400 amp feeder calculation
- Thread starter j87
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- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: 400 amp feeder calculation
First of all, please turn off the ALL CAPS feature. It is considered impolite.
Secondly, by virtue of your description that the majority of the load is fluorescent lights and computers, then I would say, ?yes you count the neutral.? Reference 310.15(B)(4)(c).
But please clarify: A ?Service? is what you get from the utility. A ?Feeder? goes from one panel to another panel. A ?Branch Circuit? goes from a panel to a load. What do you mean by ?What size feeder should you have for a 400 amp service. . . ?? Keep in mind that conductors are sized for the load. You may have a 400 amp panel, but what is the calculated load?
First of all, please turn off the ALL CAPS feature. It is considered impolite.
Secondly, by virtue of your description that the majority of the load is fluorescent lights and computers, then I would say, ?yes you count the neutral.? Reference 310.15(B)(4)(c).
But please clarify: A ?Service? is what you get from the utility. A ?Feeder? goes from one panel to another panel. A ?Branch Circuit? goes from a panel to a load. What do you mean by ?What size feeder should you have for a 400 amp service. . . ?? Keep in mind that conductors are sized for the load. You may have a 400 amp panel, but what is the calculated load?
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: 400 amp feeder calculation
Going along with what Charlie said, see 215.2 and 230.42, then notice that at the 75 degree column of 310.16 500Kcmil is a 380 amp conductor. IF your calculated load is less than 380, 240.4(B) may be used.
Going along with what Charlie said, see 215.2 and 230.42, then notice that at the 75 degree column of 310.16 500Kcmil is a 380 amp conductor. IF your calculated load is less than 380, 240.4(B) may be used.
Re: 400 amp feeder calculation
I should have been a little more detailed in my response, busy day. The answer is from 500 to 700 depending on the calculated load and interactions of 240.4(B). You would count the neutral as a current carrying conductor.
And as Charlie points out is this a service or feeder?
I should have been a little more detailed in my response, busy day. The answer is from 500 to 700 depending on the calculated load and interactions of 240.4(B). You would count the neutral as a current carrying conductor.
And as Charlie points out is this a service or feeder?
Re: 400 amp feeder calculation
Apology for the caps. To clarify, this is a building that has a 400 amp main. The tenant wants the ability of 400 amps. I guess the question is what should the service conductor size be that is entering the building in conduit?No load calculation are available in this case.
Apology for the caps. To clarify, this is a building that has a 400 amp main. The tenant wants the ability of 400 amps. I guess the question is what should the service conductor size be that is entering the building in conduit?No load calculation are available in this case.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: 400 amp feeder calculation
But back to basics. You say that no load calculation is available? Then you must perform one! The tenant might say they want 400 amps, but they might have 800 amps worth of equipment in the space, just waiting for you to give them the power. If you had not installed a 400 amp feeder on the basis of a known load under 400 amps, then the responsibility for the ensuing fire will come knocking on your front door.
I don?t mean to give you a hard time, but the building has a 400 amp main what? Is there already a meter and a disconnect? If so, that is the point at which the rules for ?service conductors? ends, and from that point to the tenant?s equipment you follow the rules for ?feeder conductors.? If you have a need for 400 amps of highly harmonic loads, then you need at least 500 amps worth of conductor. If you use a 90C rated conductor, you can de-rate from the 90C table. Thus two possible choices are a single 700 MCM or a pair of parallel 4/0. In both cases, the 90C ampacity is 520 amps, and de-rating that to 80% gives you 416 amps.
But back to basics. You say that no load calculation is available? Then you must perform one! The tenant might say they want 400 amps, but they might have 800 amps worth of equipment in the space, just waiting for you to give them the power. If you had not installed a 400 amp feeder on the basis of a known load under 400 amps, then the responsibility for the ensuing fire will come knocking on your front door.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: 400 amp feeder calculation
1. How could you end up with more then 400A load? presumably the loadcenter being installed has a 400A main that would trip long before a fire hazard came about.
2. Do you guys usually run conductors this large? Or do you prefer multiple smaller conductors in parallel?
A couple of points just out of curiousity.
1. How could you end up with more then 400A load? presumably the loadcenter being installed has a 400A main that would trip long before a fire hazard came about.
2. Do you guys usually run conductors this large? Or do you prefer multiple smaller conductors in parallel?
- Location
- Massachusetts
Re: 400 amp feeder calculation
We do not usually parallel anything smaller than 400 amp feeders / service conductors.
If you parallel this 400 amp circuit you have two choices.
