Re: Grounding, grounding, grounding! Make sure all your metal
Posted by
Ray Henry
on 2003-04-18 07:55:02 UTC
Andrew and Jeff (comments mixed in)
brass in one spot it is called single point grounding. The idea here is to
eliminate multiple paths for the ground signals to travel and to keep those
signals that are heading for ground from getting mixed up with each other.
Copper wire is for the most part a better conductor than iron so a copper
wire will look like a closer connection to electrical signals than will the
iron of the machine. You'll eliminate cross talk between devices by
connecting the grounds of all devices directly back to the same point without
looping from one to the next.
Don't confuse ground with shield. Shielded wires, like you may need for
encoders or step and direction if they travel very far in parallel with motor
signals, should be connected at only one end. That way any signals traveling
to ground will not travel along the shield. The shield will pick up and
ground stray signals transmitted by power wires or nearby radio stations.
These signals will travel along the shield and drain wire to that single
point.
with a heavy bare, green, or green and yellow striped conductor. There are a
number of differences between countries on this requirement so check local
requirements if you plan to sell these devices or show them off to your
electrically literate friends. Do not trust a bonded box to carry all
grounds within it back to a single point ground system.
this may come close to an electrical myth. I once had a car with a positive
ground.
Some switching power supplies do tie one leg to ground but linear power
supplies produce an isolated pair of signals -- one positive one negative.
So long as any loads or signals are correctly connected between the pair,
there is no need, and in fact may be some harm in forcing one side of it to
ground. Many commercial machines use more than one DC supply and have no
connections between or to ground. The only down side I can see from
isolating DC voltages is putting the clip lead of your test meter to the
frame and expecting to read a correct voltage from a + connection.
Even in household AC wiring, forcing what we (USA) call the neutral side of
the line to ground may cause harm. This is clearly set out in the mobile
home and general grounding portions of the National Electrical Code. There
are specific places where this should and should not be done.
HTH
Ray Henry
> From: "andrewyslee" <andrewlee@...>When all of the ground wires are connected to a stud or block of copper or
> Subject: Re: electrical code?
>
> "Jeff Goldberg" <jeff@w...> wrote:
> > Grounding, grounding, grounding! Make sure all your metal
>
> components are
>
> > bolted together.
>
> Will help to understand WHY. Most of the electrical boxes I have open
> seem to have only one point earthed. I don't see any wires connecting
> all the metal parts together. Probably I haven't open enough boxes.
brass in one spot it is called single point grounding. The idea here is to
eliminate multiple paths for the ground signals to travel and to keep those
signals that are heading for ground from getting mixed up with each other.
Copper wire is for the most part a better conductor than iron so a copper
wire will look like a closer connection to electrical signals than will the
iron of the machine. You'll eliminate cross talk between devices by
connecting the grounds of all devices directly back to the same point without
looping from one to the next.
Don't confuse ground with shield. Shielded wires, like you may need for
encoders or step and direction if they travel very far in parallel with motor
signals, should be connected at only one end. That way any signals traveling
to ground will not travel along the shield. The shield will pick up and
ground stray signals transmitted by power wires or nearby radio stations.
These signals will travel along the shield and drain wire to that single
point.
> > If the bolts are over paint, put in bonding jumpers. Make<s>
> > sure your machine is bonded to your control cabinet.
> What is a bonding jumper? Are they just simple wires meant to connectYes they are. Two electrical cabinets separated on a machine might be bonded
> metal parts together?
with a heavy bare, green, or green and yellow striped conductor. There are a
number of differences between countries on this requirement so check local
requirements if you plan to sell these devices or show them off to your
electrically literate friends. Do not trust a bonded box to carry all
grounds within it back to a single point ground system.
> > Make sureI've got a bit of a problem with tying all dc negatives in to ground. IMO
> > your D.C.
> > negatives are all grounded.
this may come close to an electrical myth. I once had a car with a positive
ground.
Some switching power supplies do tie one leg to ground but linear power
supplies produce an isolated pair of signals -- one positive one negative.
So long as any loads or signals are correctly connected between the pair,
there is no need, and in fact may be some harm in forcing one side of it to
ground. Many commercial machines use more than one DC supply and have no
connections between or to ground. The only down side I can see from
isolating DC voltages is putting the clip lead of your test meter to the
frame and expecting to read a correct voltage from a + connection.
Even in household AC wiring, forcing what we (USA) call the neutral side of
the line to ground may cause harm. This is clearly set out in the mobile
home and general grounding portions of the National Electrical Code. There
are specific places where this should and should not be done.
HTH
Ray Henry