IO-34 Analog Output Wiring

[jogas]

I'm putting in a job with a Tridium Enclosure (with it's own 40VA transformer),
a NPB-PWR-UN, J200, and an IO-34 that will have 3 analog output (2-10VDC) Belimo Ball
Valve Actuators (TF24-SR, 2-10VDC) that each draw 4VA. The NPB-PWR-UN, with J200
and IO-34 together draw 8.5VA. That's a total of 20.5VA on a 40VA transformer.
Seems fine to me, but I'm wondering how others lay out their 3 wire AO.
Previously, I would always use a separate transformer (with circuit breaker) and
also use separate AGC fuses for all my actuator power supplies.
But not knowing this IO-34 AO well concerns me enough to post this.
In this situation, is using the "on-board" transformer with fused power supplies to each actuator the
standard way everyone does it?

[simsd]

The only concern I would have is that inevitably something always crops up where you start adding things to the equation over time. 40 VA is rather small in my opinion and we generally only use those for individual VAV boxes (in Southern California the standard in new construction is to run a 120V ring to each VAV box and then use a transformer at each box).

Most of the time I would use a 75 VA transformer with the built in circuit breaker. We have never used individual fuses (if I'm reading it right) for the actuators.

If it was me, and you are concerned about the draw on the 40VA, then put a separate transformer with circuit breaker for power to the actuators and just connect the signal wire to the AO on the I/O board.

[jogas]

The only concern I would have is that inevitably something always crops up where you start adding things to the equation over time. 40 VA is rather small in my opinion and we generally only use those for individual VAV boxes (in Southern California the standard in new construction is to run a 120V ring to each VAV box and then use a transformer at each box).

Most of the time I would use a 75 VA transformer with the built in circuit breaker. We have never used individual fuses (if I'm reading it right) for the actuators.

If it was me, and you are concerned about the draw on the 40VA, then put a separate transformer with circuit breaker for power to the actuators and just connect the signal wire to the AO on the I/O board.

Thanks for the reply.
My concern is a potential (no pun intended, I think ) problem between the IO-34, it's transformer, and the actuator transformer when I connect the actuator transformer's common to the IO-34's common. Remember, these are 3-wire actuators and I have to bring the DC negative back home to the IO-34.
BTW, When I was talking about individually fused actuators, I was referring to DIN rail mounted fuse holders that would supply power to the panels terminal strip, where the actuator wiring would be terminated.
Now, with the economy being what it is, I see very few terminal strips. Everything is wired right to the I/O to cut costs.
Also, we're in the middle of a large college job with a pneumatic to DDC upgrade as one component. We chose to locate transformers in the Electrical Rooms, run the low voltage via bridle rings to each VAV box and fuse each separately. Very little conduit lowers the cost substantially.
But it's not Plan & Spec either.

[simsd]

You should be fine with just the signal wire but you should also be okay with the common from the second transformer as your negative.

We have just come off about four large jobs where we used terminal strips out the wazoo. No More....We wasted more time fiddle fooling with sensors and terminal strip connections than I care to remember. Never again. Even when we have them built in a panel shop we ended up changing them.

What we will use in the future is a terminal strip (say four red and four black) to allow for power to the different external devices, but all of the signals will be directly wired to the controller. That's what God invented plastic wire raceways (or Panduit raceways) - to cover up all of the wiring.

One other way to keep things neat, is that if you have a fair amount of I/O, then have all of it hit a gutter box first so you can do any crossovers in the gutter box, and then have two 2" chase nipples at each end of the gutter box go to the control panel.

With respect to how you' are running the VAV power, that's normal what you are doing. That's how we too would do a retrofit. I was just indicating where we use 40VA transformers. Frankly, I have never seen the 120V ring other than in Southern California. It was new to me when I moved here, but I started seeing it on all plans and spec's for new construction.

[ddcfreek]

I'm putting in a job with a Tridium Enclosure (with it's own 40VA transformer),
a NPB-PWR-UN, J200, and an IO-34 that will have 3 analog output (2-10VDC) Belimo Ball
Valve Actuators (TF24-SR, 2-10VDC) that each draw 4VA. The NPB-PWR-UN, with J200
and IO-34 together draw 8.5VA. That's a total of 20.5VA on a 40VA transformer.

Eliminate the power module (you don't need it with an IO-34). Then power the jace and actuators with the same transformer. Or with separate transformers and tie 24vac common to AO common.

[jogas]

Eliminate the power module (you don't need it with an IO-34). Then power the jace and actuators with the same transformer. Or with separate transformers and tie 24vac common to AO common.

You're right of course about the power module. I put the components in the panel last week.
Too many jobs going and I'm getting them mixed up. Just an IO-34 and J200.
Thanks.

[simsd]

That's exactly what I would do too. Just upsize the transformer to what you want and eliminate the power module.

[lwarren]

Pay for an add if you want to advertise!

[MatrixTransform]

Pretty sure the IO 34 power supply is isolated ... but I like to power the controller separately to the field IO devices...though we've done it both ways without trouble.

For 3-wire of course, connect the AO com wire to the 24VN in the panel.
For 4-wire connections it will end up at the field devices

The 3wire method can occasionally cause issues for the UIs cos theyre pretty sensitive (for pulse count purposes) and they tend to pick up a little bit of stray AC which can be coupled in via the 24 VN wire. This can on occasion cause some sensor drift.

If the 3-wire method creates problems, I have a nice little AX Filter Program Object that Im happy to share.

[Hensman]

I have been using this setup in the last couple mechanical rooms that I have done. In the Tridium Literature it states that the power for Jace and I/O need to be separated. I use a 40VA transformer to power the Jace and size my output transformer to the load. You will (as stated by others) have to tie your load transformer common to the common of our AO’s.

[mechdorn]

Eliminate the power module (you don't need it with an IO-34). Then power the jace and actuators with the same transformer. Or with separate transformers and tie 24vac common to AO common.

I don't think you have a choice, I'm speaking from memory ( wifey says it's shaky). You cannot physically plug in a FX60 to a power module to a NDIO34. At least not in the JCI world, the power module has to go. As far as the terminal strips, I try to keep them to a minimum. A couple of blocks per power supply is usually all we use. We all dread when we have to splice a wire out in the field. Why intentionally splice wires in a panel with terminal blocks?