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alternety
10-23-2007, 09:20 PM
I believe I read somewhere that low voltage control circuits could be in the same conduit with a 240V circuit as long as the low voltage wire had the same insulation values as the 240.

Is that true?

leejosepho
10-24-2007, 03:29 AM
The code guys will let you know for sure, but I have never heard of that being okay. Someone coming along later might not readily distinguish one wire from another and either get hurt or cause damage.

Speedy Petey
10-24-2007, 03:59 AM
I believe I read somewhere that low voltage control circuits could be in the same conduit with a 240V circuit as long as the low voltage wire had the same insulation values as the 240.

Is that true?
Yes it is, with few exceptions. This is common in commercial applications where everything is conduit.

jwelectric
10-24-2007, 07:04 AM
300.3(C) Conductors of Different Systems.
(1) 600 Volts, Nominal, or Less. Conductors of circuits rated 600 volts, nominal, or less, ac circuits, and dc circuits shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.

Exception: For solar photovoltaic systems in accordance with 690.4(B).

FPN: See 725.55(A) for Class 2 and Class 3 circuit conductors.


Someone coming along later might not readily distinguish one wire from another and either get hurt or cause damage.
This is a prime example why untrained people should stay out of electrical components.

alternety
10-24-2007, 09:25 AM
Thanks. I have a generator to install and conduit was set up assuming that the transfer switch was outside. That makes no sense to me (other than eliminating a disconnect) because there are things you want to see on automated systems and if power is out for a long time you may want to cycle the generator to conserve fuel supplies. Going out in the storm to do that seems like a poor idea.

The conduit size does not seem generous either for a 100 A circuit. I have to look at that. I need to look around for a fill and derating table. I believe I have them here somewhere.

jwelectric
10-24-2007, 09:37 AM
Thanks. I have a generator to install and conduit was set up assuming that the transfer switch was outside. is the transfer switch auto or manual?



That makes no sense to me (other than eliminating a disconnect) Unless the transfer is rated as service equipment then a disconnect can not be eliminated.


because there are things you want to see on automated systems and if power is out for a long time you may want to cycle the generator to conserve fuel supplies. Going out in the storm to do that seems like a poor idea. If the transfer is manual then going outside is no longer an option.


The conduit size does not seem generous either for a 100 A circuit. I have to look at that. I need to look around for a fill and derating table. I believe I have them here somewhere. Tables in the back of the code book. I do hope you have one if you are doing electrical installations. How else are you going to know what the codes for the installation are if you don’t have one?

alternety
10-24-2007, 09:52 AM
It is automatic. I believe it is designed to be a disconnect in sight of the generator but it does not matter. That is not what I am doing.

jwelectric
10-24-2007, 10:04 AM
It is automatic. I believe it is designed to be a disconnect in sight of the generator but it does not matter. That is not what I am doing.


Then help me a little and let me know what you are doing.

Care sohould also be taken when installing an automatic transfer switch unless the genset is sized for the whole house.

alternety
10-24-2007, 10:50 AM
The house is wired with a 100 A sub-panel that controls all circuits that need power during an outage. The transfer switch will control this panel. All loads have been used to determine and switch generator capacity.

ked
11-05-2007, 10:33 AM
In general, wiring over 600 volts shall not be in the same boxes, conduits as wiring under 600 volts (down to 60 volts.)
Communications wiring, (under 60 volts) shall also be separate. NEC 800-52
high voltage = over 600 v.
Low voltage = 60 to 600 v.
communications wiring = below 60 v.
and some comm wiring shall not be mixed with other comm wiring.

alternety
11-05-2007, 11:22 AM
Thnaks to all. Ked, I now have two conflicting answers to my original question. Speedy Petey seemed to be sure it is OK. He noted that it is common practice in industrial installations.

NEC words can be somewhat hard to interpret.

Can one of you guys comment on how I pick.

Alectrician
11-05-2007, 12:39 PM
I believe I read somewhere that low voltage control circuits could be in the same conduit with a 240V circuit as long as the low voltage wire had the same insulation values as the 240.

Is that true?

Yes. You will notice that your "240" volt wire will actually be rated at 600 volts. They don't care that the LV is in there, they just want the same protection that is offered by the isulation.

alternety
11-05-2007, 01:17 PM
Thanks Alectrician. That is how I understood it. The NEC text cited above can be read two ways. It refers to wiring; not necessairly what is actually on the wire. Hence insulation ratings. Interpreting it as the voltage imposed on the wire, if you installed a bunch of 600V rated wire and needed at a later date to put a 24V control signal on it, you would violate the code. It would appear to cause no more potential for danger than having a 240 V line in the same conduit as a 120V one. But then things are not always obvious to the casual observer.

I do understand that the wire will be rated at 600V and wet environment.

Alectrician
11-05-2007, 02:18 PM
if you installed a bunch of 600V rated wire and needed at a later date to put a 24V control signal on it, you would violate the code


How?

If the voltage is rated to that of the highest voltage, you are good.

alternety
11-05-2007, 04:00 PM
I agree. I was just trying to make the point that such (voltage on wire, not insulation rating) interpretation would not seem reasonable.

Speedy Petey
11-05-2007, 05:37 PM
Communications wiring, (under 60 volts) shall also be separate. NEC 800-52
I assume you mean 800.53 since there is no 800.52 .

Also, this does NOT apply. 800.53 in in section "II. Wires and Cables Outside and Entering Buildings" of Art. 800.

