SPIRAL OR HELIX CONDUIT BENDING

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DonL1410

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Oregon
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Electrical Contractor
Is there anyone who can shed light on a formula or method for bending conuit to match a spiral stairs? (I saw an example in a old lighthouse. It was done in rigid conduit and used for light fixtures for lighting the stairs.)
 
I think it would be no different than bending a multi-shot continuous radius bend, but with additional attention on how much to turn the pipe between each bend.
 
Thanks guys. I was hoping there was some old time manual that might show some detail on the subject. Segment bending on the horizontal is documented pretty well, but adding the pitch confuses me. As expensive as condiut is these days, a guy can't make a lot of mistakes. The job was presented to by an acquaintance, so can tell him I can or can't do it...but I would be cool.
 
Don't forget pull boxes or condulet "C"s every 360 deg.

DonL1410 said:
(I saw an example in an old lighthouse. It was done in rigid conduit and used for light fixtures for lighting the stairs.)
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Roller bender undoubtedly. I suppose you could use a hickey if it was short, you had a lot of time and weighed 250 pounds so you could wrestle it into shape. No, no formula.

-Hal
 
hbiss said:
Don't forget pull boxes or condulet "C"s every 360 deg.
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FWIW, 360 degrees of bend along the helix will end up at more than 360 degrees as seen looking down the helix's central axis. If you think of a tightly coiled helix (i.e. basically a circle), pulling the coils apart while keeping the curve confined to the surface of a cylinder has the effect of straightening the pipe, so there is somewhat less bend.

Cheers, Wayne
 
wwhitney said:
FWIW, 360 degrees of bend along the helix will end up at more than 360 degrees as seen looking down the helix's central axis. If you think of a tightly coiled helix (i.e. basically a circle), pulling the coils apart while keeping the curve confined to the surface of a cylinder has the effect of straightening the pipe, so there is somewhat less bend.

Cheers, Wayne
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If an inspector calls you out on that, he better know how to figure it out as well is all I am going to say. ;)
 
kwired said:
If an inspector calls you out on that, he better know how to figure it out as well is all I am going to say. ;)
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Maybe I wasn't clear--the effect is that mathematically you can space the pull points farther apart on the helix that one would think at first glance. So if you choose to take advantage of that, the inspector might reasonably expect you to explain why that is.

I haven't actually figured out the exact magnitude of the effect yet (it will depend on the ratio of helix radius R to the spread between coils), so my comment was primarily academic.

Cheers, Wayne
 
wwhitney said:
Maybe I wasn't clear--the effect is that mathematically you can space the pull points farther apart on the helix that one would think at first glance. So if you choose to take advantage of that, the inspector might reasonably expect you to explain why that is.

I haven't actually figured out the exact magnitude of the effect yet (it will depend on the ratio of helix radius R to the spread between coils), so my comment was primarily academic.

Cheers, Wayne
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I did misunderstand and thought one might need the pull points more often than you might normally expect. Maybe learned something today even if I will never use it.:cool:
 
wwhitney said:
Maybe I wasn't clear--the effect is that mathematically you can space the pull points farther apart on the helix that one would think at first glance.
Click to expand...
I see what you're saying. It would seem logical that, as viewed from above, the C-condulets would be stacked in a straight column.

But, if you sere to flatten the coil (without allowing the diameter to increase), the C-condulets would advance around the circle.
 
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