Multi-conductor cables

A question for any electrically minded folks:

I want to connect a relay box with a control panel. The control panel needs 12vdc (to power a bcs) and 24vac coming in (transformers housed in relay box), and 4 switched 24vac loads going out back to the relay box.
Can all these 8 lines run together in a shielded multi-conductor cable? Or is there some interference that would be caused.
Also if anyone knows a good electrical forum where I could ask something like this, a link would be greatly appreciated.

Thank you in advance, cheers!

Budzu said:

A question for any electrically minded folks:

I want to connect a relay box with a control panel. The control panel needs 12vdc (to power a bcs) and 24vac coming in (transformers housed in relay box), and 4 switched 24vac loads going out back to the relay box.
Can all these 8 lines run together in a shielded multi-conductor cable? Or is there some interference that would be caused.
Also if anyone knows a good electrical forum where I could ask something like this, a link would be greatly appreciated.

Thank you in advance, cheers!

Click to expand...

How long will this wire be? The AC could couple between lines but I don't think you'll have problems. You're not going to couple enough energy to accidentally engage a relay. The BCS should reject ripple on the DC, I expect. Now if you're running this for 100 feet, might be wise to split it up.

That's excellent news! It will be no more than 6 feet and all the loads will be quite low. Thank you for the response

Oh and P.S. should a ground wire be included in the run? I don't think the BCS requires one.

if you're using a metal case, you should ground it.

B

Budzu said:

A question for any electrically minded folks:

I want to connect a relay box with a control panel. The control panel needs 12vdc (to power a bcs) and 24vac coming in (transformers housed in relay box), and 4 switched 24vac loads going out back to the relay box.
Can all these 8 lines run together in a shielded multi-conductor cable? Or is there some interference that would be caused.
Also if anyone knows a good electrical forum where I could ask something like this, a link would be greatly appreciated.

Thank you in advance, cheers!

Click to expand...

Often times you can find multiconductor cables with twisted pairs. The twisted wires on the AC lines will cut down on the amount of radiated 60Hz emissions.

There is a good forum you can ask this at. It is http://forum.embeddedcontrolconcepts.com/index.php?sid=c593f4a1d7ffe861dde647c0bf95efc0 which is for the BCS460

Well I think I only need 1 24vac pair. 24vac negative should only be needed to wire to the switch LED's. Its just the positive going into the control panel, the other negatives go straight to the relays. I hope I'm not off here. Here's the wires bundled:

to control panel:
1 12vdc +
1 12vdc -
1 24vac +
1 24vac -
1 ground

from control panel:
4 switched 24vac +

I used a 14 conductor cable from this company to connect my control panel. All 24 VAC and one pair 110 VAC to power the PIDs. There was 7 twisted pair in it.
Mike

http://www.surplussales.com/Wire-Cable/Wire1.html

Can you let us know the patterns of your wire? What leads to what?

airbalancer said:

I used a 14 conductor cable from this company to connect my control panel. All 24 VAC and one pair 110 VAC to power the PIDs. There was 7 twisted pair in it.
Mike

http://www.surplussales.com/Wire-Cable/Wire1.html

Click to expand...

Now putting line voltage within the same shield would make me much more nervous. Normally you want more separation than that. UL would probably not accept it without an additional layer of insulation around the mains.

gbrewing said:

Can you let us know the patterns of your wire? What leads to what?

Click to expand...

to control panel:
1 12vdc + to BCS
1 12vdc - to BCS
1 24vac + to 24vac switches and led's in parallel
1 24vac - to 24vac switches (led power)
1 ground from relay box ground to control box

from control panel:
2 switched 24vac + to 2 30 amp DP relays for elements
2 switched 24vac + to 2 15 amp relays for pumps

and Hi airbalancer, actually these arrangements are based on your box's components. Your posts have been a great help. Just not sure I'm understanding all the wiring points just yet. Getting there!

Ah I just totally hurf durfed. Why would I need the BCS in the control panel? And what about its 5vdc output signals? It needs to be in the relay/main power box.
So actually this is what I'm looking at running together in a multi-conductor:

to control panel:
1 24vac + to 24vac switches and led's in parallel
1 24vac - to 24vac switches (led power)
1 ground from relay box ground to control box

from control panel:
2 switched 24vac + to 2 30 amp DP relays for elements
2 switched 24vac + to 2 15 amp relays for pumps

You are just fine with running all of them together. AC at 60 Hz over short distances won't couple at all.

That should be enough, but I'll just blather on now while I still have some apfelwein in this glass...

What you have to look out for is "di/dt" signals; that is, signals that abruptly switch high currents from On to Off, or vice-versa. For example, I would not run the outputs (load side) of a relay carrying a lot of current with other lines.

Also, you should not include signal lines with lines that drive motors or the coil side of a mechanical relay. Anything with a winding can kick back some serious positive and negative spikes that will couple to other nearby wires, especially if they are long.

Budzu said:

Ah I just totally hurf durfed.

Click to expand...

That is a new one for me. Hope you didn't get any on yourself (?)

Budzu said:

2 switched 24vac + to 2 30 amp DP relays for elements
2 switched 24vac + to 2 15 amp relays for pumps

Click to expand...

Are those SSRs or mechanical relays?

Thanks pawn, that makes sense. Just so I know, what does di/dt stand for?

There are both SSr's (2 40 amp for elements) and 24vac mechanical relays (2 30a for elements AND 2 15a for pumps).

But I may have changed my setup again. My main box came in, it is 16x14x6 inches nema 4x, and it already has a bunch of 22mm holes cut in the side. I'm thinking it will be easier to just wire everything in one box, and also eliminate 2 of the mech. relays and drive the pumps directly from the switches (pump switch). I'm not going to automate the pumps with the BCS until I feel comfortable with the system.

offtopic: I just hired an electrician to wire my outbuilding with 100 amp service. Baby steps ! Here's the building as I got it earlier this year: Outbuilding
Cheers all

Budzu said:

Thanks pawn, that makes sense. Just so I know, what does di/dt stand for?

Click to expand...

delta-current over delta-time, or change in current over change in time. This is geekspeak for how quickly the current changes. The strength of magnetic fields that couple across wires is directly related to how fast and how much current changes with respect to time. Turns out there are surprising number of engineers on this forum, so sometimes I guess it feels appropriate to mix in a bit of tech jargon if the subject allows it.