Code Requirements For Low Voltage Wiring In Conduit With 120V - Electrical - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 12-22-2009, 01:18 PM   #1
Member
 
Join Date: Apr 2009
Posts: 34
Rewards Points: 25
Default

Code requirements for low voltage wiring in conduit with 120V


I would like to install low voltage wiring in a PVC conduit that already has 120 volt hot neutral & ground running thru it. This is for a standby generator outside my house. The existing 120V is for the power. The low voltage (12V) run would be a remote start switch. Location is MA.

My question is this:

What are the code requirements in this situation. Can I run both wires in the same conduit ? Are there special requirements for the type of wire to be used ? Does the low voltage switch inside the house have any special isolation requirements ?

Advertisement

flyboy is offline   Reply With Quote
Old 12-22-2009, 01:49 PM   #2
Member
 
Join Date: Sep 2008
Location: Oregon
Posts: 1,497
Rewards Points: 500
Default

Code requirements for low voltage wiring in conduit with 120V


So far as I know, you can't do that. (National rules are subject to local amendments or not being used at all.)

And you wouldn't want to do that either!

This is a bit complex, but imagine a dog running along a fence and there are horses on the other side of the fence. The horses start running too!

This is the way electricity works when you run one wire next to another. The higher voltage wire gets electricity moving in the lower voltage wire.

And it is possible that the low voltage wire would have enough electricity in it from the other wire, that this would prevent the low voltage circuit from working properly.

Distance is a killer with this type of wiring! All sorts of weird things happen when you have long distances of low voltage wiring running next to higher voltage wires - like in a large warehouse which is several city blocks long.

This is called "inductance"...
(Following is a terribly complex explanation of this that only Einstein would understand! )
http://en.wikipedia.org/wiki/Inductance

Best to run the low voltage wire in a separate conduit and add a bit of air or dirt space between conduits.

Same with running wires inside a building. Best if there is maybe a foot of space between low voltage wires and higher voltage wires (as much as possible).

(And there is a possibility of a short from the higher voltage wire to the low voltage wire - a potential safety problem.)

Back to the "inductance" thing, this is a bigger problem when you increase the voltage. Farmers working with metal pipes and fences under high voltage towers have all sorts of problems with this. They could be zapped by just picking up a length of metal irrigation pipe off the ground...
http://www.bpa.gov/corporate/pubs/Pu...AndWorking.pdf

Advertisement

Billy_Bob is offline   Reply With Quote
Old 12-22-2009, 04:09 PM   #3
Electrical Contractor
 
jbfan's Avatar
 
Join Date: Jun 2004
Location: Newnan GA
Posts: 5,955
Rewards Points: 2,306
Default

Code requirements for low voltage wiring in conduit with 120V


As long as the insulation on the low voltage wire is rated the same as the high voltage wire, you are ok.
Not he best practice, but allowed.
__________________
Yes I am a Pirate, 200 years too late. "Jimmy Buffett"
jbfan is offline   Reply With Quote
Old 12-22-2009, 05:31 PM   #4
Member
 
Join Date: Oct 2009
Posts: 853
Rewards Points: 626
Default

Code requirements for low voltage wiring in conduit with 120V


Quote:
Originally Posted by jbfan View Post
As long as the insulation on the low voltage wire is rated the same as the high voltage wire, you are ok.
That's the key there. And how much LV wire is rated to 600v?
Anti-wingnut is offline   Reply With Quote
Old 12-22-2009, 05:50 PM   #5
Member
 
joed's Avatar
 
Join Date: Mar 2005
Location: Welland, Ontario
Posts: 8,344
Rewards Points: 3,482
Blog Entries: 4
Default

Code requirements for low voltage wiring in conduit with 120V


Quote:
Originally Posted by Anti-wingnut View Post
That's the key there. And how much LV wire is rated to 600v?
You don't use low voltage wire in this case. You use the same wire you are using for the 120 volts, #14 thwn. Only it has 12 volts on it instead of 120 volts.
__________________
Do not PM with questions that can be asked in a forum. I will not respond.
joed is offline   Reply With Quote
Old 12-23-2009, 12:36 AM   #6
Idiot Emeritus
 
Join Date: Mar 2008
Location: Fernley, Nevada (near Reno)
Posts: 1,632
Rewards Points: 1,058
Default

Code requirements for low voltage wiring in conduit with 120V


Most generator auto-start circuits have circuitry built in to them that'll cancel out the 60 HZ capacitive coupling from the power conductors.

