Hello, I am still out here reading these post - NOW I have a question.

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Kyell

Kyell

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Location
Titusville Florida USA
Hello, Everyone!

I have an engineering question, (Oh and this will be sent out to a qualified electrical engineer), but I am still asking anyway. Please be kind.
I was asked how many 125A breakers can be placed in a Panel with the main breaker rated at( 400A. 3 phase 480. ) I wanted this and the correct method to explain it to a plant manager with NO ELECTRICAL background.

Thank you for you comments

Bob
 
How many do you have? Seriously there is no limit as to the number of circuit breakers. You are limited by a load calculation as to how much load can be on the panel. The only way to determine that is to do an Article 220 load calculation.
 
If you are trying to explain it to someone with little electrical background you might reference their home electrical panel referencing the sum of the individual breaker amperes vs the main rating.
 
If they have no electrical knowledge, then you need to give them an analogy.

For example, 'How many flushometer toilets can you have in a building? What is the flow rate of an individual toilet? What is the total flow rate for the building? What would happen if people timed things to flush all the toilets at exactly the same time? How likely is such an event?'

-Jon
 
winnie said:
If they have no electrical knowledge, then you need to give them an analogy.

For example, 'How many flushometer toilets can you have in a building? What is the flow rate of an individual toilet? What is the total flow rate for the building? What would happen if people timed things to flush all the toilets at exactly the same time? How likely is such an event?'

-Jon
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Perfect. People can relate to toilets…
 
winnie said:
If they have no electrical knowledge, then you need to give them an analogy.

For example, 'How many flushometer toilets can you have in a building? What is the flow rate of an individual toilet? What is the total flow rate for the building? What would happen if people timed things to flush all the toilets at exactly the same time? How likely is such an event?'

-Jon
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When I was in college, a group scheduled a total flush in a seven story dorm.
The first floor drains overflowed.
 
I do the same thing many times I'll use sprinkler heads per zone. then zones per available water pressure. They're light bulb moment always kicks in.
 
infinity said:
How many do you have? Seriously there is no limit as to the number of circuit breakers. You are limited by a load calculation as to how much load can be on the panel. The only way to determine that is to do an Article 220 load calculation.
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I am not doing the load calculation it is going to an engineer for that however I know 8 75kva transformer are going in the new lathe department I just want to know what is going down, I am just very cautious in this so I must be able to check the load calculations after they return and quite frankly it has been a long time for me. Need to refresh
 
A 75 kva xfmrs at 480 V 3 phase is over 80 amps each. I would be real suspicious of putting right of these on a 400 amp panel, but a load calculation is required to determine if it is acceptable.
 
I would start with ask for the loads placed on the transformers. Ask for name plate data and build from there.
Amps and volts to kva
Example: four name plates 4x 45@208 3- phase
45*3*208*1.732/1000
48.6 k a for transformer #1.
@480 that would be 58.45 amp
Add this load to your 480 volt panel.

As soon on.
 
Another C10 said:
I do the same thing many times I'll use sprinkler heads per zone. then zones per available water pressure. They're light bulb moment always kicks in.
Click to expand...
Except that in every movie ever written, when the hero sets of a sprinkler head in one room, every head in the building starts spewing water.
 
Strathead said:
Except that in every movie ever written, when the hero sets of a sprinkler head in one room, every head in the building starts spewing water.
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which has lead to so many folks believing that's what happens :)
 
Tulsa Electrician said:
I would start with ask for the loads placed on the transformers. Ask for name plate data and build from there.
Amps and volts to kva
Example: four name plates 4x 45@208 3- phase
45*3*208*1.732/1000
48.6 k a for transformer #1.
@480 that would be 58.45 amp
Add this load to your 480 volt panel.

As soon on.
Click to expand...
THANK YOU, YOU HAVE CONFIRMED MY THOUGHTS I KNEW i WAS HEADED IN THE CORRECT DIRECTION
 
Kyell said:
THANK YOU, YOU HAVE CONFIRMED MY THOUGHTS I KNEW i WAS HEADED IN THE CORRECT DIRECTION
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SORRY BUT I MUST CLARIFY THE FOLLOWING, I HAVE SERIOUS TRUST ISSUES WITH THE ENGINEERING FIRM OUT OWNER USES, THEY HAVE A TRACK RECORD OF SUPPLYING THE INCORRECT INFORMATION, ( AND THEN SWEARING BY IT) IT COSTS US MONEY AND I WOULD SERIOUSLY LIKE TO AVOID THIS, BUT AT LEAST BEING ABLE TO CORRCTLY CHECK THEIR FIGURES. I HOPE THIS EXPLAINS MY MOTIVES FOR MY QUESTION BETTER AGAIN THANK YOU ALL FOR REPLYING.
BOB
 
augie47 said:
which has lead to so many folks believing that's what happens :)
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I was told that there is a wax (or something similar) plug in every sprinkler head that melts in a fire and opens the valve, and when the resultant drop in pressure in the supply line is detected, a pump is started that is strong enough to blow out the plugs in all the other heads, so yeah, that's what I thought happens.
 
ggunn said:
I was told that there is a wax (or something similar) plug in every sprinkler head that melts in a fire and opens the valve, and when the resultant drop in pressure in the supply line is detected, a pump is started that is strong enough to blow out the plugs in all the other heads, so yeah, that's what I thought happens.
Click to expand...
There is a plug in every sprinkler head that melts when a fire reaches each head. Depending on the system, there may be a pump to maintain pressure in the system. However, I don't believe it pops the plugs in all of the heads. The idea is that you sprinkle water on the areas that are hot enough to melt the plug-- and not all over the building.
But it's a more interesting movie if they all go off at once.
Just as a geyser going off when someone plows through a fire hydrant only happens if someone has left the underground valve open! Normally, if you open one of the hose connections in a hydrant, you get no water.
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