Pump station grounding

[alnajohn]

We have a sewage pump station 600' from the building. It requires 60A 208V 3 phase only, no neutral is needed, the pump panel has 2 breakers in it for the pumps and 1 for the control power transformer. There is a permanently installed Generator at the pump station. The engineer is requiring 3 phases, a full size neutral (2/0 for voltage drop), and a ground wire from the building to the transfer sw next to the pump panel. He is also calling for a four pole transfer switch. We have not seen this before, typically 3 phases and a ground wire are run to these. Can anyone explain where the neutral requirements for this is in the code. If this is for a grounding electrode conductor can it be sized per 250.66 (#4 for 2/0 SE conductor)?
If we have to have this 2/0 neutral is a ground wire still required? And if this is required on this set up why it is not used on outside condensing units, chillers or similar equipment.

 

[earlydean]

Re: Pump station grounding

250.32

 

[electricman2]

Re: Pump station grounding

The manufacturer of the pump control panel should specify the supply voltage, circuit ampacity required and whether 3 or 4 wire. There is no NEC requirement that a neutral be supplied where it is not needed. However the plans and specifications may require it. Consult with the engineer and let him explain why it is specified.

 

[tom baker]

Re: Pump station grounding

Lets set aside whether the neutral is needed or not.
What we need to focus on is
1) Ground fault return path the source
The ground fault return path is either by a seperate equipment grounding conductor, or by the grounded neutral conductor, if no parallel paths are present. The recommended practice is to use a separate equipment grounding conductor and not "reground the neutral" In your case you would size the equipment grounding conductor per table 250.122,however it would be increased in size proportionally according to the size that the ungrounded conductor was increased for voltage drop.

2) Grounding electrodes at the separate building or structure
Every SBS (seperate building or structure, ie this sewage lift station) requires a grounding electrode system, unless served by a single branch circuit, your application is a feeder (see definition of branch circuit) so a grounding electrode system is required. See 250.32

3) Disconnecting means for the separate building or structure (SBS)
The sewage pump station is a SBS, and requires a disconnecting means, this feeder disconnect must be suitable for use as a service disconnect, 225.36, which means the disconnect is marked, and has the means to bond the neutral conductor.

Other comments:
2/0 may be the correct size depending on the ungrounded conductor size after adjustment for voltage drop
To meet 225.36, your pump control panel would have to be listed as a service disconnecting means, or install a separate disconnect next to it. Most disconnects are listed as service disconnecting means.
?And if this is required on this set up why it is not used on outside condensing units, chillers or similar equipment.? Its not required as they are not SMS, but the grounded neutral is not bonded at the equipment or subpanel, per 250.142

?Typically 3 phases and a ground wire are run to these? Be careful with your terminology. The NEC does not use the term ?ground wire?. You probably are referring to an equipment grounding conductor.

[ December 20, 2003, 07:31 PM: Message edited by: tom baker ]

 

[dana1028]

Re: Pump station grounding

Originally posted by tom baker:

3) Disconnecting means for the separate building or structure (SBS)
The sewage pump station is a SBS, and requires a disconnecting means, this feeder disconnect must be suitable for use as a service disconnect, 225.36, which means the disconnect is marked, and has the means to bond the neutral conductor.

Tom - 225.36 says the feeder disconnect must be suitable as a service disconnect, and as such it has a 'means to bond the neutral conductor.'

Since this service disconnect has a means to bond the neutral, does that mean you must install a neutral?

 

[tom baker]

Re: Pump station grounding

Dana, good point,no the grounded conductor does not have to be installed.
Two listings of services are:
1. suitable for use as service disconnect, meaning a main bonding jumper can be installed, and the panel/disconnect can be used as a panelboard, where a neutral to case bond is not made
2. suitable only for use as service disconnect, meaning there is no removable main bonding jumper, and the panel/disconnect can only be used at the service.
Control panels are usually UL 508, they can be made to be allowed for use as a service, then they would have a 'susie' label. 99% of the panels we install are per #1 above. I have seen a few pumping panels that are #2 they are commonly used in oil wells where the pumping panel is a service disconnect.