Author Topic: Running Conduit Through Roof  (Read 9874 times)
nogden
Member
*****
Offline

Gender: Male
View Posts
View Gallery

Nelson Ogden


nelson.ogden w8nwo
Running Conduit Through Roof « on: July 29, 2011, 08:37:16 PM » Author: nogden
So here is a general electrical question: What is the best way to run conduit through a tar and gravel roof? I need to install an electrical outlet and a communications outlet on a roof to connect some WiFi equipment. I have a good surface to mount the electrical boxes to, I just need to find the best way to run the conduit to the boxes through the roof. Because I need power and communications, I will have to install two conduits and two boxes. Now the good news -- the roof is being patched in the near future, so I can coordinate this job with the roofing contractor. Should I just give them the conduit and let them install it? Then I can come along behind them to install the wiring and weatherproof boxes.

I plan to use 3/4" conduit for extra capacity. I had also planned to use rigid steel conduit because that is what I'm most familiar with. However, would it be better to use PVC pipe?

How should I address the conduit on the underside of the roof (inside the building)? At some point, I need to transition to flexible conduit to reach the nearest junction box. I thought about using an LB on the underside of the roof as the transition point. Thoughts?
Logged
SeanB~1
Member
***
Offline

Gender: Male
View Posts
View Gallery


Re: Running Conduit Through Roof « Reply #1 on: July 30, 2011, 01:53:42 AM » Author: SeanB~1
Rigid steel will need to be bonded to a lightning earth with a heavy cable. PVC will work, just paint it to match the roof. Use a lot of PVC weld on the joints outside, then 2 coats of PVA roof paint. Put a lightning arrestor on the wiring inside, it will save you from blowing up the electrics when there is a close strike. Take the wiring bundle inside and wind it in a coil of around 10 turns after the lightning protector, this will make a choke to reduce the spike that will be left after the arrestor. You should have plenty of room in the roof to do a 1 foot diameter coil, tied up and placed on a rafter.
Logged
Ash
Member
*****
Offline

View Posts
View Gallery


Re: Running Conduit Through Roof « Reply #2 on: July 30, 2011, 02:36:34 AM » Author: Ash
If its gonna be exposed, count in that most plastics deteriorate in sunlight. Use metallic or _black_ color UV stabilized plastic conduit (on my experience black plastic is usually more stable than other colors)

Otherwise, use any conduit

A for lighning protection : Is is meant for temporary use with a computer etc, or for permanent use with a WIFI access point etc ? If you dont mind, just disconnect both cables in the inside of the building (using plugs and sockets, or 2P switch on the electrical with good space between the contacts when off, like a 400V switch) when lightning is expected

Metallic conduit and boxes, well earthed, give further lightning protection. You can use flat rectangular conduit with detachable cover (either metallic or plastic), which enbles you to put the cables in directly and not pull them in from the end. You will need only one conduit like that (esp. if using expensive metallic), sine if you need you can insert few thin plastic conduits into it, for the electrical and the ethernet

And i dont know about your codes there, but you can use a sturdy N2XY cable for the electric with thick isolation, that is quite tough (and atleast here it is allowed to install without conduit at all). In your case if it is allowed, i guess it means that you can throw in the electric and ethernet cables together without separate conduits for each

I dont know what round metallic conduit you have there, but i suspect that it may have sharp edges etc, in this case it may make the fishtape stuck when pulling in the cable, or damage the cable isolation

Also if the conduit is damaged or sharply bent, you may be unable to pull wires thru it. Better lay it yourself or keep an eye on the workers, and in case ot plastic pipes install an extra one, to avoid trouble in case one of the pipes becomes unusable from damage or defect

Bend the ends of the conduit down, to prevent rain water getting in
Logged
Medved
Member
*****
Offline

Gender: Male
View Posts
View Gallery

Re: Running Conduit Through Roof « Reply #3 on: July 30, 2011, 03:45:30 AM » Author: Medved
I would defintelly use metallic conduit and properly ground it to the lightning protection system. The main reason is the lightning protection: If the lightning strike to the cable (it may be tiny secondary discgharge), the potential on it would be in 100's kV, so no switch is able to hold this, so only disconnecting would not work - the arc would jump to something around and cause the damage anyway.
If the conduit is metal, it would be the first target and by carrying the current out (or creating the nearest point for the discharge to jump on from the cable) it will protect you from the fire (however it does not have to be really protect the connected equipment, but his is of way lower loss)
Logged

No more selfballasted c***

nogden
Member
*****
Offline

Gender: Male
View Posts
View Gallery

Nelson Ogden


nelson.ogden w8nwo
Re: Running Conduit Through Roof « Reply #4 on: August 02, 2011, 10:15:12 AM » Author: nogden
Thanks for the replies, everyone. Also thanks for the reminder about lightning protection. For the Ethernet cable, I do have a CAT 6 rated protector that I believe is also UL rated for use as a primary entrance protector.

By the way, the power is for an electrical outlet (for holiday lights) and for possibly feeding a floodlight at some point. The WiFI equipment is powered over the Ethernet cable. Yes, the CAT 6 protector will pass power -- I checked!

When I can get up on the roof, I will take a picture so you can all see what I am trying to do.

-Nelson
Logged
SeanB~1
Member
***
Offline

Gender: Male
View Posts
View Gallery


Re: Running Conduit Through Roof « Reply #5 on: August 02, 2011, 11:56:26 AM » Author: SeanB~1
Don't forget the coil of cable, and add a few ferrite toroids over the cable as well. All will help attenuate the let through energy. May not save the protector and the POE hub it is plugged in to, but will reduce the risk of damage to the computers attached to it. Paint the conduit as well, at least 2 coats of a good quality enamel, and preferably with my favourite outdoor metal paint - Hammerite.
Logged
Lightingguy1994
Administrator
Member
*****
Offline

View Posts
View Gallery


Re: Running Conduit Through Roof « Reply #6 on: March 18, 2020, 06:43:40 PM » Author: Lightingguy1994
I like this idea, does anyone have codes locally that say you cannot do this for all the wires in your house? Ive seen what lightning can do to home electrical and would like to someday have all wires inside metal conduit
Logged

Administrator #5

Print 
© 2005-2024 Lighting-Gallery.net | SMF 2.0.19 | SMF © 2021, Simple Machines | Terms and Policies