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Topic Title: Connection of a 3 phase induction motor
Topic Summary: Is it bad practice to use a BS5467 cable to connect a 3phase induction motor
Created On: 14 June 2012 06:45 PM
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 14 June 2012 06:45 PM
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Avatar for ewan29                                            .
ewan29

Posts: 8
Joined: 25 July 2008

I am trying to find some information regarding the practice of connecting an induction motor with a XLPE/PVC/SWA BS5467 cable. I was always in the belief that you ran the SWA cable to a local isolator or JB and continued to the motor in a flexible conduit with class 5 flexible cable or a SY cable as the motor vibration can break the connections from a SWA as it is a Class 2 flexible.
Can someone please clarify if this is best practice or a manufacturers guidance or is their a standard or regulation??

Any assistance would be greatly appreciated.

Ewan
 14 June 2012 08:59 PM
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Avatar for neilparsons.
neilparsons

Posts: 31
Joined: 29 October 2002

Over the years I have worked on projects where SWA (PVC & XLPE),SY,CY,YY and flexible conduit have been used for the final connection to a motor. Normally the SY,YY flexible types are used where a motor has been supplied from a local plug/socket arrangement, I have used this method on motors as big as 160kW, SY and YY is also favoured on the continent. It really depends on the application and any standards or requirements the customer may have and the starting method to some degree, but most sites I a have worked do favour flexible conduit for the final connection. Obviously fixed conduit and pyro are generally never used. I have never had any specific problems with vibration causing conductors to break when the terminations/glands have been installed and made off correctly, if the vibration is that bad then maybe a mechanical issue may be the problem, misalignment or knackered bearings. I'm not aware of any specific regulations in the 17th relating to what you can and can't connect to a motor with (sure there will be some that relate indirectly though such as connections to equipment etc. in part 5) but there is plenty of good guidance in motor manufacturers literature (brook crompton, ABB, SEW, WEG) and good old fashioned books.
 14 June 2012 09:18 PM
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Fm

Posts: 744
Joined: 24 August 2011

Put a helix in the swa and no problem
 15 June 2012 11:52 AM
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Jaymack

Posts: 4755
Joined: 07 April 2004

Originally posted by: neilparsons
but most sites I a have worked do favour flexible conduit for the final connection.

Where a plug/socket is present, the socket should obviously be interlocked, such that power is interrupted before withdrawing the plug. Alternatively where not present, a flexible cable or conduit is not necessary for connection, even where a belt drive requires adjustment. If there is vibration, then the motor is not installed correctly and there is far more to worry about than broken cables, e.g. bearings! I have also seen the practice of providing a "loop" in armoured cable at motors.

Regards
 15 June 2012 08:33 PM
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Fm

Posts: 744
Joined: 24 August 2011

Never had any problems with a helix in swa, tray close the junction box, terminate, power and controlncanle with a helix in each, a good bit of spare for future reconnecting.

Or if there are not enough gland entries, gland into an ip box and use it as a through box, kopex with conductors straight through with no joints in the jb

Marachel plug and socket

All have there each pros and cons, depending on what your connecying up
 18 June 2012 11:45 AM
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Avatar for BigRed.
BigRed

Posts: 558
Joined: 10 November 2006

Flexi conduit from isolater or sy/yy from socket to motor is my preferred way. Makes maintence a damn sight easier.
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