You are looking for 800.133(A)(1)(c), but this applies to communication conductors. I believe the OP is asking about control circuits.

ked
11-06-2007, 05:50 AM
The reason to keep comm circuits and control circuits and other circuits below 60 v. away from high voltage is that the high voltage wires create EMF that interferes with the comm wires. The insulation on the comm wires could be 25,000 v. insulation--same problem. Also there is the possibility of short circuit or error that will destroy sensitive equipment. Do not put a 24 v. system in a conduit with a 120v or 480 v. system.

Mikey
11-06-2007, 05:55 AM
I have a 200A whole-house transfer switch (Generac RTS) inside the garage. Installation instructions for the switch specifically prohibit running the control system interconnection leads in the same conduit as the AC power wires. Generac tech support did say, however, that for lower-power installations (my generator is only 16KW) it would be OK. It's mainly an EMF interference issue, as ked pointed out.

Alectrician
11-06-2007, 08:55 AM
Do not put a 24 v. system in a conduit with a 120v or 480 v. system.


It's done every day with motor control wiring.

NuetronBill
11-07-2007, 07:01 AM
We do not put a circuit 50 volts or less in the same conduit with single phase 120 volts to ground (240 volts phase to phase).Also we do not mix 120/240 with 277/480 in the same conduit.

ked
11-09-2007, 08:04 AM
My advice is still: do not mix the voltage groups I mentioned above in the same conduit. I also think it is good practice to not mix 240 with 480 in the same conduit, even though it is Code legal. Our job is to create safe, efficient, Code legal installations. You can spend time trying to interpret the Code to let you do what you want, but can you convince an inspector to pass your job?

jwelectric
11-09-2007, 08:53 AM
My advice is still: do not mix the voltage groups I mentioned above in the same conduit. I also think it is good practice to not mix 240 with 480 in the same conduit, even though it is Code legal. Our job is to create safe, efficient, Code legal installations. You can spend time trying to interpret the Code to let you do what you want, but can you convince an inspector to pass your job?

I am confused about this post.
even though it is Code legal…… but can you convince an inspector to pass your job
If it is code legal would not the inspector have to accept?

Speedy Petey
11-09-2007, 03:39 PM
You can spend time trying to interpret the Code to let you do what you want, but can you convince an inspector to pass your job?Yeah. I don't get your point either. :confused:
Inspectors do NOT write or make up the code. They ENFORCE it. That means no making things up as they go depending on their own moods and opinions.
They may not agree with a certain code but they have NO grounds to deny a "to-code" installation.



I spend LOTS of time interpreting the code to let me do what is CODE LEGAL and SAFE. Nothing else.

criminallawyer
04-15-2009, 05:12 AM
Is there any safe and effective way to run RG-6/RG-59 cable and romex wire (power cable) through the same piece of conduit. Is there some kind of device I can purchase to restore any disturbed signal? Also, what about CAT-5 and romex wire in the same piece of conduit? Finally, if I do have to run either of these in separate pieces of conduit, would it be okay to put them in the same trench?

Speedy Petey
04-15-2009, 06:43 AM
NO, you cannot run them in the same conduit. A sleeve for protection is less clear but still not advised.

If you are talking about an underground conduit you CANNOT run romex anyway.

alternety
04-15-2009, 10:46 AM
A couple of additional points. You can get direct burial coax. It would be safer for the cable if you put it in something. If you just bury it, make sure you bed and fill around it with something that is not full of stones and sharp pieces.

Don't use RG 59 for anything. RG 6 is much better for signal loss properties. If you are going to run phone, put it in with the coax and use cat 5. If you are going to run Ethernet, add another cat 5. You can also get direct burial phone wire.

Keep the coax as far away from the power as is convenient. A foot or two would help. The coax does not have to be as deep as code requires for power. But you don't want to dig it up by accident either.

As pointed out above, you must use individual power wires in conduit.

leejosepho
04-15-2009, 03:12 PM
What about the wiring in a piece of machinery?

This turning beam will ultimately have a 480v 3-phase motor fed by a cord reel passing power on down to the hook, and we will likely use a transformer to get a little 110 for the hydraulic controls that are part of the balancing system that is pressurized by a 12-volt hydraulic pump. All considered, is it acceptable to have 12-volt DC and 110-volt AC wires running together in the pendant cord, or do we need to use contactors in a box on the beam and have a single control voltage? For fabrication and testing purposes, I presently send power up through the pendant cord.

Speedy Petey
04-15-2009, 05:07 PM
Wow. A lot of different tangents in this old thread.

It's the voltage rating of the conductors that matters, not the voltage running through them. If all the conductors in the cable are rated for at least the highest voltage present then it is fine.

leejosepho
04-15-2009, 06:11 PM
A few weeks ago, I was surprised to learn a 12v DC ground and a 120v AC ground together on the beam would not explode the hydraulic pump's supply battery!

An electrical engineer is laying out a control system to propose, and the ultimate decision about that will be made in relation to overall safety. Personally, I do not like the idea of 110 volts in the control pendant, and having two voltages there together could lead to confusion and trouble during future maintenance such as when replacing a bad switch. But, maybe all we really need to add to what we already have is the contactor for the 3-phase motor.

Speedy Petey
04-15-2009, 06:40 PM
Personally, I do not like the idea of 110 volts in the control pendant, and having two voltages there together could lead to confusion and trouble during future maintenance such as when replacing a bad switch. This is why only qualified experienced people should be working on stuff like this.