It's completely code compliant to run different voltages in the same conduit provided all conductors are rated for the highest voltage present.

As stated above, run a couple of #14 THWNs, and you'll be fine.

Rob
micromind is offline   Reply With Quote
Old 12-23-2009, 10:39 AM   #7
Member
 
Join Date: Apr 2009
Posts: 34
Rewards Points: 25
Default

Code requirements for low voltage wiring in conduit with 120V


Thanks for the info.

I am fairly confident that inductive/capacitive coupling will not be an issue in my situation.

The high voltage insulation makes sense. jbfan indicates that this is accepted by code but not the best practice. Is there a specific situation or scenario you are worried about ?

Is there a requirement regarding insulation color for the LV lines ?
flyboy is offline   Reply With Quote
Old 12-23-2009, 09:08 PM   #8
Idiot Emeritus
 
Join Date: Mar 2008
Location: Fernley, Nevada (near Reno)
Posts: 1,632
Rewards Points: 1,058
Default

Code requirements for low voltage wiring in conduit with 120V


The reasons we generally don't put high and low voltage wires in the same conduit are;

1) Possible capacitive coupling. Also known as inductance. This can superimpose the high voltage signal onto the low voltage circuit. Very rarely a problem these days, moreso in years past.

2) If the high voltage wire is big (like over 2/0) is can destroy the smaller low voltage wires when they're being pulled in.

The only color restriction is don't use green, white, or gray. Those are grounds and neutrals. You can use the same color if you wish, it's only a start circuit. Switch closes, generator starts. Switch opens, generator stops.

Rob
micromind is offline   Reply With Quote
Old 12-24-2009, 06:02 AM   #9
Chicago, IL
 
Michael Thomas's Avatar
 
Join Date: Jan 2008
Location: Chicago, IL
Posts: 1,037
Rewards Points: 500
Default

Code requirements for low voltage wiring in conduit with 120V


As I understand it, the control circuit for a typical residential air conditioner's condenser unit is a power-limited class 2 circuit, and per 725.136 cannot run in the same raceway or conduit as class 1 power and lighting circuits.
__________________
Home Inspections, Infrared (Thermal Imaging) Leak Identification and Inspection Services, Roof, Attic, Building, Basement and Foundation Moisture Intrusion and Water Leak Inspections, Troubled Building Consultations - Serving Chicago and Suburbs http://paragoninspects.com/
Michael Thomas is offline   Reply With Quote
Old 12-24-2009, 07:48 PM   #10
as seen on tv
 
Join Date: Mar 2009
Location: pa
Posts: 205
Rewards Points: 150
Default

Code requirements for low voltage wiring in conduit with 120V


You should not run low/line voltages in the same pipe. You may get away with it if your low voltage wire is shielded

Advertisement

qbert is offline   Reply With Quote
Reply

Tags
code , counduit , low voltage


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Natural Gas Grill Code Requirements adpanko Plumbing 13 05-16-2012 02:03 PM
Kitchen Wiring Requirements SS396 Electrical 24 02-07-2011 11:00 AM
What are the 'code' space requirements for a toilet in a three walled area?? 4just1don General DIY Discussions 6 05-21-2009 10:40 PM
Confused with code requirements about structural sheathing. Clutchcargo Building & Construction 19 11-20-2008 10:17 AM
What was the code requirements on amperage? rgsgww Electrical 3 09-05-2008 12:33 PM




Top of Page | View New Posts