Grounding a centrifugal pump

[masterelect1]

As per the plans, a small centrifugal 240v- 3ph -1hp is shown to be grounded to building steel AND back to the service. According to the design engineer, this is to eliminate static build up in the pump.

It seems to me that grounding the pump casing to building steel would be sufficient to eliminate static build-up and potential shock/sparking.

It does not seem correct that the Engineer would also want to ground the pump to the Electrical system.

Any opinions on this?

thanks,
John

 

[bphgravity]

You can provide all the auxillary grounding you want, but none of it is going to be all that effective. The important thing is that proper equipment grounding (bonding) is installed with the circuit conductors providing the effective fault path. This alone really should be sufficient to eliminate any charge build-ups.

 

[LarryFine]

John, isn't the pump's supply's EGC already doing this, or at least capable of doing it?

 

[don_resqcapt19]

It would be a rare pump installation (assuming metallic piping) that would need any type of bonding or grounding to eliminate static buildup. The IEEE Green Book says that a path of 1,000,000 ohms or less is sufficient to prevent the buildup of static charges.
If the piping is non-metallic, there is no real way to prevent the buildup of static chargers. Some systems require the use of conductive non-metallic pipe to prevent the static charge.

 

[weressl]

It would be a rare pump installation (assuming metallic piping) that would need any type of bonding or grounding to eliminate static buildup. The IEEE Green Book says that a path of 1,000,000 ohms or less is sufficient to prevent the buildup of static charges.
If the piping is non-metallic, there is no real way to prevent the buildup of static chargers. Some systems require the use of conductive non-metallic pipe to prevent the static charge.

External grounding is provided as a backup to the EGC. A phase conductor's integrity is always 'monitored' as single phasing would 'pop' the overload. Unless you have an EGC monitoring relay in place - not a requirement and expensive - you have no way of knowing if your grounbd is still connected. If you have everything properly bonded and all your grounding connections are bonded to each other you still get a pretty good impedance back to the source to pop your OCPD.

 

[don_resqcapt19]

External grounding is provided as a backup to the EGC. A phase conductor's integrity is always 'monitored' as single phasing would 'pop' the overload. Unless you have an EGC monitoring relay in place - not a requirement and expensive - you have no way of knowing if your grounbd is still connected. If you have everything properly bonded and all your grounding connections are bonded to each other you still get a pretty good impedance back to the source to pop your OCPD.

The original post stated that the extra grounding was to prevent static build up and that is what I was commenting on.

 

[weressl]

The original post stated that the extra grounding was to prevent static build up and that is what I was commenting on.

I did not argue with your comments, but rather tried to give support to WHY a second ground may be required. Engineers sometimes tend to make up their own explanations to practices that were 'passed' onto them.:grin:

On the other hand the EGC connected to the motor may not ground the pump itself. Fiberlgass bases are common in corrosive environment and glass lined pipes or plastic pipes are very difficult to ground.

 

[brian john]

I
If the piping is non-metallic, there is no real way to prevent the buildup of static chargers. .

PVC piping can knock the **** out of you and as noted grounding the pipe is hard to do.

 

[don_resqcapt19]

...
On the other hand the EGC connected to the motor may not ground the pump itself. Fiberlgass bases are common in corrosive environment and glass lined pipes or plastic pipes are very difficult to ground.

Yes, often industrial specs will require the external bonding jumper for the LFMC be extended from the termination on the motor junction box to the pump frame.

 

[tom baker]

. Engineers sometimes tend to make up their own explanations to practices that were 'passed' onto them.:grin:
.

Exactly. Specs stay the same from generation to generation and often are not reviewed.

 

[weressl]

Exactly. Specs stay the same from generation to generation and often are not reviewed.

They may stay the same way for good reason too. Any engineers worth their salt will not just copy-and-paste but tries to understand why certain things became a practice. Since specifications are not dissertations where it would be explained and proved in detail why such practice came into become a specification, one would try to reconstruct the reasoning. That is what I was writing about.