NEC 220.87 and upgrading equipment

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Tainted

Tainted

Senior Member
Location
New York
Occupation
Engineer (PE)
There is a 3 phase 600A panel feeding apartments. This panel is old and needs to be upgraded since it's old. According to NEC calculations it is undersized and would require 1200A.

If I monitor the load using NEC 220.87, and the max load monitored is like 400A.

Do I still need to upgrade it to a new 1200A panel? or can I just install a new 600A panel?
 
D

drktmplr12

Senior Member
Location
South Florida
Occupation
Electrical Engineer
Tainted said:
There is a 3 phase 600A panel feeding apartments. This panel is old and needs to be upgraded since it's old. According to NEC calculations it is undersized and would require 1200A.

If I monitor the load using NEC 220.87, and the max load monitored is like 400A.

Do I still need to upgrade it to a new 1200A panel? or can I just install a new 600A panel?
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If you are not adding any new load, there is a strong argument that the existing is adequate and no calculation is necessary.
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Tainted said:
There is a 3 phase 600A panel feeding apartments. This panel is old and needs to be upgraded since it's old. According to NEC calculations it is undersized and would require 1200A.

If I monitor the load using NEC 220.87, and the max load monitored is like 400A.

Do I still need to upgrade it to a new 1200A panel? or can I just install a new 600A panel?
Click to expand...
It is not unusual for the NEC load calculations to far exceed the actual load as measured.

Note what 220.87 says.

220.87 Determining Existing Loads. The calculation of a
feeder or service load for existing installations shall be permitted
to use actual maximum demand to determine the existing
load under all of the following conditions:
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Then it goes on to layout three conditions that have to exist.

(1) The maximum demand data is available for a 1-year
period.
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This can be measured in some way, either by the utility or by a recording meter.

(2) The maximum demand at 125 percent plus the new load
does not exceed the ampacity of the feeder or rating of
the service.
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IMO, this means you can only use this method if you are adding load.

(3) The feeder has overcurrent protection in accordance
with 240.4, and the service has overload protection in
accordance with 230.90.
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Would need to check and make sure but, should not be real hard to meet these requirements.
 
S

strap89

Member
petersonra said:
It is not unusual for the NEC load calculations to far exceed the actual load as measured.

Note what 220.87 says.



Then it goes on to layout three conditions that have to exist.



This can be measured in some way, either by the utility or by a recording meter.


IMO, this means you can only use this method if you are adding load.


Would need to check and make sure but, should not be real hard to meet these requirements.
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This is correct, curious if you have insight in the kW or KVA value has to be multiplied by 1.25? Most demand readings I have seen are shown in kW. I have heard some people say you need to consider the power factor first and then multiply that number by 1.25. I have heard others say the reason for the 1.25 is a basic assumption of a power factor of 0.8 being applied to most usual situations.
 
Tainted

Tainted

Senior Member
Location
New York
Occupation
Engineer (PE)
petersonra said:
It is not unusual for the NEC load calculations to far exceed the actual load as measured.

Note what 220.87 says.



Then it goes on to layout three conditions that have to exist.



This can be measured in some way, either by the utility or by a recording meter.


IMO, this means you can only use this method if you are adding load.


Would need to check and make sure but, should not be real hard to meet these requirements.
Click to expand...
So I can only use this if I’m adding load but i cannot use this if i’m replacing old equipment with the same amp capacity? That makes no sense to me…
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Tainted said:
So I can only use this if I’m adding load but i cannot use this if i’m replacing old equipment with the same amp capacity? That makes no sense to me…
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There are a lot of things in the code that don't make sense. People like to pretend that if it doesn't make sense they don't have to follow it, but I don't see it that way.
 
S

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
petersonra said:
It is not unusual for the NEC load calculations to far exceed the actual load as measured.

Note what 220.87 says.



Then it goes on to layout three conditions that have to exist.



This can be measured in some way, either by the utility or by a recording meter.


IMO, this means you can only use this method if you are adding load.


Would need to check and make sure but, should not be real hard to meet these requirements.
Click to expand...
If I were to OP, I wouldn't stress about installing the new service. One could either argue, no calculations are needed because I am merely replacing existing or that the new load is 0 and 0*1.25 is 0.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
I don't think I have ever done a load calculation when replacing like for like equipment. If it's been working fine for decades I say you are good. Obviously it doesn't matter what I think, it matters what your AHJ requires, and whether you want to argue with him where in the code it requires a load calc if no loads are added bit equipment is being replaced.
 
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