Data cabling question

[ggunn]

Can data cabling share conduit with power conductors if the insulation is rated the the same for both?

 

[GoldDigger]

Can data cabling share conduit with power conductors if the insulation is rated the the same for both?

Depends almost entirely on whether the power supply ultimately feeding the data equipment on either end is power limited or not.
Just having high enough voltage rated insulation is not enough by itself.
There may be some extra latitude if you can argue that the data wiring is control circuitry related to the power source/sink.

See 645.3(D) and linked code sections. (NEC 2011)
From there look at the rules for sharing raceway between power and Class 2 or 3 equipment conductors.

 

[ggunn]

Depends almost entirely on whether the power supply ultimately feeding the data equipment on either end is power limited or not.
Just having high enough voltage rated insulation is not enough by itself.
There may be some extra latitude if you can argue that the data wiring is control circuitry related to the power source/sink.

See 645.3(D) and linked code sections. (NEC 2011)
From there look at the rules for sharing raceway between power and Class 2 or 3 equipment conductors.

Thanks for the reference; I will check it out. The issue in question is whether we have to run separate conduit for Cat 5 (or Cat 6) cable to carry weather station data from a ground mounted array back to the monitoring equipment at the interconnect. The other conductors will be carrying 277Y/480 VAC. I know that the general answer is no, but I am investigating whether there is a workaround.

 

[GoldDigger]

Thanks for the reference; I will check it out. The issue in question is whether we have to run separate conduit for Cat 5 (or Cat 6) cable to carry weather station data from a ground mounted array back to the monitoring equipment at the interconnect. The other conductors will be carrying 277Y/480 VAC. I know that the general answer is no, but I am investigating whether there is a workaround.

Make sure that the directly connected monitoring equipment is limited power and then you will be good. A wall wart supply for a piece of data equipment will be such a limited power supply. If the data stream is actually IP, as in 10 or 100Base-T, then you can probably isolate the wiring from any non-limited-power piece of equipment using a bridge, router, or switch (with DC isolation) in between.

 

[ggunn]

Make sure that the directly connected monitoring equipment is limited power and then you will be good. A wall wart supply for a piece of data equipment will be such a limited power supply. If the data stream is actually IP, as in 10 or 100Base-T, then you can probably isolate the wiring from any non-limited-power piece of equipment using a bridge, router, or switch (with DC isolation) in between.

The data stream will be a mix of analog signal(s) from current monitoring CT's, a temperature sensor and/or irradiance sensor, and possibly modbus over RS485 and power from a 24VDC supply, but not IP (Ethernet).

 

[GoldDigger]

The data stream will be a mix of analog signal(s) from current monitoring CT's, a temperature sensor and/or irradiance sensor, and possibly modbus over RS485 and power from a 24VDC supply, but not IP (Ethernet).

Hope that you can find a 24 volt supply that is listed as limited power then....

 

[ggunn]

Hope that you can find a 24 volt supply that is listed as limited power then....

What does that mean? Any DC power supply is going to have a maximum amount of current it can deliver.

Also, can you demystify Class 1, 2, and 3 wiring for me? The code is (to me, at least) a bit obtuse in its definitions.

To cut to the chase - in the situation I have described, would you share the conduit with data and power or would you run separate conduit? I am inclined to run pipe (I know that works), but my boss is trying to save money.

 

[GoldDigger]

What does that mean? Any DC power supply is going to have a maximum amount of current it can deliver.

Also, can you demystify Class 1, 2, and 3 wiring for me? The code is (to me, at least) a bit obtuse in its definitions.

To cut to the chase - in the situation I have described, would you share the conduit with data and power or would you run separate conduit? I am inclined to run pipe (I know that works), but my boss is trying to save money.

If for no other reason than to allow for later installation of different monitoring equipment, I would hold out for the separate pipe. Better to install it now than wish you had if the needs change or you run into a bad inspector.

Since you have a combination of analog and Modbus, plus maybe some switch and relay circuits, I would be careful to call this remote control and signalling wiring rather than data communication wiring.

Class 1, 2 and 3 wiring applies to low voltage and/or power limited wiring, and the Class required of the wiring method depends on exactly how much power the supply can generate into a fault.
Regardless of its other specifications, a power supply has to be UL listed and durably marked to be treated as Class 2 or Class 3. You will typically see the Class listing information (if applicable) on or near the UL label of the power supply.

I found this a very good summary and explanation
With good enough insulation (suitable for Class 1 use) Class 2 and Class 3 wiring can share raceways with power conductors as if they were Class 1, but Class 1 can only share if functionally related to the device being powered (or arguably the device supplying power in the case of a generator or GTI.)
This restriction is what can trip you up if the inspector disagrees with you on what is "functionally associated". We have one report in another thread of an inspector who did not consider the remote start and monitoring leads of a fixed generator to be "functionally associated" with the generator system. After all, the generator could be used without it, just not very well. It happens.

See 725.48 and 725.136 for completely clear details. :lol:

 

[ggunn]

If for no other reason than to allow for later installation of different monitoring equipment, I would hold out for the separate pipe. Better to install it now than wish you had if the needs change or you run into a bad inspector.

Since you have a combination of analog and Modbus, plus maybe some switch and relay circuits, I would be careful to call this remote control and signalling wiring rather than data communication wiring.

Class 1, 2 and 3 wiring applies to low voltage and/or power limited wiring, and the Class required of the wiring method depends on exactly how much power the supply can generate into a fault.
Regardless of its other specifications, a power supply has to be UL listed and durably marked to be treated as Class 2 or Class 3. You will typically see the Class listing information (if applicable) on or near the UL label of the power supply.

I found this a very good summary and explanation
With good enough insulation (suitable for Class 1 use) Class 2 and Class 3 wiring can share raceways with power conductors as if they were Class 1, but Class 1 can only share if functionally related to the device being powered (or arguably the device supplying power in the case of a generator or GTI.)
This restriction is what can trip you up if the inspector disagrees with you on what is "functionally associated". We have one report in another thread of an inspector who did not consider the remote start and monitoring leads of a fixed generator to be "functionally associated" with the generator system. After all, the generator could be used without it, just not very well. It happens.

See 725.48 and 725.136 for completely clear details. :lol:

Never mind. He was talking about 24VDC, not 480VAC.