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Old 09-13-2011, 11:13 AM   #1
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Maximum length of Liquidtite NM conduit to rooftop AC


What is the maximum allowable length of Liquidtite NM conduit to rooftop AC. It's currently connected, but I don't like the routing because it requires some supports sitting on the roof. I have EMT conduit on a wall near the unit, then will have NM to the unit. It would be about 7' of NM if I just connect the NM to the EMT on the wall. Can you give me a reference to the NEC sections on this?

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Old 09-13-2011, 11:31 AM   #2
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Maximum length of Liquidtite NM conduit to rooftop AC


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Originally Posted by garya505 View Post
What is the maximum allowable length of Liquidtite NM conduit to rooftop AC. It's currently connected, but I don't like the routing because it requires some supports sitting on the roof. I have EMT conduit on a wall near the unit, then will have NM to the unit. It would be about 7' of NM if I just connect the NM to the EMT on the wall. Can you give me a reference to the NEC sections on this?
356.10 Uses Permitted. LFNC shall be permitted to be used
in exposed or concealed locations for the following purposes:
Informational Note: Extreme cold may cause some types of
nonmetallic conduits to become brittle and therefore more susceptible
to damage from physical contact.
(1) Where flexibility is required for installation, operation,
or maintenance.
(2) Where protection of the contained conductors is required
from vapors, liquids, or solids.
(3) For outdoor locations where listed and marked as suitable
for the purpose.
(4) For direct burial where listed and marked for the purpose.
(5) Type LFNC-B shall be permitted to be installed in
lengths longer than 1.8 m (6 ft) where secured in accordance
with 356.30.


356.12 Uses Not Permitted. LFNC shall not be used as
follows:
(1) Where subject to physical damage
(2) Where any combination of ambient and conductor temperatures
is in excess of that for which the LFNC is
approved
(3) In lengths longer than 1.8 m (6 ft), except as permitted
by 356.10(5) or where a longer length is approved as
essential for a required degree of flexibility


356.30 Securing and Supporting. Type LFNC-B shall be
securely fastened and supported in accordance with one of
the following:
(1) Where installed in lengths exceeding 1.8 m (6 ft), the
conduit shall be securely fastened at intervals not exceeding
900 mm (3 ft) and within 300 mm (12 in.) on
each side of every outlet box, junction box, cabinet, or
fitting.

(2) Securing or supporting of the conduit shall not be required
where it is fished, installed in lengths not exceeding
900 mm (3 ft) at terminals where flexibility is
required, or installed in lengths not exceeding 1.8 m
(6 ft) from a luminaire terminal connection for tap conductors
to luminaires permitted in 410.117(C).
(3) Horizontal runs of LFNC supported by openings through
framing members at intervals not exceeding 900 mm
(3 ft) and securely fastened within 300 mm (12 in.) of
termination points shall be permitted.
(4) Securing or supporting of LFNC-B shall not be required
where installed in lengths not exceeding 1.8 m
(6 ft) from the last point where the raceway is securely
fastened for connections within an accessible ceiling to
luminaire(s) or other equipment.

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Old 09-13-2011, 12:05 PM   #3
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Maximum length of Liquidtite NM conduit to rooftop AC


Thanks for the quick reply.

It looks like I could do it, but would have to fasten it every 3' and within 12" of each end. Since the distance from the EMT on the wall to the nearest side of the AC platform is just a hair over 3', and there's no place to fasten it in that span, that might be difficult.

I might be better off just putting a 90 on the EMT and then extending the EMT over to the AC platform. I can fasten the EMT to the platform. Then I would use about 3' of the liquidtite NM conduit up to the AC connection.

Can I use a box to connect the EMT to the liquidtite, and then put a wire connection inside the box? It would save me some $$$ because then I would not have to pull new wire for the entire length, just from the box to the AC unit. What kind of box should I use for that?
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Old 09-13-2011, 12:13 PM   #4
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Maximum length of Liquidtite NM conduit to rooftop AC


Quote:
Originally Posted by garya505 View Post
Thanks for the quick reply.

It looks like I could do it, but would have to fasten it every 3' and within 12" of each end. Since the distance from the EMT on the wall to the nearest side of the AC platform is just a hair over 3', and there's no place to fasten it in that span, that might be difficult.

I might be better off just putting a 90 on the EMT and then extending the EMT over to the AC platform. I can fasten the EMT to the platform. Then I would use about 3' of the liquidtite NM conduit up to the AC connection.

Can I use a box to connect the EMT to the liquidtite, and then put a wire connection inside the box? It would save me some $$$ because then I would not have to pull new wire for the entire length, just from the box to the AC unit. What kind of box should I use for that?
At 7', I would first ask the inspector if he/she would approve it.

