service size

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jociha

Member
I have a 1000a rated service panel. From the meter to service panel wire size is 1000a, the panel is labeled 1000a, it does not have a single main disconnect, it does have 6 switches labeled ''service disconnect'. If i add up all these 6 switches it equals well over 1000a, i wish to use the 1 spare switch ,the caculated load on the entire panel will be 950 amps, can i load the panel this way. john
 

bwyllie

Senior Member
Location
MA
The size of the service is based upon the calculated load not the sum of the 6 dosconnects. Refer to 230.90.A.Exception No.3
 

iwire

Moderator
Staff member
Location
Massachusetts
jociha said:
that i understand , the question is can this panel [busbars] be loaded to 100% 0r is it 80%.

Assuming you already included the continuous loads at 125% in your calculated load the bus bars will not be loaded 100% continuously.

Your panel is very likely rated 100% non-continuous.
 

jociha

Member
the problem is it is a existing service that i need to add to,and each of the 5 breakers currently being used probably has that concidered in it but even if the 6 breakers are only loaded to60% it would equal over the 1000a. the measured amp draw on the 5 breakers totals 600a, i want to use the spare 400a breaker to add a load of 290a.
 

volt102

Senior Member
Location
New Hampshire
As bwyllie stated, it is based on a calculation and not the sum of the breakers. As stated by iwire, that calc includes that required loads that are continuous to be calculated at 125%. It sounds to me that you will need to re-calculate the service before adding the load.

Jim
 

hmspe

Senior Member
Location
Temple, TX
Occupation
PE
I'd look at 220.87. A 1000A service should have a demand meter. If it's been in place for at least a year you should be able to get demand data from the utility. Base your calculations on that.
 

mshields

Senior Member
Location
Boston, MA
Question about disconnects

Question about disconnects

I apologize first of all, because, I can't find how to start a new thread.

My question relates to disconnect switches.

In any building that has fault current over 14k, we always call for all disconnect switches to be fused. This is because, if you look at the GE Buylog or competitors info, you find that disconnects without fuses are rated for no more than 14K.

What we invariably get, is an unfused disconnect at the equipment, provided by the equipment vendor. We squeek and we squak but the truth is we often end up with that as our disconnecting means.

Should we be pushing this issue more vigorously. Are we overlooking something? Are these unfused disconnects at the equipment ok. e.g. include really all HVAC equipment but it's often an issue with AHU's, Crack units, etc.

Interested in all thoughts.

Mike
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
What i dont like is all these units will thru the years likely keep adding and go unchecked till we melt some wires.The demand meters are not likely on the lets say 150 amp units but as a total of lets say 10 units that start out as maybe 7o average 5 years from now will change.
 

hmspe

Senior Member
Location
Temple, TX
Occupation
PE
Jim W in Tampa said:
The demand meters are not likely on the lets say 150 amp units ....

In this case it was stated that this is a single meter with 5 existing switches after the meter. At 1000A I'm sure it's a demand meter. Where I live I seldom see a 100A or 200A commercial meter that's not demand.

Martin
 
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