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#85627 - 07/23/03 05:52 AM Transformer Installations and Vibration
Joe Tedesco Offline

Registered: 10/07/00
Posts: 3325
Loc: Boston, Massachusetts USA
Transformers are typically wired with flexible metal conduits and we know that is usually not considered as a problem.

Question: An installer wired the primary of a transformer with a 2 inch EMT, and used a 4 inch EMT out for the secondary supply.

Does the NEC® have any rule that could be cited, or would the specifications, or the instructions require flexible connections?
Joe Tedesco, NEC Consultant

2014 / 2011 NEC & Related Books and Study Guides
#85628 - 07/23/03 06:05 AM Re: Transformer Installations and Vibration
Ron Offline

Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
Job specs only would dictate a flex requirement. No NEC requirement that I know of.

#85629 - 07/23/03 06:40 AM Re: Transformer Installations and Vibration
iwire Offline

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
I only get 9 "hits for vibration in the 2002 NEC, none of which seem to apply.

368.28 (Bussways over 600 volts)

400.7 (Cords)

422.16 (Appliances)

545.13 (Manufactured Buildings)

550.16 (Mobile Homes)

551.30 (RVs)

551.47 (RVs)

552.48 (Park Trailers)

695.12 (Fire Pumps)

I looked in 450 and some raceway articles and could find no requirement to flex in transformers, I have done it with many different methods, pipe, trough, flex, etc.

What I found strange is no requirement to use a flexible method to a motor.
Bob Badger
Construction & Maintenance Electrician

#85630 - 07/23/03 07:24 AM Re: Transformer Installations and Vibration
Joe Tedesco Offline

Registered: 10/07/00
Posts: 3325
Loc: Boston, Massachusetts USA
Thanks for the quick reply, my student Elliot is happy now!

See 430.145 Method of Grounding.
Where required, grounding shall be done in the manner specified in Part V of Article 250.

(A) Grounding Through Terminal Housings. Where the wiring to fixed motors is metal-enclosed cable or in metal raceways, junction boxes to house motor terminals shall be provided, and the armor of the cable or the metal raceways shall be connected to them in the manner specified in Article 250.

FPN: See 430.12(E) for equipment grounding connection means required at motor terminal housings.

(B) Separation of Junction Box from Motor. The junction box required by 430.145(A) shall be permitted to be separated from the motor by not more than 1.8 m (6 ft), provided the leads to the motor are Type AC cable or armored cord or are stranded leads enclosed in liquidtight flexible metal conduit, flexible metal conduit, intermediate metal conduit, rigid metal conduit, or electrical metallic tubing not smaller than metric designator 12 (trade size ), the armor or raceway being connected both to the motor and to the box.
Liquidtight flexible nonmetallic conduit and rigid nonmetallic conduit shall be permitted to enclose the leads to the motor, provided the leads are stranded and the required equipment grounding conductor is connected to both the motor and to the box.

Where stranded leads are used, protected as specified above, each strand within the conductor shall be not larger than 10 AWG and shall comply with other requirements of this Code for conductors to be used in raceways.
Joe Tedesco, NEC Consultant


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