allow the mis-wiring, etc..., as the voltage drop and heat become issues. - which oth erwise might have been my next choice.)

hat segregate the common grounds to one bus. (?) Not that I can think of t hat many right now... (Well, maybe really large capacity battery plants / inverters / chargers with built-in bus distribution.) ?

ety provision to blow the fuse(s) if someone does something stupid)?

What's the disadvantage of grouping all the grounds together?

If you do go side by side, instead of a crowbar could you add one FET on each line for reverse polarity protection?

George H.

Reply to
George Herold

I'd be just as worried about ingenious* customers lifting grounds because they "don't do anything". On account of their being tied common.

This is an equivalent consequence of the "ground loop" others have mentioned.

*Nothing can be fool-proof, because fools are so ingenious.

Individual fuses on both polarities would be a possible protection, requiring the currents to be distributed evenly. If not enforcing that they be on the correct pairs of terminal blocks. (Not that you can do that, anyway -- a current is a current.)

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

formatting link

We have a product that has (3) DC power sources, and (1) load connection. All the grounds are electrically the same. Each power source is nominally

48 VDC negative ground, individually fused at 10 amps.

On the PCB, I want to lay the board out so that each Positive and Negative get grouped together, functionally. In other words, each power source will have it's + and - presented at the PCB-mounted barrier strip right next to each other. Positive on the left, negative on the right. Each source has a dedicated 2-position barrier block terminal strip, as does the load.

This one:

formatting link

All of this will be wired at the factory. I anticipate that any need for an end-user to adjust this factory wiring during the lifetime of the product will be somewhat rare, but not zero.

My colleague is (almost) insisting that we group all the grounds together on one side of the board and present them as a "community" ground bus arrangement.

His concern is that an end-user might reverse the polarity, or inadvertently short the terminals during a repair (or re-installation) operation (while energized, of course) once it leaves our factory.

I want to keep the + and - grouped together functionally (for ease of understanding the overall device operation if nothing else, and to prevent mistakes) and just crowbar the inputs and outputs to blow the associated fuse. (We really don't have the option to bridge-rectify it and just allow the mis-wiring, etc..., as the voltage drop and heat become issues. - which otherwise might have been my next choice.)

And on top of that, I don't recall ever seeing products similar to this that segregate the common grounds to one bus. (?) Not that I can think of that many right now... (Well, maybe really large capacity battery plants / inverters / chargers with built-in bus distribution.) ?

Anyway, what do you think? Segregate all the grounds to one location, or go side-by-side (with a safety provision to blow the fuse(s) if someone does something stupid)?

Reply to
Tim Williams

On Tuesday, February 6, 2018 at 7:19:28 PM UTC-5, Tim Williams wrote: ...

...

I've always heard is as: "If you make something foolproof, only fools will use it." Which I think is saying the same thing.

This product is slated for UL approval. I think I'm just going to sit back and see if they raise it as an issue.

Reply to
mpm

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