Do you ever verify the engineer’s load calcs?

[brantmacga]

I don’t think I have previously, until today.

Small commercial tenant build out into a pizza restaurant. The existing service is 400A single phase; plans call for 400A 3-phase.

Rebuilding the service was going to require tearing out 30’ of concrete sidewalk to run new conduits from the utility pedestal.

Before ordering the gear today, I went through the load calc to verify everything was correct, and found no de-rating had been applied per 220.88. Plans show 91kva connected load. There were some items that came up in the pre-con Friday that had me questioning the E-sheets.

The HVAC on e-sheets was three 5-Ton RTU’s 3-phase. Verified with mechanical contractor they’re going to provide three 5-ton single phase split systems, which I what the M-sheets spec (I would normally verify mechanical schedule when I bid but for whatever reason skipped that on this one). Now we’re at 94kva. Derate per 220.88, my service size should be approximately 170A 3-phase; cooking appliances and water heaters are gas.

There are some 3-phase mixers, but I got the spec sheets on those and they can be connected single phase as well.

So now we’re at roughly 283A single phase and the existing service can stay.

And I just saved them about $8500 in gear, wire, and concrete work, and myself a lot of labor resources that can be used elsewhere.

And lastly, I went looking for the engineers stamp; it’s a circle with a question mark. No idea how this got through plan review. What likely happened here, and I’ve seen this before, is on these small franchise jobs they’ll have the architect just copy/paste schedules and specs from other similar stores they’ve built.


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[Buck Parrish]

The owners will bring some used ice cream machine back from a used restaurant equipment auction . Ahh Oh, it'll be 3 phase

 

[electrofelon]

Kinda related.... I am all for saving clients money. I have plenty of work and hate doing things that are not necessary....but sometimes I wonder if some of these clients care. For example right now I am working in a building that has a cell site on its own service. Service is 400A 120/208 three phase. I metered it a bunch of times and most I got was 30amps, and yes that was with the AC unit running. Many years ago I did the service for two cells towers. I never got to meter that, but I remember the service was crazy big, big copper - presumably similar load to the 30 amp one. Anyway, so not sure who comes up with these service sizes......

 

[ramsy]

Plans show 91kva connected (3Ø) load..

The HVAC on e-sheets was three 5-Ton RTU’s 3-phase. ..Now we’re at 94kva. Derate per 220.88, my service size should be approximately 170A 3-phase; cooking appliances and water heaters are gas.

So now we’re at roughly 283A single phase and the existing service can stay.

I see how similar kVA was derived from 170A 240v 3Ø Delta vs 283A 240v 1Ø. Nice work, if all those 1Ø loads ad up.

I'm lost at how 170A came from 94kVA?

Are you applying 75% Demand Factor from Table 220.88, for a restaurant using gas appliances?

 

[infinity]

Oversized engineered services are the norm where I work. We just install them as per the approved drawing. The last thing you want is for the client to install something in the future and the service you recommended is too small. Now if the client asks for the absolute minimum to save money then go for it.

 

[david luchini]

Before ordering the gear today, I went through the load calc to verify everything was correct, and found no de-rating had been applied per 220.88. Plans show 91kva connected load.

There is no derating for 91kVA (or 94kVA) per 220.88, so I'm not sure what derating you are adding to get to 170A-3ph.

 

[brantmacga]

There is no derating for 91kVA (or 94kVA) per 220.88, so I'm not sure what derating you are adding to get to 170A-3ph.

Yeh, I’m an idiot. I was reading the code book on my phone and saw 50%, which is the 2nd line down in the table.Thank god I didn’t say anything to the customer yet.

I spoke with the utility engineer this morning, he thinks they can use (3)x 300’s to do a 600/1 service, which would fit inside the existing 2”. So then I’d just need to change the base out and add another 200A disconnect to have a total of 3. Single phase demand is 450A.

Hopefully not often I look like a moron but today is definitely one of those days.


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[gadfly56]

Yeh, I’m an idiot. I was reading the code book on my phone and saw 50%, which is the 2nd line down in the table.Thank god I didn’t say anything to the customer yet.

I spoke with the utility engineer this morning, he thinks they can use (3)x 300’s to do a 600/1 service, which would fit inside the existing 2”. So then I’d just need to change the base out and add another 200A disconnect to have a total of 3. Single phase demand is 450A.

Hopefully not often I look like a moron but today is definitely one of those days.


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I make my worst mistakes when I talk off the top of my head. May have done another today; we'll see.

 

[steve66]

Did some work in an existing building that was about 20 years old.

I thought the 480V, 2000 amp service seemed really large, and when I looked at the original drawings, the engineer the load calculation at 208V.

Opps, a 900 amp service would have sufficed.

 

[petersonra]

Sometimes the engineer knows something you don't, like a potential future use that they do not want to disclose.

Personally, I am not a huge fan of doing the bare minimum as far as feeders go. It always seems to come back to haunt me and cost the end user money down the road. I don't do many services so service size is not an issue for me most of the time.

 

[WA_Sparky]

I don’t think I have previously, until today.

Small commercial tenant build out into a pizza restaurant. The existing service is 400A single phase; plans call for 400A 3-phase.

Rebuilding the service was going to require tearing out 30’ of concrete sidewalk to run new conduits from the utility pedestal.

Before ordering the gear today, I went through the load calc to verify everything was correct, and found no de-rating had been applied per 220.88. Plans show 91kva connected load. There were some items that came up in the pre-con Friday that had me questioning the E-sheets.

The HVAC on e-sheets was three 5-Ton RTU’s 3-phase. Verified with mechanical contractor they’re going to provide three 5-ton single phase split systems, which I what the M-sheets spec (I would normally verify mechanical schedule when I bid but for whatever reason skipped that on this one). Now we’re at 94kva. Derate per 220.88, my service size should be approximately 170A 3-phase; cooking appliances and water heaters are gas.

There are some 3-phase mixers, but I got the spec sheets on those and they can be connected single phase as well.

So now we’re at roughly 283A single phase and the existing service can stay.

And I just saved them about $8500 in gear, wire, and concrete work, and myself a lot of labor resources that can be used elsewhere.

And lastly, I went looking for the engineers stamp; it’s a circle with a question mark. No idea how this got through plan review. What likely happened here, and I’ve seen this before, is on these small franchise jobs they’ll have the architect just copy/paste schedules and specs from other similar stores they’ve built.


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Im not saying you're wrong by any means but I would be cautious taking the "connected load" verbiage for its face value. There have been times where im reviewing existing plans and some companies have their panel schedules show "Connected Load" values that are actually mislabeled for estimated demand.

One other thing that can easily lead to poor load calculations is a new hire designing in revit and not applying the correct demand factors as they should. Ultimately its the PE's responsibility to back check the load calcs but I could definitely see it being missed if they dont show load classifications on their panel schedules.

Also one other thing is make sure the client didnt intend on adding large future loads in the near future, that may be another reason for oversizing.