industrial distribution boards 1

[cn100]

always have trouble understanding 3phase distribution boards that supply other 3phase boards which supply either other boards or directly to electric motor isolators. very new to me at the moment. anyone have any rough guides as to loading and supplies, always in factories and industrial premises. very large subject but any practical guides would be appreciated.
many thanks
cn100

 

[rbulsara]

What part do you have trouble understanding? How it works? or with the arrangement? Sizing?

Then we can discuss loading.

 

[cn100]

sorry about topic not being that clear but definitely the arrangement and sizing.issues of loading and cable sizes ect..
thanks
cn100

 

[dpc]

Maybe this will help:

A 30A three-phase circuit implies 30A PER PHASE. So each conductor must be rated for 30A.

In a three-phase panel, you could have three-phase breakers (3-pole), or single-phase breakers (2-pole and 1-pole). A 2-pole breaker provides line-to-line voltage, so in a 208/120V panel, it would provide 208V, while a 1-pole breaker provides line-to-neutral voltage, in this case 120V.

 

[advidana]

Basically the the 3 phase panels have three power buses and one neutral bus and a ground lug. the power buses are taped by the circuit breakers. when you see a 3 pole circuit breaker, each pole is connect to a different phase or bus. The arrangement for the right side to the panel- the breakers are labeled odd numbers like 1,3,5 and the left side on the panel the breakers are labeled even numbers like 2,4,6 etc. the trip number on the handle is the ampere size that the breaker will trip or open, therefore disconnecting the circuit breaker if overloaded.

You use a large ampere panel to feed a smaller panel. basically because you may need more circuit breakers than is available on a large ampere single panel and for a lot of other reasons. Panel boards were invented to provide a organized means of protection on all circuits used in a system otherwise you would have many many more fused disconnects all over the place like was done back in the turn of the century.

All this is determined by connected loads and codes and a lot more.

If you are in this business you need to take a good NEC code class it would explain this matter and would really really help.

good luck

 

[cn100]

thank you advidana for your reply and i am moving more into the installation field as have repaired and installed electric motors for 25 years plus. so many times i am not quite sure as most of my work is heavy current application and would like to pick your brain as often as possible as experience can't be substituted.
now back to the question, then is it possible to look at the main cable feeder rated at say 125A into a dis. board
and add up all existing outgoing loads. so long as total does not exceed 125A then it's ok to keep loading up board.or how much diversity can be allowed on a common sense basis.
thanks
cn100

 

[BJC]

Call your local Cutler Hammer Rep and get a copy of the
Consulting Application Catalog
or you can go here and download one.

http://www.eatonelectrical.com/NASApp/cs/ContentServer?pagename=C-H/DocumentSupport/DSCLMain

It's a catalog for sure, but it very infromative and with pictures.

 

[rbulsara]

Diversity is based on knowlegde of what it is serving. If it is feeding general purpose receptacels that are not generally used, it can be as low as 0.3 or so. And it is serving say lights that all can be on at any given time, then it will be 1.0 (no diversity).

So you have to determine how much load will run simultaneously and come up with appropriate load estimate. According to most Codes (NEC definitely)you should size the feeders and equipment for 125% of the caclulated loads.

More further down (away from main serice and closer to indidual loads) the diveristy factor rises.