Screw Terminal Nightmare


Senior Member
I was just down in my wiring closet doing some disaster recovery planning and I was struck by just how hard it would be to recover from any significant hardware failure.

The problem is that most hardware I/O is wired via screw terminals... a lot of screw terminals. Looking at my Stargate and each of the four expander modules, I realize that to replace any one of them requires disconnecting and reconnecting 16 digital inputs and 8 relays. That's 48 screw terminals per expander! Likewise each of my RS-485 hubs has 8 channels X 4 wires per channel for a total of 32 screw terminals per hub! The 24 zones in my Caddx panel is another 36 terminals, and so on...

No matter how you slice it, swapping one of these units out is not going to be a quick or simple task and will certainly involve significant down time.

So the question is: Why don't the manufacturers of these devices use the plug-in header type of screw connectors? Not only would that make equipment troubleshooting and swap-out quick and painless but also eliminates the risk of damaging a wire during the changeover. These two benefits are more than worth the trivial cost difference for this type of connector.

I think there ought to be a law that says any security, audio, or automation device with more than 8 screw connectors MUST employ removeable header terminals. I urge everyone to write their congressman. Lets get some legislative attention on this issue!
Good to know! I have a lot of other ELK stuff and it all has "fixed" terminal blocks. I didn't realize the M1 was different. Maybe they will be a good influence on others in the industry (But I still think there oughta be a law!)
You are definitely right Mike. My HVPro and Caddx devices are both screw terminals. Lots of screwing needed to replace either device.
The big reason is money. Elk uses a type of Phoenix Contact in their systems, which works out very well as you can actually take the terminal off to connect a wire if you need to (people with aging eyes can appreciate this one B) )
When I build my own stuff, I use both kinds of screw terminals - the ones with plugs and without.

I wouldn't say that the price difference is small. It's big enough that I will keep a bunch of the non-plug ones around for normal stuff [1] but I can't afford to buy the plug ones in bulk (they are also usually a lot larger - an important consideration in a lot of applications [2]).

The cost really adds up when you are buying a lot of them (even with bulk discounts) - especially if you go with the expensive brands like Phoenix.

[1] I'll buy 100 2-terminal non-plug ones at a time. I'd have to give up food for a while to buy that many plug ones - not really, but it feels that way when you look at the totals column in your order.

[2] I really like the 0.1" spacing miniature ones you can get now (non-plug), but they are a lot more expensive that the cheap 0.2" non-plug terminals.
I agree. My AB8SS and Xantech stuff have the plug-in types, but my Applied Digital stuff does not, and it's a big 'ole pain to work with the applied digital stuff, especially if you've gotten it mounted in a tight spot.
The WGL Rain8/Relay8/etc all use removable terminal blocks. You can unplug the terminal block to bring the module inside for programming, or to switch to another module. It takes only seconds to switch over 16-20 wires.
PeterW said:
The WGL Rain8/Relay8/etc all use removable terminal blocks.  You can unplug the terminal block to bring the module inside for programming, or to switch to another module.  It takes only seconds to switch over 16-20 wires.
Yep, I love the system that WGL has. Not only that, you don't need to carry in the wall wart as it uses the PC power when "programming" the unit also. You just unplug the unit, bring it to your PC, plug in the RS-232 cable, program the unit, disconnect the RS-232 cable, then plug the unit back in to its running location. This is great because I have mine (Relay 8) in the garage controlling my sprinklers.
I did not know that! Maybe "fixed/removable screw terminals" should be one of the fields in the upcoming hardware comparison tables.
The ADI Ocelot and SECU16IR (or RLY8XA, I forget which one) do have a removable power/bus plug, but the ones that would need it most like the SECU16 don't. I agree, its a very convenient feature. One thing though; you should be able to "convert" some older devices by buying the board mounted part of the connector, plus the removable plug. Often, the board mounted part will have pins long and sturdy enough to be inserted into the existing, fixed terminal strip and screwed in. If the terminal strip is in a recessed slot (like on a SECU16) then it might be harder to do, unless you also chew up the plastic box. Watch out for the connector terminal spacing however: The removable connectors like you see on the Ocelot are "Eurostyle" connectors and have metric spacing, incompatible with many of the older screw terminal strips.
Does anyone have a link to a picture of this removable screw terminal? I checked BSR's link, but not sure what I am looking for.
You can sort of see them in this pic of the M1 or this pic of the expanders. They are the green connectors. The blue ones are fixed.