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Hi everyone, this is my first post on this board

We are going to install four 2 phase 480 volt welding receptacles at various places throughout the building. These are rated at 100 amps apiece with a 70 amp breaker is in line for protection. There is one welding machine at the facility rated at 480 volts @ 46 amps under full load. The receptacles will always be use one at a time never all at once.

There is a conflict on what the capacity of the 600 amp load center is. There are 605 amps of breakers installed in the panel now and this is more than the main breaker (600 amp).The expansion has a provision for 8 more breakers. I know that the load will never approach 605 amps because the breakers are rated at 125 to 150% According to the NEC and what I understand it to be is the capacity is determined by the ampacity of the feeders. The size of the feeders are 2 350 mcm per phase into the 600 amp main breaker. The maximum current for these feeders are 1140 amps per phase (NEC 310.14).

Is there a formula for figuring the maximum number and size of the breakers used for the individual loads on a 600 amp load center?

Any help on this would be greatly appreciated.

Thanks Gary

:wallbash:
 

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Hi everyone, this is my first post on this board

We are going to install four 2 phase 480 volt welding receptacles at various places throughout the building. These are rated at 100 amps apiece with a 70 amp breaker is in line for protection. There is one welding machine at the facility rated at 480 volts @ 46 amps under full load. The receptacles will always be use one at a time never all at once.

There is a conflict on what the capacity of the 600 amp load center is. There are 605 amps of breakers installed in the panel now and this is more than the main breaker (600 amp).The expansion has a provision for 8 more breakers. I know that the load will never approach 605 amps because the breakers are rated at 125 to 150% According to the NEC and what I understand it to be is the capacity is determined by the ampacity of the feeders. The size of the feeders are 2 350 mcm per phase into the 600 amp main breaker. The maximum current for these feeders are 1140 amps per phase (NEC 310.14).

Is there a formula for figuring the maximum number and size of the breakers used for the individual loads on a 600 amp load center?

Any help on this would be greatly appreciated.

Thanks Gary

:wallbash:


Welcme to the forum. The formula is callled a load calc. Have an electrician perform one for your facility. 310.14 is not the article you think.
 

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Discussion Starter · #3 ·
Sorry on my mistake it's 310.15(B)(7) wire table. I'm familiar with load calc and it deals with washers, dryers, ranges and lighting not MCCs, pumps and industrial load centers. I know what size breakers to use for the receptacles. I just wanted to know if it is calculated like a 200 amp service panel where you can't exceed the 42 breaker limit. On average the individual breakers rating in the panel, all totaled up,can exceed the 200 amp main breaker. Is this the same for the 600 amp commercial panel.
 

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You don't total breakers in a panel to determine loading. You can have as many breakers and sub panels as you want. Your service size is determined by what the POCO says you have and what your service entrance conductors are rated for. If you have one disconnect the service is usually rated at that disconnect amperage. If you think you are getting close on your service size then you need to do a load calculation to really know. There's some good books on how to do load calcs. Tom Henry, Mike Holt. Get all your loads. Your service voltage. Square feet. And post up your calc. I'll take a look at it.
 

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Sorry on my mistake it's 310.15(B)(7) wire table. I'm familiar with load calc and it deals with washers, dryers, ranges and lighting not MCCs, pumps and industrial load centers.
Load calcs are down for all types of loads not just 'washers, dryers, ranges and lighting'.

You need to read Article 220.

Also because this is a welder you really should read Article 630.


I know what size breakers to use for the receptacles. I just wanted to know if it is calculated like a 200 amp service panel where you can't exceed the 42 breaker limit. On average the individual breakers rating in the panel, all totaled up,can exceed the 200 amp main breaker. Is this the same for the 600 amp commercial panel.
As has been mentioned the handle ratings of the breakers have nothing at all to do with determining the load.
 

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Sorry on my mistake it's 310.15(B)(7) wire table. I'm familiar with load calc and it deals with washers, dryers, ranges and lighting not MCCs, pumps and industrial load centers. I know what size breakers to use for the receptacles. I just wanted to know if it is calculated like a 200 amp service panel where you can't exceed the 42 breaker limit. On average the individual breakers rating in the panel, all totaled up,can exceed the 200 amp main breaker. Is this the same for the 600 amp commercial panel.


Like everyone else has said a load calc must be performed. Also
since the 2008 NEC you are no longer limited to 42 spaces in a panel.
 

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Or you can get the demand data from the power company for one year.

Both of those items are covered in Article 220 which the OP should look at. :)
You really need to measure the current in each leg and make sure that everything is running. The delta 3Ph is likely to have low current on the hot leg, as it has no 120V loads connected. So, if you used the metered KW MAX Load, (which in our area you can just read on the meter) the load on the 2) 120 V legs will be higher than expected. So, you may have MAX KW of 25, with 90 amps on the 120 legs but only a 70A breaker on the generator. Some generators do better than others on surges like motor starts. You also need to allow for air conditioning loads to spike if the temperature rises. The AC current can actually triple on temp change, especially if the AC condenser is dirty. This likely does not apply to you, I have data rooms with large routers that run on 208/240. These do draw more current on 208V, where a resistance heating load, does not.
 
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