# 30 h.p.



## n5i5ken (Jun 5, 2011)

I have a 30 H.P. 575 volt motor, 484 feet away from the main. On start up, the conduit "rattles" I suspect conductors are too small for the distance. No load amps(with drive belts off is 23 amps) with drive belts on motor current is 31 or 32amps. Motor is fed with #8s. figuring out cm required (size of conductor) I come up with at least # 4 or #3. Am I correct??


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## McClary’s Electrical (Feb 21, 2009)

Even the proper size conductor might not stop that. That's pretty common


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## JRaef (Mar 23, 2009)

n5i5ken said:


> I have a 30 H.P. 575 volt motor, 484 feet away from the main. On start up, the conduit "rattles" I suspect conductors are too small for the distance. No load amps(with drive belts off is 23 amps) with drive belts on motor current is 31 or 32amps. Motor is fed with #8s. figuring out cm required (size of conductor) I come up with at least # 4 or #3. Am I correct??


First off:
Conductors must be sized at 125% of the greater of either 1) the motor nameplate FLA or 2) HP ratings and the FLA tables in the code (in your case the CEC table 44, which is very similar to the NEC). You cannot use measured running current. So 30HP @ 575V = 32A in the table, #8's would be correct without adjustment for Voltage Drop over distance. 484ft is a long distance but although I'm too lazy to do your work for you, I don't agree that #8 is likely too small. A quick on-line calculator came up with a 3.7% VD, that's not unacceptable.

But that's not likely why you hear the rattling sound. That is the result of magnetic forces on the separate conductors repelling each other inside of the conduit because of the high starting current. The solution would have been to "triplex" the conductors, i.e. twist them together before pulling them. Most likely they were installed by someone who should not have been doing that task and didn't know the right way to do it (or didn't care). 

Your choices are going to be to pull out the conductors, test them, triplex them and re-pull them and re-test them, hoping all the while you don't nick the insulation (good luck with that), or maybe put in a soft starter.


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## wendon (Sep 27, 2010)

I've heard the same thing before. Just curious, does it make any difference if the conduit is Pvc or Metal?


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## triden (Jun 13, 2012)

The conduit won't make a difference as it is a force between the conductors themselves as they have the AC current flowing through them.


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## Bbsound (Dec 16, 2011)

very common on startup currents


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## Wirenuting (Sep 12, 2010)

I put a tight offset in those types of runs 1/2 down the longest leg. Then pull the conductors tight in and out of it. 

Works well most of the time.


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## Big John (May 23, 2010)

On shorter runs I've twisted the conductors to solve this after-the-fact. One turn every couple feet seems to do the trick, just remember it pulls tougher.

-John


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## BBQ (Nov 16, 2010)

We used to service a 15 story building and all eight elevator feeders ran up from the basement to the roof through the electrical rooms on each floor. 

Every time an elevator would move the conduits would rattle, as far as I know they had been doing it for 30 years without an issue


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## JRaef (Mar 23, 2009)

BBQ said:


> We used to service a 15 story building and all eight elevator feeders ran up from the basement to the roof through the electrical rooms on each floor.
> 
> Every time an elevator would move the conduits would rattle, as far as I know they had been doing it for 30 years without an issue


Yeah, it's pretty much just annoying as all get out. But after a while people stop hearing things like that after they get used to it.

Buy them some ear plugs?


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## don_resqcapt19 (Jul 18, 2010)

JRaef said:


> ...
> The solution would have been to "triplex" the conductors, i.e. twist them together before pulling them. Most likely they were installed by someone who should not have been doing that task and didn't know the right way to do it (or didn't care).
> ...


 I have never seen or heard of that being done in the field. How would one triplex larger conductors in the field?


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## John Valdes (May 17, 2007)

don_resqcapt19 said:


> I have never seen or heard of that being done in the field. How would one triplex larger conductors in the field?


Same here. 33 years and not once did I or anyone else ever twist wires before pulling them.


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## JRaef (Mar 23, 2009)

don_resqcapt19 said:


> I have never seen or heard of that being done in the field. How would one triplex larger conductors in the field?


What do you consider large? If the conduit is relatively full or has short straight runs, rattling isn't always a problem. If you have a large conduit with low fill and long straight runs, it's almost guaranteed. I would pull all the conductors off of the reel at the length I need, twist them, then pull them. But mostly if I was going out to do a lot of motor hookups, I would order the wire triplexed from my supplier.

What can I say about others having never heard of it? I have and everyone I know does it on motor leads, which is where I learned it. Mind you since my apprenticeship 30+ years ago all of my work has been industrial and mostly motors and controls, so my viewpoint is undoubtedly skewed.


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## nolabama (Oct 3, 2007)

I never saw triplexed cable till I worked here. It's not done on the motors tho.


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## Big John (May 23, 2010)

Jraef, if it's done like that normally, it's a regional thing. I said I've done it a couple times as a quick-fix, but I don't think I've ever seen it otherwise.

-John


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## don_resqcapt19 (Jul 18, 2010)

JRaef said:


> What do you consider large? If the conduit is relatively full or has short straight runs, rattling isn't always a problem. If you have a large conduit with low fill and long straight runs, it's almost guaranteed. I would pull all the conductors off of the reel at the length I need, twist them, then pull them. But mostly if I was going out to do a lot of motor hookups, I would order the wire triplexed from my supplier.
> 
> What can I say about others having never heard of it? I have and everyone I know does it on motor leads, which is where I learned it. Mind you since my apprenticeship 30+ years ago all of my work has been industrial and mostly motors and controls, so my viewpoint is undoubtedly skewed.


I just can't see making twists in the conductors before I try to pull them. I could see using triplexed conductors it was specified, but have never seen that so specified. It certainly not a common practice in northern Illinois. 

I also work mostly industrial and have never used triplexed conductors. I don't see the rattling as even being an issue in most industrial applications. I can see it being an issue in commercial.


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## nolabama (Oct 3, 2007)

I want a remove post option


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## Guntrician (Jun 20, 2012)

Interesting. I've never heard of, seen or used this triplexed technique either. I could see how it would cure the issue though. Where I work there isn't a place quiet enough to notice conductor rattling anyway. lol!


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