The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Sprinklered equipment 26-008
by bigpapa
Yesterday at 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
Earthquake in New Zeeland
by RODALCO
11/27/16 11:25 PM
Calling all Non-US members!! (Non-US only)
by Tjia1981
11/27/16 06:33 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 15
HotLine1 10
Trumpy 8
Texas_Ranger 8
sparkyinak 7
Who's Online
0 registered (), 215 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Page 1 of 2 1 2 >
Topic Options
Rate This Topic
#65123 - 04/25/06 04:26 PM Concentric or Segmented bends
tkb Offline
Member

Registered: 12/04/04
Posts: 94
Loc: Massachusetts
I asked this within the post on conduit pet peeves. http://electrical-contractor.net/ubb/Forum1/HTML/007121.html

Does anyone still do concentric or segmented bends anymore?

I have only done a few when I needed a large radius bend for some underground when I couldn't buy the sweep in time.

This method look very nice on a rack.

I have the tools but not the time.

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#65124 - 04/25/06 04:30 PM Re: Concentric or Segmented bends
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
I am planing on trying it on an upcoming job that will have five parallel 3" EMTs

Bob
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

Top
#65125 - 04/25/06 04:52 PM Re: Concentric or Segmented bends
earlydean Offline
Member

Registered: 12/22/03
Posts: 749
Loc: Griswold, CT, USA
An old timer showed me a trick for doing perfect concentric bends: After making the first bend, mark a wide elastic suspender in 9 equal increments along the bend, then simply stretch it out a little more for each concentric bend, and bend 10 degrees on each mark. Do the math, a 90 degree bend is "3.14 times radius divided by two" in length.
_________________________
Earl

Top
#65126 - 04/25/06 04:55 PM Re: Concentric or Segmented bends
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
That is one cool low tech trick.

_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

Top
#65127 - 04/25/06 05:27 PM Re: Concentric or Segmented bends
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
http://www.porcupinepress.com/_bending/Concentric.htm

That site has a great explaination....

The suspender idea sounds interesting....
_________________________
Mark Heller
"Well - I oughta....." -Jackie Gleason

Top
#65128 - 04/25/06 05:41 PM Re: Concentric or Segmented bends
electure Offline

Member

Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
A suspender.....If that doesn't beat all.
Great idea!!

Top
#65129 - 04/25/06 06:03 PM Re: Concentric or Segmented bends
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
_________________________
Mark Heller
"Well - I oughta....." -Jackie Gleason

Top
#65130 - 04/25/06 06:05 PM Re: Concentric or Segmented bends
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
Would not be caught in these though: http://www.absoluteties.com/elsus.html
_________________________
Mark Heller
"Well - I oughta....." -Jackie Gleason

Top
#65131 - 04/26/06 04:32 AM Re: Concentric or Segmented bends
Bill39 Offline
Member

Registered: 11/28/01
Posts: 77
Loc: Indianapolis, IN, USA
The math is pretty simple. The more bends the smoother the bend, especially on large radius bends. Be sure to use some type of "anti-dog" device. Also, be careful rounding off the #'s. Small things tend to add up.

From Greenlee's conduit book:
1. Decide on # of bends/segments per 90 (90/15 = 6 degrees per bend.

2. Pick centerline radius of inside pipe's 90 (36").

3. Find developed length - radius x 1.57 (36" X 1.57 = 56.52")

4. Find distance between bends by dividing the developed length by # of shots. (56.52" / 15 = 3.77" between bends).

Next step is to find the radius of the second pipe. Suppose all pipes are 2" rigid w/2" spacing btw. pipes.

1. If the second pipe is the same size, add O.D. plus center-to-center spacing, then add that to the first radius (2" rigid = 2.375 + 2" + 36" = 40.375" radius for second pipe).

2. Find developed length - radius x 1.57 (40.375" X 1.57 = 63.39")

3. Find distance between bends by dividing the developed length by # of shots. (63.39" = 4.23" between bends).

4. Repeat steps 1,2, & 3 for every pipe (if the same size and spacing).

To find the radius increase when pipe sizes vary, add the two outside diameters of the pipe, divide answer by 2, then add the space between bends. This gives you the increase in center line radius of the next larger bend.

Top
#65132 - 04/26/06 04:09 PM Re: Concentric or Segmented bends
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
We used the elastic tape with 18 marks to give us 5 degrees per bend. It is very labor intensive work, and there is no reason to use it in most cases, especially where all of conduits are the same size, but it sure does look nice. The original plant specs where I'm at required concentric bends anytime there were four of more conduits on a horizontal rack. Some of the 90s took more than a 10' length on larger racks. The reason that concentrics were required is that lets you maintain the same conduit spacing even where you have multiple conduit sizes in the same rack. Since most of our runs are 2" or less, we now just bend all of the bends on the 2" shoe for horizontal racks. It provides the same benefits but with a much lower cost. Note this is all rigid, I'm not sure what would happen if you tried it with EMT.
Don
_________________________
Don(resqcapt19)

Top
Page 1 of 2 1 2 >



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals