Service Equip panel / remote panel question

[Marc M]

Jerry,
I have a 100 amp service Panel and we have a 100 amp breaker which serves a remote panel;
I would like to get the NEC code citation which speaks to the max allowable load which can be imposed onto the SE from a remote panel. Thanks

[Jerry Peck - Codeman]

Hi Marc,

There really is not anything which states what you are asking, however, there are some code sections which address limitations - but trying to use fuzzy logic to connect the dots would not stand up to scrutiny.

From the 2008 NEC. (underlining and bold are mine)
- ARTICLE 215 Feeders
- - 215.3 Overcurrent Protection.
- - - Feeders shall be protected against overcurrent in accordance with the provisions of Part I of Article 240. Where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.
- - - - Exception No. 1: Where the assembly, including the overcurrent devices protecting the feeder(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.
- - - - Exception No. 2: Overcurrent protection for feeders over 600 volts, nominal, shall comply with Part XI of Article 240.

- ARTICLE 220 Branch-Circuit, Feeder, and Service Calculations
- - 220.18 Maximum Loads.
- - - The total load shall not exceed the rating of the branch circuit, and it shall not exceed the maximum loads specified in 220.18(A) through (C) under the conditions specified therein.
- - - - (A) Motor-Operated and Combination Loads. Where a circuit supplies only motor-operated loads, Article 430 shall apply. Where a circuit supplies only air-conditioning equipment, refrigerating equipment, or both, Article 440 shall apply. For circuits supplying loads consisting of motor-operated utilization equipment that is fastened in place and has a motor larger than hp in combination with other loads, the total calculated load shall be based on 125 percent of the largest motor load plus the sum of the other loads.
- - - - (B) Inductive Lighting Loads. For circuits supplying lighting units that have ballasts, transformers, or autotransformers, the calculated load shall be based on the total ampere ratings of such units and not on the total watts of the lamps.
- - - - (C) Range Loads. It shall be permissible to apply demand factors for range loads in accordance with Table 220.55, including Note 4.

That recurring calculation of 80% (125% going up) is present throughout the code.

You could have 100 amp rated service entrance conductors supplying 100 amp rated service equipment with a 100 amp rated breaker feeding 100 amp rated feeders which are going to a 100 amp rated panel with breakers which total up to a sum of 500 amps. That is because you are never going to get more than 100 amps through the service equipment - that main service disconnect will (should) trip, or if you are trying to draw more than 100 amps through the panel, the breaker in the service equipment which is protecting the feeders will trip.

However, the load calculations at the time of the design and installation would be required to meet the calculations in the code.

Not sure if that helped answer your question?

[Marc M]

Thanks Jerry. You nailed it, I have'nt come across a panel that has 100A SE and 100 RP. RP is typically 60% or so.

[Jerry Peck - Codeman]

Hi Marc,

I've seen (in a commercial building) 800 amps trying to be drawn through a 400 amp service - that was the way the architect/electrical engineer drew it out.

The electrical contractor I was working for had to explain to them that would be like trying to use a fire hose to put out a fire with the fire hose being fed by a garden hose off a hose bibb - you are not going to get any more water out of the fire hose than you can get through the garden hose from that hose bibb.

The job was redesigned to function properly.