(3) In lengths longer than 1.8 m (6 ft), except as permitted
by 356.10(5) or where a longer length is approved as
essential for a required degree of flexibility
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Old 09-13-2011, 12:24 PM   #5
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Maximum length of Liquidtite NM conduit to rooftop AC


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At 7', I would first ask the inspector if he/she would approve it.

(3) In lengths longer than 1.8 m (6 ft), except as permitted
by 356.10(5) or where a longer length is approved as
essential for a required degree of flexibility
I guess if I extend the EMT then I don't have to worry about that. EMT is a pain to bend, and I've done it before.

Now I'm curious if I can add to the length of the wire with a connection in a J box, or do I have to pull new wire for the entire length from the disconnect? Our code only requires the disconnect to be within sight of the unit, and it's about 20' away.
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Old 09-13-2011, 12:47 PM   #6
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Maximum length of Liquidtite NM conduit to rooftop AC


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Originally Posted by garya505 View Post
I guess if I extend the EMT then I don't have to worry about that. EMT is a pain to bend, and I've done it before.

Now I'm curious if I can add to the length of the wire with a connection in a J box, or do I have to pull new wire for the entire length from the disconnect? Our code only requires the disconnect to be within sight of the unit, and it's about 20' away.
J box is legal for extending wires, securing rules for LNMC apply, weather proof box on a roof.
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Old 09-13-2011, 01:18 PM   #7
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Maximum length of Liquidtite NM conduit to rooftop AC


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J box is legal for extending wires, securing rules for LNMC apply, weather proof box on a roof.
Ok, here's what I'm thinking. Wher the existing EMT ends on the wall, I'll connect a 4 11/16 metal J-box and fasten that to the wall. I'll put a 90 bend in a section of EMT that will reach over to the AC platform. I'll connect the bent end of the new EMT to the J box, and fasten the other end to the AC platform. I'll connect the EMT to the AC with a short (maybe 3') section of liquidtite conduit. Then, I'll pull additional wire in the liquidtite and new section of EMT, and connect in the J-box using blue nuts, split bolts, or insul-taps.

Or, I could just pull all new wire from the disconnect and eliminate the J-box. I'd still use the short section of new EMT with a 90 in it.

On the other hand, the J-box would provide me with a good attachment point to the wall. Some of the clamps on the old EMT have already pulled loose and I had to fix them.
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Old 09-13-2011, 01:24 PM   #8
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Maximum length of Liquidtite NM conduit to rooftop AC


I have never heard of a weatherproof 4 11/16 box.
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Old 09-13-2011, 01:40 PM   #9
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Maximum length of Liquidtite NM conduit to rooftop AC


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I have never heard of a weatherproof 4 11/16 box.
Then something else weatherproof?

I'm thinking that adding a section of EMT with a 90 bend in it (or an L-box) might be a better solution. This would go over to the AC platform. I'd just have a short section of liquidtite up to the AC unit. Then pull new wire from the disconnect and I'm done.
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Old 09-13-2011, 01:46 PM   #10
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Maximum length of Liquidtite NM conduit to rooftop AC


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I have never heard of a weatherproof 4 11/16 box.
Like this:
http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

I guess it's 4.75 x 4.75
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Old 09-13-2011, 02:05 PM   #11
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Maximum length of Liquidtite NM conduit to rooftop AC


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Like this:
http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

I guess it's 4.75 x 4.75
Look at the cubic inches, it is really only a 4 x4 for volume.
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Old 09-13-2011, 02:14 PM   #12
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Maximum length of Liquidtite NM conduit to rooftop AC


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Look at the cubic inches, it is really only a 4 x4 for volume.
Is that too small? What would I need for this? I think the wire is two 10-ga for power and one 12-ga for ground.
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Old 09-13-2011, 02:21 PM   #13
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Maximum length of Liquidtite NM conduit to rooftop AC


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Is that too small? What would I need for this? I think the wire is two 10-ga for power and one 12-ga for ground.
http://ecmweb.com/nec/code-basics/el..._calculations/
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Old 09-13-2011, 02:25 PM   #14
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Maximum length of Liquidtite NM conduit to rooftop AC


Any reason you can't use PVC conduit? Much more waterproof. Easier to run.....doesn't rust....unless it's going to see a lot of sunlight....
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Old 09-13-2011, 02:34 PM   #15
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This is the only style of box that I have ever heard called a 4 11/16 box.

http://www.google.com/products/catal...ed=0CFoQ8wIwBg

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