Why loads in the downstream panelboard should be SMALL. 2

[birddogger]

I have a client who is trying to "cut fat" from a project, and one item they are proposing is moving some of the larger loads on their system from the main distribution switchboard (where breaker "real estate" is much higher) to a downstream distribution panel. We're talking a couple of 400A loads more suited to a robust 3000A 277/480V switchboard than what's basically a wall-mounted 1200A I-Line panel that we were ear-marking for more localized loads. The distance from the load to either of the two boards is about the same, so they're pressing to feed them from the I-Line panel.

Can it be done? Yeah. Is it good engineering practice? No. As a rule of thumb, big loads go on big switchboards and smaller loads go on smaller boards/panels. But I can't really figure out a way to explain why other than the standard "that's just the way it's always been done around here" response. Any suggestions as to how to make my point?

 

[busbar]

You may take the approach that your client’s requests will limit growth and make additions/modifications to the electrical system potentially much more expensive.

It may be that the subject feeders will initially have higher losses and reduced spare capacity.

 

[advidana]

The breakers should be about the same cost where the savings? or are the aic different.

 

[EEIre]

Some Ideas:

Reliability: The breaker located in the main board will be more robust and inherently more reliable

Maintenance: It is easier to isolate a particular circuit in a main board to do maintenance than in a sub-board

Cabling: There may not be enough room to terminate a large number of large cables in a sub-board.

Single Point of Failure: Putting a lot of important circuits on a sub-board creates a single point of failure

 

[birddogger]

To advidana - the main board is drawout gear with solid state tripping, the downstream panel is, like I said, an I-Line type panel with molded-case thermal magnetic breakers (they could be specified to be solid-state of course, but drawout breakers are still more costly). Coordination is not a problem, I've already ran the numbers on that.

The best argument is probably that if the breakers were installed in the I-Line panel, servicing them would require the entire panel to be shut down, whereas this would not be the case with the drawout gear. That is in fact the main selling point of drawout gear. And since downtime would be a fairly serious issue here, I can probably play up that angle to them pretty convincingly.

 

[advidana]

Why not use the i-line breaker if the cost is that much less. Since the electrical protection would be the same.

I think the draw are easly to service. But in todays thinking 1st cost carries a lot of weight. Question-If you had to pay for the installation yourself would you pick the draw-outs.