Installing Additional Panel ( Load Increasing)

[Nedhal Al-Faraj]

Hi

I'm fresh graduated Electrical Engineer and I'm working with utilities services company.

I have been asked to do calculations for installing new panel in a building supplied by 2 lines from 400 Amp Main breker.

I measured the full load current of the building ( during morning time) by using clamp meter and I faound it is 275 A.

The desired panel to be installed will be 150 Amp.

I said to the owner of building that the main breaker need to be cahnged in this case with bigger size breaker and I suggested with 500 Amp breaker((275 +150)X 1.25 = 531 Amp ==> Next Size Down = 500 Amp) .

Am I correct or wrong .

Please Help me I'm new with using NEC based on self-study since there isn't school or any institue in my country to teach how to use NEC and apply it.

Thanks

 

[roger]

Nedhal, was your 275 amp reading peak or short duration or was it sustained for a period of time?

You should take as much information as you can from the equipment on site and general lighting information (va per sq meter for part of the equation) to go along with the calculations in 220 and see what you arrive at as a comparrison.


Have you looked into Mike Holt's or Tom Henry's training materials to accompany the NEC.

Roger

 

[hmspe]

That's not normally the way I would approach this kind of project. A single clamp-on meter reading is not accurate enough to use to determine the existing load. Please see 2005 NEC 220.87 (220.35 in the 1999 or 2002 NEC) for the acceptable method for determining the existing building load. If you cannot obtain the existing demand as instructed in NEC 220.87 the only other acceptable method is to verify the load on each existing circuit breaker and calculate the feeder load per NEC Article 220.

Do you know what load is to be on the new panel? We are only required to provide power to a panel based on the calculated load for the panel. It is not mandatory to provide a full 150 amps just because a panel is rated at 150 amps.

You did not say what country you are in so I do not know what the standard electrical ratings are in your country. In the USA I would not recommend a 500 amp service. Standard sizes for electrical services here are 400 amps and 600 amps. If the existing 400 amp service is not adequate I would design for a 600 amp service.

You should also be aware that changing from a 400 amp service to a higher ampacity service might raise the available fault current at the existing panels. In many cases the existing panels have to be upgraded to a higher fault current rating or the series ratings for the existing panels have to be verified.

Martin

 

[bob]

Hi

I have been asked to do calculations for installing new panel in a building supplied by 2 lines from 400 Amp Main breaker.
I measured the full load current of the building ( during morning time) by using clamp meter and I found it is 275 A.
The desired panel to be installed will be 150 Amp.
I said to the owner of building that the main breaker need to be changed in this case with bigger size breaker and I suggested with 500 Amp breaker((275 +150)X 1.25 = 531 Amp ==> Next Size Down = 500 Amp) .

As Roger said, You need to use section 220 of the NEC to help you determine the load in the building. The 275 amp reading may not be the peak load. The code actually will allow you to use a recording meter over a 30 day period to
determine the demand load of the building. How did you arrive at the 150 amp
panel? As I understand the problem, you have 2 circuits from the 400 amp
panel to the building. You want to add another circuit from the 400 amp panel to the propose 150 amps panel. With the calculations you show,
((275 +150)X 1.25 = 531 Amp ==> Next Size Down = 500 Amp), you would not add the 275 measured load to ampacity of the added panel. You need to show the new calculated load. If the load was computed at 531 amps, you would not size down because the load now is greater that the breaker ampacity. You would size up to maybe 800 amp. Another option is to add another 400 amp panel and leave the existing one in place. How may breakers are available in the 400 amps panel? You need someone with more experience to help you.

 

[Nedhal Al-Faraj]

Hi Gentlemen
Thanks for your response.


As your advice, I reviewed NEC article 220 and I'm now collecting required information about the appliances will be used and about the area of the building to apply calculations of Art. 220.

Thanks again