1)Derate the conductors 70% as you would have 8 current carrying conductors in one raceway Table 310.15(B)(2)(a)
or
2)Run two raceways.
For 400 amps I would most likely run one 4" raceway with a set of 500 or 600 Kcmil CU.
I thought the opening question was very straight forward, why make a mountain out of a mole hill?
[ September 28, 2004, 07:24 PM: Message edited by: iwire ]
We generally run 500 or 600 Kc mil CU for a service or feeder that has 400 Amp over current protection.
We do not usually parallel anything smaller than 400 amp feeders / service conductors.
If you parallel this 400 amp circuit you have two choices.
1)Derate the conductors 70% as you would have 8 current carrying conductors in one raceway Table 310.15(B)(2)(a)
or
2)Run two raceways.
For 400 amps I would most likely run one 4" raceway with a set of 500 or 600 Kcmil CU.
I thought the opening question was very straight forward, why make a mountain out of a mole hill?
[ September 28, 2004, 07:24 PM: Message edited by: iwire ]
Re: 400 amp feeder calculation
Thanks for all the feedback. This was a 50 yr old building that was being remodeled. The main service panel was being replaced with a new panel. The old service conductors were 500mcm. Understanding just what the code wants as minimum versus we have always done it this way, is what we are up against. Our main thought was whether or not we needed to derate the wire because of the neutral conductor and the 75 degree rating of the new panel with the 90 degree C rated conductors. Thanks again. Future comment welcome.
Thanks for all the feedback. This was a 50 yr old building that was being remodeled. The main service panel was being replaced with a new panel. The old service conductors were 500mcm. Understanding just what the code wants as minimum versus we have always done it this way, is what we are up against. Our main thought was whether or not we needed to derate the wire because of the neutral conductor and the 75 degree rating of the new panel with the 90 degree C rated conductors. Thanks again. Future comment welcome.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: 400 amp feeder calculation
My point is that you select equipment on the basis of the load. Everything starts with knowledge of the load. We all know that we can design and build a good system, only to have the owner come back next week and add more load than we had built the system to handle. The owner gets the wake up all after things start tripping. But if we select a panel without knowing how much load is intended to be connected, then we are part of the creation of the problem.
It?s an old habit of mine, obtained from an industry that goes out of its way to avoid reliance upon a protective trip as the sole means of preventing an accident. You want the breaker to work, and you fully expect that it would. But you never design a system in such a way that normal operations would frequently overload that breaker, and force it to trip, as the sole means of preventing a fire.
My point is that you select equipment on the basis of the load. Everything starts with knowledge of the load. We all know that we can design and build a good system, only to have the owner come back next week and add more load than we had built the system to handle. The owner gets the wake up all after things start tripping. But if we select a panel without knowing how much load is intended to be connected, then we are part of the creation of the problem.
Re: 400 amp feeder calculation
500 mcm for all of the conductors, although remember when you have a bunch of florescent lights and computer equipment you have to watch out for the harmonic balance. Most of the time it calls for a 200% neutral or a dedicated neutral for each individual branch circuit.
500 mcm for all of the conductors, although remember when you have a bunch of florescent lights and computer equipment you have to watch out for the harmonic balance. Most of the time it calls for a 200% neutral or a dedicated neutral for each individual branch circuit.
Re: 400 amp feeder calculation
It's all about design. If you have a facility like a data center that has large non-linear loads. You would have the utility supply it with either 480, 208, or even higher voltages, leave the neutral dead-ended in the switchgear, distribute 3-phase loads like HVAC, rectifiers, and UPS panels directly from the switchgear, then delta feed a "K" rated isolation/step-down transformer with oversized neutral buses to feed critical equipment and single phase lighting. You could even take it a step further and put lighting and GP recepts on its own dedicated transformer, and critical equipment on another.
Personally I would like to know if anyone has ever measured a neutral load go over 100%. I have only seen it go to 110% two or three times in my lifetime.
Does not make since if a "K" rated transformer, or a overated panel board is not used. Seriously doubt the utility oversized the neutral.
It's all about design. If you have a facility like a data center that has large non-linear loads. You would have the utility supply it with either 480, 208, or even higher voltages, leave the neutral dead-ended in the switchgear, distribute 3-phase loads like HVAC, rectifiers, and UPS panels directly from the switchgear, then delta feed a "K" rated isolation/step-down transformer with oversized neutral buses to feed critical equipment and single phase lighting. You could even take it a step further and put lighting and GP recepts on its own dedicated transformer, and critical equipment on another.
Personally I would like to know if anyone has ever measured a neutral load go over 100%. I have only seen it go to 110% two or three times in my lifetime.
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