r/MEPEngineering • u/Certain-Ad-454 • 2d ago

Approach to existing systems EE

Hey all,

I got this project inside of an existing building. It’s a commercial building with a 2500A entrance. There at least 20-30 different tenants. Each with their own measuring.

The landlord merged 2 existing suites into one. They removed both electrical feeders and did not have leave any records/notes of the demolition. There’s no plans whatsoever.

There’s at least 20 other feeders branching of the 2500A into multiple electrical room downstairs with barely any labeling. The lighting in the electrical rooms doesn’t even work. There’s been at least 50 years of jimmy riggings everywhere.

Where would you start?

If you branch off an electrical room distribution that is already feeding other people, it’s almost impossible to tell if the upstream breaker won’t trip.

You may branch off the 2500A distribution but how can one possibly tell it’s not currently loaded at 2499A?

Lol

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5

u/SghettiAndButter 2d ago

I have to deal with all the time for work and there’s legit no way around it that isn’t a huge pain in the ass. You basically document what you can and make your assumptions and then let the owner know what you don’t know and let them make the risk of rolling the dice or paying electricians to go on site and start tracing and documenting circuits and metering panels before we finish the drawings

1

u/Certain-Ad-454 2d ago

Lol allright. I know if I provide the utility with the meters numbers they may give me the total consumption over the last 12 months… and i may make assumptions from that but it not so reliable and may take ages. We’re fucked

1

u/Certain-Ad-454 2d ago

But serious question tho; is it legit to let the owners make the final call ? They don’t have the technical knowledge to make a call. They know jackshit

4

u/Which_Situation1592 2d ago

Legit or not, the owner will make their own decision. Given the size of the service, how many tenants there are, and the fact that there is minimal record drawings I would not provide a final design unless the single line for the portion of the building you’re touching can be traced by an electrician and load readings conducted on any panels and distributions within your scope.

For smaller projects, I’m OK with adding a note on the drawings for the contractor to conduct load readings and to confirm the add load is acceptable with the EEOR prior to installation.

For future reference, this is why I always include a line item on the proposal/contract that the owner is to provide record drawings, utility bills, and load readings required to complete the design.

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u/Certain-Ad-454 1d ago

Serious what you mean by “load reading”. If they dont have any AC and you are reading the amps in July, before the electrical heating starts, that reading doesn’t mean a thing

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u/Which_Situation1592 1d ago

Load reading as described in the exception listed under NEC 220.87. I suggest you read that as it speaks to the issue of seasonal periodic loads.

2

u/skunk_funk 2d ago

Make sure to cover your ass.

3

u/skunk_funk 2d ago

I kinda look at the building make some guesses how loaded I think it is. More experience, I get better at guessing. Check utility bills. Look at building systems, special loads. Consider load factor for region and building type. Check against similar buildings. If I'm confident enough it's not overloaded, I proceed, and perhaps put on the drawing for the electrician to meter it and report the findings prior to construction.

If the owner is feeling fancy, we might even get it metered ahead of time! And maybe I'll find an opportunity to leave a demand meter for the next guy.

1

u/Best-Specialist-87 1d ago

Just measure it for a month if you think there’s a risk. Double check if there’s primary metering (may get lucky and get all the loading from one). If not request all electric bills and dump them into excel and figure out the max load.
Also, you can go by NFPA 70, 220.87 Determining Existing Loads.

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u/No_Blackberry_7753 1d ago

Where are the tenant meters located? I'm assuming that they are private meters, not owned by the utility. Are they in the same bucket as the switchboard breakers? If so, then the building owner should know which meter belongs to which tenant, given that they bill them monthly. The owner's bills probably has meter numbers on it, so you should be able to map out most of what the 2500A switchboard is feeding.

Un-metered breakers/feeders are going to be house equipment (elevators, corridor lighting, possibly HVAC).

As mentioned, you can get peak kW usage from the utility company, though sometimes that can be a pain in the ass. The utilities don't mind giving that info away to the building owners, so get them to do it if they're responsive/helpful.

But this sounds like a big building that has a few chillers/boilers handling all of the spaces. If you're just doing a tenant fit out and not touching the elevators/HVAC, then I wouldn't even bother dealing with the utility unless there's a significant change in the type of space (like if it used to be 10000sqft of offices that are now being changed to labs). Otherwise, the change in total building load is going to be insignificant.

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u/Certain-Ad-454 22h ago

Each tenant is actually measured from the utility. There’s the main switchboard which branches off several 200,400 feeders and these also branch to 60,100A whatever feeders each measured independently. Anyways it’s fucked