Stress relief at conduit exit?

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  #1  
Old 06-15-01, 05:04 PM
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Question

I have a 2/3wGnd SER coming out of the main panel via
a conduit to the basement. There the cable runs a few
feet horizontally then down into a sub panel. I have
a stress relief clamp at the subpanel, but do I need
any stress relief at either side of the conduit (inside
the main panel or where the conduit ends in the basement
stud wall)?

The SER cable from the meter to the main panel (200W)
does not have stress relief at the main panel.

No, I'm not "stressed out" over this question :-)
 
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  #2  
Old 06-16-01, 07:53 AM
Wgoodrich
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SER cable is with an outer sheath that does not require conduit protection. The sheath of the cable provides the protection in place of a conduit.

If you install the SER in a conduit then you must size the conduit as if that cable is a round single cable. According to Appenidix C of the NEC.

A coduit does not require strain relief. There is a section where if you run long sections of PVC you must install an expansion joint. There is also a section where if you are hanging a conduit verticley for about 50' and that is not exact, too lazy to look that distance up, then the conductors are required to be with strain relief at the top or bend at the top of that verticle run.

As far as I know no strain relief is required as you described you post.

If you install just the SER cable then that cable must be supported where entering the boxes by a romex connector approved for the purpose.

If you install that SER cable inside a conduit, then you must install that conduit with support where entering those boxes that are approved for the purpose. This form of support are called connectors approved for the type of conduit you are using. EMT would require EMT connectors. Sealtite would require Sealtite connnectors. Rigid conduit would require lock nuts and bushings. An so on.

Wg
 
  #3  
Old 06-16-01, 08:17 AM
s1nuber
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Just to cover some other bases as your meaning of 'strain relief' may not be mine.

Your situation has a main service panel, and a second sub panel that has SER cable run from one to the other. The main panel is on the first floor, and the sub panel is in the basement. From the main panel, you have a two screw connector that holds the SER into the main panel. The SER cable then heads toward the basement where you have a short section of conduit that sleeves the SER cable into the basement. Both ends of the conduit are open (no fitting or connector). The sub panel end of the SER has another two screw connector to hold it into the sub panel.

If the above is correct, then the only code problem that I see is not strain relief (strain relief is used when a cable is intended to move, such as an overhead drop cord), but abrasion of the SER at the conduit ends (or end if only one end is open). The ends of the conduit should have a connector and a plastic bushing installed on them to eliminate this problem. This may be what you called strain relief, and I don't mean to mince words with you, it's just that certain words and phrases have a specific meaning to a sparky.

Enjoy your day!

p.s. - The SER cable should be supported to the structure at intervals of 12" from a box or raceway, and every 4 1/2 feet thereafter (these are maximum distances). This does not have to be done inside of the conduit (it would be impossible anyway).
 
  #4  
Old 06-20-01, 07:27 AM
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I think you actually need a transition fitting (threaded one end, clamp other end) on the conduit to prevent the cable from sliding.
 
  #5  
Old 06-26-01, 11:46 PM
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s1nuber, your description is closest. The SER
runs out of the main panel through a short conduit
with bushings, but no clamps, at both ends. The conduit
is about 2.5 ft. long. The SER then runs over and down
into the sub panel where it is clamped where it
enters the panel. The total length of the SER is 13ft.

The sizing of the conduit worries me. It was only
to facilitate pulling from the main down into the
basement, through an insulated wall. If it must
meet sizing requirements for the SER, I guessing
it's too small (I think it's 2", but would need to
check).

So, currently, the ONLY clamp on the romex casing
of the SER is at the entrance to the sub panel,
where the bare romex passes through the sheet metal.
Perhaps I need another at the main where the cable
enters the conduit?

Thanks!
 
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