220.87

[augie47]

In a number of years inspecting, I have not actually has anyone use 220.87 for service calculations even though it seems to be one of the most accurate means. I am simply skeptical from lack of experience with that method.
I have an older hotel that was converted to muti-family dwellings. The ancient service was in poor condition and had a melt-down.
The original service had been tapped a number of times so there is really no "main" to reference.
There will be very limited load modifications when replacing the service. Past power bills showing demand are available. Is there any reason not to use them as noted in 220.87 to determine the new service size ?

 

[jim dungar]

There will be very limited load modifications when replacing the service. Past power bills showing demand are available. Is there any reason not to use them as noted in 220.87 to determine the new service size ?

What is that phrase?
"Past performance is not an indicator of future results"

 

[Dennis Alwon]

Are the bills from the hotel or the multifamily dwelling and are the bills available for a year. If the bills are for the mfd then I don't see an issue

 

[Dennis Alwon]

Also did the meltdown happen because it was overloaded?

 

[augie47]

Also did the meltdown happen because it was overloaded?

It appears the service conductors were overloaded (or shorted).
There has been numerous line side taps over the yeras and the original install had numerous violations including phase arrangement in the conduits (all neutrals were in one GRS conduit for rxample).

 

[JDBrown]

We use 220.87 on airport jobs all the time -- it's really all you can do when you've got a huge facility and poor/nonexistent documentation of what's installed. For what it's worth, I've never heard of an overloading problem caused by doing load calcs with 220.87. Granted, I've only been doing this for 5 years, but some of the guys I work with have been at it for 30-40 years without a problem of this type.

 

[GoldDigger]

Are the bills from the hotel or the multifamily dwelling and are the bills available for a year. If the bills are for the mfd then I don't see an issue

From a purely hypothetical and theoretical basis, the existing load may have been artificially low because the tenants knew they could not use too much power at one time without lights dimming or breakers tripping or whatever. So the real usage once the repairs are made might be higher.
But the provision in the code about using the historic values does not seem to care about that.
Just do not install more fixed loads as part of the process without factoring them in. And it sounds like you are OK on that:

There will be very limited load modifications when replacing the service.

 

[PE from the OC]

220.87 Existing Load Calculation

220.87 Existing Load Calculation

When using NEC 220.87, remember to add the required 25% of the existing load to your calculation as required by 220.87(2). Also, depending upon the type of utilization equipment in the building a power factor adjustment may also be a good idea. Most power company demand loads are in Kw, not Kva.

220.87 is usually used when new loads are being added to an existing building. Using this method to determine a new service back-feed which will be smaller than the existing service switchboard should be approached carefully so as not to go below the code minimum service size for the building type calculated by square footage.

Other than that, I have used 220.87 often for many years without incident.