4000a feeding 6000a

[Alwayslearningelec]

Excuse me for the elementary question but I am reading portion of a spec for temporary work. There is a temp 4000a temp switchboard and 6000a permanent switchboards. I don't believe this will work. Is this correct?

It specifically says " provide temp power, with permanent characteristics, to permanent mechanical equipment requiring service before permanent power is available for same. This shall be done by bringing bulk distribution from the temp service switchgear to backfeed the permanent service switchboards.

 

[mikeames]

Whats the calculated load? I would imagine if its under the 4k capacity then its ok. It is essentially a 4ka service with 6ka gear in between.

 

[Jraef]

Whats the calculated load? I would imagine if its under the 4k capacity then its ok. It is essentially a 4ka service with 6ka gear in between.

And as long as the 4kA gear has it's own Main, shouldn't be a problem like he says.

 

[BJ Conner]

Excuse me for the elementary question but I am reading portion of a spec for temporary work. There is a temp 4000a temp switchboard and 6000a permanent switchboards. I don't believe this will work. Is this correct?

It specifically says " provide temp power, with permanent characteristics, to permanent mechanical equipment requiring service before permanent power is available for same. This shall be done by bringing bulk distribution from the temp service switchgear to backfeed the permanent service switchboards.

Been there, done that. It buys time for the project. You can have a lot of your commissioning in the bag when permenant power is available.

 

[Alwayslearningelec]

I'm sorry but can you explain furthur. Do you mean calculated load of mech equipment.Would a certain size feeder be run from the temp to a breaker in the perm switchgear. So it does not matter that the temp(4000a) is feeding the perm switchgear(6000a). A breaker in the temp is feeding a breaker in the perm. Thanks.

 

[kingpb]

I'm sorry but can you explain furthur. Do you mean calculated load of mech equipment.Would a certain size feeder be run from the temp to a breaker in the perm switchgear. So it does not matter that the temp(4000a) is feeding the perm switchgear(6000a). A breaker in the temp is feeding a breaker in the perm. Thanks.

Very typical on a large project to use the temporary construction power to feed the main permanent switchgear until the permanent main service is up, tested, and running.

The feeder from the construction (temporary) power panel to the main switchgear will be sized for whatever size breaker you are going use to do this with, your choice. The size will need to be based on what testing and checkout you want to try and accomplish prior to permanent energization. It could be small whereby you are only going to basically heat it up and do system checkout, or it could be larger, to try and bump, or run motors and the like. Just depends on the schedule of activities.

 

[Alwayslearningelec]

Very typical on a large project to use the temporary construction power to feed the main permanent switchgear until the permanent main service is up, tested, and running.

The feeder from the construction (temporary) power panel to the main switchgear will be sized for whatever size breaker you are going use to do this with, your choice. The size will need to be based on what testing and checkout you want to try and accomplish prior to permanent energization. It could be small whereby you are only going to basically heat it up and do system checkout, or it could be larger, to try and bump, or run motors and the like. Just depends on the schedule of activities.

Thanks a lot King. What I was not sure about was that the temp was 4000a it was feeding the perm 6000a(smaller can't feed bigger??:roll. I thought that could not be. But maybe the temp is only feeding an 800a breaker in the perm.

But wait now I'm thinking. They are asking us to feed the 6000a perm board from the 4000a temp board. Isn't that impossible?

Sorry guys

 

[kingpb]

Not impossible, just think of it as a main panel feeding a sub-panel, just that the sub-panel is over-sized.

Although, in reading the requirements, you may want to get clarification on exactly what it is that your providing power to/for.

6000A main service is a good amount of power @ 480V that's 5000KVA worth. Probably requires bus duct as a feeder otherwise 12 x 750kcmil per phase. That's one heck of a lot of copper.

If they need 6000A temporarily, your 4000A board, ain't gonna do it!

Better get some additional clarification on exactly what you are expected to do, since the cost could quite high.

 

[BJ Conner]

Thanks a lot King. What I was not sure about was that the temp was 4000a it was feeding the perm 6000a(smaller can't feed bigger??:roll. I thought that could not be. But maybe the temp is only feeding an 800a breaker in the perm.

But wait now I'm thinking. They are asking us to feed the 6000a perm board from the 4000a temp board. Isn't that impossible?

Sorry guys

That's not impossible. What is impossible is to feed the entire building load (6,000 amps). Using 4,000 amps or maby even less will alow you to power and test all the mechanical system, the lighting panels ( and anything powered from them), etc before the utility has run the service in. It's a scheduling issue. Possibly you could run all the lighting home runs and use them to feed temporary power.
Buildings start making money for the owner when people start moving in. If they start moving in 2 or 3 months early then the extra revenue makes it worth energizing the main gear. A lot of the testing and commissioning work usually occurs later in the schedule, what your doing is helping to move that work back and shortning the overall schedule. .

 

[Alwayslearningelec]

"Provide temp power, with permanent characteristics, to permanent mechanical equipment requiring service before permanent power is available for same. This shall be done by bringing bulk distribution from the temp service switchgear to backfeed the permanent service switchboards."


So based on the above the 4000a board must feed the 6000a board but may not require the 6000 amps. Correct? Well, like said before the 4000a switch could not run 6000a feeders. Correct?

The load of the mech equipment is unknown as what will require servicing is unknown. Sorry for beating this to death...I will end it here. I very much appreciate the input.

 

[kingpb]

Not sure if they could get the occupancy permit running off of temp power.

What type of building/facility is this?