DC Power Distribution

[TimothyMoulder]

Thanks!

Hi guys!

The consensus here seems to be that the DC must be documented. I have always documented it in some form, but I wanted to ensure it wasn't overkill. It's nice to know I'm on the right track.

Now, as to HOW to document it --

Kevin : This is a very good method, and one I'll have to look into further. My usual power supplies have self-resetting overload protection, but there are fusible terminals out there that might serve this purpose very well (right, Jesper? ) I'm going to have to get some of those on order!

Eric : Excellent example, and you did a great job justifying your position. I used to put the DC terminals on the same page as the IO they involved, but it got cluttered pretty fast, so I went with the "central page" approach. Thanks for the specifics!

Rick : It's good to know the method I use is common, so with a few of the refinements we've discussed here, I'm confident going forward that my guys will be able to follow the schematic easily The extra page is a good idea - I'm going to have to look into that one.

Arik / Rick : I have no problem putting the second switch into the circuit. I just have to figure out HOW to squeeze that little sucker in there

Thanks again, everybody! I'm starting to feel a little more confident about all of this now!

TM

 

[JesperMP]

My usual power supplies have self-resetting overload protection, but there are fusible terminals out there that might serve this purpose very well (right, Jesper? )

You should group the DC into subgroups by means of suitable MCCBs.
(sorry if I confused the matter by using the term "fuse" for an MCCB). If you only use the overload protection in the DC power supply unit, then the entire installation will be "zapped" if there is a short circuit somewhere.

I only use the the isolator terminals to further narrow down the search for the short circuit. Fusible terminals are even better, but they are a bit expensive and also bigger. This can be a problem if there are many terminals that supply voltage (also via relays and PLC outputs).

 

[Kevin Hammond]

This is a little off topic but since you mentioned fuse blocks, I'll throw it out there:

I have been using Wago terminal blocks exclusively for the last few years, and they have some nice fused terminal blocks with LED blown fuse indicators. They are available for various fuse types, including my favorite - the mini-automotive blade-type.

The terminal blocks that I use are of the cage-clamp variety. Anyone still using screw terminals should take a look at a clamp style block. They are, IMO, better than screw terminals in every way (faster/easier installation, more reliable connection). Before I switched, I routinely had trouble with loose screw terminals causing intermittent problems. I have not had a single problem with clamp terminals - and I have thousands in the field. I think all of the major players in the terminal block market have a clamp style product line.

Kevin

 

[TimothyMoulder]

Ready for Review!

Drum-roll please!

Attached is the latest approach to thoroughly documenting a DC distribution. It incorporates a number of ideas discussed in our earlier discussions.

Since it's a partial view, the rails are 24 VDC supply and the octagons are line jumps. "DC 09" is a wire number for a particular DC, er, wire. The DC common is not numbered, it is always white with a blue stripe, or tagged "0 VDC" in a cable.

All criticism is welcome! I'd particularly like to hear from Tom Jenkins, since he had some trouble following the previous version.

Thanks!

TM

PS to Kevin - I do like spring cage terminals, and I'm trying some out. I also have issues with screw terminals working loose. My preference is for phoenix contact, although I hear Wago makes a good product as well.