ground system
ground system
(OP)
Hi I would like to know if we can omit the motor ground because of the fram that is supposed to be grounded.I work with someone that always say we dont need it.And I always consider bringing a wire from the ground.Maybe someone can clarify me if Im wrong or my coleage.Happy new year to all of you





RE: ground system
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: ground system
The frame would have to be grounded regardless if the motor is or isn't.
But I guess we have not answered the OP's main question whether to ground the motor or not if the frame is grounded.
<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>
RE: ground system
BEST REGARDS
RE: ground system
RE: ground system
If the motor frame is already earthed properly by means of a earth wire with the right section you can only bring three conductors to the motor.
RE: ground system
RE: ground system
By Code (like NEC) you need to bring an equipment grounding conductor with the circuit condutors. Now as far as the code is concerned, the metal raceway enclosing the conductors or the armour ( listed for grounding) of the cable is acceptable. A good design is to have a separate grounding conductor with the circuit conductors.
Now coming to you collegue, if I can hazard a guess, what he may be referring to is that in many industrial facilities the motor may be mounted on a metal frame that is already bonded with building's steel structure. If the service serving the motor is also grounded to the same steel structure, he may think that the motor is adequately grounded and in some cases it may appear to work (fuse/breakers properly opening on a ground fault). BUT this still is not an acceptable grounding conductor per Code or a good design practice.
RE: ground system
If you have, say, a block long steel printing press. It has a ground cable running from the service entrance to it.
Now you have 10 motors hung/bolted onto it.
Does each motor need a ground run with it?
Keith Cress
kcress - http://www.flaminsystems.com
RE: ground system
RE: ground system
Keith Cress
kcress - http://www.flaminsystems.com
RE: ground system
Yes. It is not to say your motors are not adequately grounded. It is not sufficient to meet "equipment grounding requirement" for motors per NEC (assuming NEC is the applicable code).
The conncetion of the frame to service ground meets one of the code requirements of bonding non-current carrying parts to a ground. But motors still need their equipment grounding conductor.
In your particular case if the "press" is factory wired and only one feed is required to an inbox and rest is factory wired, you may only be required to bring the equipment grounding conductor to the inbox and bond to the frame.
You can search NEC article 250. At one place it says that strcutral metal frame of a building shall not be used as equipment grounding conductor for ac equipment.
RE: ground system
Best regards to all of you and thanks again for your feedback
RE: ground system
RE: ground system
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: ground system
Of course these are conveyor systems. But I have worked at many controls houses and have alwasys seen where this standard was followed.
Of course most believed it was NEC code and I believe it is too.
RE: ground system