Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Sizing for Duty/Standby pumps

Sizing for Duty/Standby pumps

Sizing for Duty/Standby pumps


i need some input on this please;

i have a duty/standby pump configuration.(one of them running at a particular time).

right now the wiring of the to the pump includes a single point power with a main disconnect with 2 secondary disconnects for each pump. the main disconnect/wire are sized on the assumption that both pumps are running.

will it be possible to size down the main disconnect and wiring to as if only one pump is running as it is an duty/standby configuration?

RE: Sizing for Duty/Standby pumps

Does something, e.g. a mechanical interlock, prevent both pumps operating simultaneously?

RE: Sizing for Duty/Standby pumps

there is no mechnaical interlock, but there is a software interlock as the pumps are connected to the vfds which are connected to the plc.

RE: Sizing for Duty/Standby pumps

I would not rely on software to prevent things from turning on/off... electrical glitches have a funny way of rewriting software on the fly 3eyes

Dan - Owner

RE: Sizing for Duty/Standby pumps

how about using a hardwired interlock between the VFD's(n/o contact to Run permissive of the other?) does this follow NEC code?

RE: Sizing for Duty/Standby pumps

Can't comment on the NEC, not my patch at all.

Is there any possibility this will operate as a duty-assist mode rather than duty-standby, i.e. if the duty pump can handle the flow then the second pump stands idle, but if the duty pump can't cope alone the assist pump also cuts in?

How big is the cost difference between cable sized for one pump and cable sized for both? Are you the client, or the contractor? Is the small cable already installed, or is this question still on paper?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close