Over current protection

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sparks1

Senior Member
Location
Massachusetts
A 120/240 1 phase four hundred amp service will be fed with 250 MCM in parallel to a four gang meter bank for a commercial building.The customer would like to have (1)200 amp 40 circuit panels in each unit but the service is only 400 amps. What doe the code allow you to derate ? Can I have (4) 200 amp circuit breakers in each meter enclosure.What is the percentage allowed?

[ April 02, 2005, 07:14 PM: Message edited by: sparks1 ]
 
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pierre

Senior Member
Location
Westchester County, New York
Re: Over current protection

A little more detail would help us help you :)
It sounds like you may have a total of 16 panels?

Have you or someone else performed some load calculation? That is part of the key to this decision.
 
charlie b

charlie b

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Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Over current protection

You have to approach the problem from the other direction. What the customer "wants," in terms of panels, is not the starting point. You start with the calculated load for each tenant, and work your way towards the service.

In general, it is possible for a 400 amp service to supply panel boards whose ratings add up to more than 400 amps. But are you saying the customer wants a total of 16 panels, each rated 200 amps (i.e., four per unit times four units)? That sounds like the total calculated load will wind up being far beyond 400 amps.
 
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sparks1

Senior Member
Location
Massachusetts
Re: Over current protection

This is going from an existing 200 amp service to a four hundred amp service. In fact the load calculation is Ok for 200 amps. The customer wants to increase the service for future use and because the four existing 100 amp panels have no space.

The new service will be 400 amps 1 phase.
There will be four new panels feeding from each new meter disconnect.
Can each of the breakers in the meter disconnect be rated at 200 amps?.
What is the percentage of derate on this service?
Can I use four 200 amp breakers one in each meter disconnect to feed each new 200 amp panel?
Four 200 amp breakers = 800 amps on a four hundred amp service.
What doe the code allow?
 
George Stolz

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Re: Over current protection

What matters, as Charlie Beck has mentioned above, is the connected load. You can have 4 200 amp panels on your 400 amp service. Not all tenants would be able to physically draw 200 amps at the same time; hopefully, the main would kick. It is up to you do determine what the connected load is.

If you have two units with existing loads you can size to, see what their connected load is. From there, you can pull numbers out of the air for the two future use meters. If they are upgrading their equipment because "they ran out of space in their panels", that doesn't mean they've exceeded 100 amps. :D
 
charlie b

charlie b

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Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Over current protection

I think you need to read your own post again. It does not say what you think it says:
Originally posted by sparks1: There will be four new panels feeding from each new meter disconnect.
Click to expand...
Four panels from each meter. Four meters. That makes 16 panels.

Is this what you meant to say:
There will be four new panels, with one being fed from each of the four new meter disconnects.
Click to expand...
 
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sparks1

Senior Member
Location
Massachusetts
Re: Over current protection

The Code allows us to calculate the existing service based on the maximum actual demand *125% + the new load. The Max demand on the new service is still below 200 amps. There is no 400 Amp main disconnect required.
Now add some amps so that the total load on each panel is 125 amps. Total load is now 500 amp on the service.
Highly unlikely situation but possible. ;)
 
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bigjohn67

Senior Member
Re: Over current protection

How many square ft is each apartment? That's the basics of calculating the load.
 
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sparks1

Senior Member
Location
Massachusetts
Re: Over current protection

Bigjohn67,
The load calculation is based on the existing load conditions.The max actual demand *125% + additional loads. The additional load portion could be the sq footage added to the building or it could be the equipment. In this case there is no additional sq footage and the units are commercial businesses not appartments.
Art 220.87 determining existing loads (1),(2).

[ April 02, 2005, 10:47 PM: Message edited by: sparks1 ]
 
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